init macos make routine

.gitignore

@@ -1,4 +1,7 @@
 build/**
 .cache
 viseq
+viseq.exe
 compile_commands.json
+*.json
+.DS_STORE

MakefileMacOSarm64

@@ -0,0 +1,33 @@
+CXX = g++
+CXXFLAGS = -std=c++23 -Wall -g -fno-omit-frame-pointer -gdwarf-4 -Og -Wnarrowing
+CXXINC = -Iinclude
+
+LDLIBS = -lraylib -pthread -lobjc
+LDFLAGS = -Llib -L/usr/lib -L/usr/local/lib -framework CoreFoundation -framework Cocoa -framework IOKit
+
+hdr_files = ${wildcard src/*.h}
+
+src_files = ${wildcard src/*.cpp}
+src_files += ${wildcard include/libremidi/*.cpp}
+
+all: viseq
+	
+viseq: $(src_files) $(hdr_files)
+	mkdir -p build
+	$(CXX) ${wildcard build/*.o} -o viseq $(LDFLAGS) $(LDLIBS)
+	
+$(src_files): %.cpp : %_src
+	$(CXX) -c $@ -o build/$(*F).o $(CXXFLAGS) $(CXXINC)
+
+$(hdr_files): %.h : %_hdr
+	@echo "G++  >---------- $(*F).h -----------<"
+
+%_src:
+	@echo "G++  >---------- $(*F).cpp -----------<"
+
+%_hdr:
+	@echo "G++  >---------- $(*F).h -----------<"
+
+clean:
+	rm -f build/*
+	rm -f viseq

MakefileMingW64

@@ -0,0 +1,33 @@
+CXX = g++
+CXXFLAGS = -std=c++23 -Wall -g -fno-omit-frame-pointer -gdwarf-4 -Og -Wnarrowing -DLIBREMIDI_WINUWP=1
+CXXINC = -Iinclude
+
+LDLIBS = -lraylibdll -pthread -lwindowsapp
+LDFLAGS = -L./lib -L/usr/lib -L/usr/local/lib
+
+hdr_files = ${wildcard src/*.h}
+
+src_files = ${wildcard src/*.cpp}
+src_files += ${wildcard include/libremidi/*.cpp}
+
+all: viseq
+	
+viseq: $(src_files) $(hdr_files)
+	mkdir -p build
+	$(CXX) ${wildcard build/*.o} -o viseq $(LDFLAGS) $(LDLIBS)
+	
+$(src_files): %.cpp : %_src
+	$(CXX) -c $@ -o build/$(*F).o $(CXXFLAGS) $(CXXINC)
+
+$(hdr_files): %.h : %_hdr
+	@echo "G++  >---------- $(*F).h -----------<"
+
+%_src:
+	@echo "G++  >---------- $(*F).cpp -----------<"
+
+%_hdr:
+	@echo "G++  >---------- $(*F).h -----------<"
+
+clean:
+	rm -f build/*
+	rm -f viseq

README.md

@@ -0,0 +1,5 @@
+prerequisite for MacOS ARM64: 
+local raylib install (e.g. brew install raylib)
+
+Build:
+make -f MakefileMacOSarm64

include/libremidi/api-c.h

@@ -0,0 +1,39 @@
+#pragma once
+
+#if __cplusplus
+extern "C" {
+#endif
+
+//! MIDI API specifier arguments.
+//! To get information on which feature is supported by each back-end, check their backend file
+//! in e.g. backends/winmm.hpp, etc.
+typedef enum libremidi_api
+{
+  UNSPECIFIED = 0x0, /*!< Search for a working compiled API. */
+
+  // MIDI 1.0 APIs
+  COREMIDI = 0x1, /*!< macOS CoreMidi API. */
+  ALSA_SEQ,       /*!< Linux ALSA Sequencer API. */
+  ALSA_RAW,       /*!< Linux Raw ALSA API. */
+  JACK_MIDI,      /*!< JACK Low-Latency MIDI Server API. */
+  WINDOWS_MM,     /*!< Microsoft Multimedia MIDI API. */
+  WINDOWS_UWP,    /*!< Microsoft WinRT MIDI API. */
+  WEBMIDI,        /*!< Web MIDI API through Emscripten */
+  PIPEWIRE,       /*!< PipeWire */
+  KEYBOARD,       /*!< Computer keyboard input */
+  NETWORK,        /*!< MIDI over IP */
+
+  // MIDI 2.0 APIs
+  ALSA_RAW_UMP = 0x1000, /*!< Raw ALSA API for MIDI 2.0 */
+  ALSA_SEQ_UMP,          /*!< Linux ALSA Sequencer API for MIDI 2.0 */
+  COREMIDI_UMP,          /*!< macOS CoreMidi API for MIDI 2.0. Requires macOS 11+ */
+  WINDOWS_MIDI_SERVICES, /*!< Windows API for MIDI 2.0. Requires Windows 11 */
+  KEYBOARD_UMP,          /*!< Computer keyboard input */
+  NETWORK_UMP,           /*!< MIDI2 over IP */
+
+  DUMMY = 0xFFFF /*!< A compilable but non-functional API. */
+} libremidi_api;
+
+#if __cplusplus
+}
+#endif

include/libremidi/api.hpp

@@ -1,6 +1,8 @@
 #pragma once
+#include <libremidi/api-c.h>
 #include <libremidi/config.hpp>
 
+#include <any>
 #include <string_view>
 #include <vector>
 
@@ -9,28 +11,7 @@ namespace libremidi
 //! MIDI API specifier arguments.
 //! To get information on which feature is supported by each back-end, check their backend file
 //! in e.g. backends/winmm.hpp, etc.
-enum class API
-{
-  UNSPECIFIED, /*!< Search for a working compiled API. */
-
-  // MIDI 1.0 APIs
-  COREMIDI,    /*!< macOS CoreMidi API. */
-  ALSA_SEQ,    /*!< Linux ALSA Sequencer API. */
-  ALSA_RAW,    /*!< Linux Raw ALSA API. */
-  JACK_MIDI,   /*!< JACK Low-Latency MIDI Server API. */
-  WINDOWS_MM,  /*!< Microsoft Multimedia MIDI API. */
-  WINDOWS_UWP, /*!< Microsoft WinRT MIDI API. */
-  WEBMIDI,     /*!< Web MIDI API through Emscripten */
-  PIPEWIRE,    /*!< PipeWire */
-
-  // MIDI 2.0 APIs
-  ALSA_RAW_UMP,          /*!< Raw ALSA API for MIDI 2.0 */
-  ALSA_SEQ_UMP,          /*!< Linux ALSA Sequencer API for MIDI 2.0 */
-  COREMIDI_UMP,          /*!< macOS CoreMidi API for MIDI 2.0. Requires macOS 11+ */
-  WINDOWS_MIDI_SERVICES, /*!< Windows API for MIDI 2.0. Requires Windows 11 */
-
-  DUMMY /*!< A compilable but non-functional API. */
-};
+using API = libremidi_api;
 
 /**
  * \brief A function to determine the available compiled MIDI 1.0 APIs.
@@ -50,6 +31,9 @@ LIBREMIDI_EXPORT std::vector<libremidi::API> available_apis() noexcept;
 */
 LIBREMIDI_EXPORT std::vector<libremidi::API> available_ump_apis() noexcept;
 
+LIBREMIDI_EXPORT
+libremidi::API midi_api(const std::any& conf);
+
 //! A static function to determine the current version.
 LIBREMIDI_EXPORT std::string_view get_version() noexcept;
 
@@ -60,6 +44,17 @@ LIBREMIDI_EXPORT std::string_view get_api_display_name(libremidi::API api);
 //! Look-up an API through its name
 LIBREMIDI_EXPORT libremidi::API get_compiled_api_by_name(std::string_view api);
 
+inline constexpr bool is_midi1(libremidi::API api)
+{
+  return (static_cast<int>(api) >= 0x1 && static_cast<int>(api) < 0x1000)
+         || api == libremidi::API::DUMMY;
+}
+
+inline constexpr bool is_midi2(libremidi::API api)
+{
+  return static_cast<int>(api) >= 0x1000;
+}
+
 namespace midi1
 {
 //! Returns the default MIDI 1.0 backend to use for the target OS.

include/libremidi/backends.hpp

@@ -1,4 +1,7 @@
 #pragma once
+#include <libremidi/config.hpp>
+
+#include <any>
 #include <tuple>
 
 #if !__has_include(<weak_libjack.h>) && !__has_include(<jack/jack.h>)
@@ -44,9 +47,10 @@
 
 #if defined(LIBREMIDI_WINUWP)
   #include <libremidi/backends/winuwp.hpp>
-  #if __has_include(<winrt/Microsoft.Devices.Midi2.h>)
+#endif
+
+#if defined(LIBREMIDI_WINMIDI)
   #include <libremidi/backends/winmidi.hpp>
-  #endif
 #endif
 
 #if defined(LIBREMIDI_EMSCRIPTEN)
@@ -55,6 +59,15 @@
 
 #include <libremidi/backends/dummy.hpp>
 
+#if defined(LIBREMIDI_KEYBOARD)
+  #include <libremidi/backends/keyboard.hpp>
+#endif
+
+#if defined(LIBREMIDI_NETWORK)
+  #include <libremidi/backends/network.hpp>
+  #include <libremidi/backends/network_ump.hpp>
+#endif
+
 namespace libremidi
 {
 // The order here will control the order of the API search in
@@ -100,6 +113,14 @@ static constexpr auto available_backends = make_tl(
 #if defined(LIBREMIDI_PIPEWIRE)
     ,
     pipewire::backend{}
+#endif
+#if defined(LIBREMIDI_KEYBOARD)
+    ,
+    kbd_backend{}
+#endif
+#if defined(LIBREMIDI_NETWORK)
+    ,
+    net::backend{}
 #endif
     ,
     dummy_backend{});
@@ -135,15 +156,13 @@ static constexpr auto available_backends = make_tl(
     ,
     coremidi_ump::backend{}
 #endif
-#if defined(LIBREMIDI_JACK)
-#endif
-#if defined(LIBREMIDI_WINUWP)
-  #if __has_include(<winrt/Microsoft.Devices.Midi2.h>)
+#if defined(LIBREMIDI_WINMIDI)
     ,
     winmidi::backend{}
-  #endif
 #endif
-#if defined(LIBREMIDI_EMSCRIPTEN)
+#if defined(LIBREMIDI_NETWORK)
+    ,
+    net_ump::backend{}
 #endif
     ,
     dummy_backend{});
@@ -183,5 +202,49 @@ auto for_backend(libremidi::API api, F&& f)
   midi2::for_backend(api, f);
 }
 
+void for_input_configuration(auto f, std::any& api_conf)
+{
+  auto from_api = [&]<typename T>(T& /*backend*/) mutable {
+    if (auto conf = std::any_cast<typename T::midi_in_configuration>(&api_conf))
+    {
+      f(*conf);
+      return true;
+    }
+    return false;
+  };
+  if (std::apply([&](auto&&... b) { return (from_api(b) || ...); }, midi1::available_backends))
+    return;
+  std::apply([&](auto&&... b) { return (from_api(b) || ...); }, midi2::available_backends);
+}
+
+void for_output_configuration(auto f, std::any& api_conf)
+{
+  auto from_api = [&]<typename T>(T& /*backend*/) mutable {
+    if (auto conf = std::any_cast<typename T::midi_out_configuration>(&api_conf))
+    {
+      f(*conf);
+      return true;
+    }
+    return false;
+  };
+  if (std::apply([&](auto&&... b) { return (from_api(b) || ...); }, midi1::available_backends))
+    return;
+  std::apply([&](auto&&... b) { return (from_api(b) || ...); }, midi2::available_backends);
+}
+
+void for_observer_configuration(auto f, std::any& api_conf)
+{
+  auto from_api = [&]<typename T>(T& /*backend*/) mutable {
+    if (auto conf = std::any_cast<typename T::midi_observer_configuration>(&api_conf))
+    {
+      f(*conf);
+      return true;
+    }
+    return false;
+  };
+  if (std::apply([&](auto&&... b) { return (from_api(b) || ...); }, midi1::available_backends))
+    return;
+  std::apply([&](auto&&... b) { return (from_api(b) || ...); }, midi2::available_backends);
+}
 }
 }

include/libremidi/backends/alsa_raw/config.hpp

@@ -61,6 +61,7 @@ struct manual_poll_parameters
 struct alsa_raw_input_configuration
 {
   std::function<bool(const manual_poll_parameters&)> manual_poll;
+  std::chrono::milliseconds poll_period{2};
 };
 
 struct alsa_raw_output_configuration

include/libremidi/backends/alsa_raw/helpers.hpp

@@ -3,14 +3,9 @@
 #include <libremidi/config.hpp>
 #include <libremidi/detail/observer.hpp>
 
-#include <chrono>
 #include <functional>
-#include <iostream>
-#include <optional>
-#include <span>
 #include <string>
 #include <string_view>
-#include <thread>
 #include <vector>
 
 // Credits: greatly inspired from
@@ -87,39 +82,16 @@ struct snd_ctl_wrapper
 struct enumerator
 {
   const libasound& snd = libasound::instance();
+  const error_handler& handler;
+  const observer_configuration& configuration;
   std::vector<alsa_raw_port_info> inputs;
   std::vector<alsa_raw_port_info> outputs;
 
-  std::function<void(std::string_view)> error_callback;
-  std::function<void(std::string_view)> warn_callback;
+  explicit enumerator(const auto& self)
+      : handler{self}
+      , configuration{self.configuration}
+  {
 
-  template <typename... Args>
-  void warning(Args&&... args)
-  {
-    std::string s;
-    ((s += args), ...);
-    if (warn_callback)
-    {
-      warn_callback(std::move(s));
-    }
-    else
-    {
-      std::cerr << s << std::endl;
-    }
-  }
-  template <typename... Args>
-  void error(Args&&... args)
-  {
-    std::string s;
-    ((s += args), ...);
-    if (error_callback)
-    {
-      error_callback(std::move(s));
-    }
-    else
-    {
-      throw std::runtime_error(s.c_str());
-    }
   }
 
   // 1: is an input / output
@@ -141,9 +113,9 @@ struct enumerator
     }
     else if (status < 0 && status != -ENXIO)
     {
-      error(
-          "alsa_raw_helpers::enumerator::is: cannot get rawmidi information:", card, device, sub,
-          snd.strerror(status));
+      handler.libremidi_handle_error(
+          configuration, "Cannot get rawmidi information: " + device_identifier(card, device, sub)
+                             + " : " + snd.strerror(status));
       return status;
     }
     else
@@ -185,26 +157,23 @@ struct enumerator
     return s;
   }
 
-  void enumerate_cards()
+  stdx::error enumerate_cards()
   {
+    using namespace std::literals;
     int card = -1;
 
     int status = snd.card.next(&card);
     if (status < 0)
     {
-      error(
-          "alsa_raw_helpers::enumerator::enumerate_cards: "
-          "cannot determine card number: ",
-          snd.strerror(status));
-      return;
+      handler.libremidi_handle_error(
+          configuration, "Cannot determine card number: "s + snd.strerror(status));
+      return from_errc(status);
     }
 
     if (card < 0)
     {
-      error(
-          "alsa_raw_helpers::enumerator::enumerate_cards: "
-          "no sound cards found");
-      return;
+      handler.libremidi_handle_error(configuration, "No sound cards found");
+      return std::errc::no_such_device;
     }
 
     while (card >= 0)
@@ -213,13 +182,12 @@ struct enumerator
 
       if ((status = snd.card.next(&card)) < 0)
       {
-        error(
-            "alsa_raw_helpers::enumerator::enumerate_cards: "
-            "cannot determine card number: ",
-            snd.strerror(status));
-        break;
+        handler.libremidi_handle_error(
+            configuration, "cannot determine card number: "s + snd.strerror(status));
+        return std::errc::no_such_device;
       }
     }
+    return stdx::error{};
   }
 
   virtual void enumerate_devices(int card) = 0;
@@ -228,20 +196,22 @@ struct enumerator
 inline snd_ctl_wrapper::snd_ctl_wrapper(enumerator& self, const char* name)
     : snd{self.snd}
 {
+  using namespace std::literals;
   int status = snd.ctl.open(&ctl, name, 0);
   if (status < 0)
   {
-    self.error(
-        "alsa_raw_helpers::enumerator::snd_ctl_wrapper: "
-        "cannot open control for card",
-        name, snd.strerror(status));
+    self.handler.libremidi_handle_error(
+        self.configuration, "cannot open control for card"s + name + " : " + snd.strerror(status));
   }
 }
 
 struct midi1_enumerator : enumerator
 {
+  using alsa_raw::enumerator::enumerator;
+
   void enumerate_devices(int card) override
   {
+    using namespace std::literals;
     char name[128];
 
     sprintf(name, "hw:%d", card);
@@ -261,10 +231,8 @@ struct midi1_enumerator : enumerator
 
       if (status < 0)
       {
-        error(
-            "alsa_raw::midi1_enumerator::enumerate_devices: "
-            "cannot determine device number: ",
-            snd.strerror(status));
+        handler.libremidi_handle_error(
+            configuration, "Cannot determine device number: "s + snd.strerror(status));
         break;
       }
 

include/libremidi/backends/alsa_raw/midi_in.hpp

@@ -33,83 +33,72 @@ public:
 
   ~midi_in_impl() override { }
 
-  bool open_virtual_port(std::string_view) override
-  {
-    warning(configuration, "midi_in_alsa_raw: open_virtual_port unsupported");
-    return false;
-  }
-  void set_client_name(std::string_view) override
-  {
-    warning(configuration, "midi_in_alsa_raw: set_client_name unsupported");
-  }
-  void set_port_name(std::string_view) override
-  {
-    warning(configuration, "midi_in_alsa_raw: set_port_name unsupported");
-  }
-
   libremidi::API get_current_api() const noexcept override { return libremidi::API::ALSA_RAW; }
 
   // Must be a string such as: "hw:2,4,1"
-  [[nodiscard]] int do_init_port(const char* portname)
+  [[nodiscard]] stdx::error do_init_port(const char* portname)
   {
     constexpr int mode = SND_RAWMIDI_NONBLOCK;
     if (const int err = snd.rawmidi.open(&midiport_, nullptr, portname, mode); err < 0)
     {
-      error<driver_error>(this->configuration, "midi_in_alsa_raw::open_port: cannot open device.");
-      return err;
+      libremidi_handle_error(this->configuration, "cannot open device.");
+      return from_errc(err);
     }
 
     snd_rawmidi_params_t* params{};
     snd_rawmidi_params_alloca(&params);
 
     if (const int err = snd.rawmidi.params_current(midiport_, params); err < 0)
-      return err;
+      return from_errc(err);
     if (const int err = snd.rawmidi.params_set_no_active_sensing(midiport_, params, 1); err < 0)
-      return err;
+      return from_errc(err);
 #if LIBREMIDI_ALSA_HAS_RAWMIDI_TREAD
     if (configuration.timestamps == timestamp_mode::NoTimestamp)
     {
       if (const int err
           = snd.rawmidi.params_set_read_mode(midiport_, params, SND_RAWMIDI_READ_STANDARD);
           err < 0)
-        return err;
+        return from_errc(err);
       if (const int err
           = snd.rawmidi.params_set_clock_type(midiport_, params, SND_RAWMIDI_CLOCK_NONE);
           err < 0)
-        return err;
+        return from_errc(err);
     }
     else
     {
       if (const int err
           = snd.rawmidi.params_set_read_mode(midiport_, params, SND_RAWMIDI_READ_TSTAMP);
           err < 0)
-        return err;
+        return from_errc(err);
       if (const int err
           = snd.rawmidi.params_set_clock_type(midiport_, params, SND_RAWMIDI_CLOCK_MONOTONIC);
           err < 0)
-        return err;
+        return from_errc(err);
     }
 #endif
 
     if (const int err = snd.rawmidi.params(midiport_, params); err < 0)
-      return err;
+      return from_errc(err);
 
     return init_pollfd();
   }
 
-  [[nodiscard]] int init_port(const port_information& p)
+  [[nodiscard]] stdx::error init_port(const port_information& p)
   {
     return do_init_port(raw_from_port_handle(p.port).to_string().c_str());
   }
 
-  [[nodiscard]] int init_pollfd()
+  [[nodiscard]] stdx::error init_pollfd()
   {
     const int num_fds = snd.rawmidi.poll_descriptors_count(this->midiport_);
 
     this->fds_.clear();
     this->fds_.resize(num_fds);
 
-    return snd.rawmidi.poll_descriptors(this->midiport_, fds_.data(), num_fds);
+    int ret = snd.rawmidi.poll_descriptors(this->midiport_, fds_.data(), num_fds);
+    if (ret < 0)
+      return from_errc(ret);
+    return stdx::error{};
   }
 
   ssize_t do_read_events(auto parse_func, std::span<pollfd> fds)
@@ -155,7 +144,8 @@ public:
     while ((err = snd.rawmidi.read(this->midiport_, bytes, nbytes)) > 0)
     {
       const auto to_ns = [this] { return absolute_timestamp(); };
-      decoder_.on_bytes({bytes, bytes + err}, decoder_.timestamp<timestamp_info>(to_ns, 0));
+      m_processing.on_bytes(
+          {bytes, bytes + err}, m_processing.timestamp<timestamp_info>(to_ns, 0));
     }
     return err;
   }
@@ -180,7 +170,8 @@ public:
       const auto to_ns = [ts] {
         return static_cast<int64_t>(ts.tv_sec) * 1'000'000'000 + static_cast<int64_t>(ts.tv_nsec);
       };
-      decoder_.on_bytes({bytes, bytes + err}, decoder_.timestamp<timestamp_info>(to_ns, 0));
+      m_processing.on_bytes(
+          {bytes, bytes + err}, m_processing.timestamp<timestamp_info>(to_ns, 0));
     }
     return err;
   }
@@ -188,18 +179,19 @@ public:
   ssize_t read_input_buffer_with_timestamps() { return read_input_buffer(); }
 #endif
 
-  void close_port() override
+  stdx::error close_port() override
   {
     if (midiport_)
       snd.rawmidi.close(midiport_);
     midiport_ = nullptr;
+    return stdx::error{};
   }
 
   timestamp absolute_timestamp() const noexcept final override { return system_ns(); }
 
   snd_rawmidi_t* midiport_{};
   std::vector<pollfd> fds_;
-  midi1::input_state_machine decoder_{this->configuration};
+  midi1::input_state_machine m_processing{this->configuration};
 };
 
 class midi_in_alsa_raw_threaded : public midi_in_impl
@@ -210,26 +202,33 @@ public:
   {
     if (this->termination_event < 0)
     {
-      error<driver_error>(
-          this->configuration, "midi_in_alsa::initialize: error creating eventfd.");
+      libremidi_handle_error(this->configuration, "error creating eventfd.");
+      return;
     }
+
+    client_open_ = stdx::error{};
   }
 
   ~midi_in_alsa_raw_threaded() override
   {
     // Close a connection if it exists.
     this->midi_in_alsa_raw_threaded::close_port();
+
+    client_open_ = std::errc::not_connected;
   }
 
 private:
   void run_thread(auto parse_func)
   {
     fds_.push_back(this->termination_event);
+    const auto period
+        = std::chrono::duration_cast<std::chrono::milliseconds>(this->configuration.poll_period)
+              .count();
 
     for (;;)
     {
       // Poll
-      ssize_t err = poll(fds_.data(), fds_.size(), -1);
+      ssize_t err = poll(fds_.data(), fds_.size(), period);
       if (err == -EAGAIN)
         continue;
       else if (err < 0)
@@ -245,7 +244,7 @@ private:
     }
   }
 
-  [[nodiscard]] ssize_t start_thread()
+  [[nodiscard]] stdx::error start_thread()
   {
     try
     {
@@ -258,36 +257,37 @@ private:
         this->thread_ = std::thread{
             [this] { run_thread(&midi_in_impl::read_input_buffer_with_timestamps); }};
       }
+      return stdx::error{};
     }
     catch (const std::system_error& e)
     {
       using namespace std::literals;
 
-      error<thread_error>(
+      libremidi_handle_error(
           this->configuration,
-          "midi_in_alsa::start_thread: error starting MIDI input thread: "s + e.what());
-      return false;
+          "error starting MIDI input thread: "s + e.what());
+      return e.code();
     }
-    return true;
+    return stdx::error{};
   }
 
-  bool open_port(const input_port& port, std::string_view /*name*/) override
+  stdx::error open_port(const input_port& port, std::string_view /*name*/) override
   {
-    if (const int err = midi_in_impl::init_port(port); err < 0)
-      return false;
-    if (!start_thread())
-      return false;
-    return true;
+    if (auto err = midi_in_impl::init_port(port); err != stdx::error{})
+      return err;
+    if (auto err = start_thread(); err != stdx::error{})
+      return err;
+    return stdx::error{};
   }
 
-  void close_port() override
+  stdx::error close_port() override
   {
     termination_event.notify();
     if (thread_.joinable())
       thread_.join();
     termination_event.consume(); // Reset to zero
 
-    midi_in_impl::close_port();
+    return midi_in_impl::close_port();
   }
 
   std::thread thread_;
@@ -297,12 +297,18 @@ private:
 class midi_in_alsa_raw_manual : public midi_in_impl
 {
 public:
-  using midi_in_impl::midi_in_impl;
+  midi_in_alsa_raw_manual(input_configuration&& conf, alsa_raw_input_configuration&& apiconf)
+      : midi_in_impl{std::move(conf), std::move(apiconf)}
+  {
+    client_open_ = stdx::error{};
+  }
 
   ~midi_in_alsa_raw_manual()
   {
     // Close a connection if it exists.
     this->close_port();
+
+    client_open_ = std::errc::not_connected;
   }
 
 private:
@@ -326,12 +332,12 @@ private:
     }
   }
 
-  bool open_port(const input_port& p, std::string_view /*name*/) override
+  stdx::error open_port(const input_port& p, std::string_view /*name*/) override
   {
-    if (midi_in_impl::init_port(p) < 0)
-      return false;
+    if (auto err = midi_in_impl::init_port(p); err != stdx::error{})
+      return err;
     send_poll_callback();
-    return true;
+    return stdx::error{};
   }
 };
 }

include/libremidi/backends/alsa_raw/midi_out.hpp

@@ -26,83 +26,73 @@ public:
   midi_out_impl(output_configuration&& conf, alsa_raw_output_configuration&& apiconf)
       : configuration{std::move(conf), std::move(apiconf)}
   {
+    client_open_ = stdx::error{};
   }
 
   ~midi_out_impl() override
   {
     // Close a connection if it exists.
     midi_out_impl::close_port();
+    client_open_ = std::errc::not_connected;
   }
 
   libremidi::API get_current_api() const noexcept override { return libremidi::API::ALSA_RAW; }
 
-  bool open_virtual_port(std::string_view) override
-  {
-    warning(configuration, "midi_out_alsa_raw: open_virtual_port unsupported");
-    return false;
-  }
-  void set_client_name(std::string_view) override
-  {
-    warning(configuration, "midi_out_alsa_raw: set_client_name unsupported");
-  }
-  void set_port_name(std::string_view) override
-  {
-    warning(configuration, "midi_out_alsa_raw: set_port_name unsupported");
-  }
-
-  int connect_port(const char* portname)
+  stdx::error connect_port(const char* portname)
   {
     constexpr int mode = SND_RAWMIDI_SYNC;
     int status = snd.rawmidi.open(NULL, &midiport_, portname, mode);
     if (status < 0)
     {
-      error<driver_error>(
-          this->configuration, "midi_out_alsa_raw::open_port: cannot open device.");
-      return status;
+      libremidi_handle_error(
+          this->configuration, "cannot open device.");
+      return from_errc(status);
     }
-    return status;
+    return stdx::error{};
   }
 
-  bool open_port(const output_port& p, std::string_view) override
+  stdx::error open_port(const output_port& p, std::string_view) override
   {
-    return connect_port(raw_from_port_handle(p.port).to_string().c_str()) == 0;
+    return connect_port(raw_from_port_handle(p.port).to_string().c_str());
   }
 
-  void close_port() override
+  stdx::error close_port() override
   {
     if (midiport_)
       snd.rawmidi.close(midiport_);
     midiport_ = nullptr;
+
+    return stdx::error{};
   }
 
-  void send_message(const unsigned char* message, size_t size) override
+  stdx::error send_message(const unsigned char* message, size_t size) override
   {
     if (!midiport_)
-      error<invalid_use_error>(
+      libremidi_handle_error(
           this->configuration,
-          "midi_out_alsa_raw::send_message: trying to send a message without an open "
+          "trying to send a message without an open "
           "port.");
 
     if (!this->configuration.chunking)
     {
-      write(message, size);
+      return write(message, size);
     }
     else
     {
-      write_chunked(message, size);
+      return write_chunked(message, size);
     }
   }
 
-  bool write(const unsigned char* message, size_t size)
+  stdx::error write(const unsigned char* message, size_t size)
   {
-    if (snd.rawmidi.write(midiport_, message, size) < 0)
+    if (auto err = snd.rawmidi.write(midiport_, message, size); err < 0)
     {
-      error<driver_error>(
-          this->configuration, "midi_out_alsa_raw::send_message: cannot write message.");
-      return false;
+      libremidi_handle_error(
+          this->configuration, "cannot write message.");
+      return from_errc(err);
     }
 
-    return true;
+    return stdx::error{};
   }
 
   std::size_t get_chunk_size() const noexcept
@@ -125,7 +115,7 @@ public:
   }
 
   // inspired from ALSA amidi.c source code
-  void write_chunked(const unsigned char* const begin, size_t size)
+  stdx::error write_chunked(const unsigned char* const begin, size_t size)
   {
     const unsigned char* data = begin;
     const unsigned char* end = begin + size;
@@ -135,8 +125,8 @@ public:
     // Send the first buffer
     std::size_t len = chunk_size;
 
-    if (!write(data, len))
-      return;
+    if (auto err = write(data, len); err != stdx::error{})
+      return err;
 
     data += len;
 
@@ -149,11 +139,11 @@ public:
       {
         if (!configuration.chunking->wait(
                 std::chrono::microseconds((chunk_size - available) * 320), written_bytes))
-          return;
+          return std::errc::protocol_error;
       };
 
       if (!configuration.chunking->wait(configuration.chunking->interval, written_bytes))
-        return;
+        return std::errc::protocol_error;
 
       // Write more data
       len = end - data;
@@ -165,11 +155,13 @@ public:
       if (len > chunk_size)
         len = chunk_size;
 
-      if (!write(data, len))
-        return;
+      if (auto err = write(data, len); err != stdx::error{})
+        return err;
 
       data += len;
     }
+
+    return stdx::error{};
   }
 
   snd_rawmidi_t* midiport_{};

include/libremidi/backends/alsa_raw/observer.hpp

@@ -8,12 +8,12 @@
   #include <libremidi/backends/linux/udev.hpp>
   #include <libremidi/detail/observer.hpp>
 
-  #include <stdexcept>
-
 namespace libremidi::alsa_raw
 {
 template <typename Enumerator>
-class observer_impl_base : public observer_api
+class observer_impl_base
+    : public observer_api
+    , public error_handler
 {
 public:
   struct
@@ -54,7 +54,7 @@ public:
   std::vector<libremidi::input_port> get_input_ports() const noexcept override
   {
     std::vector<libremidi::input_port> ret;
-    Enumerator new_devs;
+    Enumerator new_devs{*this};
 
     new_devs.enumerate_cards();
     for (auto& d : new_devs.inputs)
@@ -67,7 +67,7 @@ public:
   std::vector<libremidi::output_port> get_output_ports() const noexcept override
   {
     std::vector<libremidi::output_port> ret;
-    Enumerator new_devs;
+    Enumerator new_devs{*this};
 
     new_devs.enumerate_cards();
     for (auto& d : new_devs.outputs)
@@ -147,7 +147,7 @@ private:
 
   void check_devices()
   {
-    Enumerator new_devs;
+    Enumerator new_devs{*this};
 
     new_devs.enumerate_cards();
 

include/libremidi/backends/alsa_raw_ump/config.hpp

@@ -6,6 +6,7 @@ namespace libremidi::alsa_raw_ump
 struct input_configuration
 {
   std::function<bool(const manual_poll_parameters&)> manual_poll;
+  std::chrono::milliseconds poll_period{2};
 };
 
 struct output_configuration

include/libremidi/backends/alsa_raw_ump/helpers.hpp

@@ -7,8 +7,10 @@ namespace libremidi::alsa_raw_ump
 {
 struct midi2_enumerator : alsa_raw::enumerator
 {
+  using alsa_raw::enumerator::enumerator;
   void enumerate_devices(int card) override
   {
+    using namespace std::literals;
     char name[128];
 
     sprintf(name, "hw:%d", card);
@@ -28,10 +30,8 @@ struct midi2_enumerator : alsa_raw::enumerator
 
       if (status < 0)
       {
-        error(
-            "alsa_raw_ump::midi2_enumerator::enumerate_devices: "
-            "cannot determine device number: ",
-            snd.strerror(status));
+        handler.libremidi_handle_error(
+            configuration, "Cannot determine device number: "s + snd.strerror(status));
         break;
       }
 

include/libremidi/backends/alsa_raw_ump/midi_in.hpp

@@ -35,32 +35,17 @@ public:
 
   ~midi_in_impl() override { }
 
-  bool open_virtual_port(std::string_view) override
-  {
-    warning(configuration, "alsa_raw_ump::ump: open_virtual_port unsupported");
-    return false;
-  }
-  void set_client_name(std::string_view) override
-  {
-    warning(configuration, "alsa_raw_ump::ump: set_client_name unsupported");
-  }
-  void set_port_name(std::string_view) override
-  {
-    warning(configuration, "alsa_raw_ump::ump: set_port_name unsupported");
-  }
-
   libremidi::API get_current_api() const noexcept override { return libremidi::API::ALSA_RAW_UMP; }
 
   // Must be a string such as: "hw:2,4,1"
-  [[nodiscard]] int do_init_port(const char* portname)
+  [[nodiscard]] stdx::error do_init_port(const char* portname)
   {
     constexpr int mode = 0;
-    SND_RAWMIDI_NONBLOCK;
+    SND_RAWMIDI_NONBLOCK; // fixme
     if (int err = snd.ump.open(&midiport_, 0, portname, mode); err < 0)
     {
-      error<driver_error>(
-          this->configuration, "alsa_raw_ump::ump::open_port: cannot open device.");
-      return err;
+      libremidi_handle_error(this->configuration, "alsa_raw_ump::ump::open_port: cannot open device.");
+      return from_errc(err);
     }
 
     snd_rawmidi_params_t* params{};
@@ -69,49 +54,52 @@ public:
     auto rawmidi = snd.ump.rawmidi(midiport_);
 
     if (int err = snd.ump.rawmidi_params_current(midiport_, params); err < 0)
-      return err;
+      return from_errc(err);
     if (int err = snd.rawmidi.params_set_no_active_sensing(rawmidi, params, 1); err < 0)
-      return err;
+      return from_errc(err);
 
     if (configuration.timestamps == timestamp_mode::NoTimestamp)
     {
       if (int err = snd.rawmidi.params_set_read_mode(rawmidi, params, SND_RAWMIDI_READ_STANDARD);
           err < 0)
-        return err;
+        return from_errc(err);
       if (int err = snd.rawmidi.params_set_clock_type(rawmidi, params, SND_RAWMIDI_CLOCK_NONE);
           err < 0)
-        return err;
+        return from_errc(err);
     }
     else
     {
       if (int err = snd.rawmidi.params_set_read_mode(rawmidi, params, SND_RAWMIDI_READ_TSTAMP);
           err < 0)
-        return err;
+        return from_errc(err);
       if (int err
           = snd.rawmidi.params_set_clock_type(rawmidi, params, SND_RAWMIDI_CLOCK_MONOTONIC);
           err < 0)
-        return err;
+        return from_errc(err);
     }
 
     if (int err = snd.ump.rawmidi_params(midiport_, params); err < 0)
-      return err;
+      return from_errc(err);
 
     return init_pollfd();
   }
 
-  [[nodiscard]] int init_port(const port_information& p)
+  [[nodiscard]] stdx::error init_port(const port_information& p)
   {
     return do_init_port(raw_from_port_handle(p.port).to_string().c_str());
   }
 
-  [[nodiscard]] int init_pollfd()
+  [[nodiscard]] stdx::error init_pollfd()
   {
     int num_fds = snd.ump.poll_descriptors_count(this->midiport_);
 
     this->fds_.clear();
     this->fds_.resize(num_fds);
 
-    return snd.ump.poll_descriptors(this->midiport_, fds_.data(), num_fds);
+    int ret = snd.ump.poll_descriptors(this->midiport_, fds_.data(), num_fds);
+    if (ret < 0)
+      return from_errc(ret);
+    return stdx::error{};
   }
 
   ssize_t do_read_events(auto parse_func, std::span<pollfd> fds)
@@ -143,95 +131,60 @@ public:
 
   ssize_t read_input_buffer()
   {
-    static const constexpr int nbytes = 1024;
-
-    unsigned char bytes[nbytes];
+    static constexpr timestamp_backend_info timestamp_info{
+        .has_absolute_timestamps = false,
+        .absolute_is_monotonic = false,
+        .has_samples = false,
+    };
+    static const constexpr int nwords = 64;
+    uint32_t words[nwords];
 
     ssize_t err = 0;
-    while ((err = snd.ump.read(this->midiport_, bytes, nbytes)) > 0)
+    while ((err = snd.ump.read(this->midiport_, words, nwords * 4)) > 0)
     {
-      std::cerr << "We read: " << nbytes << "bytes !!!!";
-      return 1;
-      // err is the amount of bytes read
-      // decoder_.add_bytes(bytes, err);
+      const auto to_ns = [this] { return absolute_timestamp(); };
+      m_processing.on_bytes({words, words + err / 4}, m_processing.timestamp<timestamp_info>(to_ns, 0));
     }
     return err;
   }
 
-  void set_timestamp(struct timespec ts, timestamp& res)
-  {
-    static constexpr int64_t nanos = 1e9;
-    switch (configuration.timestamps)
-    {
-      // Unneeded here
-      case timestamp_mode::NoTimestamp:
-        break;
-      case timestamp_mode::Relative: {
-        const auto t = static_cast<int64_t>(ts.tv_sec) * nanos + static_cast<int64_t>(ts.tv_nsec);
-        if (firstMessage == true)
-        {
-          firstMessage = false;
-          res = 0;
-        }
-        else
-        {
-          res = t - last_time;
-        }
-        last_time = t;
-        break;
-      }
-      case timestamp_mode::Absolute:
-      case timestamp_mode::SystemMonotonic:
-        res = static_cast<int64_t>(ts.tv_sec) * nanos + static_cast<int64_t>(ts.tv_nsec);
-        break;
-      case timestamp_mode::Custom:
-        res = configuration.get_timestamp(
-            static_cast<int64_t>(ts.tv_sec) * nanos + static_cast<int64_t>(ts.tv_nsec));
-        break;
-    }
-  }
-
   ssize_t read_input_buffer_with_timestamps()
   {
-    static const constexpr int nbytes = 1024;
+    static constexpr timestamp_backend_info timestamp_info{
+        .has_absolute_timestamps = true,
+        .absolute_is_monotonic = true,
+        .has_samples = false,
+    };
 
-    unsigned char bytes[nbytes];
+    static const constexpr int nwords = 64;
+    uint32_t words[nwords];
     struct timespec ts;
 
     ssize_t err = 0;
-    while ((err = snd.ump.tread(this->midiport_, &ts, bytes, nbytes)) > 0)
+    while ((err = snd.ump.tread(this->midiport_, &ts, words, nwords * 4)) > 0)
     {
-      // err is the amount of bytes read
-      int64_t ns{};
-      set_timestamp(ts, ns);
-      std::cerr << "We read: " << nbytes << "bytes !!!!";
-      return 1;
-      // decoder_.add_bytes(bytes, err, ns);
+      const auto to_ns = [ts] {
+        return static_cast<int64_t>(ts.tv_sec) * 1'000'000'000 + static_cast<int64_t>(ts.tv_nsec);
+      };
+      m_processing.on_bytes({words, words + err / 4}, m_processing.timestamp<timestamp_info>(to_ns, 0));
     }
     return err;
   }
 
-  void close_port() override
+  stdx::error close_port() override
   {
     if (midiport_)
       snd.ump.close(midiport_);
     midiport_ = nullptr;
+
+    return stdx::error{};
   }
 
   timestamp absolute_timestamp() const noexcept override { return system_ns(); }
 
-  midi2_enumerator get_device_enumerator() const noexcept
-  {
-    midi2_enumerator device_list;
-    device_list.error_callback
-        = [this](std::string_view text) { this->error<driver_error>(this->configuration, text); };
-    return device_list;
-  }
-
   snd_ump_t* midiport_{};
   std::vector<pollfd> fds_;
-  // midi_stream_decoder decoder_{this->configuration.on_message};
-  int64_t last_time{};
+  midi2::input_state_machine m_processing{this->configuration};
 };
 
 class midi_in_impl_threaded : public midi_in_impl
@@ -243,26 +196,32 @@ public:
   {
     if (this->termination_event < 0)
     {
-      error<driver_error>(
-          this->configuration, "midi_in_alsa::initialize: error creating eventfd.");
+      libremidi_handle_error(this->configuration, "error creating eventfd.");
+      return;
     }
+
+    client_open_ = stdx::error{};
   }
 
   ~midi_in_impl_threaded()
   {
     // Close a connection if it exists.
     this->close_port();
+    client_open_ = std::errc::not_connected;
   }
 
 private:
   void run_thread(auto parse_func)
   {
     fds_.push_back(this->termination_event);
+    const auto period
+        = std::chrono::duration_cast<std::chrono::milliseconds>(this->configuration.poll_period)
+              .count();
 
     for (;;)
     {
       // Poll
-      ssize_t err = poll(fds_.data(), fds_.size(), -1);
+      ssize_t err = poll(fds_.data(), fds_.size(), period);
       if (err == -EAGAIN)
         continue;
       else if (err < 0)
@@ -278,7 +237,7 @@ private:
     }
   }
 
-  [[nodiscard]] int start_thread()
+  [[nodiscard]] stdx::error start_thread()
   {
     try
     {
@@ -291,36 +250,37 @@ private:
         this->thread_ = std::thread{
             [this] { run_thread(&midi_in_impl::read_input_buffer_with_timestamps); }};
       }
+      return stdx::error{};
     }
     catch (const std::system_error& e)
     {
       using namespace std::literals;
 
-      error<thread_error>(
+      libremidi_handle_error(
           this->configuration,
-          "midi_in_alsa::start_thread: error starting MIDI input thread: "s + e.what());
-      return false;
+          "error starting MIDI input thread: "s + e.what());
+      return e.code();
     }
-    return true;
+    return stdx::error{};
   }
 
-  bool open_port(const input_port& port, [[maybe_unused]] std::string_view name) override
+  stdx::error open_port(const input_port& port, [[maybe_unused]] std::string_view name) override
   {
-    if (int err = midi_in_impl::init_port(port); err < 0)
-      return false;
-    if (!start_thread())
-      return false;
-    return true;
+    if (auto err = midi_in_impl::init_port(port); err != stdx::error{})
+      return err;
+    if (auto err = start_thread(); err != stdx::error{})
+      return err;
+    return stdx::error{};
   }
 
-  void close_port() override
+  stdx::error close_port() override
   {
     termination_event.notify();
     if (thread_.joinable())
       thread_.join();
     termination_event.consume(); // Reset to zero
 
-    midi_in_impl::close_port();
+    return midi_in_impl::close_port();
   }
 
   std::thread thread_;
@@ -330,12 +290,18 @@ private:
 class midi_in_impl_manual : public midi_in_impl
 {
 public:
-  using midi_in_impl::midi_in_impl;
+  midi_in_impl_manual(ump_input_configuration&& conf, alsa_raw_ump::input_configuration&& apiconf)
+      : midi_in_impl{std::move(conf), std::move(apiconf)}
+  {
+    client_open_ = stdx::error{};
+  }
 
   ~midi_in_impl_manual()
   {
     // Close a connection if it exists.
     this->close_port();
+
+    client_open_ = std::errc::not_connected;
   }
 
 private:
@@ -359,12 +325,12 @@ private:
     }
   }
 
-  bool open_port(const input_port& p, [[maybe_unused]] std::string_view name) override
+  stdx::error open_port(const input_port& p, [[maybe_unused]] std::string_view name) override
   {
-    if (midi_in_impl::init_port(p) < 0)
-      return false;
+    if (auto err = midi_in_impl::init_port(p); err != stdx::error{})
+      return err;
     send_poll_callback();
-    return true;
+    return stdx::error{};
   }
 };
 }

include/libremidi/backends/alsa_raw_ump/midi_out.hpp

@@ -29,76 +29,63 @@ public:
       : configuration{std::move(conf), std::move(apiconf)}
   {
     assert(snd.ump.available);
+    client_open_ = stdx::error{};
   }
 
   ~midi_out_impl() override
   {
     // Close a connection if it exists.
     midi_out_impl::close_port();
+    client_open_ = std::errc::not_connected;
   }
 
-  libremidi::API get_current_api() const noexcept override { return libremidi::API::ALSA_RAW; }
+  libremidi::API get_current_api() const noexcept override { return libremidi::API::ALSA_RAW_UMP; }
 
-  bool open_virtual_port(std::string_view) override
-  {
-    warning(configuration, "midi_out_alsa_raw: open_virtual_port unsupported");
-    return false;
-  }
-  void set_client_name(std::string_view) override
-  {
-    warning(configuration, "midi_out_alsa_raw: set_client_name unsupported");
-  }
-  void set_port_name(std::string_view) override
-  {
-    warning(configuration, "midi_out_alsa_raw: set_port_name unsupported");
-  }
-
-  int connect_port(const char* portname)
+  stdx::error connect_port(const char* portname)
   {
     constexpr int mode = SND_RAWMIDI_SYNC;
-    int status = snd.ump.open(NULL, &midiport_, portname, mode);
-    if (status < 0)
+    int ret = snd.ump.open(NULL, &midiport_, portname, mode);
+    if (ret < 0)
     {
-      error<driver_error>(
-          this->configuration, "midi_out_alsa_raw::open_port: cannot open device.");
-      return status;
+      libremidi_handle_error(this->configuration, "cannot open device.");
+      return from_errc(ret);
     }
-    return status;
+    return stdx::error{};
   }
 
-  bool open_port(const output_port& p, std::string_view) override
+  stdx::error open_port(const output_port& p, std::string_view) override
   {
-    return connect_port(raw_from_port_handle(p.port).to_string().c_str()) == 0;
+    return connect_port(raw_from_port_handle(p.port).to_string().c_str());
   }
 
-  void close_port() override
+  stdx::error close_port() override
   {
     if (midiport_)
       snd.ump.close(midiport_);
     midiport_ = nullptr;
+    return stdx::error{};
   }
 
-  void send_ump(const uint32_t* ump_stream, std::size_t count) override
+  stdx::error send_ump(const uint32_t* ump_stream, std::size_t count) override
   {
     if (!midiport_)
-      error<invalid_use_error>(
+      libremidi_handle_error(
           this->configuration,
-          "midi_out_alsa_raw::send_message: trying to send a message without an open "
+          "trying to send a message without an open "
           "port.");
 
-    write(ump_stream, count * sizeof(uint32_t));
+    return write(ump_stream, count * sizeof(uint32_t));
   }
 
-  bool write(const uint32_t* ump_stream, size_t bytes)
+  stdx::error write(const uint32_t* ump_stream, size_t bytes)
   {
-    if (snd.ump.write(midiport_, ump_stream, bytes) < 0)
+    if (auto err = snd.ump.write(midiport_, ump_stream, bytes); err < 0)
     {
-      error<driver_error>(
-          this->configuration, "midi_out_alsa_raw::send_message: cannot write message.");
-      return false;
+      libremidi_handle_error(this->configuration, "cannot write message.");
+      return from_errc(err);
     }
 
-    return true;
+    return stdx::error{};
   }
 
   snd_ump_t* midiport_{};

include/libremidi/backends/alsa_seq/config.hpp

@@ -38,6 +38,7 @@ struct input_configuration
   snd_seq_t* context{};
   std::function<bool(const poll_parameters&)> manual_poll;
   std::function<bool(snd_seq_addr_t)> stop_poll;
+  std::chrono::milliseconds poll_period{2};
 
   static constexpr int midi_version = 1;
 };
@@ -56,6 +57,7 @@ struct observer_configuration
   snd_seq_t* context{};
   std::function<bool(const poll_parameters&)> manual_poll;
   std::function<bool(snd_seq_addr_t)> stop_poll;
+  std::chrono::milliseconds poll_period{100};
 
   static constexpr int midi_version = 1;
 };

include/libremidi/backends/alsa_seq/helpers.hpp

@@ -177,18 +177,20 @@ struct alsa_data
     }
   }
 
-  void set_client_name(std::string_view clientName)
+  stdx::error set_client_name(std::string_view clientName)
   {
-    snd.seq.set_client_name(seq, clientName.data());
+    int ret = snd.seq.set_client_name(seq, clientName.data());
+    return from_errc(ret);
   }
 
-  void set_port_name(std::string_view portName)
+  stdx::error set_port_name(std::string_view portName)
   {
     snd_seq_port_info_t* pinfo;
     snd_seq_port_info_alloca(&pinfo);
     snd.seq.get_port_info(seq, vport, pinfo);
     snd.seq.port_info_set_name(pinfo, portName.data());
-    snd.seq.set_port_info(seq, vport, pinfo);
+    int ret = snd.seq.set_port_info(seq, vport, pinfo);
+    return from_errc(ret);
   }
 
   unsigned int get_port_count(int caps) const
@@ -209,9 +211,9 @@ struct alsa_data
     // snd.seq.port_info_set_port(src_pinfo, port);
 
     // {
-    //   self.template error<invalid_parameter_error>(
+    //   self.libremidi_handle_error(
     //       self.configuration,
-    //       "alsa::get_port_info: invalid 'portNumber' argument: " + std::to_string(portNumber));
+    //       "invalid 'portNumber' argument: " + std::to_string(portNumber));
     //   return {};
     // }
     snd_seq_addr_t addr;
@@ -270,8 +272,8 @@ struct alsa_data
     // Make subscription
     if (int err = snd.seq.port_subscribe_malloc(&this->subscription); err < 0)
     {
-      self.template error<driver_error>(
-          self.configuration, "create_connection: ALSA error allocation port subscription.");
+      self.libremidi_handle_error(
+          self.configuration, "ALSA error allocation port subscription.");
       return err;
     }
 

include/libremidi/backends/alsa_seq/midi_in.hpp

@@ -17,7 +17,7 @@ using midi_in_base
     = std::conditional_t<ConfigurationImpl::midi_version == 1, midi1::in_api, midi2::in_api>;
 template <typename ConfigurationImpl>
 using midi_in_processing = std::conditional_t<
-    ConfigurationImpl::midi_version == 1, midi1::input_state_machine, dummy_processing>;
+    ConfigurationImpl::midi_version == 1, midi1::input_state_machine, midi2::input_state_machine>;
 
 template <typename ConfigurationBase, typename ConfigurationImpl>
 class midi_in_impl
@@ -55,9 +55,9 @@ public:
   {
     if (init_client(configuration) < 0)
     {
-      error<driver_error>(
+      libremidi_handle_error(
           this->configuration,
-          "midi_in_alsa::initialize: error creating ALSA sequencer client "
+          "error creating ALSA sequencer client "
           "object.");
       return;
     }
@@ -80,8 +80,7 @@ public:
       int result = snd.midi.event_new(0, &coder);
       if (result < 0)
       {
-        error<driver_error>(
-            this->configuration, "midi_in_alsa::initialize: error during snd_midi_event_new.");
+        libremidi_handle_error(this->configuration, "error during snd_midi_event_new.");
         return;
       }
       snd.midi.event_init(coder);
@@ -105,7 +104,13 @@ public:
       snd.seq.close(this->seq);
   }
 
-  libremidi::API get_current_api() const noexcept override { return libremidi::API::ALSA_SEQ; }
+  libremidi::API get_current_api() const noexcept override
+  {
+    if constexpr (ConfigurationImpl::midi_version == 1)
+      return libremidi::API::ALSA_SEQ;
+    else
+      return libremidi::API::ALSA_SEQ_UMP;
+  }
 
   [[nodiscard]] int create_port(std::string_view portName)
   {
@@ -157,14 +162,13 @@ public:
 
     if (int ret = create_port(portName); ret < 0)
     {
-      error<driver_error>(configuration, "midi_in_alsa::create_port: ALSA error creating port.");
+      libremidi_handle_error(configuration, "ALSA error creating port.");
       return ret;
     }
 
     if (int ret = connect_port(*source); ret < 0)
     {
-      error<driver_error>(
-          configuration, "midi_in_alsa::create_port: ALSA error making port connection.");
+      libremidi_handle_error(configuration, "ALSA error making port connection.");
       return ret;
     }
 
@@ -184,63 +188,21 @@ public:
     return 0;
   }
 
-  void close_port() override
+  stdx::error close_port() override
   {
     unsubscribe();
     stop_queue();
+    return stdx::error{};
   }
 
-  void set_client_name(std::string_view clientName) override
+  stdx::error set_client_name(std::string_view clientName) override
   {
-    alsa_data::set_client_name(clientName);
+    return alsa_data::set_client_name(clientName);
   }
 
-  void set_port_name(std::string_view portName) override { alsa_data::set_port_name(portName); }
-
-protected:
-  void set_timestamp(const auto& ev, auto& msg) noexcept
+  stdx::error set_port_name(std::string_view portName) override
   {
-    static constexpr int64_t nanos = 1e9;
-    switch (configuration.timestamps)
-    {
-      case timestamp_mode::NoTimestamp:
-        msg.timestamp = 0;
-        return;
-      case timestamp_mode::Relative: {
-        const auto t1 = static_cast<int64_t>(ev.time.time.tv_sec) * nanos
-                        + static_cast<int64_t>(ev.time.time.tv_nsec);
-        const auto t0 = static_cast<int64_t>(last_time.tv_sec) * nanos
-                        + static_cast<int64_t>(last_time.tv_nsec);
-        const auto time = t1 - t0;
-
-        last_time = ev.time.time;
-
-        if (this->firstMessage == true)
-        {
-          this->firstMessage = false;
-          msg.timestamp = 0;
-        }
-        else
-        {
-          msg.timestamp = time;
-        }
-        return;
-      }
-      case timestamp_mode::Absolute: {
-        msg.timestamp = ev.time.time.tv_sec * nanos + ev.time.time.tv_nsec;
-        break;
-      }
-      case timestamp_mode::Custom: {
-        msg.timestamp
-            = configuration.get_timestamp(ev.time.time.tv_sec * nanos + ev.time.time.tv_nsec);
-        break;
-      }
-      case timestamp_mode::SystemMonotonic: {
-        namespace clk = std::chrono;
-        msg.timestamp = system_ns();
-        break;
-      }
-    }
+    return alsa_data::set_port_name(portName);
   }
 
   timestamp absolute_timestamp() const noexcept override
@@ -303,12 +265,14 @@ protected:
       snd_seq_event_t* ev{};
       event_handle handle{snd};
       int result = 0;
-      while ((result = snd.seq.event_input(seq, &ev)) > 0)
+      if ((result = snd.seq.event_input(seq, &ev)) > 0)
       {
         handle.reset(ev);
         if (int err = process_event(*ev); err < 0)
+        {
           return err;
         }
+      }
       return result;
     }
     else
@@ -346,11 +310,17 @@ protected:
       }
     }
 
-    // MIDI 2 : no decoder, we can just send the UMP data directly, yay
-    libremidi::ump ump;
-    std::memcpy(ump.data, ev.ump, sizeof(ev.ump));
-    set_timestamp(ev, ump);
-    configuration.on_message(std::move(ump));
+    static constexpr timestamp_backend_info timestamp_info{
+        .has_absolute_timestamps = true,
+        .absolute_is_monotonic = false,
+        .has_samples = false,
+    };
+    const auto to_ns = [ts = ev.time.time] {
+      return static_cast<int64_t>(ts.tv_sec) * 1'000'000'000 + static_cast<int64_t>(ts.tv_nsec);
+    };
+
+    m_processing.on_bytes_multi(
+        {ev.ump, ev.ump + 4}, m_processing.template timestamp<timestamp_info>(to_ns, 0));
     return 0;
   }
 
@@ -370,7 +340,6 @@ protected:
 #endif
 
   int queue_id{}; // an input queue is needed to get timestamped events
-  snd_seq_real_time_t last_time{};
 
   // Only needed for midi 1
   std::vector<unsigned char> decoding_buffer = std::vector<unsigned char>(4096);
@@ -386,62 +355,65 @@ public:
   {
     if (this->termination_event < 0)
     {
-      this->template error<driver_error>(
-          this->configuration, "midi_in_alsa::initialize: error creating eventfd.");
-    }
+      this->libremidi_handle_error(this->configuration, "error creating eventfd.");
+      return;
     }
 
-  ~midi_in_alsa_threaded() { this->close_port(); }
+    this->client_open_ = stdx::error{};
+  }
+
+  ~midi_in_alsa_threaded()
+  {
+    this->close_port();
+    this->client_open_ = std::errc::not_connected;
+  }
 
 private:
-  bool open_port(const input_port& pt, std::string_view local_port_name) override
+  stdx::error open_port(const input_port& pt, std::string_view local_port_name) override
   {
     if (int err = this->init_port(this->to_address(pt), local_port_name); err < 0)
-      return false;
+      return from_errc(err);
 
-    if (!start_thread())
-      return false;
-
-    return true;
+    return this->start_thread();
   }
 
-  bool open_virtual_port(std::string_view portName) override
+  stdx::error open_virtual_port(std::string_view portName) override
   {
     if (int err = this->init_virtual_port(portName); err < 0)
-      return false;
+      return from_errc(err);
 
-    if (!this->start_thread())
-      return false;
-    return true;
+    return this->start_thread();
   }
 
-  void close_port() override
+  stdx::error close_port() override
   {
-    midi_in_impl<ConfigurationBase, ConfigurationImpl>::close_port();
+    // FIXME shouldn't we always close the thread
+    auto err = midi_in_impl<ConfigurationBase, ConfigurationImpl>::close_port();
 
     stop_thread();
+
+    return err;
   }
 
-  [[nodiscard]] int start_thread()
+  [[nodiscard]] stdx::error start_thread()
   {
     try
     {
       this->thread = std::thread([this] { thread_handler(); });
+      return stdx::error{};
     }
     catch (const std::system_error& e)
     {
       using namespace std::literals;
       this->unsubscribe();
 
-      this->template error<thread_error>(
-          this->configuration,
-          "midi_in_alsa::start_thread: error starting MIDI input thread: "s + e.what());
-      return false;
+      this->libremidi_handle_error(
+          this->configuration, "error starting MIDI input thread: "s + e.what());
+      return e.code();
     }
-    return true;
   }
 
-  void stop_thread()
+  stdx::error stop_thread()
   {
     termination_event.notify();
 
@@ -449,6 +421,7 @@ private:
       this->thread.join();
 
     termination_event.consume();
+    return stdx::error{};
   }
 
   void thread_handler()
@@ -458,12 +431,15 @@ private:
     poll_fds[0] = this->termination_event;
     alsa_data::snd.seq.poll_descriptors(this->seq, poll_fds + 1, poll_fd_count - 1, POLLIN);
 
+    const auto period
+        = std::chrono::duration_cast<std::chrono::milliseconds>(this->configuration.poll_period)
+              .count();
     for (;;)
     {
       if (alsa_data::snd.seq.event_input_pending(this->seq, 1) == 0)
       {
         // No data pending
-        if (poll(poll_fds, poll_fd_count, -1) >= 0)
+        if (poll(poll_fds, poll_fd_count, period) >= 0)
         {
           // We got our stop-thread signal
           if (termination_event.ready(poll_fds[0]))
@@ -486,12 +462,8 @@ private:
       }
 #endif
 
-      (void)res;
-#if defined(__LIBREMIDI_DEBUG__)
       if (res < 0)
-        std::cerr << "midi_in_alsa::thread_handler: MIDI input error: " << snd.strerror(res)
-                  << "\n";
-#endif
+        LIBREMIDI_LOG("MIDI input error: ", this->snd.strerror(res));
     }
   }
 
@@ -527,31 +499,33 @@ public:
 
   ~midi_in_alsa_manual() { this->close_port(); }
 
-  bool open_port(const input_port& pt, std::string_view local_port_name) override
+  stdx::error open_port(const input_port& pt, std::string_view local_port_name) override
   {
     if (int err = this->init_port(this->to_address(pt), local_port_name); err < 0)
-      return false;
+      return from_errc(err);
 
     if (int err = init_callback(); err < 0)
-      return false;
-    return true;
+      return from_errc(err);
+
+    return stdx::error{};
   }
 
-  bool open_virtual_port(std::string_view name) override
+  stdx::error open_virtual_port(std::string_view name) override
   {
     if (int err = this->init_virtual_port(name); err < 0)
-      return false;
+      return from_errc(err);
 
     if (int err = init_callback(); err < 0)
-      return false;
-    return true;
+      return from_errc(err);
+
+    return stdx::error{};
   }
 
-  void close_port() override
+  stdx::error close_port() override
   {
     this->configuration.stop_poll(this->vaddr);
 
-    midi_in_impl<ConfigurationBase, ConfigurationImpl>::close_port();
+    return midi_in_impl<ConfigurationBase, ConfigurationImpl>::close_port();
   }
 };
 }

include/libremidi/backends/alsa_seq/midi_out.hpp

@@ -23,22 +23,21 @@ public:
   {
     if (init_client(configuration) < 0)
     {
-      error<driver_error>(
+      libremidi_handle_error(
           this->configuration,
-          "midi_in_alsa::initialize: error creating ALSA sequencer client "
+          "error creating ALSA sequencer client "
           "object.");
       return;
     }
 
     if (snd.midi.event_new(this->bufferSize, &this->coder) < 0)
     {
-      error<driver_error>(
-          this->configuration,
-          "midi_out_alsa::initialize: error initializing MIDI event "
-          "parser.");
+      libremidi_handle_error(this->configuration, "error initializing MIDI event parser.");
       return;
     }
     snd.midi.event_init(this->coder);
+
+    this->client_open_ = stdx::error{};
   }
 
   ~midi_out_impl() override
@@ -54,6 +53,8 @@ public:
 
     if (!configuration.context)
       snd.seq.close(this->seq);
+
+    client_open_ = std::errc::not_connected;
   }
 
   libremidi::API get_current_api() const noexcept override { return libremidi::API::ALSA_SEQ; }
@@ -65,55 +66,60 @@ public:
         SND_SEQ_PORT_TYPE_MIDI_GENERIC | SND_SEQ_PORT_TYPE_APPLICATION, std::nullopt);
   }
 
-  bool open_port(const output_port& p, std::string_view portName) override
+  stdx::error open_port(const output_port& p, std::string_view portName) override
   {
     unsigned int nSrc = this->get_port_count(SND_SEQ_PORT_CAP_WRITE | SND_SEQ_PORT_CAP_SUBS_WRITE);
     if (nSrc < 1)
     {
-      error<no_devices_found_error>(
-          this->configuration, "midi_out_alsa::open_port: no MIDI output sources found!");
-      return false;
+      libremidi_handle_error(this->configuration, "no MIDI output sources found!");
+      return make_error_code(std::errc::no_such_device);
     }
 
     auto sink = get_port_info(p);
     if (!sink)
-      return false;
+      return std::errc::invalid_argument;
 
     if (int err = create_port(portName); err < 0)
     {
-      error<driver_error>(configuration, "midi_out_alsa::create_port: ALSA error creating port.");
-      return false;
+      libremidi_handle_error(configuration, "ALSA error creating port.");
+      return from_errc(err);
     }
 
     snd_seq_addr_t source{
         .client = (unsigned char)snd.seq.client_id(this->seq), .port = (unsigned char)this->vport};
     if (int err = create_connection(*this, source, *sink, true); err < 0)
     {
-      error<driver_error>(
-          configuration, "midi_out_alsa::create_port: ALSA error making port connection.");
-      return false;
+      libremidi_handle_error(configuration, "ALSA error making port connection.");
+      return from_errc(err);
     }
 
-    return true;
+    return stdx::error{};
   }
 
-  bool open_virtual_port(std::string_view portName) override
+  stdx::error open_virtual_port(std::string_view portName) override
   {
     if (int err = create_port(portName); err < 0)
-      return false;
-    return true;
+      return from_errc(err);
+    return stdx::error{};
   }
 
-  void close_port() override { unsubscribe(); }
-
-  void set_client_name(std::string_view clientName) override
+  stdx::error close_port() override
   {
-    alsa_data::set_client_name(clientName);
+    unsubscribe();
+    return stdx::error{};
   }
 
-  void set_port_name(std::string_view portName) override { alsa_data::set_port_name(portName); }
+  stdx::error set_client_name(std::string_view clientName) override
+  {
+    return alsa_data::set_client_name(clientName);
+  }
 
-  void send_message(const unsigned char* message, std::size_t size) override
+  stdx::error set_port_name(std::string_view portName) override
+  {
+    return alsa_data::set_port_name(portName);
+  }
+
+  stdx::error send_message(const unsigned char* message, std::size_t size) override
   {
     int64_t result{};
     if (size > this->bufferSize)
@@ -122,11 +128,11 @@ public:
       result = snd.midi.event_resize_buffer(this->coder, size);
       if (result != 0)
       {
-        error<driver_error>(
+        libremidi_handle_error(
             this->configuration,
-            "midi_out_alsa::send_message: ALSA error resizing MIDI event "
+            "ALSA error resizing MIDI event "
             "buffer.");
-        return;
+        return std::errc::no_buffer_space;
       }
     }
 
@@ -144,14 +150,14 @@ public:
       result = snd.midi.event_encode(this->coder, message + offset, (long)(nBytes - offset), &ev);
       if (result < 0)
       {
-        warning(this->configuration, "midi_out_alsa::send_message: event parsing error!");
-        return;
+        libremidi_handle_warning(this->configuration, "event parsing error!");
+        return std::errc::bad_message;
       }
 
       if (ev.type == SND_SEQ_EVENT_NONE)
       {
-        warning(this->configuration, "midi_out_alsa::send_message: incomplete message!");
-        return;
+        libremidi_handle_warning(this->configuration, "incomplete message!");
+        return std::errc::message_size;
       }
 
       offset += result;
@@ -159,13 +165,12 @@ public:
       result = snd.seq.event_output(this->seq, &ev);
       if (result < 0)
       {
-        warning(
-            this->configuration,
-            "midi_out_alsa::send_message: error sending MIDI message to port.");
-        return;
+        libremidi_handle_warning(this->configuration, "error sending MIDI message to port.");
+        return std::errc::io_error;
       }
     }
     snd.seq.drain_output(this->seq);
+    return stdx::error{};
   }
 
 private:

include/libremidi/backends/alsa_seq/observer.hpp

@@ -2,6 +2,7 @@
 #include <libremidi/backends/alsa_seq/config.hpp>
 #include <libremidi/backends/alsa_seq/helpers.hpp>
 #include <libremidi/backends/linux/helpers.hpp>
+#include <libremidi/detail/midi_api.hpp>
 #include <libremidi/detail/observer.hpp>
 
 #include <alsa/asoundlib.h>
@@ -26,6 +27,7 @@ template <typename ConfigurationImpl>
 class observer_impl
     : public observer_api
     , public alsa_data
+    , public error_handler
 {
 public:
   struct
@@ -40,7 +42,11 @@ public:
     using namespace std::literals;
     if (int err = init_client(configuration); err < 0)
     {
-      throw driver_error("observer_alsa: snd_seq_open failed");
+      libremidi_handle_error(
+          this->configuration,
+          "error creating ALSA sequencer client "
+          "object.");
+      return;
     }
 
     if (!configuration.has_callbacks())
@@ -65,7 +71,8 @@ public:
           *this, "libremidi-observe", caps, SND_SEQ_PORT_TYPE_APPLICATION, false);
       if (err < 0)
       {
-        throw driver_error("observer: ALSA error creating port.");
+        libremidi_handle_error(this->configuration, "error creating ALSA sequencer port.");
+        return;
       }
     }
 
@@ -75,7 +82,8 @@ public:
           = snd.seq.connect_from(seq, vport, SND_SEQ_CLIENT_SYSTEM, SND_SEQ_PORT_SYSTEM_ANNOUNCE);
       if (err < 0)
       {
-        throw driver_error("observer_alsa: snd_seq_connect_from failed");
+        libremidi_handle_error(this->configuration, "error connecting to ALSA sequencer.");
+        return;
       }
     }
   }
@@ -98,9 +106,13 @@ public:
 
     const auto tp = snd.seq.port_info_get_type(pinfo);
     bool ok = this->configuration.track_any;
+
+    static constexpr auto virtual_port
+        = SND_SEQ_PORT_TYPE_SOFTWARE | SND_SEQ_PORT_TYPE_SYNTHESIZER;
+
     if ((tp & SND_SEQ_PORT_TYPE_HARDWARE) && this->configuration.track_hardware)
       ok = true;
-    else if ((tp & SND_SEQ_PORT_TYPE_SOFTWARE) && this->configuration.track_virtual)
+    else if ((tp & virtual_port) && this->configuration.track_virtual)
       ok = true;
     if (!ok)
       return {};
@@ -271,9 +283,12 @@ public:
     // Start the listening thread
     thread = std::thread{[this] {
       auto& snd = alsa_data::snd;
+      const auto period
+          = std::chrono::duration_cast<std::chrono::milliseconds>(this->configuration.poll_period)
+                .count();
       for (;;)
       {
-        int err = poll(descriptors_.data(), descriptors_.size(), -1);
+        int err = poll(descriptors_.data(), descriptors_.size(), period);
         if (err >= 0)
         {
           // We got our stop-thread signal

include/libremidi/backends/alsa_seq_ump/config.hpp

@@ -28,6 +28,7 @@ struct input_configuration
   snd_seq_t* context{};
   std::function<bool(const poll_parameters&)> manual_poll;
   std::function<bool(snd_seq_addr_t)> stop_poll;
+  std::chrono::milliseconds poll_period{2};
 
   static constexpr int midi_version = 2;
 };
@@ -46,6 +47,7 @@ struct observer_configuration
   snd_seq_t* context{};
   std::function<bool(const libremidi::alsa_seq::poll_parameters&)> manual_poll;
   std::function<bool(snd_seq_addr_t)> stop_poll;
+  std::chrono::milliseconds poll_period{100};
 
   static constexpr int midi_version = 2;
 };

include/libremidi/backends/alsa_seq_ump/midi_out.hpp

@@ -27,22 +27,14 @@ public:
     assert(snd.seq.ump.available);
     if (init_client(configuration) < 0)
     {
-      error<driver_error>(
+      libremidi_handle_error(
           this->configuration,
-          "midi_in_alsa::initialize: error creating ALSA sequencer client "
+          "error creating ALSA sequencer client "
           "object.");
       return;
     }
 
-    if (snd.midi.event_new(this->bufferSize, &this->coder) < 0)
-    {
-      error<driver_error>(
-          this->configuration,
-          "midi_out_alsa::initialize: error initializing MIDI event "
-          "parser.");
-      return;
-    }
-    snd.midi.event_init(this->coder);
+    this->client_open_ = stdx::error{};
   }
 
   ~midi_out_impl() override
@@ -53,14 +45,14 @@ public:
     // Cleanup.
     if (this->vport >= 0)
       snd.seq.delete_port(this->seq, this->vport);
-    if (this->coder)
-      snd.midi.event_free(this->coder);
 
     if (!configuration.context)
       snd.seq.close(this->seq);
+
+    client_open_ = std::errc::not_connected;
   }
 
-  libremidi::API get_current_api() const noexcept override { return libremidi::API::ALSA_SEQ; }
+  libremidi::API get_current_api() const noexcept override { return libremidi::API::ALSA_SEQ_UMP; }
 
   [[nodiscard]] int create_port(std::string_view portName)
   {
@@ -70,55 +62,60 @@ public:
         SND_SEQ_PORT_TYPE_MIDI_GENERIC | SND_SEQ_PORT_TYPE_APPLICATION, std::nullopt);
   }
 
-  bool open_port(const output_port& p, std::string_view portName) override
+  stdx::error open_port(const output_port& p, std::string_view portName) override
   {
     unsigned int nSrc = this->get_port_count(SND_SEQ_PORT_CAP_WRITE | SND_SEQ_PORT_CAP_SUBS_WRITE);
     if (nSrc < 1)
     {
-      error<no_devices_found_error>(
-          this->configuration, "midi_out_alsa::open_port: no MIDI output sources found!");
-      return false;
+      libremidi_handle_error(this->configuration, "no MIDI output sources found!");
+      return make_error_code(std::errc::no_such_device);
     }
 
     auto sink = get_port_info(p);
     if (!sink)
-      return false;
+      return std::errc::invalid_argument;
 
     if (int err = create_port(portName); err < 0)
     {
-      error<driver_error>(configuration, "midi_out_alsa::create_port: ALSA error creating port.");
-      return false;
+      libremidi_handle_error(configuration, "ALSA error creating port.");
+      return from_errc(err);
     }
 
     snd_seq_addr_t source{
         .client = (unsigned char)snd.seq.client_id(this->seq), .port = (unsigned char)this->vport};
     if (int err = create_connection(*this, source, *sink, true); err < 0)
     {
-      error<driver_error>(
-          configuration, "midi_out_alsa::create_port: ALSA error making port connection.");
-      return false;
+      libremidi_handle_error(configuration, "ALSA error making port connection.");
+      return from_errc(err);
     }
 
-    return true;
+    return stdx::error{};
   }
 
-  bool open_virtual_port(std::string_view portName) override
+  stdx::error open_virtual_port(std::string_view portName) override
   {
     if (int err = create_port(portName); err < 0)
-      return false;
-    return true;
+      return from_errc(err);
+    return stdx::error{};
   }
 
-  void close_port() override { unsubscribe(); }
-
-  void set_client_name(std::string_view clientName) override
+  stdx::error close_port() override
   {
-    alsa_data::set_client_name(clientName);
+    unsubscribe();
+    return stdx::error{};
   }
 
-  void set_port_name(std::string_view portName) override { alsa_data::set_port_name(portName); }
+  stdx::error set_client_name(std::string_view clientName) override
+  {
+    return alsa_data::set_client_name(clientName);
+  }
 
-  void send_ump(const uint32_t* ump_stream, std::size_t count) override
+  stdx::error set_port_name(std::string_view portName) override
+  {
+    return alsa_data::set_port_name(portName);
+  }
+
+  stdx::error send_ump(const uint32_t* ump_stream, std::size_t count) override
   {
     snd_seq_ump_event_t ev;
 
@@ -128,24 +125,20 @@ public:
     snd_seq_ev_set_subs(&ev);
     snd_seq_ev_set_direct(&ev);
 
-    auto write_func = [this, &ev](const uint32_t* ump, int64_t bytes) {
+    auto write_func = [this, &ev](const uint32_t* ump, int64_t bytes) -> std::errc {
       std::memcpy(ev.ump, ump, bytes);
-      const int result = snd.seq.ump.event_output_direct(this->seq, &ev);
-      if (result < 0)
+      const int ret = snd.seq.ump.event_output_direct(this->seq, &ev);
+      if (ret < 0)
       {
-        warning(
-            this->configuration,
-            "midi_out_alsa::send_message: error sending MIDI message to port.");
-        return libremidi::segmentation_error::other;
+        libremidi_handle_warning(this->configuration, "error sending MIDI message to port.");
+        return static_cast<std::errc>(-ret);
       }
-      return libremidi::segmentation_error::no_error;
+      return std::errc{0};
     };
     segment_ump_stream(ump_stream, count, write_func, []() {});
 
     snd.seq.drain_output(this->seq);
+    return stdx::error{};
   }
-
-private:
-  unsigned int bufferSize{32};
 };
 }

include/libremidi/backends/coremidi/config.hpp

@@ -16,6 +16,7 @@ typedef UInt32 MIDIObjectRef;
 typedef MIDIObjectRef MIDIClientRef;
 #else
 using MIDIClientRef = uint32_t;
+using MIDIObjectRef = uint32_t;
 #endif
 namespace libremidi
 {

include/libremidi/backends/coremidi/error_domain.hpp

@@ -0,0 +1,72 @@
+#pragma once
+#include <libremidi/error.hpp>
+
+#include <CoreMIDI/CoreMIDI.h>
+
+namespace libremidi
+{
+struct coremidi_error_domain : public stdx::error_domain
+{
+public:
+  constexpr coremidi_error_domain() noexcept
+      : error_domain{{0xa32b080ac770514eULL, 0xef59a407f921da43ULL}}
+  {
+  }
+
+  stdx::string_ref name() const noexcept override { return "coremidi"; }
+
+  bool equivalent(const stdx::error& lhs, const stdx::error& rhs) const noexcept override
+  {
+    if (lhs.domain() == rhs.domain())
+      return error_cast<std::errc>(lhs) == error_cast<std::errc>(rhs);
+
+    return false;
+  }
+
+  stdx::string_ref message(const stdx::error& e) const noexcept override
+  {
+    switch (error_cast<OSStatus>(e))
+    {
+      case kMIDIInvalidClient:
+        return "Invalid Client";
+      case kMIDIInvalidPort:
+        return "Invalid Port";
+      case kMIDIWrongEndpointType:
+        return "Wrong EndpointT ype";
+      case kMIDINoConnection:
+        return "No Connection";
+      case kMIDIUnknownEndpoint:
+        return "Unknown Endpoint";
+      case kMIDIUnknownProperty:
+        return "Unknown Property";
+      case kMIDIWrongPropertyType:
+        return "Wrong Property Type";
+      case kMIDINoCurrentSetup:
+        return "No Current Setup";
+      case kMIDIMessageSendErr:
+        return "Message Send Error";
+      case kMIDIServerStartErr:
+        return "Server Start Error";
+      case kMIDISetupFormatErr:
+        return "Setup Format Error";
+      case kMIDIWrongThread:
+        return "Wrong Thread";
+      case kMIDIObjectNotFound:
+        return "Object Not Found";
+      case kMIDIIDNotUnique:
+        return "ID Not Unique";
+      case kMIDINotPermitted:
+        return "Not Permitted";
+      case kMIDIUnknownError:
+        return "Unknown Error";
+    }
+    return "Unknown error code";
+  }
+};
+
+inline stdx::error from_osstatus(OSStatus ret) noexcept
+{
+  static constexpr coremidi_error_domain domain{};
+  return {ret, domain};
+}
+}

include/libremidi/backends/coremidi/helpers.hpp

@@ -1,7 +1,9 @@
 #pragma once
 #include <libremidi/detail/memory.hpp>
 #include <libremidi/detail/midi_api.hpp>
+#include <libremidi/error_handler.hpp>
 #include <libremidi/input_configuration.hpp>
+#include <libremidi/backends/coremidi/error_domain.hpp>
 
 #include <CoreMIDI/CoreMIDI.h>
 #include <CoreServices/CoreServices.h>
@@ -28,7 +30,8 @@ namespace
 static inline std::string get_string_property(MIDIObjectRef object, CFStringRef property) noexcept
 {
   CFStringRef res;
-  MIDIObjectGetStringProperty(object, property, &res);
+  if (MIDIObjectGetStringProperty(object, property, &res) || !res)
+    return {};
 
   char name[256];
   CFStringGetCString(res, name, sizeof(name), kCFStringEncodingUTF8);
@@ -215,15 +218,15 @@ locate_object(auto& self, const port_information& info, MIDIObjectType requested
   auto ret = MIDIObjectFindByUniqueID(uid, &object, &type);
   if (ret != noErr)
   {
-    self.template error<invalid_parameter_error>(
-        self.configuration, "coremidi::locate_object: cannot find port: " + info.port_name);
+    self.libremidi_handle_error(
+        self.configuration, "cannot find port: " + info.port_name);
     return 0;
   }
 
   if (type != requested_type || object == 0)
   {
-    self.template error<invalid_parameter_error>(
-        self.configuration, "coremidi::locate_object: invalid object: " + info.port_name + " : "
+    self.libremidi_handle_error(
+        self.configuration, "invalid object: " + info.port_name + " : "
                                 + std::to_string(object));
     return 0;
   }
@@ -255,6 +258,13 @@ struct coremidi_data
     }
   }
 
+  void close_client(auto& self)
+  {
+    self.client_open_ = std::errc::not_connected;
+    if (!self.configuration.context)
+      MIDIClientDispose(self.client);
+  }
+
   static uint64_t time_in_nanos(MIDITimeStamp tp) noexcept
   {
     if (tp == 0)
@@ -319,6 +329,23 @@ struct coremidi_data
       }
     }
   }
+
+  stdx::error close_port()
+  {
+    if (this->endpoint)
+    {
+      MIDIEndpointDispose(this->endpoint);
+      this->endpoint = 0;
+    }
+
+    if (this->port)
+    {
+      MIDIPortDispose(this->port);
+      this->port = 0;
+    }
+
+    return stdx::error{};
+  }
 };
 
 }

include/libremidi/backends/coremidi/midi_in.hpp

@@ -8,10 +8,11 @@ namespace libremidi
 {
 class midi_in_core final
     : public midi1::in_api
-    , private coremidi_data
+    , public coremidi_data
     , public error_handler
 {
 public:
+  using midi_api::client_open_;
   struct
       : input_configuration
       , coremidi_input_configuration
@@ -23,11 +24,14 @@ public:
   {
     if (auto result = init_client(configuration); result != noErr)
     {
-      error<driver_error>(
+      libremidi_handle_error(
           this->configuration,
-          "midi_in_core: error creating MIDI client object: " + std::to_string(result));
+          "error creating MIDI client object: " + std::to_string(result));
+      client_open_ = from_osstatus(result);
       return;
     }
+
+    client_open_ = stdx::error{};
   }
 
   ~midi_in_core() override
@@ -38,33 +42,18 @@ public:
     if (this->endpoint)
       MIDIEndpointDispose(this->endpoint);
 
-    close_client();
-  }
-
-  void close_client()
-  {
-    if (!configuration.context)
-      MIDIClientDispose(this->client);
-  }
-
-  void set_client_name(std::string_view) override
-  {
-    warning(configuration, "midi_in_core: set_client_name unsupported");
-  }
-  void set_port_name(std::string_view) override
-  {
-    warning(configuration, "midi_in_core: set_port_name unsupported");
+    close_client(*this);
   }
 
   libremidi::API get_current_api() const noexcept override { return libremidi::API::COREMIDI; }
 
-  bool open_port(const input_port& info, std::string_view portName) override
+  stdx::error open_port(const input_port& info, std::string_view portName) override
   {
     CFRunLoopRunInMode(kCFRunLoopDefaultMode, 0, false);
 
     auto source = locate_object(*this, info, kMIDIObjectType_Source);
     if (source == 0)
-      return false;
+      return std::errc::invalid_argument;
 
     // Create our local sink
     MIDIPortRef port;
@@ -73,29 +62,29 @@ public:
 
     if (result != noErr)
     {
-      close_client();
-      error<driver_error>(
-          this->configuration, "midi_in_core::open_port: error creating macOS MIDI input port: "
+      close_client(*this);
+      libremidi_handle_error(
+          this->configuration, "error creating macOS MIDI input port: "
                                    + std::to_string(result));
-      return false;
+      return from_osstatus(result);
     }
 
     // Make the connection.
     if (result = MIDIPortConnectSource(port, source, nullptr); result != noErr)
     {
       MIDIPortDispose(port);
-      close_client();
-      error<driver_error>(
-          this->configuration, "midi_in_core::open_port: error connecting macOS MIDI input port.");
-      return false;
+      close_client(*this);
+      libremidi_handle_error(
+          this->configuration, "error connecting macOS MIDI input port.");
+      return from_osstatus(result);
     }
 
     // Save our api-specific port information.
     this->port = port;
-    return true;
+    return stdx::error{};
   }
 
-  bool open_virtual_port(std::string_view portName) override
+  stdx::error open_virtual_port(std::string_view portName) override
   {
     // Create a virtual MIDI input destination.
     MIDIEndpointRef endpoint;
@@ -104,31 +93,21 @@ public:
 
     if (result != noErr)
     {
-      error<driver_error>(
+      libremidi_handle_error(
           this->configuration,
-          "midi_in_core::open_virtual_port: error creating virtual macOS MIDI "
+          "error creating virtual macOS MIDI "
           "destination.");
-      return false;
+      return from_osstatus(result);
     }
 
     // Save our api-specific connection information.
     this->endpoint = endpoint;
-    return true;
+    return stdx::error{};
   }
 
-  void close_port() override
+  stdx::error close_port() override
   {
-    if (this->endpoint)
-    {
-      MIDIEndpointDispose(this->endpoint);
-      this->endpoint = 0;
-    }
-
-    if (this->port)
-    {
-      MIDIPortDispose(this->port);
-      this->port = 0;
-    }
+    return coremidi_data::close_port();
   }
 
   timestamp absolute_timestamp() const noexcept override
@@ -158,16 +137,13 @@ public:
       // MIDIPacketLists, they must be handled by multiple calls to this
       // function.
 
-      if (packet->length == 0)
+      if (packet->length > 0)
       {
-        packet = MIDIPacketNext(packet);
-        continue;
-      }
-
         auto to_ns = [packet] { return time_in_nanos(packet->timeStamp); };
         self.m_processing.on_bytes_multi(
             {packet->data, packet->data + packet->length},
             self.m_processing.timestamp<timestamp_info>(to_ns, 0));
+      }
 
       packet = MIDIPacketNext(packet);
     }

include/libremidi/backends/coremidi/midi_out.hpp

@@ -7,10 +7,11 @@ namespace libremidi
 {
 class midi_out_core final
     : public midi1::out_api
-    , private coremidi_data
+    , public coremidi_data
     , public error_handler
 {
 public:
+  using midi_api::client_open_;
   struct
       : output_configuration
       , coremidi_output_configuration
@@ -22,11 +23,14 @@ public:
   {
     if (auto result = init_client(configuration); result != noErr)
     {
-      error<driver_error>(
+      libremidi_handle_error(
           this->configuration,
-          "midi_out_core: error creating MIDI client object: " + std::to_string(result));
+          "error creating MIDI client object: " + std::to_string(result));
+      client_open_ = from_osstatus(result);
       return;
     }
+
+    client_open_ = stdx::error{};
   }
 
   ~midi_out_core()
@@ -36,112 +40,79 @@ public:
     if (this->endpoint)
       MIDIEndpointDispose(this->endpoint);
 
-    close_client();
-  }
-
-  void close_client()
-  {
-    if (!configuration.context)
-      MIDIClientDispose(this->client);
-  }
-
-  void set_client_name(std::string_view) override
-  {
-    warning(configuration, "midi_out_core: set_client_name unsupported");
-  }
-  void set_port_name(std::string_view) override
-  {
-    warning(configuration, "midi_out_core: set_port_name unsupported");
+    close_client(*this);
   }
 
   libremidi::API get_current_api() const noexcept override { return libremidi::API::COREMIDI; }
 
-  bool open_port(const output_port& info, std::string_view portName) override
+  stdx::error open_port(const output_port& info, std::string_view portName) override
   {
     CFRunLoopRunInMode(kCFRunLoopDefaultMode, 0, false);
 
     // Find where we want to send
     auto destination = locate_object(*this, info, kMIDIObjectType_Destination);
     if (destination == 0)
-      return false;
+      return std::errc::invalid_argument;
 
     // Create our local source
     MIDIPortRef port;
     OSStatus result = MIDIOutputPortCreate(this->client, toCFString(portName).get(), &port);
     if (result != noErr)
     {
-      close_client();
-      error<driver_error>(
-          this->configuration, "midi_out_core::open_port: error creating macOS MIDI output port.");
-      return false;
+      close_client(*this);
+      libremidi_handle_error(
+          this->configuration, "error creating macOS MIDI output port.");
+      return from_osstatus(result);
     }
 
     // Save our api-specific connection information.
     this->port = port;
     this->destinationId = destination;
 
-    return true;
+    return stdx::error{};
   }
 
-  bool open_virtual_port(std::string_view portName) override
+  stdx::error open_virtual_port(std::string_view portName) override
   {
-    if (this->endpoint)
-    {
-      warning(
-          configuration,
-          "midi_out_core::open_virtual_port: a virtual output port already "
-          "exists!");
-      return false;
-    }
-
     // Create a virtual MIDI output source.
     MIDIEndpointRef endpoint;
     OSStatus result = MIDISourceCreate(this->client, toCFString(portName).get(), &endpoint);
 
     if (result != noErr)
     {
-      error<driver_error>(
+      libremidi_handle_error(
           this->configuration,
-          "midi_out_core::initialize: error creating macOS virtual MIDI source.");
-      return false;
+          "error creating macOS virtual MIDI source.");
+
+      return from_osstatus(result);
     }
 
     // Save our api-specific connection information.
     this->endpoint = endpoint;
-    return true;
+    return stdx::error{};
   }
 
-  void close_port() override
+  stdx::error close_port() override
   {
-    if (this->endpoint)
-    {
-      MIDIEndpointDispose(this->endpoint);
-      this->endpoint = 0;
+    return coremidi_data::close_port();
   }
 
-    if (this->port)
-    {
-      MIDIPortDispose(this->port);
-      this->port = 0;
-    }
-  }
-
-  void send_message(const unsigned char* message, size_t size) override
+  stdx::error send_message(const unsigned char* message, size_t size) override
   {
     unsigned int nBytes = static_cast<unsigned int>(size);
     if (nBytes == 0)
     {
-      warning(configuration, "midi_out_core::send_message: no data in message argument!");
-      return;
+      libremidi_handle_warning(configuration, "no data in message argument!");
+      return std::errc::invalid_argument;
     }
 
     if (message[0] != 0xF0 && nBytes > 3)
     {
-      warning(
+      libremidi_handle_warning(
           configuration,
-          "midi_out_core::send_message: message format problem ... not sysex but "
+          "message format problem ... not sysex but "
           "> 3 bytes?");
-      return;
+      return std::errc::bad_message;
     }
 
     const MIDITimeStamp timestamp = LIBREMIDI_AUDIO_GET_CURRENT_HOST_TIME();
@@ -166,9 +137,10 @@ public:
 
       if (!packet)
       {
-        error<driver_error>(
-            this->configuration, "midi_out_core::send_message: could not allocate packet list");
-        return;
+        libremidi_handle_error(
+            this->configuration, "could not allocate packet list");
+
+        return std::errc::message_size;
       }
 
       // Send to any destinations that may have connected to us.
@@ -177,10 +149,11 @@ public:
         auto result = MIDIReceived(this->endpoint, packetList);
         if (result != noErr)
         {
-          warning(
+          libremidi_handle_warning(
               this->configuration,
-              "midi_out_core::send_message: error sending MIDI to virtual "
+              "error sending MIDI to virtual "
               "destinations.");
+          return std::errc::io_error;
         }
       }
 
@@ -190,12 +163,14 @@ public:
         auto result = MIDISend(this->port, this->destinationId, packetList);
         if (result != noErr)
         {
-          warning(
+          libremidi_handle_warning(
               this->configuration,
-              "midi_out_core::send_message: error sending MIDI message to port.");
+              "error sending MIDI message to port.");
+          return std::errc::io_error;
         }
       }
     }
+    return stdx::error{};
   }
 
   MIDIEndpointRef destinationId{};

include/libremidi/backends/coremidi/observer.hpp

@@ -38,9 +38,9 @@ public:
 
     if (result != noErr)
     {
-      error<driver_error>(
+      libremidi_handle_error(
           this->configuration,
-          "midi_in_core: error creating MIDI client object: " + std::to_string(result));
+          "error creating MIDI client object: " + std::to_string(result));
       return;
     }
 
@@ -69,11 +69,11 @@ public:
     MIDIEndpointGetEntity(obj, &e);
     bool physical = bool(e);
 
-    bool ok = false;
+    bool ok = this->configuration.track_any;
     if (physical && this->configuration.track_hardware)
-      ok = true;
+      ok |= true;
     else if ((!physical) && this->configuration.track_virtual)
-      ok = true;
+      ok |= true;
 
     if (!ok)
       return {};

include/libremidi/backends/coremidi_ump.hpp

@@ -10,9 +10,9 @@ struct backend
   using midi_in = midi_in_impl;
   using midi_out = midi_out_impl;
   using midi_observer = observer_impl;
-  using midi_in_configuration = coremidi_input_configuration;
-  using midi_out_configuration = coremidi_output_configuration;
-  using midi_observer_configuration = coremidi_observer_configuration;
+  using midi_in_configuration = coremidi_ump::input_configuration;
+  using midi_out_configuration = coremidi_ump::output_configuration;
+  using midi_observer_configuration = coremidi_ump::observer_configuration;
   static const constexpr auto API = libremidi::API::COREMIDI_UMP;
   static const constexpr auto name = "core_ump";
   static const constexpr auto display_name = "CoreMIDI UMP";

include/libremidi/backends/coremidi_ump/config.hpp

@@ -3,7 +3,21 @@
 
 namespace libremidi::coremidi_ump
 {
-using input_configuration = coremidi_input_configuration;
-using output_configuration = coremidi_output_configuration;
-using observer_configuration = coremidi_observer_configuration;
+struct input_configuration
+{
+  std::string client_name = "libremidi client";
+  std::optional<MIDIClientRef> context{};
+};
+
+struct output_configuration
+{
+  std::string client_name = "libremidi client";
+  std::optional<MIDIClientRef> context{};
+};
+
+struct observer_configuration
+{
+  std::string client_name = "libremidi client";
+  std::function<void(MIDIClientRef)> on_create_context{};
+};
 }

include/libremidi/backends/coremidi_ump/midi_in.hpp

@@ -2,32 +2,37 @@
 #include <libremidi/backends/coremidi_ump/config.hpp>
 #include <libremidi/backends/coremidi_ump/helpers.hpp>
 #include <libremidi/detail/midi_in.hpp>
+#include <libremidi/detail/midi_stream_decoder.hpp>
 
 namespace libremidi::coremidi_ump
 {
 
 class midi_in_impl final
     : public midi2::in_api
-    , private coremidi_data
+    , public coremidi_data
     , public error_handler
 {
 public:
+  using midi_api::client_open_;
   struct
       : ump_input_configuration
       , coremidi_ump::input_configuration
   {
   } configuration;
 
-  midi_in_impl(ump_input_configuration&& conf, coremidi_input_configuration&& apiconf)
+  midi_in_impl(ump_input_configuration&& conf, coremidi_ump::input_configuration&& apiconf)
       : configuration{std::move(conf), std::move(apiconf)}
   {
     if (auto result = init_client(configuration); result != noErr)
     {
-      error<driver_error>(
+      libremidi_handle_error(
           this->configuration,
-          "midi_in_core: error creating MIDI client object: " + std::to_string(result));
+          "error creating MIDI client object: " + std::to_string(result));
+      client_open_ = from_osstatus(result);
       return;
     }
+
+    client_open_ = stdx::error{};
   }
 
   ~midi_in_impl() override
@@ -38,33 +43,18 @@ public:
     if (this->endpoint)
       MIDIEndpointDispose(this->endpoint);
 
-    close_client();
-  }
-
-  void close_client()
-  {
-    if (!configuration.context)
-      MIDIClientDispose(this->client);
-  }
-
-  void set_client_name(std::string_view) override
-  {
-    warning(configuration, "midi_in_core: set_client_name unsupported");
-  }
-  void set_port_name(std::string_view) override
-  {
-    warning(configuration, "midi_in_core: set_port_name unsupported");
+    close_client(*this);
   }
 
   libremidi::API get_current_api() const noexcept override { return libremidi::API::COREMIDI_UMP; }
 
-  bool open_port(const input_port& info, std::string_view portName) override
+  stdx::error open_port(const input_port& info, std::string_view portName) override
   {
     CFRunLoopRunInMode(kCFRunLoopDefaultMode, 0, false);
 
     auto source = locate_object(*this, info, kMIDIObjectType_Source);
     if (source == 0)
-      return false;
+      return std::errc::invalid_argument;
 
     // Create our local sink
     MIDIPortRef port;
@@ -77,29 +67,29 @@ public:
 
     if (result != noErr)
     {
-      close_client();
-      error<driver_error>(
-          this->configuration, "midi_in_core::open_port: error creating macOS MIDI input port: "
+      close_client(*this);
+      libremidi_handle_error(
+          this->configuration, "error creating macOS MIDI input port: "
                                    + std::to_string(result));
-      return false;
+      return from_osstatus(result);
     }
 
     // Make the connection.
     if (result = MIDIPortConnectSource(port, source, nullptr); result != noErr)
     {
       MIDIPortDispose(port);
-      close_client();
-      error<driver_error>(
-          this->configuration, "midi_in_core::open_port: error connecting macOS MIDI input port.");
-      return false;
+      close_client(*this);
+      libremidi_handle_error(
+          this->configuration, "error connecting macOS MIDI input port.");
+      return from_osstatus(result);
     }
 
     // Save our api-specific port information.
     this->port = port;
-    return true;
+    return stdx::error{};
   }
 
-  bool open_virtual_port(std::string_view portName) override
+  stdx::error open_virtual_port(std::string_view portName) override
   {
     // Create a virtual MIDI input destination.
     MIDIEndpointRef endpoint;
@@ -111,37 +101,21 @@ public:
 
     if (result != noErr)
     {
-      error<driver_error>(
+      libremidi_handle_error(
           this->configuration,
-          "midi_in_core::open_virtual_port: error creating virtual macOS MIDI "
+          "error creating virtual macOS MIDI "
           "destination.");
-      return false;
+      return from_osstatus(result);
     }
 
     // Save our api-specific connection information.
     this->endpoint = endpoint;
-    return true;
+    return stdx::error{};
   }
 
-  void close_port() override
-  {
-    if (this->endpoint)
-    {
-      MIDIEndpointDispose(this->endpoint);
-      this->endpoint = 0;
-    }
-
-    if (this->port)
-    {
-      MIDIPortDispose(this->port);
-      this->port = 0;
-    }
-  }
-
-  void set_timestamp(
-      [[maybe_unused]] const MIDIEventPacket& packet,
-      [[maybe_unused]] libremidi::ump& msg) noexcept
+  stdx::error close_port() override
   {
+    return coremidi_data::close_port();
   }
 
   timestamp absolute_timestamp() const noexcept override
@@ -151,33 +125,28 @@ public:
 
   void midiInputCallback(const MIDIEventList* list, void* /*srcRef*/)
   {
-    unsigned short nBytes{};
+    static constexpr timestamp_backend_info timestamp_info{
+        .has_absolute_timestamps = true,
+        .absolute_is_monotonic = false,
+        .has_samples = false,
+    };
 
     const MIDIEventPacket* packet = &list->packet[0];
     for (unsigned int i = 0; i < list->numPackets; ++i)
     {
-      nBytes = packet->wordCount;
-      if (nBytes == 0)
+      if (packet->wordCount > 0)
       {
-        packet = MIDIEventPacketNext(packet);
-        continue;
+        auto to_ns = [packet] { return time_in_nanos(packet->timeStamp); };
+        m_processing.on_bytes_multi(
+            {packet->words, packet->words + packet->wordCount},
+            m_processing.timestamp<timestamp_info>(to_ns, 0));
       }
 
-      libremidi::ump msg;
-      coremidi_data::set_timestamp(*this, packet->timeStamp, msg.timestamp);
-
-      if (packet->wordCount <= 4)
-      {
-        std::copy_n(packet->words, packet->wordCount, msg.data);
-        configuration.on_message(std::move(msg));
-      }
-      last_time = time_in_nanos(packet->timeStamp);
-
       packet = MIDIEventPacketNext(packet);
     }
   }
 
-  unsigned long long last_time{};
+  midi2::input_state_machine m_processing{this->configuration};
 };
 
 }

include/libremidi/backends/coremidi_ump/midi_out.hpp

@@ -9,10 +9,11 @@ namespace libremidi::coremidi_ump
 {
 class midi_out_impl final
     : public midi2::out_api
-    , private coremidi_data
+    , public coremidi_data
     , public error_handler
 {
 public:
+  using midi_api::client_open_;
   struct
       : libremidi::output_configuration
       , coremidi_ump::output_configuration
@@ -25,11 +26,14 @@ public:
   {
     if (auto result = init_client(configuration); result != noErr)
     {
-      error<driver_error>(
+      libremidi_handle_error(
           this->configuration,
-          "midi_out_impl: error creating MIDI client object: " + std::to_string(result));
+          "error creating MIDI client object: " + std::to_string(result));
+      client_open_ = from_osstatus(result);
       return;
     }
+
+    client_open_ = stdx::error{};
   }
 
   ~midi_out_impl()
@@ -39,64 +43,40 @@ public:
     if (this->endpoint)
       MIDIEndpointDispose(this->endpoint);
 
-    close_client();
-  }
-
-  void close_client()
-  {
-    if (!configuration.context)
-      MIDIClientDispose(this->client);
-  }
-
-  void set_client_name(std::string_view) override
-  {
-    warning(configuration, "midi_out_impl: set_client_name unsupported");
-  }
-  void set_port_name(std::string_view) override
-  {
-    warning(configuration, "midi_out_impl: set_port_name unsupported");
+    close_client(*this);
   }
 
   libremidi::API get_current_api() const noexcept override { return libremidi::API::COREMIDI_UMP; }
 
-  bool open_port(const output_port& info, std::string_view portName) override
+  stdx::error open_port(const output_port& info, std::string_view portName) override
   {
     CFRunLoopRunInMode(kCFRunLoopDefaultMode, 0, false);
 
     // Find where we want to send
     auto destination = locate_object(*this, info, kMIDIObjectType_Destination);
     if (destination == 0)
-      return false;
+      return std::errc::invalid_argument;
 
     // Create our local source
     MIDIPortRef port;
     OSStatus result = MIDIOutputPortCreate(this->client, toCFString(portName).get(), &port);
     if (result != noErr)
     {
-      close_client();
-      error<driver_error>(
-          this->configuration, "midi_out_impl::open_port: error creating macOS MIDI output port.");
-      return false;
+      close_client(*this);
+      libremidi_handle_error(
+          this->configuration, "error creating macOS MIDI output port.");
+      return from_osstatus(result);
     }
 
     // Save our api-specific connection information.
     this->port = port;
     this->destinationId = destination;
 
-    return true;
+    return stdx::error{};
   }
 
-  bool open_virtual_port(std::string_view portName) override
+  stdx::error open_virtual_port(std::string_view portName) override
   {
-    if (this->endpoint)
-    {
-      warning(
-          configuration,
-          "midi_out_impl::open_virtual_port: a virtual output port already "
-          "exists!");
-      return false;
-    }
-
     // Create a virtual MIDI output source.
     OSStatus result = MIDISourceCreateWithProtocol(
         this->client, toCFString(portName).get(), kMIDIProtocol_2_0, &this->endpoint);
@@ -104,42 +84,33 @@ public:
     if (result != noErr)
     {
       this->endpoint = 0;
-      error<driver_error>(
+      libremidi_handle_error(
           this->configuration,
-          "midi_out_impl::initialize: error creating macOS virtual MIDI source.");
-      return false;
+          "error creating macOS virtual MIDI source.");
+
+      return from_osstatus(result);
     }
 
-    return true;
+    return stdx::error{};
   }
 
-  void close_port() override
+  stdx::error close_port() override
   {
-    if (this->endpoint)
-    {
-      MIDIEndpointDispose(this->endpoint);
-      this->endpoint = 0;
+    return coremidi_data::close_port();
   }
 
-    if (this->port)
-    {
-      MIDIPortDispose(this->port);
-      this->port = 0;
-    }
-  }
-
-  void send_ump(const uint32_t* ump_stream, std::size_t count) override
+  stdx::error send_ump(const uint32_t* ump_stream, std::size_t count) override
   {
     MIDIEventList* eventList = reinterpret_cast<MIDIEventList*>(m_eventListBuffer);
     MIDIEventPacket* packet = MIDIEventListInit(eventList, kMIDIProtocol_2_0);
     const MIDITimeStamp ts = LIBREMIDI_AUDIO_GET_CURRENT_HOST_TIME();
 
-    auto write_fun = [ts, &packet, &eventList](const uint32_t* ump, int bytes) {
+    auto write_fun = [ts, &packet, &eventList](const uint32_t* ump, int bytes) -> std::errc {
       packet = MIDIEventListAdd(eventList, event_list_max_size, packet, ts, bytes / 4, ump);
       if (packet)
-        return segmentation_error::no_error;
+        return std::errc{0};
       else
-        return segmentation_error::need_space;
+        return std::errc::not_enough_memory;
     };
 
     auto realloc_fun = [this, &packet, &eventList] {
@@ -148,20 +119,21 @@ public:
     };
 
     segment_ump_stream(ump_stream, count, write_fun, realloc_fun);
-    push_event_list(eventList);
+    return push_event_list(eventList);
   }
 
-  void push_event_list(MIDIEventList* eventList)
+  stdx::error push_event_list(MIDIEventList* eventList)
   {
     if (this->endpoint)
     {
       auto result = MIDIReceivedEventList(this->endpoint, eventList);
       if (result != noErr)
       {
-        warning(
+        libremidi_handle_warning(
             this->configuration,
-            "midi_out_core::send_message: error sending MIDI to virtual "
+            "error sending MIDI to virtual "
             "destinations.");
+        return std::errc::io_error;
       }
     }
 
@@ -170,11 +142,13 @@ public:
       auto result = MIDISendEventList(this->port, this->destinationId, eventList);
       if (result != noErr)
       {
-        warning(
+        libremidi_handle_warning(
             this->configuration,
-            "midi_out_core::send_message: error sending MIDI message to port.");
+            "error sending MIDI message to port.");
+        return std::errc::io_error;
       }
     }
+    return stdx::error{};
   }
 
   MIDIEndpointRef destinationId{};

include/libremidi/backends/coremidi_ump/observer.hpp

@@ -1,4 +1,5 @@
 #pragma once
+#include <libremidi/backends/coremidi_ump/config.hpp>
 #include <libremidi/backends/coremidi/observer.hpp>
 
 namespace libremidi::coremidi_ump
@@ -6,7 +7,13 @@ namespace libremidi::coremidi_ump
 
 class observer_impl final : public libremidi::observer_core
 {
-  using observer_core::observer_core;
+public:
+  explicit observer_impl(libremidi::observer_configuration&& conf, coremidi_ump::observer_configuration&& apiconf)
+      : observer_core{std::move(conf), coremidi_observer_configuration{apiconf.client_name, apiconf.on_create_context}}
+  {
+
+  }
+
   libremidi::API get_current_api() const noexcept override { return libremidi::API::COREMIDI_UMP; }
 };
 

include/libremidi/backends/dummy.hpp

@@ -23,20 +23,33 @@ class midi_in_dummy final
     , public error_handler
 {
 public:
-  explicit midi_in_dummy(const auto& configuration, const auto&)
+  explicit midi_in_dummy(const input_configuration& configuration, std::any)
   {
-    warning(configuration, "midi_in_dummy: This class provides no functionality.");
+    libremidi_handle_warning(configuration, "This class provides no functionality.");
+  }
+  explicit midi_in_dummy(const ump_input_configuration& configuration, std::any)
+  {
+    libremidi_handle_warning(configuration, "This class provides no functionality.");
   }
 
   libremidi::API get_current_api() const noexcept override { return libremidi::API::DUMMY; }
-  bool open_port(const input_port& /*pt*/, std::string_view /*local_port_name*/) override
+  stdx::error open_port(const input_port& /*pt*/, std::string_view /*local_port_name*/) override
   {
-    return true;
+    return stdx::error{};
+  }
+  stdx::error open_virtual_port(std::string_view /*portName*/) override
+  {
+    return stdx::error{};
+  }
+  stdx::error close_port() override { return stdx::error{}; }
+  stdx::error set_client_name(std::string_view /*clientName*/) override
+  {
+    return stdx::error{};
+  }
+  stdx::error set_port_name(std::string_view /*portName*/) override
+  {
+    return stdx::error{};
   }
-  bool open_virtual_port(std::string_view /*portName*/) override { return true; }
-  void close_port() override { }
-  void set_client_name(std::string_view /*clientName*/) override { }
-  void set_port_name(std::string_view /*portName*/) override { }
   timestamp absolute_timestamp() const noexcept override { return 0; }
 };
 
@@ -45,22 +58,34 @@ class midi_out_dummy final
     , public error_handler
 {
 public:
-  explicit midi_out_dummy(const auto& configuration, const auto&)
+  explicit midi_out_dummy(const output_configuration& configuration, std::any)
   {
-    warning(configuration, "midi_out_dummy: This class provides no functionality.");
+    libremidi_handle_warning(configuration, "This class provides no functionality.");
   }
 
   libremidi::API get_current_api() const noexcept override { return libremidi::API::DUMMY; }
-  bool open_port(const output_port& /*pt*/, std::string_view /*local_port_name*/) override
+  stdx::error open_port(const output_port& /*pt*/, std::string_view /*local_port_name*/) override
   {
-    return true;
+    return stdx::error{};
+  }
+  stdx::error open_virtual_port(std::string_view /*portName*/) override
+  {
+    return stdx::error{};
   }
-  bool open_virtual_port(std::string_view /*portName*/) override { return true; }
 
-  void close_port() override { }
-  void set_client_name(std::string_view /*clientName*/) override { }
-  void set_port_name(std::string_view /*portName*/) override { }
-  void send_message(const unsigned char* /*message*/, size_t /*size*/) override { }
+  stdx::error close_port() override { return stdx::error{}; }
+  stdx::error set_client_name(std::string_view /*clientName*/) override
+  {
+    return stdx::error{};
+  }
+  stdx::error set_port_name(std::string_view /*portName*/) override
+  {
+    return stdx::error{};
+  }
+  stdx::error send_message(const unsigned char* /*message*/, size_t /*size*/) override
+  {
+    return stdx::error{};
+  }
 };
 
 struct dummy_backend

include/libremidi/backends/emscripten/midi_access.hpp

@@ -204,7 +204,7 @@ public:
     }
   }
 
-  void send_message(int port_index, const char* bytes, int len)
+  stdx::error send_message(int port_index, const char* bytes, int len)
   {
     const auto& id = m_current_outputs[port_index].id;
     EM_ASM(

include/libremidi/backends/emscripten/midi_in.cpp

@@ -11,12 +11,14 @@ LIBREMIDI_INLINE midi_in_emscripten::midi_in_emscripten(
     input_configuration&& conf, emscripten_input_configuration&& apiconf)
     : configuration{std::move(conf), std::move(apiconf)}
 {
+  client_open_ = stdx::error{};
 }
 
 LIBREMIDI_INLINE midi_in_emscripten::~midi_in_emscripten()
 {
   // Close a connection if it exists.
   midi_in_emscripten::close_port();
+  client_open_ = std::errc::not_connected;
 }
 
 LIBREMIDI_INLINE libremidi::API midi_in_emscripten::get_current_api() const noexcept
@@ -24,49 +26,35 @@ LIBREMIDI_INLINE libremidi::API midi_in_emscripten::get_current_api() const noex
   return libremidi::API::WEBMIDI;
 }
 
-LIBREMIDI_INLINE bool midi_in_emscripten::open_port(int portNumber, std::string_view)
+LIBREMIDI_INLINE stdx::error midi_in_emscripten::open_port(int portNumber, std::string_view)
 {
   auto& midi = webmidi_helpers::midi_access_emscripten::instance();
 
   if (portNumber < 0 || portNumber >= midi.input_count())
   {
-    error<no_devices_found_error>(
-        this->configuration, "midi_in_emscripten::open_port: no MIDI output sources found.");
-    return false;
+    libremidi_handle_error(
+        this->configuration, "no MIDI output sources found.");
+    return std::errc::invalid_argument;
   }
 
   midi.open_input(portNumber, *this);
   portNumber_ = portNumber;
-  return true;
+  return stdx::error{};
 }
 
-LIBREMIDI_INLINE bool
+LIBREMIDI_INLINE stdx::error
 midi_in_emscripten::open_port(const libremidi::input_port& p, std::string_view nm)
 {
   return open_port(p.port, nm);
 }
 
-LIBREMIDI_INLINE bool midi_in_emscripten::open_virtual_port(std::string_view)
-{
-  warning(configuration, "midi_in_emscripten::open_virtual_port: unsupported.");
-  return false;
-}
-
-LIBREMIDI_INLINE void midi_in_emscripten::close_port()
+LIBREMIDI_INLINE stdx::error midi_in_emscripten::close_port()
 {
   auto& midi = webmidi_helpers::midi_access_emscripten::instance();
 
   midi.close_input(portNumber_, *this);
-}
 
-LIBREMIDI_INLINE void midi_in_emscripten::set_client_name(std::string_view)
-{
-  warning(configuration, "midi_in_emscripten::set_client_name: unsupported.");
-}
-
-LIBREMIDI_INLINE void midi_in_emscripten::set_port_name(std::string_view)
-{
-  warning(configuration, "midi_in_emscripten::set_port_name: unsupported.");
+  return stdx::error{};
 }
 
 LIBREMIDI_INLINE int64_t midi_in_emscripten::absolute_timestamp() const noexcept

include/libremidi/backends/emscripten/midi_in.hpp

@@ -22,13 +22,10 @@ public:
 
   libremidi::API get_current_api() const noexcept override;
 
-  bool open_port(int portNumber, std::string_view);
-  bool open_port(const input_port& p, std::string_view) override;
-  bool open_virtual_port(std::string_view) override;
-  void close_port() override;
+  stdx::error open_port(int portNumber, std::string_view);
+  stdx::error open_port(const input_port& p, std::string_view) override;
+  stdx::error close_port() override;
 
-  void set_client_name(std::string_view clientName) override;
-  void set_port_name(std::string_view portName) override;
   timestamp absolute_timestamp() const noexcept override;
 
   void on_input(double ts, unsigned char* begin, unsigned char* end);

include/libremidi/backends/emscripten/midi_out.cpp

@@ -8,12 +8,14 @@ LIBREMIDI_INLINE midi_out_emscripten::midi_out_emscripten(
     output_configuration&& conf, emscripten_output_configuration&& apiconf)
     : configuration{std::move(conf), std::move(apiconf)}
 {
+  client_open_ = stdx::error{};
 }
 
 LIBREMIDI_INLINE midi_out_emscripten::~midi_out_emscripten()
 {
   // Close a connection if it exists.
   midi_out_emscripten::close_port();
+  client_open_ = std::errc::not_connected;
 }
 
 LIBREMIDI_INLINE libremidi::API midi_out_emscripten::get_current_api() const noexcept
@@ -21,54 +23,41 @@ LIBREMIDI_INLINE libremidi::API midi_out_emscripten::get_current_api() const noe
   return libremidi::API::WEBMIDI;
 }
 
-LIBREMIDI_INLINE bool midi_out_emscripten::open_port(unsigned int portNumber, std::string_view)
+LIBREMIDI_INLINE stdx::error midi_out_emscripten::open_port(int portNumber, std::string_view)
 {
   auto& midi = webmidi_helpers::midi_access_emscripten::instance();
 
   if (portNumber >= midi.output_count())
   {
-    error<no_devices_found_error>(
-        this->configuration, "midi_out_emscripten::open_port: no MIDI output sources found.");
-    return false;
+    libremidi_handle_error(
+        this->configuration, "no MIDI output sources found.");
+    return std::errc::invalid_argument;
   }
 
   portNumber_ = portNumber;
-  return true;
+  return stdx::error{};
 }
 
-LIBREMIDI_INLINE bool midi_out_emscripten::open_port(const output_port& p, std::string_view nm)
+LIBREMIDI_INLINE stdx::error midi_out_emscripten::open_port(const output_port& p, std::string_view nm)
 {
   return open_port(p.port, nm);
 }
 
-LIBREMIDI_INLINE void midi_out_emscripten::close_port() { }
-
-LIBREMIDI_INLINE void midi_out_emscripten::set_client_name(std::string_view clientName)
-{
-  warning(configuration, "midi_out_emscripten::set_client_name: unsupported.");
+LIBREMIDI_INLINE stdx::error midi_out_emscripten::close_port() { 
+  return stdx::error{};
 }
 
-LIBREMIDI_INLINE void midi_out_emscripten::set_port_name(std::string_view portName)
-{
-  warning(configuration, "midi_out_emscripten::set_port_name: unsupported.");
-}
-
-LIBREMIDI_INLINE bool midi_out_emscripten::open_virtual_port(std::string_view)
-{
-  warning(configuration, "midi_in_emscripten::open_virtual_port: unsupported.");
-  return false;
-}
-
-LIBREMIDI_INLINE void midi_out_emscripten::send_message(const unsigned char* message, size_t size)
+LIBREMIDI_INLINE stdx::error midi_out_emscripten::send_message(const unsigned char* message, size_t size)
 {
   if (portNumber_ < 0)
-    error<invalid_use_error>(
+    libremidi_handle_error(
         this->configuration,
-        "midi_out_emscripten::send_message: trying to send a message without an open "
+        "trying to send a message without an open "
         "port.");
 
   webmidi_helpers::midi_access_emscripten::instance().send_message(
       portNumber_, reinterpret_cast<const char*>(message), size);
+  return stdx::error{};
 }
 }
 #endif

include/libremidi/backends/emscripten/midi_out.hpp

@@ -21,15 +21,11 @@ public:
 
   libremidi::API get_current_api() const noexcept override;
 
-  bool open_port(unsigned int portNumber, std::string_view);
-  bool open_port(const output_port& p, std::string_view) override;
-  bool open_virtual_port(std::string_view) override;
-  void close_port() override;
+  stdx::error open_port(int portNumber, std::string_view);
+  stdx::error open_port(const output_port& p, std::string_view) override;
+  stdx::error close_port() override;
 
-  void set_client_name(std::string_view clientName) override;
-  void set_port_name(std::string_view portName) override;
-
-  void send_message(const unsigned char* message, size_t size) override;
+  stdx::error send_message(const unsigned char* message, size_t size) override;
 
 private:
   int portNumber_{-1};

include/libremidi/backends/jack/config.hpp

@@ -1,7 +1,6 @@
 #pragma once
 #include <libremidi/config.hpp>
 
-#include <cinttypes>
 #include <cstdint>
 #include <functional>
 #include <string>
@@ -25,8 +24,8 @@ struct jack_input_configuration
   std::string client_name = "libremidi client";
 
   jack_client_t* context{};
-  std::function<void(jack_callback)> set_process_func;
-  std::function<void(int64_t)> clear_process_func;
+  std::function<void(jack_callback)> set_process_func{};
+  std::function<void(int64_t)> clear_process_func{};
 };
 
 struct jack_output_configuration
@@ -34,8 +33,8 @@ struct jack_output_configuration
   std::string client_name = "libremidi client";
 
   jack_client_t* context{};
-  std::function<void(jack_callback)> set_process_func;
-  std::function<void(int64_t)> clear_process_func;
+  std::function<void(jack_callback)> set_process_func{};
+  std::function<void(int64_t)> clear_process_func{};
 
   int32_t ringbuffer_size = 16384;
   bool direct = false;

include/libremidi/backends/jack/error_domain.hpp

@@ -0,0 +1,78 @@
+#pragma once
+#include <libremidi/error.hpp>
+
+#if __has_include(<weakjack/weak_libjack.h>)
+  #include <weakjack/weak_libjack.h>
+#elif __has_include(<weak_libjack.h>)
+  #include <weak_libjack.h>
+#elif __has_include(<jack/jack.h> )
+  #include <jack/jack.h>
+  #include <jack/midiport.h>
+  #include <jack/ringbuffer.h>
+#endif
+
+namespace libremidi
+{
+struct jack_error_domain : public stdx::error_domain
+{
+public:
+  constexpr jack_error_domain() noexcept
+      : error_domain{{0xc714ea32b705080aULL, 0xe409a437daf5f921ULL}}
+  {
+  }
+
+  stdx::string_ref name() const noexcept override { return "jack"; }
+
+  bool equivalent(const stdx::error& lhs, const stdx::error& rhs) const noexcept override
+  {
+    if (lhs.domain() == rhs.domain())
+      return error_cast<jack_status_t>(lhs) == error_cast<jack_status_t>(rhs);
+
+    return false;
+  }
+
+  stdx::string_ref message(const stdx::error& e) const noexcept override
+  {
+    const auto status = error_cast<jack_status_t>(e);
+    if(status == jack_status_t{})
+      return "Success";
+
+    if(status & JackInvalidOption)
+      return "The operation contained an invalid or unsupported option";
+    if(status & JackServerFailed)
+      return "Unable to connect to the JACK server";
+    if(status & JackServerError)
+      return "Communication error with the JACK server";
+    if(status & JackNoSuchClient)
+      return "Requested client does not exist";
+    if(status & JackLoadFailure)
+      return "Unable to load internal client";
+    if(status & JackInitFailure)
+      return "Unable to initialize client";
+    if(status & JackShmFailure)
+      return "Unable to access shared memory";
+    if(status & JackVersionError)
+      return "Client's protocol version does not match";
+    if(status & JackBackendError)
+      return "Backend error";
+    if(status & JackClientZombie)
+      return "Client zombified failure";
+    if(status & JackFailure)
+      return "Failure";
+    if(status & JackNameNotUnique)
+      return "The desired client name was not unique";
+
+    // Can't happen in libremidi as we set JackNoStartServer
+    if(status & JackServerStarted)
+      return "Server was started";
+
+    return "Unknown JACK status code";
+  }
+};
+
+inline stdx::error from_jack_status(jack_status_t ret) noexcept
+{
+  static constexpr jack_error_domain domain{};
+  return {ret, domain};
+}
+}

include/libremidi/backends/jack/helpers.hpp

@@ -1,14 +1,6 @@
 #pragma once
 
-#if __has_include(<weakjack/weak_libjack.h>)
-  #include <weakjack/weak_libjack.h>
-#elif __has_include(<weak_libjack.h>)
-  #include <weak_libjack.h>
-#elif __has_include(<jack/jack.h> )
-  #include <jack/jack.h>
-  #include <jack/midiport.h>
-  #include <jack/ringbuffer.h>
-#endif
+#include <libremidi/backends/jack/error_domain.hpp>
 #include <libremidi/detail/midi_in.hpp>
 #include <libremidi/detail/semaphore.hpp>
 
@@ -157,6 +149,10 @@ struct jack_helpers : jack_client
           = jack_client_open(configuration.client_name.c_str(), JackNoStartServer, &status);
       if (this->client != nullptr)
       {
+        if(status & JackNameNotUnique) {
+          self.libremidi_handle_warning(self.configuration, "JACK client with the same name already exists, renamed.");
+        }
+
         jack_set_process_callback(
             this->client,
             +[](jack_nframes_t nf, void* ctx) -> int {
@@ -192,9 +188,12 @@ struct jack_helpers : jack_client
 
     if (this->client && !self.configuration.context)
       jack_client_close(this->client);
+
+    self.client_open_ = std::errc::not_connected;
   }
 
-  bool create_local_port(const auto& self, std::string_view portName, JackPortFlags flags)
+  stdx::error
+  create_local_port(const auto& self, std::string_view portName, JackPortFlags flags)
   {
     // full name: "client_name:port_name\0"
     if (portName.empty())
@@ -203,9 +202,9 @@ struct jack_helpers : jack_client
     if (self.configuration.client_name.size() + portName.size() + 2u
         >= static_cast<size_t>(jack_port_name_size()))
     {
-      self.template error<invalid_use_error>(
-          self.configuration, "JACK: port name length limit exceeded");
-      return false;
+      self.libremidi_handle_error(
+          self.configuration, "port name length limit exceeded");
+      return std::errc::invalid_argument;
     }
 
     if (!this->port)
@@ -216,16 +215,16 @@ struct jack_helpers : jack_client
 
     if (!this->port)
     {
-      self.template error<driver_error>(self.configuration, "JACK: error creating port");
-      return false;
+      self.libremidi_handle_error(self.configuration, "error creating port");
+      return std::errc::operation_not_supported;
     }
-    return true;
+    return stdx::error{};
   }
 
-  void do_close_port()
+  stdx::error do_close_port()
   {
     if (this->port == nullptr)
-      return;
+      return stdx::error{};
 
     // 1. Ensure that the next time the cycle runs it sees the port as nullptr
     jack_port_t* port_ptr = this->port.impl->load();
@@ -235,7 +234,8 @@ struct jack_helpers : jack_client
     this->thread_lock.prepare_release_client();
 
     // 3. Now we are sure that the client is not going to use the port anymore
-    jack_port_unregister(this->client, port_ptr);
+    int err = jack_port_unregister(this->client, port_ptr);
+    return from_errc(err);
   }
 };
 }

include/libremidi/backends/jack/midi_in.hpp

@@ -14,6 +14,7 @@ class midi_in_jack final
     , public error_handler
 {
 public:
+  using midi_api::client_open_;
   struct
       : input_configuration
       , jack_input_configuration
@@ -24,8 +25,14 @@ public:
       : configuration{std::move(conf), std::move(apiconf)}
   {
     auto status = connect(*this);
-    if (status != jack_status_t{})
-      warning(configuration, "midi_in_jack: " + std::to_string((int)jack_status_t{}));
+    if (!this->client)
+    {
+      libremidi_handle_error(configuration, "Could not create JACK client");
+      client_open_ = from_jack_status(status);
+      return;
+    }
+
+    client_open_ = stdx::error{};
   }
 
   ~midi_in_jack() override
@@ -35,39 +42,35 @@ public:
     disconnect(*this);
   }
 
-  void set_client_name(std::string_view) override
-  {
-    warning(configuration, "midi_in_jack: set_client_name unsupported");
-  }
-
   libremidi::API get_current_api() const noexcept override { return libremidi::API::JACK_MIDI; }
 
-  bool open_port(const input_port& port, std::string_view portName) override
+  stdx::error open_port(const input_port& port, std::string_view portName) override
   {
-    if (!create_local_port(*this, portName, JackPortIsInput))
-      return false;
+    if (auto err = create_local_port(*this, portName, JackPortIsInput); err != stdx::error{})
+      return err;
 
-    if (auto ret = jack_connect(this->client, port.port_name.c_str(), jack_port_name(this->port));
-        ret != 0)
+    if (int err = jack_connect(this->client, port.port_name.c_str(), jack_port_name(this->port));
+        err != 0 && err != EEXIST)
     {
-      error<invalid_parameter_error>(
-          configuration, "JACK: could not connect to port: " + port.port_name + " -> "
+      libremidi_handle_error(
+          configuration, "could not connect to port: " + port.port_name + " -> "
                              + jack_port_name(this->port));
-      return false;
+      return from_errc(err);
     }
-    return true;
+    return stdx::error{};
   }
 
-  bool open_virtual_port(std::string_view portName) override
+  stdx::error open_virtual_port(std::string_view portName) override
   {
     return create_local_port(*this, portName, JackPortIsInput);
   }
 
-  void close_port() override { return do_close_port(); }
+  stdx::error close_port() override { return do_close_port(); }
 
-  void set_port_name(std::string_view portName) override
+  stdx::error set_port_name(std::string_view portName) override
   {
-    jack_port_rename(this->client, this->port, portName.data());
+    int ret = jack_port_rename(this->client, this->port, portName.data());
+    return from_errc(ret);
   }
 
   timestamp absolute_timestamp() const noexcept override

include/libremidi/backends/jack/midi_out.hpp

@@ -37,16 +37,18 @@ public:
       jack_ringbuffer_free(ringbuffer);
   }
 
-  void write(const unsigned char* data, int64_t sz) const noexcept
+  stdx::error write(const unsigned char* data, int64_t sz) const noexcept
   {
     if (static_cast<std::size_t>(sz + size_sz) > ringbuffer_space)
-      return;
+      return std::errc::no_buffer_space;
 
     while (jack_ringbuffer_write_space(ringbuffer) < sz + size_sz)
       sched_yield();
 
     jack_ringbuffer_write(ringbuffer, reinterpret_cast<char*>(&sz), size_sz);
     jack_ringbuffer_write(ringbuffer, reinterpret_cast<const char*>(data), sz);
+
+    return stdx::error{};
   }
 
   void read(void* jack_events) const noexcept
@@ -74,6 +76,7 @@ class midi_out_jack
     , public error_handler
 {
 public:
+  using midi_api::client_open_;
   struct
       : output_configuration
       , jack_output_configuration
@@ -87,39 +90,36 @@ public:
 
   ~midi_out_jack() override { }
 
-  void set_client_name(std::string_view) override
-  {
-    warning(configuration, "midi_out_jack: set_client_name unsupported");
-  }
-
   libremidi::API get_current_api() const noexcept override { return libremidi::API::JACK_MIDI; }
 
-  bool open_port(const output_port& port, std::string_view portName) override
+  stdx::error open_port(const output_port& port, std::string_view portName) override
   {
-    if (!create_local_port(*this, portName, JackPortIsOutput))
-      return false;
+    if (auto err = create_local_port(*this, portName, JackPortIsOutput); err != stdx::error{})
+      return err;
 
     // Connecting to the output
-    if (jack_connect(this->client, jack_port_name(this->port), port.port_name.c_str()) != 0)
+    if (int err = jack_connect(this->client, jack_port_name(this->port), port.port_name.c_str());
+        err != 0 && err != EEXIST)
     {
-      error<invalid_parameter_error>(
-          configuration, "JACK: could not connect to port" + port.port_name);
-      return false;
+      libremidi_handle_error(
+          configuration, "could not connect to port" + port.port_name);
+      return from_errc(err);
     }
 
-    return true;
+    return stdx::error{};
   }
 
-  bool open_virtual_port(std::string_view portName) override
+  stdx::error open_virtual_port(std::string_view portName) override
   {
     return create_local_port(*this, portName, JackPortIsOutput);
   }
 
-  void close_port() override { return do_close_port(); }
+  stdx::error close_port() override { return do_close_port(); }
 
-  void set_port_name(std::string_view portName) override
+  stdx::error set_port_name(std::string_view portName) override
   {
-    jack_port_rename(this->client, this->port, portName.data());
+    int ret = jack_port_rename(this->client, this->port, portName.data());
+    return from_errc(ret);
   }
 };
 
@@ -131,8 +131,14 @@ public:
       , queue{configuration.ringbuffer_size}
   {
     auto status = connect(*this);
-    if (status != jack_status_t{})
-      warning(configuration, "midi_out_jack_queued: " + std::to_string((int)jack_status_t{}));
+    if (!this->client)
+    {
+      libremidi_handle_error(configuration, "Could not create JACK client");
+      client_open_ = from_jack_status(status);
+      return;
+    }
+
+    client_open_ = stdx::error{};
   }
 
   ~midi_out_jack_queued() override
@@ -142,9 +148,9 @@ public:
     disconnect(*this);
   }
 
-  void send_message(const unsigned char* message, std::size_t size) override
+  stdx::error send_message(const unsigned char* message, std::size_t size) override
   {
-    queue.write(message, size);
+    return queue.write(message, size);
   }
 
   int process(jack_nframes_t nframes)
@@ -168,10 +174,15 @@ public:
       : midi_out_jack{std::move(conf), std::move(apiconf)}
   {
     auto status = connect(*this);
-    if (status != jack_status_t{})
-      warning(configuration, "midi_out_jack_direct: " + std::to_string((int)jack_status_t{}));
+    if (!this->client)
+    {
+      libremidi_handle_error(configuration, "Could not create JACK client");
+      client_open_ = from_jack_status(status);
+      return;
+    }
 
     buffer_size = jack_get_buffer_size(this->client);
+    client_open_ = stdx::error{};
   }
 
   ~midi_out_jack_direct() override
@@ -188,10 +199,11 @@ public:
     return 0;
   }
 
-  void send_message(const unsigned char* message, size_t size) override
+  stdx::error send_message(const unsigned char* message, size_t size) override
   {
     void* buff = jack_port_get_buffer(this->port, buffer_size);
-    jack_midi_event_write(buff, 0, message, size);
+    int ret = jack_midi_event_write(buff, 0, message, size);
+    return from_errc(ret);
   }
 
   int convert_timestamp(int64_t user) const noexcept
@@ -207,10 +219,11 @@ public:
     }
   }
 
-  void schedule_message(int64_t ts, const unsigned char* message, size_t size) override
+  stdx::error schedule_message(int64_t ts, const unsigned char* message, size_t size) override
   {
     void* buff = jack_port_get_buffer(this->port, buffer_size);
-    jack_midi_event_write(buff, convert_timestamp(ts), message, size);
+    int ret = jack_midi_event_write(buff, convert_timestamp(ts), message, size);
+    return from_errc(ret);
   }
 
   int buffer_size{};

include/libremidi/backends/jack/observer.hpp

@@ -34,7 +34,7 @@ public:
       this->client
           = jack_client_open(configuration.client_name.c_str(), JackNoStartServer, &status);
       if (status != jack_status_t{})
-        warning(configuration, "observer_jack: " + std::to_string((int)jack_status_t{}));
+        libremidi_handle_error(configuration, std::to_string((int)status));
 
       if (this->client != nullptr)
       {

include/libremidi/backends/keyboard.hpp

@@ -0,0 +1,21 @@
+#pragma once
+#include <libremidi/backends/dummy.hpp>
+#include <libremidi/backends/keyboard/midi_in.hpp>
+
+namespace libremidi
+{
+struct kbd_backend
+{
+  using midi_in = midi_in_kbd;
+  using midi_in_configuration = kbd_input_configuration;
+  using midi_out = midi_out_dummy;
+  using midi_observer = observer_dummy;
+  using midi_out_configuration = dummy_configuration;
+  using midi_observer_configuration = dummy_configuration;
+  static const constexpr auto API = libremidi::API::KEYBOARD;
+  static const constexpr auto name = "keyboard";
+  static const constexpr auto display_name = "Computer keyboard";
+
+  static inline bool available() noexcept { return true; }
+};
+}

include/libremidi/backends/keyboard/config.hpp

@@ -0,0 +1,92 @@
+#pragma once
+#include <libremidi/config.hpp>
+
+#include <functional>
+#include <map>
+
+namespace libremidi
+{
+/**
+ * Used to set up keyboard input.
+ * Your app should pass a function that will give you a callback
+ * that you should call whenever you are getting a key input (press or release).
+ */
+struct kbd_input_configuration
+{
+  using scancode_callback = std::function<void(int)>;
+  // First argument is on key press, second on key release
+  std::function<void(scancode_callback, scancode_callback)> set_input_scancode_callbacks
+      = [](scancode_callback, scancode_callback) {};
+
+  enum kbd_event
+  {
+    NOTE_0 = 0x0,         // C
+    VEL_0 = NOTE_0 + 128, // Set velocity to 0
+    OCT_0 = VEL_0 + 128,  // Set octave to 0
+    OCTAVE_PLUS = OCT_0 + 128,
+    OCTAVE_MINUS,
+    VELOCITY_PLUS,
+    VELOCITY_MINUS,
+  };
+
+  // Default map
+  //
+  // ,---,---,---,---,---,---,---,---,---,---,---,---,---,-------,
+  // | V0| V1| V2| V3| V4| V5| V6| V7| V8| V9|V10|V11|V12| <-    |
+  // |---'-,-'-,-'-,-'-,-'-,-'-,-'-,-'-,-'-,-'-,-'-,-'-,-'-,-----|
+  // | ->| |   | C#| D#|   | F#| G#| A#|   | C#| D#|   | F#|     |
+  // |-----',--',--',--',--',--',--',--',--',--',--',--',--'|    |
+  // | Caps | C | D | E | F | G | A | B | C | D | E | F | G |    |
+  // |----,-'-,-'-,-'-,-'-,-'-,-'-,-'-,-'-,-'-,-'-,-'-,-'---'----|
+  // | -^ |   | O-| O+| V-| V+|   |   |   |   |   |   |   ----^  |
+  // |----'-,-',--'--,'---'---'---'---'---'---'-,-'---',--,------|
+  // | ctrl |  | alt |                          |altgr |  | ctrl |
+  // '------'  '-----'--------------------------'------'  '------'
+
+  // clang-format off
+  // Use: https://kbdlayout.info/KBDUSX/scancodes
+  std::map<int, int> scancode_map{
+      { 0x1E, NOTE_0}, // C0
+      { 0x11, NOTE_0 + 1},
+      { 0x1F, NOTE_0 + 2},
+      { 0x12, NOTE_0 + 3},
+      { 0x20, NOTE_0 + 4},
+      { 0x21, NOTE_0 + 5},
+      { 0x14, NOTE_0 + 6},
+      { 0x22, NOTE_0 + 7},
+      { 0x15, NOTE_0 + 8},
+      { 0x23, NOTE_0 + 9},
+      { 0x16, NOTE_0 + 10},
+      { 0x24, NOTE_0 + 11},
+      { 0x25, NOTE_0 + 12}, // C1
+      { 0x18, NOTE_0 + 13}, 
+      { 0x26, NOTE_0 + 14}, 
+      { 0x19, NOTE_0 + 15},
+      { 0x27, NOTE_0 + 16},
+      { 0x28, NOTE_0 + 17},
+      { 0x1B, NOTE_0 + 18},
+      { 0x2B, NOTE_0 + 19},
+
+      { 0x29, VEL_0 + int(0)},
+      { 0x02, VEL_0 + int(1 * 127 / 12)},
+      { 0x03, VEL_0 + int(2 * 127 / 12)},
+      { 0x04, VEL_0 + int(3 * 127 / 12)},
+      { 0x05, VEL_0 + int(4 * 127 / 12)},
+      { 0x06, VEL_0 + int(5 * 127 / 12)},
+      { 0x07, VEL_0 + int(6 * 127 / 12)},
+      { 0x08, VEL_0 + int(7 * 127 / 12)},
+      { 0x09, VEL_0 + int(8 * 127 / 12)},
+      { 0x0A, VEL_0 + int(9 * 127 / 12)},
+      { 0x0B, VEL_0 + int(10 * 127 / 12)},
+      { 0x0C, VEL_0 + int(11 * 127 / 12)},
+      { 0x0D, VEL_0 + int(127)},
+
+      { 0x2C, OCTAVE_MINUS },
+      { 0x2D, OCTAVE_PLUS },
+      { 0x2E, VELOCITY_MINUS },
+      { 0x2F, VELOCITY_PLUS}, 
+  };
+  // clang-format on
+};
+
+}

include/libremidi/backends/keyboard/midi_in.hpp

@@ -0,0 +1,112 @@
+#pragma once
+#include <libremidi/backends/keyboard/config.hpp>
+#include <libremidi/detail/midi_in.hpp>
+
+#include <chrono>
+#include <unordered_map>
+
+namespace libremidi
+{
+class midi_in_kbd final
+    : public midi1::in_api
+    , public error_handler
+{
+public:
+  using midi_api::client_open_;
+  struct
+      : input_configuration
+      , kbd_input_configuration
+  {
+  } configuration;
+
+  explicit midi_in_kbd(input_configuration&& conf, kbd_input_configuration&& apiconf)
+      : configuration{std::move(conf), std::move(apiconf)}
+  {
+    configuration.set_input_scancode_callbacks(
+        [this](int v) { on_keypress(v); }, [this](int v) { on_keyrelease(v); });
+  }
+
+  ~midi_in_kbd() override { }
+
+  libremidi::API get_current_api() const noexcept override { return libremidi::API::KEYBOARD; }
+
+  stdx::error open_port(const input_port&, std::string_view) override { return stdx::error{}; }
+
+  stdx::error open_virtual_port(std::string_view) override { return stdx::error{}; }
+
+  stdx::error close_port() override { return stdx::error{}; }
+
+  stdx::error set_port_name(std::string_view) override { return stdx::error{}; }
+
+  timestamp absolute_timestamp() const noexcept override
+  {
+    return std::chrono::steady_clock::now().time_since_epoch().count();
+  }
+
+  void on_keypress(int scancode)
+  {
+    using kevent = kbd_input_configuration::kbd_event;
+
+    auto it = configuration.scancode_map.find(scancode);
+    if (it == configuration.scancode_map.end())
+      return;
+
+    if (it->second >= kevent::NOTE_0 && it->second < (kevent::NOTE_0 + 128))
+    {
+      int note = it->second - kevent::NOTE_0 + 12 * m_current_octave;
+      this->configuration.on_message(
+          libremidi::channel_events::note_on(0, note, m_current_velocity));
+      m_current_notes_scancodes[scancode] = note;
+    }
+    else if (it->second >= kevent::VEL_0 && it->second < (kevent::VEL_0 + 128))
+    {
+      m_current_velocity = it->second - kevent::VEL_0;
+    }
+    else if (it->second >= kevent::OCT_0 && it->second < (kevent::OCT_0 + 128))
+    {
+      m_current_octave = it->second - kevent::OCT_0;
+    }
+    else
+    {
+      switch (it->second)
+      {
+        case kevent::VELOCITY_MINUS:
+          m_current_velocity = std::clamp(m_current_velocity - 10, 0, 127);
+          break;
+        case kevent::VELOCITY_PLUS:
+          m_current_velocity = std::clamp(m_current_velocity + 10, 0, 127);
+          break;
+        case kevent::OCTAVE_MINUS:
+          m_current_octave = std::clamp(m_current_octave - 1, 0, 127);
+          break;
+        case kevent::OCTAVE_PLUS:
+          m_current_octave = std::clamp(m_current_octave + 1, 0, 127);
+          break;
+      }
+    }
+  }
+
+  void on_keyrelease(int scancode)
+  {
+    using kevent = kbd_input_configuration::kbd_event;
+
+    auto it = configuration.scancode_map.find(scancode);
+    if (it == configuration.scancode_map.end())
+      return;
+
+    if (it->second >= kevent::NOTE_0 && it->second < (kevent::NOTE_0 + 128))
+    {
+      if (auto note_it = m_current_notes_scancodes.find(scancode);
+          note_it != m_current_notes_scancodes.end())
+      {
+        this->configuration.on_message(libremidi::channel_events::note_off(0, note_it->second, 0));
+        m_current_notes_scancodes.erase(note_it);
+      }
+    }
+  }
+
+  int m_current_octave{3};
+  int m_current_velocity{80};
+  std::unordered_map<int, int> m_current_notes_scancodes;
+};
+}

include/libremidi/backends/linux/alsa.hpp

@@ -57,13 +57,13 @@ struct libasound
         return;
       }
 
-      LIBREMIDI_SYMBOL_INIT(snd_card, get_name);
-      LIBREMIDI_SYMBOL_INIT(snd_card, next);
+      LIBREMIDI_SYMBOL_INIT(snd_card, get_name)
+      LIBREMIDI_SYMBOL_INIT(snd_card, next)
     }
     bool available{true};
 
-    LIBREMIDI_SYMBOL_DEF(snd_card, get_name);
-    LIBREMIDI_SYMBOL_DEF(snd_card, next);
+    LIBREMIDI_SYMBOL_DEF(snd_card, get_name)
+    LIBREMIDI_SYMBOL_DEF(snd_card, next)
   } card{library};
 
   struct ctl_t
@@ -80,13 +80,13 @@ struct libasound
         return;
       }
 
-      LIBREMIDI_SYMBOL_INIT(snd_ctl, close);
-      LIBREMIDI_SYMBOL_INIT(snd_ctl, open);
+      LIBREMIDI_SYMBOL_INIT(snd_ctl, close)
+      LIBREMIDI_SYMBOL_INIT(snd_ctl, open)
     }
     bool available{true};
 
-    LIBREMIDI_SYMBOL_DEF(snd_ctl, close);
-    LIBREMIDI_SYMBOL_DEF(snd_ctl, open);
+    LIBREMIDI_SYMBOL_DEF(snd_ctl, close)
+    LIBREMIDI_SYMBOL_DEF(snd_ctl, open)
 
     struct rawmidi_t
     {
@@ -98,12 +98,12 @@ struct libasound
           return;
         }
 
-        LIBREMIDI_SYMBOL_INIT(snd_ctl_rawmidi, info);
-        LIBREMIDI_SYMBOL_INIT(snd_ctl_rawmidi, next_device);
+        LIBREMIDI_SYMBOL_INIT(snd_ctl_rawmidi, info)
+        LIBREMIDI_SYMBOL_INIT(snd_ctl_rawmidi, next_device)
       }
       bool available{true};
-      LIBREMIDI_SYMBOL_DEF(snd_ctl_rawmidi, info);
-      LIBREMIDI_SYMBOL_DEF(snd_ctl_rawmidi, next_device);
+      LIBREMIDI_SYMBOL_DEF(snd_ctl_rawmidi, info)
+      LIBREMIDI_SYMBOL_DEF(snd_ctl_rawmidi, next_device)
     } rawmidi;
 
 #if LIBREMIDI_ALSA_HAS_UMP
@@ -117,14 +117,14 @@ struct libasound
           return;
         }
 
-        LIBREMIDI_SYMBOL_INIT(snd_ctl_ump, block_info);
-        LIBREMIDI_SYMBOL_INIT(snd_ctl_ump, endpoint_info);
-        LIBREMIDI_SYMBOL_INIT(snd_ctl_ump, next_device);
+        LIBREMIDI_SYMBOL_INIT(snd_ctl_ump, block_info)
+        LIBREMIDI_SYMBOL_INIT(snd_ctl_ump, endpoint_info)
+        LIBREMIDI_SYMBOL_INIT(snd_ctl_ump, next_device)
       }
       bool available{true};
-      LIBREMIDI_SYMBOL_DEF(snd_ctl_ump, block_info);
-      LIBREMIDI_SYMBOL_DEF(snd_ctl_ump, endpoint_info);
-      LIBREMIDI_SYMBOL_DEF(snd_ctl_ump, next_device);
+      LIBREMIDI_SYMBOL_DEF(snd_ctl_ump, block_info)
+      LIBREMIDI_SYMBOL_DEF(snd_ctl_ump, endpoint_info)
+      LIBREMIDI_SYMBOL_DEF(snd_ctl_ump, next_device)
     } ump;
 #endif
   } ctl{library};
@@ -139,23 +139,23 @@ struct libasound
         return;
       }
 
-      LIBREMIDI_SYMBOL_INIT(snd_midi, event_decode);
-      LIBREMIDI_SYMBOL_INIT(snd_midi, event_encode);
-      LIBREMIDI_SYMBOL_INIT(snd_midi, event_free);
-      LIBREMIDI_SYMBOL_INIT(snd_midi, event_init);
-      LIBREMIDI_SYMBOL_INIT(snd_midi, event_new);
-      LIBREMIDI_SYMBOL_INIT(snd_midi, event_no_status);
-      LIBREMIDI_SYMBOL_INIT(snd_midi, event_resize_buffer);
+      LIBREMIDI_SYMBOL_INIT(snd_midi, event_decode)
+      LIBREMIDI_SYMBOL_INIT(snd_midi, event_encode)
+      LIBREMIDI_SYMBOL_INIT(snd_midi, event_free)
+      LIBREMIDI_SYMBOL_INIT(snd_midi, event_init)
+      LIBREMIDI_SYMBOL_INIT(snd_midi, event_new)
+      LIBREMIDI_SYMBOL_INIT(snd_midi, event_no_status)
+      LIBREMIDI_SYMBOL_INIT(snd_midi, event_resize_buffer)
     }
 
     bool available{true};
-    LIBREMIDI_SYMBOL_DEF(snd_midi, event_decode);
-    LIBREMIDI_SYMBOL_DEF(snd_midi, event_encode);
-    LIBREMIDI_SYMBOL_DEF(snd_midi, event_free);
-    LIBREMIDI_SYMBOL_DEF(snd_midi, event_init);
-    LIBREMIDI_SYMBOL_DEF(snd_midi, event_new);
-    LIBREMIDI_SYMBOL_DEF(snd_midi, event_no_status);
-    LIBREMIDI_SYMBOL_DEF(snd_midi, event_resize_buffer);
+    LIBREMIDI_SYMBOL_DEF(snd_midi, event_decode)
+    LIBREMIDI_SYMBOL_DEF(snd_midi, event_encode)
+    LIBREMIDI_SYMBOL_DEF(snd_midi, event_free)
+    LIBREMIDI_SYMBOL_DEF(snd_midi, event_init)
+    LIBREMIDI_SYMBOL_DEF(snd_midi, event_new)
+    LIBREMIDI_SYMBOL_DEF(snd_midi, event_no_status)
+    LIBREMIDI_SYMBOL_DEF(snd_midi, event_resize_buffer)
   } midi{library};
 
 #if LIBREMIDI_ALSA_HAS_RAMWIDI
@@ -168,59 +168,59 @@ struct libasound
         available = false;
         return;
       }
-      LIBREMIDI_SYMBOL_INIT(snd_rawmidi, close);
-      LIBREMIDI_SYMBOL_INIT(snd_rawmidi, info_get_name);
-      LIBREMIDI_SYMBOL_INIT(snd_rawmidi, info_get_subdevice_name);
-      LIBREMIDI_SYMBOL_INIT(snd_rawmidi, info_get_subdevices_count);
-      LIBREMIDI_SYMBOL_INIT(snd_rawmidi, info_set_device);
-      LIBREMIDI_SYMBOL_INIT(snd_rawmidi, info_set_stream);
-      LIBREMIDI_SYMBOL_INIT(snd_rawmidi, info_set_subdevice);
-      LIBREMIDI_SYMBOL_INIT(snd_rawmidi, info_sizeof);
-      LIBREMIDI_SYMBOL_INIT(snd_rawmidi, open);
-      LIBREMIDI_SYMBOL_INIT(snd_rawmidi, params);
-      LIBREMIDI_SYMBOL_INIT(snd_rawmidi, params_current);
-      LIBREMIDI_SYMBOL_INIT(snd_rawmidi, params_get_buffer_size);
-      LIBREMIDI_SYMBOL_INIT(snd_rawmidi, params_set_clock_type);
-      LIBREMIDI_SYMBOL_INIT(snd_rawmidi, params_set_no_active_sensing);
-      LIBREMIDI_SYMBOL_INIT(snd_rawmidi, params_set_read_mode);
-      LIBREMIDI_SYMBOL_INIT(snd_rawmidi, params_sizeof);
-      LIBREMIDI_SYMBOL_INIT(snd_rawmidi, poll_descriptors);
-      LIBREMIDI_SYMBOL_INIT(snd_rawmidi, poll_descriptors_count);
-      LIBREMIDI_SYMBOL_INIT(snd_rawmidi, poll_descriptors_revents);
-      LIBREMIDI_SYMBOL_INIT(snd_rawmidi, read);
-      LIBREMIDI_SYMBOL_INIT(snd_rawmidi, status);
-      LIBREMIDI_SYMBOL_INIT(snd_rawmidi, status_get_avail);
-      LIBREMIDI_SYMBOL_INIT(snd_rawmidi, status_sizeof);
-      LIBREMIDI_SYMBOL_INIT(snd_rawmidi, tread);
-      LIBREMIDI_SYMBOL_INIT(snd_rawmidi, write);
+      LIBREMIDI_SYMBOL_INIT(snd_rawmidi, close)
+      LIBREMIDI_SYMBOL_INIT(snd_rawmidi, info_get_name)
+      LIBREMIDI_SYMBOL_INIT(snd_rawmidi, info_get_subdevice_name)
+      LIBREMIDI_SYMBOL_INIT(snd_rawmidi, info_get_subdevices_count)
+      LIBREMIDI_SYMBOL_INIT(snd_rawmidi, info_set_device)
+      LIBREMIDI_SYMBOL_INIT(snd_rawmidi, info_set_stream)
+      LIBREMIDI_SYMBOL_INIT(snd_rawmidi, info_set_subdevice)
+      LIBREMIDI_SYMBOL_INIT(snd_rawmidi, info_sizeof)
+      LIBREMIDI_SYMBOL_INIT(snd_rawmidi, open)
+      LIBREMIDI_SYMBOL_INIT(snd_rawmidi, params)
+      LIBREMIDI_SYMBOL_INIT(snd_rawmidi, params_current)
+      LIBREMIDI_SYMBOL_INIT(snd_rawmidi, params_get_buffer_size)
+      LIBREMIDI_SYMBOL_INIT(snd_rawmidi, params_set_clock_type)
+      LIBREMIDI_SYMBOL_INIT(snd_rawmidi, params_set_no_active_sensing)
+      LIBREMIDI_SYMBOL_INIT(snd_rawmidi, params_set_read_mode)
+      LIBREMIDI_SYMBOL_INIT(snd_rawmidi, params_sizeof)
+      LIBREMIDI_SYMBOL_INIT(snd_rawmidi, poll_descriptors)
+      LIBREMIDI_SYMBOL_INIT(snd_rawmidi, poll_descriptors_count)
+      LIBREMIDI_SYMBOL_INIT(snd_rawmidi, poll_descriptors_revents)
+      LIBREMIDI_SYMBOL_INIT(snd_rawmidi, read)
+      LIBREMIDI_SYMBOL_INIT(snd_rawmidi, status)
+      LIBREMIDI_SYMBOL_INIT(snd_rawmidi, status_get_avail)
+      LIBREMIDI_SYMBOL_INIT(snd_rawmidi, status_sizeof)
+      LIBREMIDI_SYMBOL_INIT(snd_rawmidi, tread)
+      LIBREMIDI_SYMBOL_INIT(snd_rawmidi, write)
     }
 
     bool available{true};
-    LIBREMIDI_SYMBOL_DEF(snd_rawmidi, close);
-    LIBREMIDI_SYMBOL_DEF(snd_rawmidi, info_get_name);
-    LIBREMIDI_SYMBOL_DEF(snd_rawmidi, info_get_subdevice_name);
-    LIBREMIDI_SYMBOL_DEF(snd_rawmidi, info_get_subdevices_count);
-    LIBREMIDI_SYMBOL_DEF(snd_rawmidi, info_set_device);
-    LIBREMIDI_SYMBOL_DEF(snd_rawmidi, info_set_stream);
-    LIBREMIDI_SYMBOL_DEF(snd_rawmidi, info_set_subdevice);
-    LIBREMIDI_SYMBOL_DEF(snd_rawmidi, info_sizeof);
-    LIBREMIDI_SYMBOL_DEF(snd_rawmidi, open);
-    LIBREMIDI_SYMBOL_DEF(snd_rawmidi, params);
-    LIBREMIDI_SYMBOL_DEF(snd_rawmidi, params_current);
-    LIBREMIDI_SYMBOL_DEF(snd_rawmidi, params_get_buffer_size);
-    LIBREMIDI_SYMBOL_DEF(snd_rawmidi, params_set_clock_type);
-    LIBREMIDI_SYMBOL_DEF(snd_rawmidi, params_set_no_active_sensing);
-    LIBREMIDI_SYMBOL_DEF(snd_rawmidi, params_set_read_mode);
-    LIBREMIDI_SYMBOL_DEF(snd_rawmidi, params_sizeof);
-    LIBREMIDI_SYMBOL_DEF(snd_rawmidi, poll_descriptors);
-    LIBREMIDI_SYMBOL_DEF(snd_rawmidi, poll_descriptors_count);
-    LIBREMIDI_SYMBOL_DEF(snd_rawmidi, poll_descriptors_revents);
-    LIBREMIDI_SYMBOL_DEF(snd_rawmidi, read);
-    LIBREMIDI_SYMBOL_DEF(snd_rawmidi, status);
-    LIBREMIDI_SYMBOL_DEF(snd_rawmidi, status_get_avail);
-    LIBREMIDI_SYMBOL_DEF(snd_rawmidi, status_sizeof);
-    LIBREMIDI_SYMBOL_DEF(snd_rawmidi, tread);
-    LIBREMIDI_SYMBOL_DEF(snd_rawmidi, write);
+    LIBREMIDI_SYMBOL_DEF(snd_rawmidi, close)
+    LIBREMIDI_SYMBOL_DEF(snd_rawmidi, info_get_name)
+    LIBREMIDI_SYMBOL_DEF(snd_rawmidi, info_get_subdevice_name)
+    LIBREMIDI_SYMBOL_DEF(snd_rawmidi, info_get_subdevices_count)
+    LIBREMIDI_SYMBOL_DEF(snd_rawmidi, info_set_device)
+    LIBREMIDI_SYMBOL_DEF(snd_rawmidi, info_set_stream)
+    LIBREMIDI_SYMBOL_DEF(snd_rawmidi, info_set_subdevice)
+    LIBREMIDI_SYMBOL_DEF(snd_rawmidi, info_sizeof)
+    LIBREMIDI_SYMBOL_DEF(snd_rawmidi, open)
+    LIBREMIDI_SYMBOL_DEF(snd_rawmidi, params)
+    LIBREMIDI_SYMBOL_DEF(snd_rawmidi, params_current)
+    LIBREMIDI_SYMBOL_DEF(snd_rawmidi, params_get_buffer_size)
+    LIBREMIDI_SYMBOL_DEF(snd_rawmidi, params_set_clock_type)
+    LIBREMIDI_SYMBOL_DEF(snd_rawmidi, params_set_no_active_sensing)
+    LIBREMIDI_SYMBOL_DEF(snd_rawmidi, params_set_read_mode)
+    LIBREMIDI_SYMBOL_DEF(snd_rawmidi, params_sizeof)
+    LIBREMIDI_SYMBOL_DEF(snd_rawmidi, poll_descriptors)
+    LIBREMIDI_SYMBOL_DEF(snd_rawmidi, poll_descriptors_count)
+    LIBREMIDI_SYMBOL_DEF(snd_rawmidi, poll_descriptors_revents)
+    LIBREMIDI_SYMBOL_DEF(snd_rawmidi, read)
+    LIBREMIDI_SYMBOL_DEF(snd_rawmidi, status)
+    LIBREMIDI_SYMBOL_DEF(snd_rawmidi, status_get_avail)
+    LIBREMIDI_SYMBOL_DEF(snd_rawmidi, status_sizeof)
+    LIBREMIDI_SYMBOL_DEF(snd_rawmidi, tread)
+    LIBREMIDI_SYMBOL_DEF(snd_rawmidi, write)
   } rawmidi{library};
 #endif
 
@@ -237,118 +237,118 @@ struct libasound
         return;
       }
 
-      LIBREMIDI_SYMBOL_INIT(snd_seq, alloc_queue);
-      LIBREMIDI_SYMBOL_INIT(snd_seq, client_id);
-      LIBREMIDI_SYMBOL_INIT(snd_seq, client_info_get_client);
-      LIBREMIDI_SYMBOL_INIT(snd_seq, client_info_get_name);
-      LIBREMIDI_SYMBOL_INIT(snd_seq, client_info_set_client);
-      LIBREMIDI_SYMBOL_INIT(snd_seq, client_info_sizeof);
-      LIBREMIDI_SYMBOL_INIT(snd_seq, close);
-      LIBREMIDI_SYMBOL_INIT(snd_seq, connect_from);
-      LIBREMIDI_SYMBOL_INIT(snd_seq, control_queue);
-      LIBREMIDI_SYMBOL_INIT(snd_seq, create_port);
-      LIBREMIDI_SYMBOL_INIT(snd_seq, delete_port);
-      LIBREMIDI_SYMBOL_INIT(snd_seq, drain_output);
-      LIBREMIDI_SYMBOL_INIT(snd_seq, event_input);
-      LIBREMIDI_SYMBOL_INIT(snd_seq, event_input_pending);
-      LIBREMIDI_SYMBOL_INIT(snd_seq, event_output);
-      LIBREMIDI_SYMBOL_INIT(snd_seq, free_event);
-      LIBREMIDI_SYMBOL_INIT(snd_seq, free_queue);
-      LIBREMIDI_SYMBOL_INIT(snd_seq, get_any_client_info);
-      LIBREMIDI_SYMBOL_INIT(snd_seq, get_any_port_info);
-      LIBREMIDI_SYMBOL_INIT(snd_seq, get_port_info);
-      LIBREMIDI_SYMBOL_INIT(snd_seq, open);
-      LIBREMIDI_SYMBOL_INIT(snd_seq, poll_descriptors);
-      LIBREMIDI_SYMBOL_INIT(snd_seq, poll_descriptors_count);
-      LIBREMIDI_SYMBOL_INIT(snd_seq, port_info_get_addr);
-      LIBREMIDI_SYMBOL_INIT(snd_seq, port_info_get_capability);
-      LIBREMIDI_SYMBOL_INIT(snd_seq, port_info_get_name);
-      LIBREMIDI_SYMBOL_INIT(snd_seq, port_info_get_port);
-      LIBREMIDI_SYMBOL_INIT(snd_seq, port_info_get_type);
-      LIBREMIDI_SYMBOL_INIT(snd_seq, port_info_set_capability);
-      LIBREMIDI_SYMBOL_INIT(snd_seq, port_info_set_client);
-      LIBREMIDI_SYMBOL_INIT(snd_seq, port_info_set_midi_channels);
-      LIBREMIDI_SYMBOL_INIT(snd_seq, port_info_set_name);
-      LIBREMIDI_SYMBOL_INIT(snd_seq, port_info_set_port);
-      LIBREMIDI_SYMBOL_INIT(snd_seq, port_info_set_timestamping);
-      LIBREMIDI_SYMBOL_INIT(snd_seq, port_info_set_timestamp_queue);
-      LIBREMIDI_SYMBOL_INIT(snd_seq, port_info_set_timestamp_real);
-      LIBREMIDI_SYMBOL_INIT(snd_seq, port_info_set_type);
-      LIBREMIDI_SYMBOL_INIT(snd_seq, port_info_sizeof);
-      LIBREMIDI_SYMBOL_INIT(snd_seq, port_subscribe_free);
-      LIBREMIDI_SYMBOL_INIT(snd_seq, port_subscribe_malloc);
-      LIBREMIDI_SYMBOL_INIT(snd_seq, port_subscribe_set_dest);
-      LIBREMIDI_SYMBOL_INIT(snd_seq, port_subscribe_set_sender);
-      LIBREMIDI_SYMBOL_INIT(snd_seq, port_subscribe_set_time_real);
-      LIBREMIDI_SYMBOL_INIT(snd_seq, port_subscribe_set_time_update);
-      LIBREMIDI_SYMBOL_INIT(snd_seq, query_next_client);
-      LIBREMIDI_SYMBOL_INIT(snd_seq, query_next_port);
-      LIBREMIDI_SYMBOL_INIT(snd_seq, queue_tempo_set_ppq);
-      LIBREMIDI_SYMBOL_INIT(snd_seq, queue_tempo_set_tempo);
-      LIBREMIDI_SYMBOL_INIT(snd_seq, queue_tempo_sizeof);
-      LIBREMIDI_SYMBOL_INIT(snd_seq, set_client_name);
-      LIBREMIDI_SYMBOL_INIT(snd_seq, set_port_info);
-      LIBREMIDI_SYMBOL_INIT(snd_seq, set_queue_tempo);
-      LIBREMIDI_SYMBOL_INIT(snd_seq, subscribe_port);
-      LIBREMIDI_SYMBOL_INIT(snd_seq, unsubscribe_port);
+      LIBREMIDI_SYMBOL_INIT(snd_seq, alloc_queue)
+      LIBREMIDI_SYMBOL_INIT(snd_seq, client_id)
+      LIBREMIDI_SYMBOL_INIT(snd_seq, client_info_get_client)
+      LIBREMIDI_SYMBOL_INIT(snd_seq, client_info_get_name)
+      LIBREMIDI_SYMBOL_INIT(snd_seq, client_info_set_client)
+      LIBREMIDI_SYMBOL_INIT(snd_seq, client_info_sizeof)
+      LIBREMIDI_SYMBOL_INIT(snd_seq, close)
+      LIBREMIDI_SYMBOL_INIT(snd_seq, connect_from)
+      LIBREMIDI_SYMBOL_INIT(snd_seq, control_queue)
+      LIBREMIDI_SYMBOL_INIT(snd_seq, create_port)
+      LIBREMIDI_SYMBOL_INIT(snd_seq, delete_port)
+      LIBREMIDI_SYMBOL_INIT(snd_seq, drain_output)
+      LIBREMIDI_SYMBOL_INIT(snd_seq, event_input)
+      LIBREMIDI_SYMBOL_INIT(snd_seq, event_input_pending)
+      LIBREMIDI_SYMBOL_INIT(snd_seq, event_output)
+      LIBREMIDI_SYMBOL_INIT(snd_seq, free_event)
+      LIBREMIDI_SYMBOL_INIT(snd_seq, free_queue)
+      LIBREMIDI_SYMBOL_INIT(snd_seq, get_any_client_info)
+      LIBREMIDI_SYMBOL_INIT(snd_seq, get_any_port_info)
+      LIBREMIDI_SYMBOL_INIT(snd_seq, get_port_info)
+      LIBREMIDI_SYMBOL_INIT(snd_seq, open)
+      LIBREMIDI_SYMBOL_INIT(snd_seq, poll_descriptors)
+      LIBREMIDI_SYMBOL_INIT(snd_seq, poll_descriptors_count)
+      LIBREMIDI_SYMBOL_INIT(snd_seq, port_info_get_addr)
+      LIBREMIDI_SYMBOL_INIT(snd_seq, port_info_get_capability)
+      LIBREMIDI_SYMBOL_INIT(snd_seq, port_info_get_name)
+      LIBREMIDI_SYMBOL_INIT(snd_seq, port_info_get_port)
+      LIBREMIDI_SYMBOL_INIT(snd_seq, port_info_get_type)
+      LIBREMIDI_SYMBOL_INIT(snd_seq, port_info_set_capability)
+      LIBREMIDI_SYMBOL_INIT(snd_seq, port_info_set_client)
+      LIBREMIDI_SYMBOL_INIT(snd_seq, port_info_set_midi_channels)
+      LIBREMIDI_SYMBOL_INIT(snd_seq, port_info_set_name)
+      LIBREMIDI_SYMBOL_INIT(snd_seq, port_info_set_port)
+      LIBREMIDI_SYMBOL_INIT(snd_seq, port_info_set_timestamping)
+      LIBREMIDI_SYMBOL_INIT(snd_seq, port_info_set_timestamp_queue)
+      LIBREMIDI_SYMBOL_INIT(snd_seq, port_info_set_timestamp_real)
+      LIBREMIDI_SYMBOL_INIT(snd_seq, port_info_set_type)
+      LIBREMIDI_SYMBOL_INIT(snd_seq, port_info_sizeof)
+      LIBREMIDI_SYMBOL_INIT(snd_seq, port_subscribe_free)
+      LIBREMIDI_SYMBOL_INIT(snd_seq, port_subscribe_malloc)
+      LIBREMIDI_SYMBOL_INIT(snd_seq, port_subscribe_set_dest)
+      LIBREMIDI_SYMBOL_INIT(snd_seq, port_subscribe_set_sender)
+      LIBREMIDI_SYMBOL_INIT(snd_seq, port_subscribe_set_time_real)
+      LIBREMIDI_SYMBOL_INIT(snd_seq, port_subscribe_set_time_update)
+      LIBREMIDI_SYMBOL_INIT(snd_seq, query_next_client)
+      LIBREMIDI_SYMBOL_INIT(snd_seq, query_next_port)
+      LIBREMIDI_SYMBOL_INIT(snd_seq, queue_tempo_set_ppq)
+      LIBREMIDI_SYMBOL_INIT(snd_seq, queue_tempo_set_tempo)
+      LIBREMIDI_SYMBOL_INIT(snd_seq, queue_tempo_sizeof)
+      LIBREMIDI_SYMBOL_INIT(snd_seq, set_client_name)
+      LIBREMIDI_SYMBOL_INIT(snd_seq, set_port_info)
+      LIBREMIDI_SYMBOL_INIT(snd_seq, set_queue_tempo)
+      LIBREMIDI_SYMBOL_INIT(snd_seq, subscribe_port)
+      LIBREMIDI_SYMBOL_INIT(snd_seq, unsubscribe_port)
     }
 
     bool available{true};
-    LIBREMIDI_SYMBOL_DEF(snd_seq, alloc_queue);
-    LIBREMIDI_SYMBOL_DEF(snd_seq, client_id);
-    LIBREMIDI_SYMBOL_DEF(snd_seq, client_info_get_client);
-    LIBREMIDI_SYMBOL_DEF(snd_seq, client_info_get_name);
-    LIBREMIDI_SYMBOL_DEF(snd_seq, client_info_set_client);
-    LIBREMIDI_SYMBOL_DEF(snd_seq, client_info_sizeof);
-    LIBREMIDI_SYMBOL_DEF(snd_seq, close);
-    LIBREMIDI_SYMBOL_DEF(snd_seq, connect_from);
-    LIBREMIDI_SYMBOL_DEF(snd_seq, control_queue);
-    LIBREMIDI_SYMBOL_DEF(snd_seq, create_port);
-    LIBREMIDI_SYMBOL_DEF(snd_seq, delete_port);
-    LIBREMIDI_SYMBOL_DEF(snd_seq, drain_output);
-    LIBREMIDI_SYMBOL_DEF(snd_seq, event_input);
-    LIBREMIDI_SYMBOL_DEF(snd_seq, event_input_pending);
-    LIBREMIDI_SYMBOL_DEF(snd_seq, event_output);
-    LIBREMIDI_SYMBOL_DEF(snd_seq, free_event);
-    LIBREMIDI_SYMBOL_DEF(snd_seq, free_queue);
-    LIBREMIDI_SYMBOL_DEF(snd_seq, get_any_client_info);
-    LIBREMIDI_SYMBOL_DEF(snd_seq, get_any_port_info);
-    LIBREMIDI_SYMBOL_DEF(snd_seq, get_port_info);
-    LIBREMIDI_SYMBOL_DEF(snd_seq, open);
-    LIBREMIDI_SYMBOL_DEF(snd_seq, poll_descriptors);
-    LIBREMIDI_SYMBOL_DEF(snd_seq, poll_descriptors_count);
-    LIBREMIDI_SYMBOL_DEF(snd_seq, port_info_get_addr);
-    LIBREMIDI_SYMBOL_DEF(snd_seq, port_info_get_capability);
-    LIBREMIDI_SYMBOL_DEF(snd_seq, port_info_get_name);
-    LIBREMIDI_SYMBOL_DEF(snd_seq, port_info_get_port);
-    LIBREMIDI_SYMBOL_DEF(snd_seq, port_info_get_type);
-    LIBREMIDI_SYMBOL_DEF(snd_seq, port_info_set_capability);
-    LIBREMIDI_SYMBOL_DEF(snd_seq, port_info_set_client);
-    LIBREMIDI_SYMBOL_DEF(snd_seq, port_info_set_midi_channels);
-    LIBREMIDI_SYMBOL_DEF(snd_seq, port_info_set_name);
-    LIBREMIDI_SYMBOL_DEF(snd_seq, port_info_set_port);
-    LIBREMIDI_SYMBOL_DEF(snd_seq, port_info_set_timestamping);
-    LIBREMIDI_SYMBOL_DEF(snd_seq, port_info_set_timestamp_queue);
-    LIBREMIDI_SYMBOL_DEF(snd_seq, port_info_set_timestamp_real);
-    LIBREMIDI_SYMBOL_DEF(snd_seq, port_info_set_type);
-    LIBREMIDI_SYMBOL_DEF(snd_seq, port_info_sizeof);
-    LIBREMIDI_SYMBOL_DEF(snd_seq, port_subscribe_free);
-    LIBREMIDI_SYMBOL_DEF(snd_seq, port_subscribe_malloc);
-    LIBREMIDI_SYMBOL_DEF(snd_seq, port_subscribe_set_dest);
-    LIBREMIDI_SYMBOL_DEF(snd_seq, port_subscribe_set_sender);
-    LIBREMIDI_SYMBOL_DEF(snd_seq, port_subscribe_set_time_real);
-    LIBREMIDI_SYMBOL_DEF(snd_seq, port_subscribe_set_time_update);
-    LIBREMIDI_SYMBOL_DEF(snd_seq, query_next_client);
-    LIBREMIDI_SYMBOL_DEF(snd_seq, query_next_port);
-    LIBREMIDI_SYMBOL_DEF(snd_seq, queue_tempo_set_ppq);
-    LIBREMIDI_SYMBOL_DEF(snd_seq, queue_tempo_set_tempo);
-    LIBREMIDI_SYMBOL_DEF(snd_seq, queue_tempo_sizeof);
+    LIBREMIDI_SYMBOL_DEF(snd_seq, alloc_queue)
+    LIBREMIDI_SYMBOL_DEF(snd_seq, client_id)
+    LIBREMIDI_SYMBOL_DEF(snd_seq, client_info_get_client)
+    LIBREMIDI_SYMBOL_DEF(snd_seq, client_info_get_name)
+    LIBREMIDI_SYMBOL_DEF(snd_seq, client_info_set_client)
+    LIBREMIDI_SYMBOL_DEF(snd_seq, client_info_sizeof)
+    LIBREMIDI_SYMBOL_DEF(snd_seq, close)
+    LIBREMIDI_SYMBOL_DEF(snd_seq, connect_from)
+    LIBREMIDI_SYMBOL_DEF(snd_seq, control_queue)
+    LIBREMIDI_SYMBOL_DEF(snd_seq, create_port)
+    LIBREMIDI_SYMBOL_DEF(snd_seq, delete_port)
+    LIBREMIDI_SYMBOL_DEF(snd_seq, drain_output)
+    LIBREMIDI_SYMBOL_DEF(snd_seq, event_input)
+    LIBREMIDI_SYMBOL_DEF(snd_seq, event_input_pending)
+    LIBREMIDI_SYMBOL_DEF(snd_seq, event_output)
+    LIBREMIDI_SYMBOL_DEF(snd_seq, free_event)
+    LIBREMIDI_SYMBOL_DEF(snd_seq, free_queue)
+    LIBREMIDI_SYMBOL_DEF(snd_seq, get_any_client_info)
+    LIBREMIDI_SYMBOL_DEF(snd_seq, get_any_port_info)
+    LIBREMIDI_SYMBOL_DEF(snd_seq, get_port_info)
+    LIBREMIDI_SYMBOL_DEF(snd_seq, open)
+    LIBREMIDI_SYMBOL_DEF(snd_seq, poll_descriptors)
+    LIBREMIDI_SYMBOL_DEF(snd_seq, poll_descriptors_count)
+    LIBREMIDI_SYMBOL_DEF(snd_seq, port_info_get_addr)
+    LIBREMIDI_SYMBOL_DEF(snd_seq, port_info_get_capability)
+    LIBREMIDI_SYMBOL_DEF(snd_seq, port_info_get_name)
+    LIBREMIDI_SYMBOL_DEF(snd_seq, port_info_get_port)
+    LIBREMIDI_SYMBOL_DEF(snd_seq, port_info_get_type)
+    LIBREMIDI_SYMBOL_DEF(snd_seq, port_info_set_capability)
+    LIBREMIDI_SYMBOL_DEF(snd_seq, port_info_set_client)
+    LIBREMIDI_SYMBOL_DEF(snd_seq, port_info_set_midi_channels)
+    LIBREMIDI_SYMBOL_DEF(snd_seq, port_info_set_name)
+    LIBREMIDI_SYMBOL_DEF(snd_seq, port_info_set_port)
+    LIBREMIDI_SYMBOL_DEF(snd_seq, port_info_set_timestamping)
+    LIBREMIDI_SYMBOL_DEF(snd_seq, port_info_set_timestamp_queue)
+    LIBREMIDI_SYMBOL_DEF(snd_seq, port_info_set_timestamp_real)
+    LIBREMIDI_SYMBOL_DEF(snd_seq, port_info_set_type)
+    LIBREMIDI_SYMBOL_DEF(snd_seq, port_info_sizeof)
+    LIBREMIDI_SYMBOL_DEF(snd_seq, port_subscribe_free)
+    LIBREMIDI_SYMBOL_DEF(snd_seq, port_subscribe_malloc)
+    LIBREMIDI_SYMBOL_DEF(snd_seq, port_subscribe_set_dest)
+    LIBREMIDI_SYMBOL_DEF(snd_seq, port_subscribe_set_sender)
+    LIBREMIDI_SYMBOL_DEF(snd_seq, port_subscribe_set_time_real)
+    LIBREMIDI_SYMBOL_DEF(snd_seq, port_subscribe_set_time_update)
+    LIBREMIDI_SYMBOL_DEF(snd_seq, query_next_client)
+    LIBREMIDI_SYMBOL_DEF(snd_seq, query_next_port)
+    LIBREMIDI_SYMBOL_DEF(snd_seq, queue_tempo_set_ppq)
+    LIBREMIDI_SYMBOL_DEF(snd_seq, queue_tempo_set_tempo)
+    LIBREMIDI_SYMBOL_DEF(snd_seq, queue_tempo_sizeof)
 
-    LIBREMIDI_SYMBOL_DEF(snd_seq, set_client_name);
-    LIBREMIDI_SYMBOL_DEF(snd_seq, set_port_info);
-    LIBREMIDI_SYMBOL_DEF(snd_seq, set_queue_tempo);
-    LIBREMIDI_SYMBOL_DEF(snd_seq, subscribe_port);
-    LIBREMIDI_SYMBOL_DEF(snd_seq, unsubscribe_port);
+    LIBREMIDI_SYMBOL_DEF(snd_seq, set_client_name)
+    LIBREMIDI_SYMBOL_DEF(snd_seq, set_port_info)
+    LIBREMIDI_SYMBOL_DEF(snd_seq, set_queue_tempo)
+    LIBREMIDI_SYMBOL_DEF(snd_seq, subscribe_port)
+    LIBREMIDI_SYMBOL_DEF(snd_seq, unsubscribe_port)
 
 #if LIBREMIDI_ALSA_HAS_UMP
     struct ump_t
@@ -360,18 +360,18 @@ struct libasound
           available = false;
           return;
         }
-        LIBREMIDI_SYMBOL_INIT(snd_seq, set_client_midi_version);
-        LIBREMIDI_SYMBOL_INIT(snd_seq_ump, event_input);
-        LIBREMIDI_SYMBOL_INIT(snd_seq_ump, event_output);
-        LIBREMIDI_SYMBOL_INIT(snd_seq_ump, event_output_direct);
+        LIBREMIDI_SYMBOL_INIT(snd_seq, set_client_midi_version)
+        LIBREMIDI_SYMBOL_INIT(snd_seq_ump, event_input)
+        LIBREMIDI_SYMBOL_INIT(snd_seq_ump, event_output)
+        LIBREMIDI_SYMBOL_INIT(snd_seq_ump, event_output_direct)
       }
 
       bool available{true};
 
-      LIBREMIDI_SYMBOL_DEF(snd_seq, set_client_midi_version);
-      LIBREMIDI_SYMBOL_DEF(snd_seq_ump, event_input);
-      LIBREMIDI_SYMBOL_DEF(snd_seq_ump, event_output);
-      LIBREMIDI_SYMBOL_DEF(snd_seq_ump, event_output_direct);
+      LIBREMIDI_SYMBOL_DEF(snd_seq, set_client_midi_version)
+      LIBREMIDI_SYMBOL_DEF(snd_seq_ump, event_input)
+      LIBREMIDI_SYMBOL_DEF(snd_seq_ump, event_output)
+      LIBREMIDI_SYMBOL_DEF(snd_seq_ump, event_output_direct)
     } ump;
 #endif
   } seq{library};
@@ -387,39 +387,39 @@ struct libasound
         return;
       }
 
-      LIBREMIDI_SYMBOL_INIT(snd_ump, block_info_get_name);
-      LIBREMIDI_SYMBOL_INIT(snd_ump, block_info_sizeof);
-      LIBREMIDI_SYMBOL_INIT(snd_ump, close);
-      LIBREMIDI_SYMBOL_INIT(snd_ump, endpoint_info_get_name);
-      LIBREMIDI_SYMBOL_INIT(snd_ump, endpoint_info_sizeof);
-      LIBREMIDI_SYMBOL_INIT(snd_ump, open);
-      LIBREMIDI_SYMBOL_INIT(snd_ump, poll_descriptors);
-      LIBREMIDI_SYMBOL_INIT(snd_ump, poll_descriptors_count);
-      LIBREMIDI_SYMBOL_INIT(snd_ump, poll_descriptors_revents);
-      LIBREMIDI_SYMBOL_INIT(snd_ump, rawmidi);
-      LIBREMIDI_SYMBOL_INIT(snd_ump, rawmidi_params);
-      LIBREMIDI_SYMBOL_INIT(snd_ump, rawmidi_params_current);
-      LIBREMIDI_SYMBOL_INIT(snd_ump, read);
-      LIBREMIDI_SYMBOL_INIT(snd_ump, tread);
-      LIBREMIDI_SYMBOL_INIT(snd_ump, write);
+      LIBREMIDI_SYMBOL_INIT(snd_ump, block_info_get_name)
+      LIBREMIDI_SYMBOL_INIT(snd_ump, block_info_sizeof)
+      LIBREMIDI_SYMBOL_INIT(snd_ump, close)
+      LIBREMIDI_SYMBOL_INIT(snd_ump, endpoint_info_get_name)
+      LIBREMIDI_SYMBOL_INIT(snd_ump, endpoint_info_sizeof)
+      LIBREMIDI_SYMBOL_INIT(snd_ump, open)
+      LIBREMIDI_SYMBOL_INIT(snd_ump, poll_descriptors)
+      LIBREMIDI_SYMBOL_INIT(snd_ump, poll_descriptors_count)
+      LIBREMIDI_SYMBOL_INIT(snd_ump, poll_descriptors_revents)
+      LIBREMIDI_SYMBOL_INIT(snd_ump, rawmidi)
+      LIBREMIDI_SYMBOL_INIT(snd_ump, rawmidi_params)
+      LIBREMIDI_SYMBOL_INIT(snd_ump, rawmidi_params_current)
+      LIBREMIDI_SYMBOL_INIT(snd_ump, read)
+      LIBREMIDI_SYMBOL_INIT(snd_ump, tread)
+      LIBREMIDI_SYMBOL_INIT(snd_ump, write)
     }
 
     bool available{true};
-    LIBREMIDI_SYMBOL_DEF(snd_ump, block_info_get_name);
-    LIBREMIDI_SYMBOL_DEF(snd_ump, block_info_sizeof);
-    LIBREMIDI_SYMBOL_DEF(snd_ump, close);
-    LIBREMIDI_SYMBOL_DEF(snd_ump, endpoint_info_get_name);
-    LIBREMIDI_SYMBOL_DEF(snd_ump, endpoint_info_sizeof);
-    LIBREMIDI_SYMBOL_DEF(snd_ump, open);
-    LIBREMIDI_SYMBOL_DEF(snd_ump, poll_descriptors);
-    LIBREMIDI_SYMBOL_DEF(snd_ump, poll_descriptors_count);
-    LIBREMIDI_SYMBOL_DEF(snd_ump, poll_descriptors_revents);
-    LIBREMIDI_SYMBOL_DEF(snd_ump, rawmidi);
-    LIBREMIDI_SYMBOL_DEF(snd_ump, rawmidi_params);
-    LIBREMIDI_SYMBOL_DEF(snd_ump, rawmidi_params_current);
-    LIBREMIDI_SYMBOL_DEF(snd_ump, read);
-    LIBREMIDI_SYMBOL_DEF(snd_ump, tread);
-    LIBREMIDI_SYMBOL_DEF(snd_ump, write);
+    LIBREMIDI_SYMBOL_DEF(snd_ump, block_info_get_name)
+    LIBREMIDI_SYMBOL_DEF(snd_ump, block_info_sizeof)
+    LIBREMIDI_SYMBOL_DEF(snd_ump, close)
+    LIBREMIDI_SYMBOL_DEF(snd_ump, endpoint_info_get_name)
+    LIBREMIDI_SYMBOL_DEF(snd_ump, endpoint_info_sizeof)
+    LIBREMIDI_SYMBOL_DEF(snd_ump, open)
+    LIBREMIDI_SYMBOL_DEF(snd_ump, poll_descriptors)
+    LIBREMIDI_SYMBOL_DEF(snd_ump, poll_descriptors_count)
+    LIBREMIDI_SYMBOL_DEF(snd_ump, poll_descriptors_revents)
+    LIBREMIDI_SYMBOL_DEF(snd_ump, rawmidi)
+    LIBREMIDI_SYMBOL_DEF(snd_ump, rawmidi_params)
+    LIBREMIDI_SYMBOL_DEF(snd_ump, rawmidi_params_current)
+    LIBREMIDI_SYMBOL_DEF(snd_ump, read)
+    LIBREMIDI_SYMBOL_DEF(snd_ump, tread)
+    LIBREMIDI_SYMBOL_DEF(snd_ump, write)
   } ump{library};
 #endif
 };

include/libremidi/backends/linux/udev.hpp

@@ -23,16 +23,16 @@ struct libudev
       return;
     }
 
-    LIBREMIDI_SYMBOL_INIT(udev, device_get_action);
-    LIBREMIDI_SYMBOL_INIT(udev, device_get_subsystem);
-    LIBREMIDI_SYMBOL_INIT(udev, device_unref);
-    LIBREMIDI_SYMBOL_INIT(udev, monitor_enable_receiving);
-    LIBREMIDI_SYMBOL_INIT(udev, monitor_get_fd);
-    LIBREMIDI_SYMBOL_INIT(udev, monitor_new_from_netlink);
-    LIBREMIDI_SYMBOL_INIT(udev, monitor_receive_device);
-    LIBREMIDI_SYMBOL_INIT(udev, monitor_unref);
-    LIBREMIDI_SYMBOL_INIT2(udev, new, create);
-    LIBREMIDI_SYMBOL_INIT(udev, unref);
+    LIBREMIDI_SYMBOL_INIT(udev, device_get_action)
+    LIBREMIDI_SYMBOL_INIT(udev, device_get_subsystem)
+    LIBREMIDI_SYMBOL_INIT(udev, device_unref)
+    LIBREMIDI_SYMBOL_INIT(udev, monitor_enable_receiving)
+    LIBREMIDI_SYMBOL_INIT(udev, monitor_get_fd)
+    LIBREMIDI_SYMBOL_INIT(udev, monitor_new_from_netlink)
+    LIBREMIDI_SYMBOL_INIT(udev, monitor_receive_device)
+    LIBREMIDI_SYMBOL_INIT(udev, monitor_unref)
+    LIBREMIDI_SYMBOL_INIT2(udev, new, create)
+    LIBREMIDI_SYMBOL_INIT(udev, unref)
   }
 
   static const libudev& instance()
@@ -44,16 +44,16 @@ struct libudev
   dylib_loader library;
   bool available{true};
 
-  LIBREMIDI_SYMBOL_DEF(udev, device_get_action);
-  LIBREMIDI_SYMBOL_DEF(udev, device_get_subsystem);
-  LIBREMIDI_SYMBOL_DEF(udev, device_unref);
-  LIBREMIDI_SYMBOL_DEF(udev, monitor_enable_receiving);
-  LIBREMIDI_SYMBOL_DEF(udev, monitor_get_fd);
-  LIBREMIDI_SYMBOL_DEF(udev, monitor_new_from_netlink);
-  LIBREMIDI_SYMBOL_DEF(udev, monitor_receive_device);
-  LIBREMIDI_SYMBOL_DEF(udev, monitor_unref);
-  LIBREMIDI_SYMBOL_DEF2(udev, new, create);
-  LIBREMIDI_SYMBOL_DEF(udev, unref);
+  LIBREMIDI_SYMBOL_DEF(udev, device_get_action)
+  LIBREMIDI_SYMBOL_DEF(udev, device_get_subsystem)
+  LIBREMIDI_SYMBOL_DEF(udev, device_unref)
+  LIBREMIDI_SYMBOL_DEF(udev, monitor_enable_receiving)
+  LIBREMIDI_SYMBOL_DEF(udev, monitor_get_fd)
+  LIBREMIDI_SYMBOL_DEF(udev, monitor_new_from_netlink)
+  LIBREMIDI_SYMBOL_DEF(udev, monitor_receive_device)
+  LIBREMIDI_SYMBOL_DEF(udev, monitor_unref)
+  LIBREMIDI_SYMBOL_DEF2(udev, new, create)
+  LIBREMIDI_SYMBOL_DEF(udev, unref)
 };
 
 struct udev_helper

include/libremidi/backends/net/config.hpp

@@ -0,0 +1,86 @@
+#pragma once
+#include <libremidi/config.hpp>
+
+#include <string>
+namespace boost::asio
+{
+struct io_context;
+}
+
+namespace libremidi::net
+{
+enum class protocol
+{
+  OSC_MIDI,
+};
+
+struct dgram_input_configuration
+{
+  std::string client_name = "libremidi client";
+
+  enum protocol protocol = protocol::OSC_MIDI;
+  std::string accept = "0.0.0.0";
+  int port{};
+
+  boost::asio::io_context* io_context{};
+};
+
+struct dgram_output_configuration
+{
+  std::string client_name = "libremidi client";
+
+  enum protocol protocol = protocol::OSC_MIDI;
+  std::string host = "127.0.0.1";
+  int port{};
+  bool broadcast{};
+
+  boost::asio::io_context* io_context{};
+};
+
+struct dgram_observer_configuration
+{
+  std::string client_name = "libremidi client";
+
+  boost::asio::io_context* io_context{};
+};
+
+}
+
+namespace libremidi::net_ump
+{
+enum class protocol
+{
+  OSC_MIDI2,
+};
+
+struct dgram_input_configuration
+{
+  std::string client_name = "libremidi client";
+
+  enum protocol protocol = protocol::OSC_MIDI2;
+  std::string accept = "0.0.0.0";
+  int port{};
+
+  boost::asio::io_context* io_context{};
+};
+
+struct dgram_output_configuration
+{
+  std::string client_name = "libremidi client";
+
+  enum protocol protocol = protocol::OSC_MIDI2;
+  std::string host = "127.0.0.1";
+  int port{};
+  bool broadcast{};
+
+  boost::asio::io_context* io_context{};
+};
+
+struct dgram_observer_configuration
+{
+  std::string client_name = "libremidi client";
+
+  boost::asio::io_context* io_context{};
+};
+
+}

include/libremidi/backends/net/helpers.hpp

@@ -0,0 +1,91 @@
+#pragma once
+#include <libremidi/config.hpp>
+
+#include <boost/asio/ip/udp.hpp>
+
+#include <memory>
+namespace stdx
+{ /*
+
+class boost_system_error_domain : public error_domain
+{
+public:
+  constexpr boost_system_error_domain() noexcept
+      : error_domain{
+            {1 - 0x3c223c0aa3cf45e5ULL, 1 - 0x80dac24345cfb9fcULL},
+            default_error_resource_management_t<detail::exception_ptr_wrapper>{}}
+  {
+  }
+
+  string_ref name() const noexcept override { return "boost::system_error domain"; }
+
+  bool equivalent(const error& lhs, const error& rhs) const noexcept override { return false; }
+
+  string_ref message(const error& e) const noexcept override {
+    auto err = e.m_value;
+    
+  }
+
+  [[noreturn]] void throw_exception(const error& e) const override
+  {
+    assert(e.domain() == *this);
+    std::rethrow_exception(error_cast<detail::exception_ptr_wrapper>(e).get());
+  }
+};
+*/
+}
+
+namespace libremidi
+{
+template <typename T>
+struct optionally_owned
+{
+public:
+  explicit optionally_owned(T* maybe_existing)
+      : storage{.ref = maybe_existing}
+  {
+    if (storage.ref)
+    {
+      ownership = unowned;
+      return;
+    }
+    else
+    {
+      std::destroy_at(&storage.ref);
+      std::construct_at<T>(reinterpret_cast<T*>(storage.object));
+      ownership = owned;
+    }
+  }
+
+  ~optionally_owned()
+  {
+    if (is_owned())
+      std::destroy_at(reinterpret_cast<T*>(storage.object));
+  }
+
+  T& get() noexcept { return *(is_owned() ? reinterpret_cast<T*>(&storage.object) : storage.ref); }
+  const T& get() const noexcept
+  {
+    return *(is_owned() ? reinterpret_cast<T*>(&storage.object) : storage.ref);
+  }
+
+  optionally_owned(const optionally_owned&) = delete;
+  optionally_owned(optionally_owned&&) noexcept = delete;
+  optionally_owned& operator=(const optionally_owned&) = delete;
+  optionally_owned& operator=(optionally_owned&&) noexcept = delete;
+
+  bool is_owned() const noexcept { return ownership == owned; }
+
+private:
+  union
+  {
+    alignas(T) unsigned char object[sizeof(T)];
+    T* ref;
+  } storage;
+  enum
+  {
+    owned,
+    unowned
+  } ownership{};
+};
+}

include/libremidi/backends/net/midi_in.hpp

@@ -0,0 +1,440 @@
+#pragma once
+#include <libremidi/backends/net/config.hpp>
+#include <libremidi/backends/net/helpers.hpp>
+#include <libremidi/detail/midi_in.hpp>
+#include <libremidi/detail/midi_stream_decoder.hpp>
+
+namespace libremidi
+{
+template <typename Impl, typename F>
+struct osc_parser
+{
+  [[no_unique_address]]
+  Impl impl;
+  F on_message;
+  std::string_view port_name;
+
+  stdx::error parse_bundle(const char* data, std::size_t sz)
+  {
+    std::string_view txt(data, sz);
+    if (!txt.starts_with("#bundle"))
+      return std::errc::bad_message;
+    return std::errc::protocol_not_supported;
+  }
+
+  stdx::error parse_message(const char* data, std::size_t sz)
+  {
+    const auto begin = data;
+    const auto end = data + sz;
+    std::size_t pattern_len = strnlen(data, sz);
+    if (pattern_len == sz)
+      return std::errc::bad_message;
+
+    if (auto pat = std::string_view(data, pattern_len); pat != port_name)
+      return std::errc::bad_address;
+
+    data += pattern_len;
+    for (; data < end; ++data)
+      if (*data == 0)
+        continue;
+      else
+        break;
+
+    // Now we shold reach the typetag beginning, ","
+    if (data == end)
+      return std::errc::bad_message;
+    if ((data - begin) % 4 != 0)
+      return std::errc::bad_message;
+    if (*data++ != ',')
+      return std::errc::bad_message;
+
+    // Count the ,mmmmm arguments... yummy
+    int num_msgs = 0;
+    for (; data < end; ++data)
+      if (*data == Impl::typetag)
+        num_msgs++;
+      else if (*data == 0)
+        break;
+      else
+        return std::errc::bad_message;
+
+    if (num_msgs == 0)
+      return std::errc::no_message;
+
+    // By now there's at least 5 bytes left as the ,mmm has to be round-up to 4 and padded with zeros:
+    if (end - data < 4)
+      return std::errc::bad_message;
+
+    switch ((1 + num_msgs) % 4)
+    {
+      case 0:
+        data += 4;
+        break;
+      case 1:
+        data += 3;
+        break;
+      case 2:
+        data += 2;
+        break;
+      case 3:
+        data += 1;
+        break;
+    }
+
+    // Data starts
+    return impl.process_midi_bytes(on_message, num_msgs, data, end - data);
+  }
+
+  stdx::error parse_int_message(const char* /* data */, std::size_t /* sz */)
+  {
+    return std::errc::protocol_not_supported;
+  }
+
+  stdx::error parse_packet(const char* data, std::size_t sz)
+  {
+    if (sz == 0)
+      return std::errc::no_message;
+
+    switch (data[0])
+    {
+      case '#':
+        return parse_bundle(data, sz);
+        break;
+      case '/':
+        return parse_message(data, sz);
+        break;
+      case '\0':
+        return parse_int_message(data, sz);
+        break;
+      default:
+        return std::errc::bad_message;
+    }
+  }
+};
+
+}
+
+namespace libremidi::net
+{
+
+struct osc_parser_midi1
+{
+  static constexpr char typetag = 'm';
+
+  stdx::error
+  process_midi_bytes(auto& on_message, std::size_t num_msgs, const char* data, std::size_t sz)
+  {
+    if (sz != num_msgs * 4)
+      return std::errc::bad_message;
+
+    auto end = data + sz;
+    for (; data < end; data += 4)
+      on_message(data + 1);
+
+    return {};
+  }
+};
+
+class midi_in final
+    : public midi1::in_api
+    , public error_handler
+{
+public:
+  using midi_api::client_open_;
+  struct
+      : input_configuration
+      , dgram_input_configuration
+  {
+  } configuration;
+
+  explicit midi_in(input_configuration&& conf, dgram_input_configuration&& apiconf)
+      : configuration{std::move(conf), std::move(apiconf)}
+      , m_ctx{configuration.io_context}
+      , m_socket{m_ctx.get()}
+  {
+    m_socket.open(boost::asio::ip::udp::v4());
+    m_socket.set_option(boost::asio::ip::udp::socket::reuse_address(true));
+
+    m_endpoint
+        = {boost::asio::ip::make_address(this->configuration.accept),
+           static_cast<unsigned short>(this->configuration.port)};
+
+    boost::system::error_code ec;
+    m_socket.bind(m_endpoint, ec);
+    if (ec != boost::system::error_code{})
+    {
+      client_open_ = std::errc::address_in_use;
+      return;
+    }
+
+    client_open_ = stdx::error{};
+  }
+
+  ~midi_in() override { close_port(); }
+
+  libremidi::API get_current_api() const noexcept override { return libremidi::API::NETWORK; }
+
+  stdx::error open_port(const input_port&, std::string_view port) override
+  {
+    return open_virtual_port(port);
+  }
+
+  stdx::error open_virtual_port(std::string_view port) override
+  {
+    m_portname = std::string(port);
+
+    receive();
+
+    if (m_ctx.is_owned())
+    {
+      m_thread = std::jthread{[this, &ctx = m_ctx.get()] {
+        auto wg = boost::asio::make_work_guard(m_ctx);
+        ctx.run();
+      }};
+    }
+
+    return stdx::error{};
+  }
+
+  void receive()
+  {
+    m_socket.async_receive_from(
+        boost::asio::mutable_buffer(&m_data[0], std::size(m_data)), m_endpoint,
+        [this](auto ec, std::size_t sz) {
+      if (ec == boost::asio::error::operation_aborted)
+        return;
+
+      if (!ec && sz > 0)
+        this->on_bytes(reinterpret_cast<const char*>(m_data), sz);
+
+      this->receive();
+    });
+  }
+
+  stdx::error close_port() override
+  {
+    // FIXME async close
+    if (m_socket.is_open())
+      m_socket.close();
+    return {};
+  }
+
+  stdx::error set_port_name(std::string_view) override { return stdx::error{}; }
+
+  timestamp absolute_timestamp() const noexcept override
+  {
+    return std::chrono::steady_clock::now().time_since_epoch().count();
+  }
+
+  void on_bytes(const char* data, std::size_t size)
+  {
+    const auto on_msg = [this](const char* bytes) { this->on_message(bytes); };
+    osc_parser<osc_parser_midi1, decltype(on_msg)> parser{{}, on_msg, m_portname};
+    parser.parse_packet(data, size);
+  }
+
+  void on_message(const char* data)
+  {
+    // OSC enforces always 3 bytes
+    static constexpr timestamp_backend_info timestamp_info{
+        .has_absolute_timestamps = false,
+        .absolute_is_monotonic = false,
+        .has_samples = false,
+    };
+
+    static constexpr auto to_ns = []() {
+      return std::chrono::duration_cast<std::chrono::nanoseconds>(
+                 std::chrono::steady_clock::now().time_since_epoch())
+          .count();
+    };
+
+    auto ptr = reinterpret_cast<const uint8_t*>(data);
+    m_processing.on_bytes({ptr, ptr + 3}, m_processing.timestamp<timestamp_info>(to_ns, 0));
+  }
+
+  midi1::input_state_machine m_processing{this->configuration};
+
+  libremidi::optionally_owned<boost::asio::io_context> m_ctx;
+  boost::asio::ip::udp::endpoint m_endpoint;
+  boost::asio::ip::udp::socket m_socket;
+
+  std::jthread m_thread;
+
+  std::string m_portname;
+  alignas(16) unsigned char m_data[65535];
+};
+}
+
+namespace libremidi::net_ump
+{
+struct osc_parser_midi2
+{
+  static constexpr char typetag = 'M';
+
+  stdx::error
+  process_midi_bytes(auto& on_message, std::size_t num_msgs, const char* data, std::size_t byte_sz)
+  {
+    if (byte_sz % 4 != 0)
+      return std::errc::bad_message;
+
+    auto sz = byte_sz / 4;
+
+    auto begin = reinterpret_cast<const uint32_t*>(data);
+    auto end = begin + sz;
+    std::size_t accounted = 0;
+    for (auto it = begin; it < end && accounted < num_msgs;)
+    {
+      const auto N = cmidi2_ump_get_message_size_bytes(it) / 4;
+      switch (N)
+      {
+        case 1:
+        case 2:
+        case 4:
+          if (it + N <= end)
+          {
+            on_message(it, N);
+            accounted++;
+          }
+          else
+            return std::errc::bad_message;
+          break;
+        default:
+          return std::errc::bad_message;
+      }
+      it += N;
+    }
+
+    return {};
+  }
+};
+
+class midi_in final
+    : public midi2::in_api
+    , public error_handler
+{
+public:
+  using midi_api::client_open_;
+  struct
+      : ump_input_configuration
+      , dgram_input_configuration
+  {
+  } configuration;
+
+  explicit midi_in(ump_input_configuration&& conf, dgram_input_configuration&& apiconf)
+      : configuration{std::move(conf), std::move(apiconf)}
+      , m_ctx{configuration.io_context}
+      , m_socket{m_ctx.get()}
+  {
+    m_socket.open(boost::asio::ip::udp::v4());
+    m_socket.set_option(boost::asio::ip::udp::socket::reuse_address(true));
+
+    m_endpoint
+        = {boost::asio::ip::make_address(this->configuration.accept),
+           static_cast<unsigned short>(this->configuration.port)};
+
+    boost::system::error_code ec;
+    m_socket.bind(m_endpoint, ec);
+    if (ec != boost::system::error_code{})
+    {
+      client_open_ = std::errc::address_in_use;
+      return;
+    }
+
+    client_open_ = stdx::error{};
+  }
+
+  ~midi_in() override { close_port(); }
+
+  libremidi::API get_current_api() const noexcept override { return libremidi::API::NETWORK_UMP; }
+
+  stdx::error open_port(const input_port&, std::string_view port) override
+  {
+    return open_virtual_port(port);
+  }
+
+  stdx::error open_virtual_port(std::string_view port) override
+  {
+    m_portname = std::string(port);
+
+    receive();
+
+    if (m_ctx.is_owned())
+    {
+      m_thread = std::jthread{[this, &ctx = m_ctx.get()] {
+        auto wg = boost::asio::make_work_guard(m_ctx);
+        ctx.run();
+      }};
+    }
+    return stdx::error{};
+  }
+
+  void receive()
+  {
+    m_socket.async_receive_from(
+        boost::asio::mutable_buffer(&m_data[0], std::size(m_data)), m_endpoint,
+        [this](auto ec, std::size_t sz) {
+      if (ec == boost::asio::error::operation_aborted)
+        return;
+
+      if (!ec && sz > 0)
+        this->on_bytes(reinterpret_cast<const char*>(m_data), sz);
+
+      this->receive();
+    });
+  }
+
+  stdx::error close_port() override
+  {
+    // FIXME async close
+    if (m_ctx.is_owned())
+      m_ctx.get().stop();
+
+    if (m_socket.is_open())
+      m_socket.close();
+    return {};
+  }
+
+  stdx::error set_port_name(std::string_view) override { return stdx::error{}; }
+
+  timestamp absolute_timestamp() const noexcept override
+  {
+    return std::chrono::steady_clock::now().time_since_epoch().count();
+  }
+
+  void on_bytes(const char* data, std::size_t size)
+  {
+    const auto on_msg
+        = [this](const uint32_t* bytes, std::size_t N) { this->on_message(bytes, N); };
+    osc_parser<osc_parser_midi2, decltype(on_msg)> parser{{}, on_msg, m_portname};
+    parser.parse_packet(data, size);
+  }
+
+  void on_message(const uint32_t* ump, std::size_t sz)
+  {
+    static constexpr timestamp_backend_info timestamp_info{
+        .has_absolute_timestamps = false,
+        .absolute_is_monotonic = false,
+        .has_samples = false,
+    };
+
+    static constexpr auto to_ns = []() {
+      return std::chrono::duration_cast<std::chrono::nanoseconds>(
+                 std::chrono::steady_clock::now().time_since_epoch())
+          .count();
+    };
+
+    m_processing.on_bytes({ump, sz}, m_processing.timestamp<timestamp_info>(to_ns, 0));
+  }
+
+  midi2::input_state_machine m_processing{this->configuration};
+
+  libremidi::optionally_owned<boost::asio::io_context> m_ctx;
+  boost::asio::ip::udp::endpoint m_endpoint;
+  boost::asio::ip::udp::socket m_socket;
+
+  std::jthread m_thread;
+
+  std::string m_portname;
+  alignas(16) unsigned char m_data[65535];
+};
+}

include/libremidi/backends/net/midi_out.hpp

@@ -0,0 +1,288 @@
+#pragma once
+#include <libremidi/backends/net/config.hpp>
+#include <libremidi/backends/net/helpers.hpp>
+#include <libremidi/cmidi2.hpp>
+#include <libremidi/detail/midi_out.hpp>
+
+#include <boost/asio/io_context.hpp>
+#include <boost/asio/ip/udp.hpp>
+#include <boost/endian.hpp>
+
+namespace libremidi::net
+{
+
+struct osc_midi1_packet
+{
+  stdx::error init_packet(std::string_view osc_pattern)
+  {
+    int i = 0;
+    for (; i < std::ssize(osc_pattern); i++)
+      if (osc_pattern.data()[i] != 0)
+        bytes[i] = osc_pattern.data()[i];
+      else
+        break;
+    bytes[i] = 0;
+    while (i % 4 != 3)
+    {
+      ++i;
+      bytes[i] = 0;
+    }
+
+    bytes[++i] = ',';
+    bytes[++i] = 'm';
+    bytes[++i] = 0;
+    bytes[++i] = 0;
+
+    // MIDI message (m) spec: port n°, status byte, data 1, data 2
+    bytes[++i] = 0;
+    message_size = ++i + 3;
+
+    return stdx::error{}; // FIXME
+  }
+
+  stdx::error deinit()
+  {
+    message_size = 0;
+    return stdx::error{};
+  }
+
+  stdx::error set_packet_content(const unsigned char* message, size_t size)
+  {
+    if (message_size == 0)
+      return std::errc::not_connected;
+
+    if (size != 3)
+      return std::errc::message_size;
+
+    std::memcpy(this->bytes + message_size - 3, message, 3);
+
+    return stdx::error{};
+  }
+
+  std::span<const char> get_data() { return std::span(this->bytes, this->message_size); }
+  char bytes[512 + 8 + 8];
+  int message_size{};
+};
+
+class midi_out final
+    : public midi1::out_api
+    , public error_handler
+{
+public:
+  struct
+      : output_configuration
+      , dgram_output_configuration
+  {
+  } configuration;
+
+  midi_out(output_configuration&& conf, dgram_output_configuration&& apiconf)
+      : configuration{std::move(conf), std::move(apiconf)}
+      , ctx{configuration.io_context}
+      , m_socket{ctx.get()}
+  {
+    m_socket.open(boost::asio::ip::udp::v4());
+    m_socket.set_option(boost::asio::ip::udp::socket::reuse_address(true));
+    m_socket.set_option(boost::asio::socket_base::broadcast(true));
+
+    m_endpoint
+        = {boost::asio::ip::make_address(this->configuration.host),
+           static_cast<unsigned short>(this->configuration.port)};
+
+    this->client_open_ = stdx::error{};
+  }
+
+  ~midi_out() override { close_port(); }
+
+  libremidi::API get_current_api() const noexcept override { return libremidi::API::NETWORK; }
+
+  stdx::error open_port(const output_port& /* port */, std::string_view portName) override
+  {
+    return open_virtual_port(portName);
+  }
+
+  stdx::error open_virtual_port(std::string_view portName) override
+  {
+    // Random arbitrary limit to avoid abuse
+    if (portName.size() >= 512)
+      return std::errc::invalid_argument;
+
+    pkt.init_packet(portName);
+
+    return stdx::error{};
+  }
+
+  stdx::error close_port() override
+  {
+    pkt.deinit();
+    // FIXME async close
+    if (m_socket.is_open())
+      m_socket.close();
+    return {};
+  }
+
+  stdx::error send_message(const unsigned char* message, size_t size) override
+  {
+    if (auto err = pkt.set_packet_content(message, size); err != stdx::error{})
+      return err;
+
+    auto dat = pkt.get_data();
+    boost::system::error_code ec;
+    m_socket.send_to(boost::asio::const_buffer(dat.data(), dat.size()), m_endpoint, 0, ec);
+    return stdx::error{}; // FIXME
+  }
+
+  stdx::error schedule_message(int64_t, const unsigned char*, size_t) override
+  {
+    int ret = 0;
+    return from_errc(ret);
+  }
+
+  libremidi::optionally_owned<boost::asio::io_context> ctx;
+  boost::asio::ip::udp::endpoint m_endpoint;
+  boost::asio::ip::udp::socket m_socket;
+
+  osc_midi1_packet pkt;
+};
+
+}
+
+namespace libremidi::net_ump
+{
+struct osc_midi2_packet
+{
+  stdx::error init_packet(std::string_view osc_pattern)
+  {
+    int i = 0;
+    for (; i < std::ssize(osc_pattern); i++)
+      if (osc_pattern.data()[i] != 0)
+        bytes[i] = osc_pattern.data()[i];
+      else
+        break;
+    bytes[i] = 0;
+    while (i % 4 != 3)
+    {
+      ++i;
+      bytes[i] = 0;
+    }
+
+    bytes[++i] = ',';
+    bytes[++i] = 'M';
+    bytes[++i] = 0;
+    bytes[++i] = 0;
+
+    // MIDI 2 message (M) spec: an UMP
+    header_size = ++i;
+
+    return stdx::error{}; // FIXME
+  }
+
+  stdx::error deinit()
+  {
+    header_size = 0;
+    return stdx::error{};
+  }
+
+  stdx::error set_packet_content(const uint32_t* message, size_t size)
+  {
+    if (header_size == 0)
+      return std::errc::not_connected;
+
+    if (size > 4)
+      return std::errc::message_size;
+
+    message_size = 4 * size;
+
+    std::memcpy(this->bytes + header_size, message, message_size);
+
+    return stdx::error{};
+  }
+
+  std::span<const char> get_data()
+  {
+    return std::span(this->bytes, this->header_size + this->message_size);
+  }
+  char bytes[512 + 8 + 64];
+  int header_size{};
+  int message_size{};
+};
+
+class midi_out final
+    : public midi2::out_api
+    , public error_handler
+{
+public:
+  struct
+      : output_configuration
+      , dgram_output_configuration
+  {
+  } configuration;
+
+  midi_out(output_configuration&& conf, dgram_output_configuration&& apiconf)
+      : configuration{std::move(conf), std::move(apiconf)}
+      , ctx{configuration.io_context}
+      , m_socket{ctx.get()}
+  {
+    m_socket.open(boost::asio::ip::udp::v4());
+    m_socket.set_option(boost::asio::ip::udp::socket::reuse_address(true));
+    m_socket.set_option(boost::asio::socket_base::broadcast(true));
+
+    m_endpoint
+        = {boost::asio::ip::make_address(this->configuration.host),
+           static_cast<unsigned short>(this->configuration.port)};
+
+    this->client_open_ = stdx::error{};
+  }
+
+  ~midi_out() override { close_port(); }
+
+  libremidi::API get_current_api() const noexcept override { return libremidi::API::NETWORK_UMP; }
+
+  stdx::error open_port(const output_port& /* port */, std::string_view portName) override
+  {
+    return open_virtual_port(portName);
+  }
+
+  stdx::error open_virtual_port(std::string_view portName) override
+  {
+    // Random arbitrary limit to avoid abuse
+    if (portName.size() >= 512)
+      return std::errc::invalid_argument;
+
+    pkt.init_packet(portName);
+
+    return stdx::error{};
+  }
+
+  stdx::error close_port() override
+  {
+    pkt.deinit();
+    if (m_socket.is_open())
+      m_socket.close();
+    return {};
+  }
+
+  stdx::error send_ump(const uint32_t* message, size_t size) override
+  {
+    if (auto err = pkt.set_packet_content(message, size); err != stdx::error{})
+      return err;
+
+    auto dat = pkt.get_data();
+    boost::system::error_code ec;
+    m_socket.send_to(boost::asio::const_buffer(dat.data(), dat.size()), m_endpoint, 0, ec);
+    return stdx::error{}; // FIXME
+  }
+
+  stdx::error schedule_ump(int64_t, const uint32_t*, size_t) override
+  {
+    int ret = 0;
+    return from_errc(ret);
+  }
+
+  libremidi::optionally_owned<boost::asio::io_context> ctx;
+  boost::asio::ip::udp::endpoint m_endpoint;
+  boost::asio::ip::udp::socket m_socket;
+
+  osc_midi2_packet pkt;
+};
+
+}

include/libremidi/backends/net/observer.hpp

@@ -0,0 +1,14 @@
+#pragma once
+#include <libremidi/backends/dummy.hpp>
+
+namespace libremidi::net
+{
+using net_observer_configuration = libremidi::dummy_configuration;
+using observer = libremidi::observer_dummy;
+}
+
+namespace libremidi::net_ump
+{
+using net_observer_configuration = libremidi::dummy_configuration;
+using observer = libremidi::observer_dummy;
+}

include/libremidi/backends/network.hpp

@@ -0,0 +1,24 @@
+#pragma once
+#include <libremidi/backends/dummy.hpp>
+#include <libremidi/backends/net/config.hpp>
+#include <libremidi/backends/net/midi_in.hpp>
+#include <libremidi/backends/net/midi_out.hpp>
+#include <libremidi/backends/net/observer.hpp>
+
+namespace libremidi::net
+{
+struct backend
+{
+  using midi_in = libremidi::net::midi_in;
+  using midi_out = libremidi::net::midi_out;
+  using midi_observer = libremidi::net::observer;
+  using midi_in_configuration = libremidi::net::dgram_input_configuration;
+  using midi_out_configuration = libremidi::net::dgram_output_configuration;
+  using midi_observer_configuration = libremidi::net::net_observer_configuration;
+  static const constexpr auto API = libremidi::API::NETWORK;
+  static const constexpr auto name = "network";
+  static const constexpr auto display_name = "Network";
+
+  static inline bool available() noexcept { return true; }
+};
+}

include/libremidi/backends/network_ump.hpp

@@ -0,0 +1,23 @@
+#pragma once
+#include <libremidi/backends/net/config.hpp>
+#include <libremidi/backends/net/midi_in.hpp>
+#include <libremidi/backends/net/midi_out.hpp>
+#include <libremidi/backends/net/observer.hpp>
+
+namespace libremidi::net_ump
+{
+struct backend
+{
+  using midi_in = libremidi::net_ump::midi_in;
+  using midi_out = libremidi::net_ump::midi_out;
+  using midi_observer = libremidi::net_ump::observer;
+  using midi_in_configuration = libremidi::net_ump::dgram_input_configuration;
+  using midi_out_configuration = libremidi::net_ump::dgram_output_configuration;
+  using midi_observer_configuration = libremidi::net_ump::net_observer_configuration;
+  static const constexpr auto API = libremidi::API::NETWORK_UMP;
+  static const constexpr auto name = "network (UMP)";
+  static const constexpr auto display_name = "Network (UMP)";
+
+  static inline bool available() noexcept { return true; }
+};
+}

include/libremidi/backends/pipewire/config.hpp

@@ -27,8 +27,8 @@ struct pipewire_input_configuration
 
   pw_main_loop* context{};
   pw_filter* filter{};
-  std::function<void(pipewire_callback)> set_process_func;
-  std::function<void(int64_t)> clear_process_func;
+  std::function<void(pipewire_callback)> set_process_func{};
+  std::function<void(int64_t)> clear_process_func{};
 };
 
 struct pipewire_output_configuration
@@ -37,8 +37,8 @@ struct pipewire_output_configuration
 
   pw_main_loop* context{};
   pw_filter* filter{};
-  std::function<void(pipewire_callback)> set_process_func;
-  std::function<void(int64_t)> clear_process_func;
+  std::function<void(pipewire_callback)> set_process_func{};
+  std::function<void(int64_t)> clear_process_func{};
 
   int64_t output_buffer_size{65536};
 };

include/libremidi/backends/pipewire/context.hpp

@@ -1,6 +1,7 @@
 #pragma once
 #include <libremidi/backends/linux/pipewire.hpp>
 #include <libremidi/detail/memory.hpp>
+#include <libremidi/error.hpp>
 
 #include <pipewire/filter.h>
 #include <pipewire/pipewire.h>
@@ -128,7 +129,7 @@ struct pipewire_context
     this->main_loop = pw.main_loop_new(nullptr);
     if (!this->main_loop)
     {
-      // libremidi::logger().error("PipeWire: main_loop_new failed!");
+      // libremidi::logger().libremidi_handle_error("main_loop_new failed!");
       return;
     }
     initialize();
@@ -139,28 +140,28 @@ struct pipewire_context
     this->lp = pw.main_loop_get_loop(this->main_loop);
     if (!lp)
     {
-      // libremidi::logger().error("PipeWire: main_loop_get_loop failed!");
+      // libremidi::logger().libremidi_handle_error("main_loop_get_loop failed!");
       return;
     }
 
     this->context = pw.context_new(lp, nullptr, 0);
     if (!this->context)
     {
-      // libremidi::logger().error("PipeWire: context_new failed!");
+      // libremidi::logger().libremidi_handle_error("context_new failed!");
       return;
     }
 
     this->core = pw.context_connect(this->context, nullptr, 0);
     if (!this->core)
     {
-      // libremidi::logger().error("PipeWire: context_connect failed!");
+      // libremidi::logger().libremidi_handle_error("context_connect failed!");
       return;
     }
 
     this->registry = pw_core_get_registry(this->core, PW_VERSION_REGISTRY, 0);
     if (!this->registry)
     {
-      // libremidi::logger().error("PipeWire: core_get_registry failed!");
+      // libremidi::logger().libremidi_handle_error("core_get_registry failed!");
       return;
     }
 
@@ -297,7 +298,6 @@ struct pipewire_context
 
     if (!proxy)
     {
-      std::cerr << "PipeWire: could not allocate link\n";
       pw.properties_free(props);
       return nullptr;
     }
@@ -476,7 +476,7 @@ struct pipewire_filter
             PW_KEY_MEDIA_TYPE, "Midi",
             PW_KEY_MEDIA_CATEGORY, "Filter",
             PW_KEY_MEDIA_ROLE, "DSP",
-            PW_KEY_MEDIA_NAME, "libremidi",
+            PW_KEY_MEDIA_NAME, "",
 #if defined(PW_KEY_NODE_LOCK_RATE)
             PW_KEY_NODE_LOCK_RATE, "true",
 #endif
@@ -498,7 +498,7 @@ struct pipewire_filter
       pw.filter_destroy(this->filter);
   }
 
-  void create_local_port(std::string_view port_name, spa_direction direction)
+  stdx::error create_local_port(std::string_view port_name, spa_direction direction)
   {
     // clang-format off
     this->port = (struct port*)pw.filter_add_port(
@@ -512,7 +512,9 @@ struct pipewire_filter
             nullptr),
         nullptr, 0);
     // clang-format on
-    assert(port);
+    if (!port)
+      return std::errc::invalid_argument;
+    return stdx::error{};
   }
 
   void set_port_buffer(int bytes)
@@ -537,31 +539,41 @@ struct pipewire_filter
     pw.filter_update_params(this->filter, this->port, params, 1);
   }
 
-  void remove_port()
+  stdx::error remove_port()
   {
     assert(this->port);
-    pw.filter_remove_port(this->port);
+    int ret = pw.filter_remove_port(this->port);
     this->port = nullptr;
+    return from_errc(ret);
   }
 
-  void rename_port(std::string_view port_name)
+  stdx::error rename_port(std::string_view port_name)
+  {
+    if (this->port)
     {
-    assert(this->port);
       spa_dict_item items[1] = {
           SPA_DICT_ITEM_INIT(PW_KEY_PORT_NAME, port_name.data()),
       };
 
       auto properties = SPA_DICT_INIT(items, 1);
-    pw.filter_update_properties(this->filter, this->port, &properties);
-    this->port = nullptr;
+      int ret = pw.filter_update_properties(this->filter, this->port, &properties);
+      return from_errc(ret);
+    }
+    else
+    {
+      return std::errc::not_connected;
+    }
   }
 
-  void start_filter()
+  [[nodiscard]] stdx::error start_filter()
   {
-    if (pw.filter_connect(this->filter, PW_FILTER_FLAG_RT_PROCESS, NULL, 0) < 0)
+    if (int ret = pw.filter_connect(this->filter, PW_FILTER_FLAG_RT_PROCESS, NULL, 0); ret < 0)
     {
-      std::cerr << "can't connect\n";
-      return;
+      return from_errc(ret);
+    }
+    else
+    {
+      return stdx::error{};
     }
   }
 

include/libremidi/backends/pipewire/helpers.hpp

@@ -2,6 +2,7 @@
 
 #include <libremidi/backends/linux/helpers.hpp>
 #include <libremidi/backends/linux/pipewire.hpp>
+#include <libremidi/backends/pipewire/config.hpp>
 #include <libremidi/backends/pipewire/context.hpp>
 #include <libremidi/detail/memory.hpp>
 #include <libremidi/detail/midi_in.hpp>
@@ -55,10 +56,10 @@ struct pipewire_helpers
   }
 
   template <typename Self>
-  void create_filter(Self& self)
+  stdx::error create_filter(Self& self)
   {
     if (this->filter)
-      return;
+      return stdx::error{};
 
     auto& configuration = self.configuration;
     if (configuration.context && configuration.filter && configuration.set_process_func)
@@ -90,8 +91,9 @@ struct pipewire_helpers
 #pragma GCC diagnostic pop
 
       this->filter->create_filter(self.configuration.client_name, filter_events, &self);
-      this->filter->start_filter();
+      return this->filter->start_filter();
     }
+    return stdx::error{};
   }
 
   template <typename Self>
@@ -117,10 +119,10 @@ struct pipewire_helpers
   }
 
   template <typename Self>
-  int create_context(Self& self)
+  stdx::error create_context(Self& self)
   {
     if (this->global_context)
-      return 0;
+      return stdx::error{};
 
     // Initialize PipeWire client
     auto& configuration = self.configuration;
@@ -133,7 +135,10 @@ struct pipewire_helpers
       this->global_instance = std::make_shared<pipewire_instance>();
       this->global_context = std::make_shared<pipewire_context>(this->global_instance);
     }
-    return 0;
+    if (!this->global_context->main_loop)
+      return std::errc::connection_refused;
+
+    return stdx::error{};
   }
 
   void destroy_context()
@@ -170,7 +175,9 @@ struct pipewire_helpers
           {
             int result = pw_loop_iterate(lp, 0);
             if (result < 0)
-              std::cerr << "pw_loop_iterate: " << spa_strerror(result) << "\n";
+            {
+              LIBREMIDI_LOG(spa_strerror(result));
+            }
           }
           fds[0].revents = 0;
         }
@@ -190,7 +197,7 @@ struct pipewire_helpers
   }
 
   template <typename Self>
-  bool create_local_port(Self& self, std::string_view portName, spa_direction direction)
+  stdx::error create_local_port(Self& self, std::string_view portName, spa_direction direction)
   {
     assert(this->global_context);
     assert(this->filter);
@@ -200,15 +207,15 @@ struct pipewire_helpers
 
     if (!this->filter->port)
     {
-      this->filter->create_local_port(portName.data(), direction);
+      auto ret = this->filter->create_local_port(portName.data(), direction);
+      if (ret != stdx::error{})
+      {
+        self.libremidi_handle_error(self.configuration, "error creating port");
+        return ret;
+      }
     }
 
-    if (!this->filter->port)
-    {
-      self.template error<driver_error>(self.configuration, "PipeWire: error creating port");
-      return false;
-    }
-    return true;
+    return stdx::error{};
   }
 
   void add_callbacks(const observer_configuration& conf)
@@ -293,12 +300,12 @@ struct pipewire_helpers
     }
   }
 
-  void do_close_port()
+  stdx::error do_close_port()
   {
     if (!this->filter)
-      return;
+      return stdx::error{};
     if (!this->filter->port)
-      return;
+      return stdx::error{};
 
     if (!this->global_context->owns_main_loop)
     {
@@ -307,13 +314,19 @@ struct pipewire_helpers
     }
 
     unlink_ports();
-    this->filter->remove_port();
+    return this->filter->remove_port();
   }
 
-  void rename_port(std::string_view port_name)
+  stdx::error rename_port(std::string_view port_name)
   {
     if (this->filter)
-      this->filter->rename_port(port_name);
+    {
+      return this->filter->rename_port(port_name);
+    }
+    else
+    {
+      return std::errc::not_connected;
+    }
   }
 
   void unlink_ports()
@@ -325,7 +338,7 @@ struct pipewire_helpers
     }
   }
 
-  bool link_ports(auto& self, const input_port& in_port)
+  stdx::error link_ports(auto& self, const input_port& in_port)
   {
     // Wait for the pipewire server to send us back our node's info
     for (int i = 0; i < 1000; i++)
@@ -335,19 +348,13 @@ struct pipewire_helpers
     auto& midi = this->global_context->current_graph.software_midi;
     auto node_it = midi.find(this_node);
     if (node_it == midi.end())
-    {
-      std::cerr << "Node " << this_node << " not found! \n";
-      return false;
-    }
+      return std::errc::invalid_argument;
 
     // Wait for the pipewire server to send us back our node's ports
     this->filter->synchronize_ports(node_it->second);
 
     if (node_it->second.inputs.empty())
-    {
-      std::cerr << "Node " << this_node << " has no ports! \n";
-      return false;
-    }
+      return std::errc::no_link;
 
     // Link ports
     const auto& p = node_it->second.inputs.front();
@@ -355,16 +362,16 @@ struct pipewire_helpers
     pw_loop_iterate(this->global_context->lp, 1);
     if (!link)
     {
-      self.template error<invalid_parameter_error>(
+      self.libremidi_handle_error(
           self.configuration,
-          "PipeWire: could not connect to port: " + in_port.port_name + " -> " + p.port_name);
-      return false;
+          "could not connect to port: " + in_port.port_name + " -> " + p.port_name);
+      return std::errc::no_link;
     }
 
-    return true;
+    return stdx::error{};
   }
 
-  bool link_ports(auto& self, const output_port& out_port)
+  stdx::error link_ports(auto& self, const output_port& out_port)
   {
     // Wait for the pipewire server to send us back our node's info
     for (int i = 0; i < 1000; i++)
@@ -375,8 +382,7 @@ struct pipewire_helpers
     auto node_it = midi.find(this_node);
     if (node_it == midi.end())
     {
-      std::cerr << "Node " << this_node << " not found! \n";
-      return false;
+      return std::errc::invalid_argument;
     }
 
     // Wait for the pipewire server to send us back our node's ports
@@ -384,8 +390,7 @@ struct pipewire_helpers
 
     if (node_it->second.outputs.empty())
     {
-      std::cerr << "Node " << this_node << " has no ports! \n";
-      return false;
+      return std::errc::no_link;
     }
 
     // Link ports
@@ -394,13 +399,13 @@ struct pipewire_helpers
     pw_loop_iterate(this->global_context->lp, 1);
     if (!link)
     {
-      self.template error<invalid_parameter_error>(
+      self.libremidi_handle_error(
           self.configuration,
-          "PipeWire: could not connect to port: " + p.port_name + " -> " + out_port.port_name);
-      return false;
+          "could not connect to port: " + p.port_name + " -> " + out_port.port_name);
+      return std::errc::no_link;
     }
 
-    return true;
+    return stdx::error{};
   }
 
   template <spa_direction Direction>
@@ -432,7 +437,8 @@ struct pipewire_helpers
   // Note: keep in mind that an "input" port for us (e.g. a keyboard that goes to the computer)
   // is an "output" port from the point of view of pipewire as data will come out of it
   template <spa_direction Direction>
-  static auto get_ports(const pipewire_context& ctx) noexcept -> std::vector<
+  static auto get_ports(const observer_configuration& conf, const pipewire_context& ctx) noexcept
+      -> std::vector<
           std::conditional_t<Direction == SPA_DIRECTION_OUTPUT, input_port, output_port>>
   {
     std::vector<std::conditional_t<Direction == SPA_DIRECTION_OUTPUT, input_port, output_port>>
@@ -440,20 +446,23 @@ struct pipewire_helpers
 
     {
       std::lock_guard _{ctx.current_graph.mtx};
+      if (conf.track_any || conf.track_hardware)
         for (auto& node : ctx.current_graph.physical_midi)
         {
-        for (auto& p :
+          for (auto& port :
                (Direction == SPA_DIRECTION_INPUT ? node.second.inputs : node.second.outputs))
           {
-          ret.push_back(to_port_info<Direction>(p));
+            ret.push_back(to_port_info<Direction>(port));
           }
         }
+
+      if (conf.track_any || conf.track_virtual)
         for (auto& node : ctx.current_graph.software_midi)
         {
-        for (auto& p :
+          for (auto& port :
                (Direction == SPA_DIRECTION_INPUT ? node.second.inputs : node.second.outputs))
           {
-          ret.push_back(to_port_info<Direction>(p));
+            ret.push_back(to_port_info<Direction>(port));
           }
         }
     }

include/libremidi/backends/pipewire/midi_in.hpp

@@ -4,8 +4,6 @@
 #include <libremidi/detail/midi_in.hpp>
 #include <libremidi/detail/midi_stream_decoder.hpp>
 
-#include <chrono>
-
 namespace libremidi
 {
 class midi_in_pipewire final
@@ -23,8 +21,17 @@ public:
   explicit midi_in_pipewire(input_configuration&& conf, pipewire_input_configuration&& apiconf)
       : configuration{std::move(conf), std::move(apiconf)}
   {
-    create_context(*this);
-    create_filter(*this);
+    if (auto ret = create_context(*this); ret != stdx::error{})
+    {
+      client_open_ = ret;
+      return;
+    }
+    if (auto ret = create_filter(*this); ret != stdx::error{})
+    {
+      client_open_ = ret;
+      return;
+    }
+    client_open_ = stdx::error{};
   }
 
   ~midi_in_pipewire() override
@@ -33,43 +40,42 @@ public:
     do_close_port();
     destroy_filter(*this);
     destroy_context();
-  }
-
-  void set_client_name(std::string_view) override
-  {
-    warning(configuration, "midi_in_pipewire: set_client_name unsupported");
+    client_open_ = std::errc::not_connected;
   }
 
   libremidi::API get_current_api() const noexcept override { return libremidi::API::PIPEWIRE; }
 
-  bool open_port(const input_port& in_port, std::string_view name) override
+  stdx::error open_port(const input_port& in_port, std::string_view name) override
   {
-    if (!create_local_port(*this, name, SPA_DIRECTION_INPUT))
-      return false;
+    if (auto err = create_local_port(*this, name, SPA_DIRECTION_INPUT); err != stdx::error{})
+      return err;
 
-    if (!link_ports(*this, in_port))
-      return false;
+    if (auto err = link_ports(*this, in_port); err != stdx::error{})
+      return err;
 
     start_thread();
-    return true;
+    return stdx::error{};
   }
 
-  bool open_virtual_port(std::string_view name) override
+  stdx::error open_virtual_port(std::string_view name) override
   {
-    if (!create_local_port(*this, name, SPA_DIRECTION_INPUT))
-      return false;
+    if (auto err = create_local_port(*this, name, SPA_DIRECTION_INPUT); err != stdx::error{})
+      return err;
 
     start_thread();
-    return true;
+    return stdx::error{};
   }
 
-  void close_port() override
+  stdx::error close_port() override
   {
     stop_thread();
-    do_close_port();
+    return do_close_port();
   }
 
-  void set_port_name(std::string_view port_name) override { rename_port(port_name); }
+  stdx::error set_port_name(std::string_view port_name) override
+  {
+    return rename_port(port_name);
+  }
 
   timestamp absolute_timestamp() const noexcept override { return system_ns(); }
 

include/libremidi/backends/pipewire/midi_out.hpp

@@ -24,8 +24,17 @@ public:
   midi_out_pipewire(output_configuration&& conf, pipewire_output_configuration&& apiconf)
       : configuration{std::move(conf), std::move(apiconf)}
   {
-    create_context(*this);
-    create_filter(*this);
+    if (auto ret = create_context(*this); ret != stdx::error{})
+    {
+      client_open_ = ret;
+      return;
+    }
+    if (auto ret = create_filter(*this); ret != stdx::error{})
+    {
+      client_open_ = ret;
+      return;
+    }
+    client_open_ = stdx::error{};
   }
 
   ~midi_out_pipewire() override
@@ -34,47 +43,46 @@ public:
     do_close_port();
     destroy_filter(*this);
     destroy_context();
-  }
-
-  void set_client_name(std::string_view) override
-  {
-    warning(configuration, "midi_out_pipewire: set_client_name unsupported");
+    client_open_ = std::errc::not_connected;
   }
 
   libremidi::API get_current_api() const noexcept override { return libremidi::API::PIPEWIRE; }
 
-  bool open_port(const output_port& out_port, std::string_view name) override
+  stdx::error open_port(const output_port& out_port, std::string_view name) override
   {
-    if (!create_local_port(*this, name, SPA_DIRECTION_OUTPUT))
-      return false;
+    if (auto err = create_local_port(*this, name, SPA_DIRECTION_OUTPUT); err != stdx::error{})
+      return err;
 
     this->filter->set_port_buffer(configuration.output_buffer_size);
 
-    if (!link_ports(*this, out_port))
-      return false;
+    if (auto err = link_ports(*this, out_port); err != stdx::error{})
+      return err;
 
     start_thread();
-    return true;
+    return stdx::error{};
   }
 
-  bool open_virtual_port(std::string_view name) override
+  stdx::error open_virtual_port(std::string_view name) override
   {
-    if (!create_local_port(*this, name, SPA_DIRECTION_OUTPUT))
-      return false;
+    if (auto err = create_local_port(*this, name, SPA_DIRECTION_OUTPUT); err != stdx::error{})
+      return err;
 
     this->filter->set_port_buffer(configuration.output_buffer_size);
 
     start_thread();
-    return true;
+    return stdx::error{};
   }
 
-  void close_port() override
+  stdx::error close_port() override
   {
     stop_thread();
-    do_close_port();
+    return do_close_port();
   }
 
-  void set_port_name(std::string_view port_name) override { rename_port(port_name); }
+  stdx::error set_port_name(std::string_view port_name) override
+  {
+    return rename_port(port_name);
+  }
 
   int process(spa_io_position* pos)
   {
@@ -120,6 +128,8 @@ public:
       if (res == -ENOSPC)
         break;
 
+      // Recycle the memory
+      m_gcqueue.enqueue(std::move(m));
       m_queue.pop();
     }
     spa_pod_builder_pop(&build, &f);
@@ -141,9 +151,14 @@ public:
     return 0;
   }
 
-  void send_message(const unsigned char* message, size_t size) override
+  stdx::error send_message(const unsigned char* message, size_t size) override
   {
-    m_queue.enqueue(libremidi::message(midi_bytes{message, message + size}, 0));
+    libremidi::message m;
+    m_gcqueue.try_dequeue(m);
+    m.bytes.assign(message, message + size);
+    m.timestamp = 0;
+    m_queue.enqueue(std::move(m));
+    return stdx::error{};
   }
 
   int convert_timestamp(int64_t user) const noexcept
@@ -159,13 +174,15 @@ public:
     }
   }
 
-  void schedule_message(int64_t ts, const unsigned char* message, size_t size) override
+  stdx::error schedule_message(int64_t ts, const unsigned char* message, size_t size) override
   {
     m_queue.enqueue(
         libremidi::message(midi_bytes{message, message + size}, convert_timestamp(ts)));
+    return stdx::error{};
   }
 
   moodycamel::ReaderWriterQueue<libremidi::message> m_queue;
+  moodycamel::ReaderWriterQueue<libremidi::message> m_gcqueue;
   std::atomic_int64_t m_process_clock = 0;
 };
 }

include/libremidi/backends/pipewire/observer.hpp

@@ -39,18 +39,29 @@ public:
       this->add_callbacks(configuration);
       this->start_thread();
     }
+
+    if (configuration.notify_in_constructor)
+    {
+      if (configuration.input_added)
+        for (const auto& p : get_input_ports())
+          configuration.input_added(p);
+
+      if (configuration.output_added)
+        for (const auto& p : get_output_ports())
+          configuration.output_added(p);
+    }
   }
 
   libremidi::API get_current_api() const noexcept override { return libremidi::API::PIPEWIRE; }
 
   std::vector<libremidi::input_port> get_input_ports() const noexcept override
   {
-    return get_ports<SPA_DIRECTION_OUTPUT>(*this->global_context);
+    return get_ports<SPA_DIRECTION_OUTPUT>(this->configuration, *this->global_context);
   }
 
   std::vector<libremidi::output_port> get_output_ports() const noexcept override
   {
-    return get_ports<SPA_DIRECTION_INPUT>(*this->global_context);
+    return get_ports<SPA_DIRECTION_INPUT>(this->configuration, *this->global_context);
   }
 
   ~observer_pipewire()

include/libremidi/backends/winmidi/helpers.hpp

@@ -5,15 +5,23 @@
 #include <libremidi/detail/midi_api.hpp>
 
 #include <mutex>
+#include <cctype>
 #include <string>
 #include <thread>
 #include <vector>
 #include <guiddef.h>
+
 #include <winrt/Windows.Foundation.h>
 #include <winrt/Windows.Foundation.Collections.h>
 #include <winrt/Windows.Devices.Enumeration.h>
+#include <winrt/Windows.Devices.Midi2.h>
+
+
+namespace midi2 = winrt::Windows::Devices::Midi2;
+namespace foundation = winrt::Windows::Foundation;
+namespace collections = winrt::Windows::Foundation::Collections;
+
 
-#include <winrt/Microsoft.Devices.Midi2.h>
 // clang-format on
 
 namespace libremidi::winmidi
@@ -22,6 +30,31 @@ using namespace winrt;
 using namespace winrt::Windows::Foundation;
 using namespace winrt::Windows::Devices::Enumeration;
 using namespace winrt::Windows::Storage::Streams;
-using namespace Microsoft::Devices::Midi2;
+using namespace winrt::Windows::Devices::Midi2;
 using namespace Windows::Devices::Enumeration;
+
+inline bool ichar_equals(char a, char b)
+{
+  return std::tolower(static_cast<unsigned char>(a)) ==
+         std::tolower(static_cast<unsigned char>(b));
+}
+inline bool iequals(std::string_view lhs, std::string_view rhs)
+{
+  return std::ranges::equal(lhs, rhs, ichar_equals);
+}
+
+inline winrt::Windows::Devices::Midi2::MidiEndpointDeviceInformation
+get_port_by_name(const std::string& port) {
+  auto eps = MidiEndpointDeviceInformation::FindAll();
+  for (const auto& ep : eps)
+  {
+    auto str = to_string(ep.Id());
+    if (str.empty())
+      continue;
+
+    if (iequals(str, port))
+      return ep;
+  }
+  return {nullptr};
+}
 }

include/libremidi/backends/winmidi/midi_in.hpp

@@ -3,6 +3,9 @@
 #include <libremidi/backends/winmidi/helpers.hpp>
 #include <libremidi/backends/winmidi/observer.hpp>
 #include <libremidi/detail/midi_in.hpp>
+#include <libremidi/detail/midi_stream_decoder.hpp>
+
+#include <iostream>
 
 namespace libremidi::winmidi
 {
@@ -21,23 +24,15 @@ public:
   explicit midi_in_impl(
       libremidi::ump_input_configuration&& conf, winmidi::input_configuration&& apiconf)
       : configuration{std::move(conf), std::move(apiconf)}
+      , m_session{MidiSession::CreateSession(L"libremidi session")}
   {
+    this->client_open_ = stdx::error{};
   }
 
-  ~midi_in_impl() override { close_port(); }
-
-  bool open_virtual_port(std::string_view) override
+  ~midi_in_impl() override
   {
-    warning(configuration, "midi_in_winmidi: open_virtual_port unsupported");
-    return false;
-  }
-  void set_client_name(std::string_view) override
-  {
-    warning(configuration, "midi_in_winmidi: set_client_name unsupported");
-  }
-  void set_port_name(std::string_view) override
-  {
-    warning(configuration, "midi_in_winmidi: set_port_name unsupported");
+    close_port();
+    this->client_open_ = std::errc::not_connected;
   }
 
   libremidi::API get_current_api() const noexcept override
@@ -45,50 +40,58 @@ public:
     return libremidi::API::WINDOWS_MIDI_SERVICES;
   }
 
-  bool open_port(const input_port& port, std::string_view) override
+  stdx::error open_port(const input_port& port, std::string_view) override
   {
-#if 0
-    const auto id = winrt::to_hstring(port.port_name);
-    if (id.empty())
-      return false;
+    auto ep = get_port_by_name(port.port_name);
+    if (!ep)
+      return std::errc::address_not_available;
 
-    port_ = get(MidiInPort::FromIdAsync(id));
-    if (!port_)
-      return false;
-    port_.MessageReceived(
-        [=](const winrt::Windows::Devices::Midi::IMidiInPort& inputPort,
-            const winrt::Windows::Devices::Midi::MidiMessageReceivedEventArgs& args) {
-      this->process_message(args.Message());
+    m_endpoint = m_session.CreateEndpointConnection(ep.Id());
+
+    m_revoke_token = m_endpoint.MessageReceived(
+        [&](const foundation::IInspectable& sender,
+            const winrt::Windows::Devices::Midi2::MidiMessageReceivedEventArgs& args) {
+      process_message(args);
     });
 
-#endif
-    return true;
+    m_endpoint.Open();
+
+    return stdx::error{};
   }
 
-#if 0
-  void process_message(const winrt::Windows::Devices::Midi::IMidiMessage& msg)
+  void process_message(const winrt::Windows::Devices::Midi2::MidiMessageReceivedEventArgs& msg)
   {
-    auto reader = DataReader::FromBuffer(msg.RawData());
-    auto begin = msg.RawData().data();
-    auto end = begin + msg.RawData().Length();
+    static constexpr timestamp_backend_info timestamp_info{
+        .has_absolute_timestamps = true,
+        .absolute_is_monotonic = false,
+        .has_samples = false,
+    };
 
-    auto t = msg.Timestamp().count();
-    this->configuration.on_message(libremidi::message{{begin, end}, t});
-  }
-#endif
+    const auto& ump = msg.GetMessagePacket();
+    const auto& b = ump.GetAllWords();
 
-  void close_port() override
-  {
-#if 0
-    if (port_)
-    {
-      port_.Close();
-      port_ = nullptr;
+    uint32_t ump_space[64];
+    array_view<uint32_t> ref{ump_space};
+    b.GetMany(0, ref);
+
+    auto to_ns = [t = ump.Timestamp()] { return t; };
+    m_processing.on_bytes(
+        {ump_space, ump_space + b.Size()}, m_processing.timestamp<timestamp_info>(to_ns, 0));
   }
-#endif
+
+  stdx::error close_port() override
+  {
+    m_endpoint.MessageReceived(m_revoke_token);
+    m_session.DisconnectEndpointConnection(m_endpoint.ConnectionId());
+    return stdx::error{};
   }
 
+  virtual timestamp absolute_timestamp() const noexcept override { return {}; }
+
 private:
-  // winrt::Microsoft::Devices::Midi2::IMidiInPort port_{nullptr};
+  MidiSession m_session;
+  winrt::event_token m_revoke_token{};
+  winrt::Windows::Devices::Midi2::MidiEndpointConnection m_endpoint{nullptr};
+  midi2::input_state_machine m_processing{this->configuration};
 };
 }

include/libremidi/backends/winmidi/midi_out.hpp

@@ -1,4 +1,5 @@
 #pragma once
+#include <libremidi/detail/ump_stream.hpp>
 #include <libremidi/backends/winmidi/config.hpp>
 #include <libremidi/backends/winmidi/helpers.hpp>
 #include <libremidi/backends/winmidi/observer.hpp>
@@ -20,72 +21,69 @@ public:
 
   midi_out_impl(libremidi::output_configuration&& conf, winmidi::output_configuration&& apiconf)
       : configuration{std::move(conf), std::move(apiconf)}
+      , m_session{MidiSession::CreateSession(L"libremidi session")}
   {
+    this->client_open_ = stdx::error{};
   }
 
   ~midi_out_impl() override { close_port(); }
 
-  bool open_virtual_port(std::string_view) override
-  {
-    warning(configuration, "midi_out_winmidi: open_virtual_port unsupported");
-    return false;
-  }
-  void set_client_name(std::string_view) override
-  {
-    warning(configuration, "midi_out_winmidi: set_client_name unsupported");
-  }
-  void set_port_name(std::string_view) override
-  {
-    warning(configuration, "midi_out_winmidi: set_port_name unsupported");
-  }
-
   libremidi::API get_current_api() const noexcept override
   {
     return libremidi::API::WINDOWS_MIDI_SERVICES;
   }
 
-  bool open_port(const output_port& port, std::string_view) override
+  stdx::error open_port(const output_port& port, std::string_view) override
   {
-#if 0
-    const auto id = winrt::to_hstring(port.port_name);
-    if (id.empty())
-      return false;
+    auto ep = get_port_by_name(port.port_name);
+    if (!ep)
+      return std::errc::address_not_available;
 
-    port_ = get(MidiOutPort::FromIdAsync(id));
-    return bool(port_);
-#endif
-    return true;
+    m_endpoint = m_session.CreateEndpointConnection(ep.Id());
+    m_endpoint.Open();
+
+    return stdx::error{};
   }
 
-  void close_port() override
+  stdx::error close_port() override
   {
-#if 0
-    if (port_)
-    {
-      port_.Close();
-      port_ = {};
-    }
-#endif
+    m_session.DisconnectEndpointConnection(m_endpoint.ConnectionId());
+    return stdx::error{};
   }
 
-  void send_ump(const uint32_t* message, size_t size) override
+  stdx::error send_ump(const uint32_t* message, size_t size) override
   {
-#if 0
-    if (!port_)
-      return;
+    auto write_func = [this](const uint32_t* ump, int64_t bytes) -> std::errc {
+      MidiSendMessageResults ret{};
+      switch(bytes / 4)
+      {
+        case 1:
+          ret = m_endpoint.SendSingleMessagePacket(MidiMessage32(0, ump[0]));
+          break;
+        case 2:
+          ret = m_endpoint.SendSingleMessagePacket(MidiMessage64(0, ump[0], ump[1]));
+          break;
+        case 3:
+          ret = m_endpoint.SendSingleMessagePacket(MidiMessage96(0, ump[0], ump[1], ump[2]));
+          break;
+        case 4:
+          ret = m_endpoint.SendSingleMessagePacket(MidiMessage128(0, ump[0], ump[1], ump[2], ump[3]));
+          break;
+        default:
+          return std::errc::bad_message;
+      }
 
-    InMemoryRandomAccessStream str;
-    DataWriter rb(str);
-    rb.WriteBytes(
-        winrt::array_view<const uint8_t>{(const uint8_t*)message, (const uint8_t*)message + size});
-    port_.SendBuffer(rb.DetachBuffer());
-#endif
+      if(ret != MidiSendMessageResults::Succeeded)
+        return std::errc::bad_message;
+      return std::errc{0};
+    };
+
+    return segment_ump_stream(message, size, write_func, []() {});
   }
 
 private:
-#if 0
-winrt::Windows::Devices::Midi2::IMidiOutPort port_{nullptr};
-#endif
+  MidiSession m_session;
+  winrt::Windows::Devices::Midi2::MidiEndpointConnection m_endpoint{nullptr};
 };
 
 }

include/libremidi/backends/winmidi/observer.hpp

@@ -20,13 +20,11 @@ public:
   {
   } configuration;
 
-  MidiSession session;
 
   explicit observer_impl(
       libremidi::observer_configuration&& conf, winmidi::observer_configuration&& apiconf)
       : configuration{std::move(conf), std::move(apiconf)}
-      , session{
-            MidiSession::CreateNewSession(L"libremidi session", MidiSessionSettings::Default())}
+      , session{MidiSession::CreateSession(L"libremidi session")}
   {
     if (!configuration.has_callbacks())
       return;
@@ -36,6 +34,7 @@ public:
       if (configuration.input_added)
         for (const auto& p : get_input_ports())
           configuration.input_added(p);
+
       if (configuration.output_added)
         for (const auto& p : get_output_ports())
           configuration.output_added(p);
@@ -87,10 +86,14 @@ public:
 
     auto deviceSelector = MidiEndpointConnection::GetDeviceSelector();
     auto endpointDevices = DeviceInformation::FindAllAsync(deviceSelector).get();
-    for (const auto& selectedEndpointInformation : endpointDevices)
+    for (const auto& ep : endpointDevices)
     {
+      if(ep.Name().starts_with(L"Diagnostics")) {
+        continue;
+      }
       // FIXME if(has input...)
-      ret.emplace_back(to_port_info(selectedEndpointInformation));
+
+      ret.emplace_back(to_port_info<true>(ep));
     }
 
     return ret;
@@ -102,10 +105,13 @@ public:
 
     auto deviceSelector = MidiEndpointConnection::GetDeviceSelector();
     auto endpointDevices = DeviceInformation::FindAllAsync(deviceSelector).get();
-    for (const auto& selectedEndpointInformation : endpointDevices)
+    for (const auto& ep : endpointDevices)
     {
+      if(ep.Name().starts_with(L"Diagnostics")) {
+        continue;
+      }
       // FIXME if(has output...)
-      ret.emplace_back(to_port_info(selectedEndpointInformation));
+      ret.emplace_back(to_port_info<false>(ep));
     }
 
     return ret;
@@ -114,38 +120,29 @@ public:
   void on_input_added(const DeviceInformation& name)
   {
     if (configuration.input_added)
-      configuration.input_added(to_port_info(name));
+      configuration.input_added(to_port_info<true>(name));
   }
 
   void on_input_removed(const DeviceInformation& name)
   {
     if (configuration.input_removed)
-      configuration.input_removed(to_port_info(name));
+      configuration.input_removed(to_port_info<true>(name));
   }
 
   void on_output_added(const DeviceInformation& name)
   {
     if (configuration.output_added)
-      configuration.output_added(to_port_info(name));
+      configuration.output_added(to_port_info<false>(name));
   }
 
   void on_output_removed(const DeviceInformation& name)
   {
     if (configuration.output_removed)
-      configuration.output_removed(to_port_info(name));
+      configuration.output_removed(to_port_info<false>(name));
   }
 
 private:
-#if 0
-  static inline observer_winmidi_internal internalInPortObserver_{MidiInPort::GetDeviceSelector()};
-  static inline observer_winmidi_internal internalOutPortObserver_{
-      MidiOutPort::GetDeviceSelector()};
-
-  int evTokenOnInputAdded_{-1};
-  int evTokenOnInputRemoved_{-1};
-  int evTokenOnOutputAdded_{-1};
-  int evTokenOnOutputRemoved_{-1};
-#endif
+  MidiSession session;
 };
 
 }

include/libremidi/backends/winmm/error_domain.hpp

@@ -0,0 +1,70 @@
+#pragma once
+// clang-format off
+#define NOMINMAX 1
+#define WIN32_LEAN_AND_MEAN 1
+
+#include <windows.h>
+#include <mmsystem.h>
+// clang-format on
+
+#include <libremidi/error.hpp>
+
+namespace libremidi
+{
+
+struct winmm_error_domain : public stdx::error_domain
+{
+public:
+  constexpr winmm_error_domain() noexcept
+      : error_domain{{0xa32b080ac770514eULL, 0xef59a407f921da43ULL}}
+  {
+  }
+
+  stdx::string_ref name() const noexcept override { return "winmm"; }
+
+  bool equivalent(const stdx::error& lhs, const stdx::error& rhs) const noexcept override
+  {
+    if (lhs.domain() == rhs.domain())
+      return error_cast<int>(lhs) == error_cast<int>(rhs);
+
+    return false;
+  }
+
+  stdx::string_ref message(const stdx::error& e) const noexcept override
+  {
+    switch (error_cast<int>(e))
+    {
+      case MMSYSERR_NOERROR: return "No error";
+      case MMSYSERR_ERROR: return "Error";
+      case MMSYSERR_BADDEVICEID: return "Bad device ID";
+      case MMSYSERR_NOTENABLED: return "Not enabled";
+      case MMSYSERR_ALLOCATED: return "Allocated";
+      case MMSYSERR_INVALHANDLE: return "Invalid handle";
+      case MMSYSERR_NODRIVER: return "No driver";
+      case MMSYSERR_NOMEM: return "No memory";
+      case MMSYSERR_NOTSUPPORTED: return "Not supported";
+      case MMSYSERR_BADERRNUM: return "Bad errnum";
+      case MMSYSERR_INVALFLAG: return "Invalid flag";
+      case MMSYSERR_INVALPARAM: return "Invalid parameter";
+      case MMSYSERR_HANDLEBUSY: return "Handle busy";
+      case MMSYSERR_INVALIDALIAS: return "Invalid alias";
+      case MMSYSERR_BADDB: return "Bad database";
+      case MMSYSERR_KEYNOTFOUND: return "Key not found";
+      case MMSYSERR_READERROR: return "Read error";
+      case MMSYSERR_WRITEERROR: return "Write error";
+      case MMSYSERR_DELETEERROR: return "Delete error";
+      case MMSYSERR_VALNOTFOUND: return "Value not found";
+      case MMSYSERR_NODRIVERCB: return "No driver callback";
+      case MMSYSERR_MOREDATA: return "More data";
+    }
+    return "Unknown error code";
+  }
+};
+
+inline stdx::error from_mmerr(int ret) noexcept
+{
+  static constexpr winmm_error_domain domain;
+  return {ret, domain};
+}
+
+}

include/libremidi/backends/winmm/helpers.hpp

@@ -1,15 +1,8 @@
 #pragma once
-#define NOMINMAX 1
-#define WIN32_LEAN_AND_MEAN 1
+#include <libremidi/backends/winmm/error_domain.hpp>
 #include <libremidi/detail/midi_api.hpp>
-
 #include <algorithm>
 
-// clang-format off
-#include <windows.h>
-#include <mmsystem.h>
-// clang-format on
-
 namespace libremidi
 {
 
@@ -44,10 +37,10 @@ inline std::string ConvertToUTF8(const TCHAR* str)
 // Next functions add the portNumber to the name so that
 // the device's names are sure to be listed with individual names
 // even when they have the same brand name
-inline void MakeUniqueInPortName(std::string& deviceName, unsigned int portNumber)
+inline void MakeUniqueInPortName(std::string& deviceName, std::size_t portNumber)
 {
   int x = 1;
-  for (unsigned int i = 0; i < portNumber; i++)
+  for (std::size_t i = 0; i < portNumber; i++)
   {
     MIDIINCAPS deviceCaps;
     midiInGetDevCaps(i, &deviceCaps, sizeof(MIDIINCAPS));
@@ -61,10 +54,10 @@ inline void MakeUniqueInPortName(std::string& deviceName, unsigned int portNumbe
   deviceName += std::to_string(x);
 }
 
-inline void MakeUniqueOutPortName(std::string& deviceName, unsigned int portNumber)
+inline void MakeUniqueOutPortName(std::string& deviceName, std::size_t portNumber)
 {
   int x = 1;
-  for (unsigned int i = 0; i < portNumber; i++)
+  for (std::size_t i = 0; i < portNumber; i++)
   {
     MIDIOUTCAPS deviceCaps;
     midiOutGetDevCaps(i, &deviceCaps, sizeof(MIDIOUTCAPS));

include/libremidi/backends/winmm/midi_in.hpp

@@ -22,20 +22,17 @@ public:
   explicit midi_in_winmm(input_configuration&& conf, winmm_input_configuration&& apiconf)
       : configuration{std::move(conf), std::move(apiconf)}
   {
-    // We'll issue a warning here if no devices are available but not
-    // throw an error since the user can plugin something later.
-    if (midiInGetNumDevs() == 0)
-    {
-      warning(
-          configuration, "midi_in_winmm::initialize: no MIDI input devices currently available.");
-    }
-
     if (!InitializeCriticalSectionAndSpinCount(&(this->_mutex), 0x00000400))
     {
-      warning(
+      libremidi_handle_error(
           configuration,
-          "midi_in_winmm::initialize: InitializeCriticalSectionAndSpinCount failed.");
+          "InitializeCriticalSectionAndSpinCount failed.");
+
+      this->client_open_ = std::errc::too_many_files_open;
+      return;
     }
+
+    this->client_open_ = stdx::error{};
   }
 
   ~midi_in_winmm() override
@@ -43,35 +40,22 @@ public:
     // Close a connection if it exists.
     midi_in_winmm::close_port();
 
+    if(this->client_open_ == stdx::error{})
       DeleteCriticalSection(&(this->_mutex));
   }
 
-  bool open_virtual_port(std::string_view) override
-  {
-    warning(configuration, "midi_in_winmm: open_virtual_port unsupported");
-    return false;
-  }
-  void set_client_name(std::string_view) override
-  {
-    warning(configuration, "midi_in_winmm: set_client_name unsupported");
-  }
-  void set_port_name(std::string_view) override
-  {
-    warning(configuration, "midi_in_winmm: set_port_name unsupported");
-  }
-
   libremidi::API get_current_api() const noexcept override { return libremidi::API::WINDOWS_MM; }
 
-  bool do_open(unsigned int portNumber)
+  stdx::error do_open(std::size_t portNumber)
   {
     MMRESULT result = midiInOpen(
         &this->inHandle, portNumber, std::bit_cast<DWORD_PTR>(&midiInputCallback),
         std::bit_cast<DWORD_PTR>(this), CALLBACK_FUNCTION);
     if (result != MMSYSERR_NOERROR)
     {
-      error<driver_error>(
-          configuration, "midi_in_winmm::open_port: error creating Windows MM MIDI input port.");
-      return false;
+      libremidi_handle_error(
+          configuration, "error creating Windows MM MIDI input port.");
+      return from_mmerr(result);
     }
 
     // Allocate and init the sysex buffers.
@@ -90,11 +74,11 @@ public:
       {
         midiInClose(this->inHandle);
         this->inHandle = nullptr;
-        error<driver_error>(
+        libremidi_handle_error(
             configuration,
-            "midi_in_winmm::open_port: error starting Windows MM MIDI input port "
+            "error starting Windows MM MIDI input port "
             "(PrepareHeader).");
-        return false;
+        return from_mmerr(result);
       }
 
       // Register the buffer.
@@ -103,11 +87,11 @@ public:
       {
         midiInClose(this->inHandle);
         this->inHandle = nullptr;
-        error<driver_error>(
+        libremidi_handle_error(
             configuration,
-            "midi_in_winmm::open_port: error starting Windows MM MIDI input port "
+            "error starting Windows MM MIDI input port "
             "(AddBuffer).");
-        return false;
+        return from_mmerr(result);
       }
     }
 
@@ -117,15 +101,15 @@ public:
     {
       midiInClose(this->inHandle);
       this->inHandle = nullptr;
-      error<driver_error>(
-          configuration, "midi_in_winmm::open_port: error starting Windows MM MIDI input port.");
-      return false;
+      libremidi_handle_error(
+          configuration, "error starting Windows MM MIDI input port.");
+      return from_mmerr(result);
     }
 
-    return true;
+    return stdx::error{};
   }
 
-  bool open_port(const input_port& p, std::string_view) override
+  stdx::error open_port(const input_port& p, std::string_view) override
   {
     observer_winmm obs{{}, winmm_observer_configuration{}};
     auto ports = obs.get_input_ports();
@@ -142,12 +126,12 @@ public:
       if (p.port_name == port.port_name)
         return do_open(port.port);
     }
-    error<invalid_parameter_error>(
-        configuration, "midi_in_winmm::open_port: port not found: " + p.port_name);
-    return false;
+    libremidi_handle_error(
+        configuration, "port not found: " + p.port_name);
+    return std::errc::invalid_argument;
   }
 
-  void close_port() override
+  stdx::error close_port() override
   {
     if (connected_)
     {
@@ -170,9 +154,9 @@ public:
 
         if (res != MMSYSERR_NOERROR)
         {
-          warning(
+          libremidi_handle_warning(
               configuration,
-              "midi_in_winmm::open_port: error closing Windows MM MIDI input "
+              "error closing Windows MM MIDI input "
               "port (midiInUnprepareHeader).");
           continue;
         }
@@ -187,6 +171,7 @@ public:
       this->inHandle = nullptr;
       LeaveCriticalSection(&(this->_mutex));
     }
+    return stdx::error{};
   }
 
 private:
@@ -255,8 +240,7 @@ private:
       const auto* sysex = reinterpret_cast<MIDIHDR*>(midiMessage);
       if(inputStatus == MIM_LONGERROR)
       {
-        self.m_processing.message.bytes.clear();
-        self.m_processing.state = self.m_processing.main;
+        self.m_processing.reset();
       }
       else if (!self.configuration.ignore_sysex)
       {
@@ -286,10 +270,9 @@ private:
         LeaveCriticalSection(&(self._mutex));
         if (result != MMSYSERR_NOERROR)
         {
-#if defined(__LIBREMIDI_DEBUG__)
-          std::cerr << "\nmidi_in::midiInputCallback: error sending sysex to "
-                       "Midi device!!\n\n";
-#endif
+          LIBREMIDI_LOG(
+              "error sending sysex to "
+              "Midi device!!");
         }
       }
     }

include/libremidi/backends/winmm/midi_out.hpp

@@ -1,6 +1,7 @@
 #pragma once
 #include <libremidi/backends/winmm/config.hpp>
 #include <libremidi/backends/winmm/helpers.hpp>
+#include <libremidi/backends/winmm/observer.hpp>
 #include <libremidi/detail/midi_out.hpp>
 
 namespace libremidi
@@ -20,55 +21,34 @@ public:
   midi_out_winmm(output_configuration&& conf, winmm_output_configuration&& apiconf)
       : configuration{std::move(conf), std::move(apiconf)}
   {
-    // We'll issue a warning here if no devices are available but not
-    // throw an error since the user can plug something in later.
-    if (midiOutGetNumDevs() == 0)
-    {
-      warning(
-          configuration,
-          "midi_out_winmm::initialize: no MIDI output devices currently "
-          "available.");
-    }
+    this->client_open_ = stdx::error{};
   }
 
   ~midi_out_winmm() override
   {
     // Close a connection if it exists.
     midi_out_winmm::close_port();
-  }
-
-  bool open_virtual_port(std::string_view) override
-  {
-    warning(configuration, "midi_out_winmm: open_virtual_port unsupported");
-    return false;
-  }
-  void set_client_name(std::string_view) override
-  {
-    warning(configuration, "midi_out_winmm: set_client_name unsupported");
-  }
-  void set_port_name(std::string_view) override
-  {
-    warning(configuration, "midi_out_winmm: set_port_name unsupported");
+    this->client_open_ = std::errc::not_connected;
   }
 
   libremidi::API get_current_api() const noexcept override { return libremidi::API::WINDOWS_MM; }
 
-  [[nodiscard]] bool do_open(unsigned int portNumber)
+  [[nodiscard]] stdx::error do_open(unsigned int portNumber)
   {
     MMRESULT result = midiOutOpen(&this->outHandle, portNumber, 0, 0, CALLBACK_NULL);
     if (result != MMSYSERR_NOERROR)
     {
-      error<driver_error>(
+      libremidi_handle_error(
           configuration,
-          "midi_out_winmm::open_port: error creating Windows MM MIDI output "
+          "error creating Windows MM MIDI output "
           "port.");
-      return false;
+      return from_mmerr(result);
     }
 
-    return true;
+    return stdx::error{};
   }
 
-  bool open_port(const output_port& p, std::string_view) override
+  stdx::error open_port(const output_port& p, std::string_view) override
   {
     observer_winmm obs{{}, winmm_observer_configuration{}};
     auto ports = obs.get_output_ports();
@@ -85,29 +65,30 @@ public:
       if (p.port_name == port.port_name)
         return do_open(port.port);
     }
-    error<invalid_parameter_error>(
-        configuration, "midi_out_winmm::open_port: port not found: " + p.port_name);
-    return false;
+    libremidi_handle_error(
+        configuration, "port not found: " + p.port_name);
+    return std::errc::invalid_argument;
   }
 
-  void close_port() override
+  stdx::error close_port() override
   {
     if (this->outHandle)
       midiOutClose(this->outHandle);
 
     this->outHandle = nullptr;
     connected_ = false;
+    return stdx::error{};
   }
 
-  void send_message(const unsigned char* message, size_t size) override
+  stdx::error send_message(const unsigned char* message, size_t size) override
   {
     if (!connected_)
-      return;
+      return std::errc::not_connected;
 
     if (size == 0)
     {
-      warning(configuration, "midi_out_winmm::send_message: message argument is empty!");
-      return;
+      libremidi_handle_warning(configuration, "message argument is empty!");
+      return std::errc::invalid_argument;
     }
 
     if (message[0] == 0xF0)
@@ -126,18 +107,18 @@ public:
       auto result = midiOutPrepareHeader(this->outHandle, &sysex, sizeof(MIDIHDR));
       if (result != MMSYSERR_NOERROR)
       {
-        error<driver_error>(
-            configuration, "midi_out_winmm::send_message: error preparing sysex header.");
-        return;
+        libremidi_handle_error(
+            configuration, "error preparing sysex header.");
+        return from_mmerr(result);
       }
 
       // Send the message.
       result = midiOutLongMsg(this->outHandle, &sysex, sizeof(MIDIHDR));
       if (result != MMSYSERR_NOERROR)
       {
-        error<driver_error>(
-            configuration, "midi_out_winmm::send_message: error sending sysex message.");
-        return;
+        libremidi_handle_error(
+            configuration, "error sending sysex message.");
+        return from_mmerr(result);
       }
 
       // Unprepare the buffer and MIDIHDR.
@@ -152,11 +133,11 @@ public:
       // Make sure the message size isn't too big.
       if (size > 3)
       {
-        warning(
+        libremidi_handle_warning(
             configuration,
-            "midi_out_winmm::send_message: message size is greater than 3 bytes "
+            "message size is greater than 3 bytes "
             "(and not sysex)!");
-        return;
+        return std::errc::message_size;
       }
 
       // Pack MIDI bytes into double word.
@@ -167,10 +148,12 @@ public:
       auto result = midiOutShortMsg(this->outHandle, packet);
       if (result != MMSYSERR_NOERROR)
       {
-        error<driver_error>(
-            configuration, "midi_out_winmm::send_message: error sending MIDI message.");
+        libremidi_handle_error(
+            configuration, "error sending MIDI message.");
+        return from_mmerr(result);
       }
     }
+    return stdx::error{};
   }
 
 private:

include/libremidi/backends/winuwp/midi_in.hpp

@@ -21,38 +21,28 @@ public:
 
   explicit midi_in_winuwp(input_configuration&& conf, winuwp_input_configuration&& apiconf)
       : configuration{std::move(conf), std::move(apiconf)}
-
   {
     winrt_init();
+    this->client_open_ = stdx::error{};
   }
 
-  ~midi_in_winuwp() override { close_port(); }
-
-  bool open_virtual_port(std::string_view) override
+  ~midi_in_winuwp() override
   {
-    warning(configuration, "midi_in_winuwp: open_virtual_port unsupported");
-    return false;
-  }
-  void set_client_name(std::string_view) override
-  {
-    warning(configuration, "midi_in_winuwp: set_client_name unsupported");
-  }
-  void set_port_name(std::string_view) override
-  {
-    warning(configuration, "midi_in_winuwp: set_port_name unsupported");
+    close_port();
+    this->client_open_ = std::errc::not_connected;
   }
 
   libremidi::API get_current_api() const noexcept override { return libremidi::API::WINDOWS_UWP; }
 
-  bool open_port(const input_port& port, std::string_view) override
+  stdx::error open_port(const input_port& port, std::string_view) override
   {
     const auto id = winrt::to_hstring(port.port_name);
     if (id.empty())
-      return false;
+      return std::errc::invalid_argument;
 
     port_ = get(MidiInPort::FromIdAsync(id));
     if (!port_)
-      return false;
+      return std::errc::io_error;
 
     midi_start_timestamp = std::chrono::steady_clock::now();
 
@@ -62,7 +52,7 @@ public:
       this->process_message(args.Message());
     });
 
-    return true;
+    return stdx::error{};
   }
 
   void process_message(const winrt::Windows::Devices::Midi::IMidiMessage& msg)
@@ -81,13 +71,14 @@ public:
     m_processing.on_bytes({begin, end}, m_processing.timestamp<timestamp_info>(to_ns, 0));
   }
 
-  void close_port() override
+  stdx::error close_port() override
   {
     if (port_)
     {
       port_.Close();
       port_ = nullptr;
     }
+    return stdx::error{};
   }
 
   timestamp absolute_timestamp() const noexcept override

include/libremidi/backends/winuwp/midi_out.hpp

@@ -22,55 +22,52 @@ public:
       : configuration{std::move(conf), std::move(apiconf)}
   {
     winrt_init();
+    this->client_open_ = stdx::error{};
   }
 
-  ~midi_out_winuwp() override { close_port(); }
-
-  bool open_virtual_port(std::string_view) override
+  ~midi_out_winuwp() override
   {
-    warning(configuration, "midi_out_winuwp: open_virtual_port unsupported");
-    return false;
-  }
-  void set_client_name(std::string_view) override
-  {
-    warning(configuration, "midi_out_winuwp: set_client_name unsupported");
-  }
-  void set_port_name(std::string_view) override
-  {
-    warning(configuration, "midi_out_winuwp: set_port_name unsupported");
+    close_port();
+    this->client_open_ = std::errc::not_connected;
   }
 
   libremidi::API get_current_api() const noexcept override { return libremidi::API::WINDOWS_UWP; }
 
-  bool open_port(const output_port& port, std::string_view) override
+  stdx::error open_port(const output_port& port, std::string_view) override
   {
     const auto id = winrt::to_hstring(port.port_name);
     if (id.empty())
-      return false;
+      return std::errc::invalid_argument;
 
     port_ = get(MidiOutPort::FromIdAsync(id));
-    return bool(port_);
+    if (!bool(port_))
+      return std::errc::io_error;
+
+    return stdx::error{};
   }
 
-  void close_port() override
+  stdx::error close_port() override
   {
     if (port_)
     {
       port_.Close();
       port_ = {};
     }
+    return stdx::error{};
   }
 
-  void send_message(const unsigned char* message, size_t size) override
+  stdx::error send_message(const unsigned char* message, size_t size) override
   {
     if (!port_)
-      return;
+      return std::errc::not_connected;
 
     InMemoryRandomAccessStream str;
     DataWriter rb(str);
     rb.WriteBytes(
         winrt::array_view<const uint8_t>{(const uint8_t*)message, (const uint8_t*)message + size});
     port_.SendBuffer(rb.DetachBuffer());
+
+    return stdx::error{};
   }
 
 private:

include/libremidi/client.hpp

@@ -31,7 +31,7 @@ struct client_configuration
     best to set the error callback function before opening a port.
   */
   midi_error_callback on_error{};
-  midi_error_callback on_warning{};
+  midi_warning_callback on_warning{};
 
   //! Poll period for observation polling operations, if relevant to the backend
   std::chrono::milliseconds poll_period{100};
@@ -115,9 +115,9 @@ public:
         port,
         input_configuration{
             .on_message
-            = [this, port](libremidi::message&& m) {
-      configuration.on_message(port, std::move(m));
-            },
+            = [this,
+               port](libremidi::message&& m) { configuration.on_message(port, std::move(m)); },
+            .on_raw_data = {},
             .get_timestamp = {},
 
             .on_error = configuration.on_error,
@@ -153,32 +153,40 @@ public:
   void remove_input(const input_port& port) { m_inputs.erase(port); }
   void remove_output(const output_port& port) { m_outputs.erase(port); }
 
-  void send_message(const unsigned char* message, size_t size)
+  stdx::error send_message(const unsigned char* message, size_t size)
   {
     for (auto& [_, out] : m_outputs)
     {
-      out.send_message(message, size);
+      if (auto err = out.send_message(message, size); err != stdx::error{})
+        return err;
     }
+    return stdx::error{};
   }
 
-  void send_ump(const uint32_t* message, size_t size)
+  stdx::error send_ump(const uint32_t* message, size_t size)
   {
     for (auto& [_, out] : m_outputs)
     {
-      out.send_ump(message, size);
+      if (auto err = out.send_ump(message, size); err != stdx::error{})
+        return err;
     }
+    return stdx::error{};
   }
 
-  void send_message(const output_port& port, const unsigned char* message, size_t size)
+  stdx::error send_message(const output_port& port, const unsigned char* message, size_t size)
   {
     if (auto it = m_outputs.find(port); it != m_outputs.end())
-      it->second.send_message(message, size);
+      return it->second.send_message(message, size);
+
+    return stdx::error{};
   }
 
-  void send_ump(const output_port& port, const uint32_t* message, size_t size)
+  stdx::error send_ump(const output_port& port, const uint32_t* message, size_t size)
   {
     if (auto it = m_outputs.find(port); it != m_outputs.end())
-      it->second.send_ump(message, size);
+      return it->second.send_ump(message, size);
+
+    return stdx::error{};
   }
 
 private:

include/libremidi/cmidi2.hpp

@@ -2559,6 +2559,7 @@ enum cmidi2_midi_conversion_result
   CMIDI2_CONVERSION_RESULT_INVALID_DTE_SEQUENCE = 0x11,
   CMIDI2_CONVERSION_RESULT_INVALID_STATUS = 0x13,
   CMIDI2_CONVERSION_RESULT_INCOMPLETE_SYSEX7 = 0x20,
+  CMIDI2_CONVERSION_RESULT_INVALID_INPUT = 0x40,
 };
 
 static inline void
@@ -2686,7 +2687,11 @@ cmidi2_convert_midi1_to_ump(cmidi2_midi_conversion_context* context)
     else
     {
       // fixed sized message
-      size_t len = cmidi2_midi1_get_message_size(context->midi1 + *sIdx, sLen - *sIdx);
+      size_t remaining = sLen - *sIdx;
+      size_t len = cmidi2_midi1_get_message_size(context->midi1 + *sIdx, remaining);
+      if (len > remaining)
+        return CMIDI2_CONVERSION_RESULT_INVALID_INPUT;
+
       uint8_t byte2 = context->midi1[*sIdx + 1];
       uint8_t byte3 = len > 2 ? context->midi1[*sIdx + 2] : 0;
       uint8_t channel = context->midi1[*sIdx] & 0xF;

include/libremidi/config.hpp

@@ -4,11 +4,6 @@
   #define NOMINMAX 1
   #define WIN32_LEAN_AND_MEAN
 #endif
-#include <algorithm>
-#include <cinttypes>
-#include <memory>
-#include <stdexcept>
-#include <vector>
 
 #if defined(LIBREMIDI_EXPORTS)
   #if defined(_MSC_VER)
@@ -51,6 +46,7 @@ using midi_bytes = boost::container::small_vector<unsigned char, small_vector_mi
 }
   #endif
 #else
+  #include <vector>
 namespace libremidi
 {
 using midi_bytes = std::vector<unsigned char>;

include/libremidi/configurations.hpp

@@ -1,29 +1,19 @@
 #pragma once
 
-#if defined(__linux__)
-  #include <libremidi/backends/alsa_raw/config.hpp>
-  #include <libremidi/backends/alsa_raw_ump/config.hpp>
-  #include <libremidi/backends/alsa_seq/config.hpp>
-  #include <libremidi/backends/alsa_seq_ump/config.hpp>
-  #include <libremidi/backends/pipewire/config.hpp>
-#endif
-
-#if defined(__APPLE__)
-  #include <libremidi/backends/coremidi/config.hpp>
-  #include <libremidi/backends/coremidi_ump/config.hpp>
-#endif
-
-#if defined(_WIN32)
-  #include <libremidi/backends/winmidi/config.hpp>
-  #include <libremidi/backends/winmm/config.hpp>
-  #include <libremidi/backends/winuwp/config.hpp>
-#endif
-
-#if defined(__EMSCRIPTEN__)
-  #include <libremidi/backends/emscripten/config.hpp>
-#endif
-
+#include <libremidi/backends/alsa_raw/config.hpp>
+#include <libremidi/backends/alsa_raw_ump/config.hpp>
+#include <libremidi/backends/alsa_seq/config.hpp>
+#include <libremidi/backends/alsa_seq_ump/config.hpp>
+#include <libremidi/backends/coremidi/config.hpp>
+#include <libremidi/backends/coremidi_ump/config.hpp>
+#include <libremidi/backends/emscripten/config.hpp>
 #include <libremidi/backends/jack/config.hpp>
+#include <libremidi/backends/keyboard/config.hpp>
+#include <libremidi/backends/net/config.hpp>
+#include <libremidi/backends/pipewire/config.hpp>
+#include <libremidi/backends/winmidi/config.hpp>
+#include <libremidi/backends/winmm/config.hpp>
+#include <libremidi/backends/winuwp/config.hpp>
 
 namespace libremidi
 {
@@ -31,5 +21,4 @@ namespace libremidi
 struct dummy_configuration
 {
 };
-
 }

include/libremidi/detail/conversion.hpp

@@ -0,0 +1,59 @@
+#pragma once
+// clang-format off
+#include <libremidi/config.hpp>
+// clang-format on
+
+#include <libremidi/cmidi2.hpp>
+#include <libremidi/error.hpp>
+#include <libremidi/message.hpp>
+#include <libremidi/ump.hpp>
+namespace libremidi
+{
+struct midi1_to_midi2
+{
+  stdx::error
+  convert(const unsigned char* message, std::size_t size, int64_t timestamp, auto on_ump)
+  {
+    context.midi1 = const_cast<unsigned char*>(message);
+    context.midi1_num_bytes = size;
+    context.midi1_proceeded_bytes = 0;
+    context.ump = ump;
+    context.ump_num_bytes = sizeof(ump);
+    context.ump_proceeded_bytes = 0;
+
+    if (auto res = cmidi2_convert_midi1_to_ump(&context); res != CMIDI2_CONVERSION_RESULT_OK)
+      return std::errc::invalid_argument;
+
+    return on_ump(context.ump, context.ump_proceeded_bytes / 4, timestamp);
+  }
+
+  cmidi2_midi_conversion_context context = [] {
+    cmidi2_midi_conversion_context tmp;
+    cmidi2_midi_conversion_context_initialize(&tmp);
+    return tmp;
+  }();
+  uint32_t ump[65536 / 4];
+};
+
+struct midi2_to_midi1
+{
+  stdx::error
+  convert(const uint32_t* message, std::size_t /* size */, int64_t timestamp, auto on_midi)
+  {
+    auto n
+        = cmidi2_convert_single_ump_to_midi1(midi, sizeof(midi), const_cast<uint32_t*>(message));
+    if (n > 0)
+      return on_midi(midi, n, timestamp);
+    else
+      return std::errc::no_buffer_space;
+  }
+
+  cmidi2_midi_conversion_context context = [] {
+    cmidi2_midi_conversion_context tmp;
+    cmidi2_midi_conversion_context_initialize(&tmp);
+    return tmp;
+  }();
+  uint8_t midi[65536];
+};
+
+}

include/libremidi/detail/midi_api.hpp

@@ -2,61 +2,11 @@
 #include <libremidi/api.hpp>
 #include <libremidi/config.hpp>
 #include <libremidi/error.hpp>
-#include <libremidi/observer_configuration.hpp>
 
-#include <iostream>
 #include <string_view>
 
 namespace libremidi
 {
-struct error_handler
-{
-  //! Error reporting function for libremidi classes. Throws.
-  template <typename Error_T>
-  void error(auto& configuration, std::string_view errorString) const
-  {
-    if (configuration.on_error)
-    {
-      if (first_error)
-        return;
-
-      first_error = true;
-      configuration.on_error(Error_T::code, errorString);
-      first_error = false;
-    }
-    else
-    {
-#if defined(__LIBREMIDI_DEBUG__)
-      std::cerr << '\n' << errorString << "\n\n";
-#endif
-      throw Error_T{errorString.data()};
-    }
-  }
-
-  //! Warning reporting function for libremidi classes.
-  void warning(auto& configuration, std::string_view errorString) const
-  {
-    if (configuration.on_warning)
-    {
-      if (first_warning)
-        return;
-
-      first_warning = true;
-      configuration.on_warning(midi_error::WARNING, errorString);
-      first_warning = false;
-      return;
-    }
-
-#if defined(__LIBREMIDI_DEBUG__)
-    std::cerr << '\n' << errorString << "\n\n";
-#endif
-  }
-
-  // To prevent infinite error loops
-  mutable bool first_error{};
-  mutable bool first_warning{};
-};
-
 class midi_api
 {
 public:
@@ -69,18 +19,29 @@ public:
 
   [[nodiscard]] virtual libremidi::API get_current_api() const noexcept = 0;
 
-  [[nodiscard]] virtual bool open_virtual_port(std::string_view) = 0;
+  [[nodiscard]] virtual stdx::error open_virtual_port(std::string_view)
+  {
+    return std::errc::function_not_supported;
+  }
+  virtual stdx::error set_client_name(std::string_view)
+  {
+    return std::errc::function_not_supported;
+  }
+  virtual stdx::error set_port_name(std::string_view)
+  {
+    return std::errc::function_not_supported;
+  }
 
-  virtual void close_port() = 0;
-  virtual void set_client_name(std::string_view) = 0;
-  virtual void set_port_name(std::string_view) = 0;
+  virtual stdx::error close_port() = 0;
 
-  bool is_port_open() const noexcept { return bool(port_open_); }
-  bool is_port_connected() const noexcept { return bool(connected_); }
+  stdx::error is_client_open() const noexcept { return client_open_; }
+  bool is_port_open() const noexcept { return port_open_; }
+  bool is_port_connected() const noexcept { return connected_; }
 
 protected:
   friend class midi_in;
   friend class midi_out;
+  stdx::error client_open_{std::errc::not_connected};
   bool port_open_{};
   bool connected_{};
 };

include/libremidi/detail/midi_in.hpp

@@ -1,6 +1,8 @@
 #pragma once
 #include <libremidi/detail/midi_api.hpp>
+#include <libremidi/observer_configuration.hpp>
 #include <libremidi/input_configuration.hpp>
+#include <libremidi/error_handler.hpp>
 
 namespace libremidi
 {
@@ -14,7 +16,9 @@ public:
   midi_in_api& operator=(const midi_in_api&) = delete;
   midi_in_api& operator=(midi_in_api&&) = delete;
 
-  [[nodiscard]] virtual bool open_port(const input_port& pt, std::string_view local_port_name) = 0;
+  [[nodiscard]] virtual stdx::error
+  open_port(const input_port& pt, std::string_view local_port_name)
+      = 0;
   [[nodiscard]] virtual timestamp absolute_timestamp() const noexcept = 0;
 };
 

include/libremidi/detail/midi_out.hpp

@@ -1,6 +1,7 @@
 #pragma once
-#include <libremidi/cmidi2.hpp>
+#include <libremidi/detail/conversion.hpp>
 #include <libremidi/detail/midi_api.hpp>
+#include <libremidi/error_handler.hpp>
 #include <libremidi/output_configuration.hpp>
 
 #include <string_view>
@@ -18,19 +19,21 @@ public:
   midi_out_api& operator=(const midi_out_api&) = delete;
   midi_out_api& operator=(midi_out_api&&) = delete;
 
-  [[nodiscard]] virtual bool open_port(const output_port& pt, std::string_view local_port_name)
+  [[nodiscard]] virtual stdx::error
+  open_port(const output_port& pt, std::string_view local_port_name)
       = 0;
 
   [[nodiscard]] virtual int64_t current_time() const noexcept { return 0; }
 
-  virtual void send_message(const unsigned char* message, std::size_t size) = 0;
-  virtual void schedule_message(int64_t /*ts*/, const unsigned char* message, std::size_t size)
+  virtual stdx::error send_message(const unsigned char* message, std::size_t size) = 0;
+  virtual stdx::error
+  schedule_message(int64_t /*ts*/, const unsigned char* message, std::size_t size)
   {
     return send_message(message, size);
   }
 
-  virtual void send_ump(const uint32_t* message, std::size_t size) = 0;
-  virtual void schedule_ump(int64_t /*ts*/, const uint32_t* ump, std::size_t size)
+  virtual stdx::error send_ump(const uint32_t* message, std::size_t size) = 0;
+  virtual stdx::error schedule_ump(int64_t /*ts*/, const uint32_t* ump, std::size_t size)
   {
     return send_ump(ump, size);
   }
@@ -45,14 +48,15 @@ class out_api : public midi_out_api
 public:
   using midi_out_api::midi_out_api;
 
-  void send_ump(const uint32_t* message, std::size_t /*size*/)
+  stdx::error send_ump(const uint32_t* message, std::size_t size)
   {
-    uint8_t midi[65536];
-    const auto n
-        = cmidi2_convert_single_ump_to_midi1(midi, sizeof(midi), const_cast<uint32_t*>(message));
-    if (n > 0)
-      send_message(midi, n);
+    return converter.convert(
+        message, size, 0, [this](const unsigned char* midi, std::size_t n, int64_t /* ts */) {
+      return send_message(midi, n);
+    });
   }
+
+  midi2_to_midi1 converter;
 };
 }
 
@@ -65,25 +69,15 @@ class out_api : public midi_out_api
 public:
   using midi_out_api::midi_out_api;
 
-  void send_message(const unsigned char* message, std::size_t size)
+  stdx::error send_message(const unsigned char* message, std::size_t size)
   {
-    cmidi2_midi_conversion_context context{};
-    cmidi2_midi_conversion_context_initialize(&context);
-
-    uint32_t ump[65536 / 4];
-
-    context.midi1 = const_cast<unsigned char*>(message);
-    context.midi1_num_bytes = size;
-    context.midi1_proceeded_bytes = 0;
-    context.ump = ump;
-    context.ump_num_bytes = sizeof(ump);
-    context.ump_proceeded_bytes = 0;
-
-    if (auto res = cmidi2_convert_midi1_to_ump(&context); res != CMIDI2_CONVERSION_RESULT_OK)
-      return;
-
-    send_ump(context.ump, context.ump_proceeded_bytes / 4);
+    return converter.convert(
+        message, size, 0, [this](const uint32_t* ump, std::size_t count, int64_t /* ts */) {
+      return send_ump(ump, count);
+    });
   }
+
+  midi1_to_midi2 converter;
 };
 }
 

include/libremidi/detail/midi_stream_decoder.hpp

@@ -2,6 +2,7 @@
 
 #include <libremidi/detail/midi_in.hpp>
 
+#include <libremidi/cmidi2.hpp>
 #include <chrono>
 #include <cstdint>
 #include <cinttypes>
@@ -28,16 +29,87 @@ struct timestamp_backend_info
   bool has_samples{};
 };
 
-namespace midi1
+template<typename Configuration>
+struct input_state_machine_base
 {
-struct input_state_machine
-{
-  const input_configuration& configuration;
-  explicit input_state_machine(const input_configuration& conf)
+  const Configuration& configuration;
+
+  explicit input_state_machine_base(const Configuration& conf)
       : configuration{conf}
   {
   }
 
+  template <timestamp_backend_info info>
+  int64_t timestamp(auto to_ns, int64_t samples)
+  {
+    switch (configuration.timestamps)
+    {
+      default:
+      case timestamp_mode::NoTimestamp:
+        return 0;
+
+      case timestamp_mode::Relative: {
+        int64_t time_ns;
+
+        if constexpr (info.has_absolute_timestamps)
+          time_ns = to_ns();
+        else
+          time_ns = system_ns();
+
+        int64_t res;
+        if (first_message)
+        {
+          first_message = false;
+          res = 0;
+        }
+        else
+        {
+          res = time_ns - last_time_ns;
+        }
+
+        last_time_ns = time_ns;
+        return res;
+      }
+
+      case timestamp_mode::Absolute:
+        if constexpr (info.has_absolute_timestamps)
+          return to_ns();
+        else
+          return system_ns();
+
+      case timestamp_mode::SystemMonotonic:
+        if constexpr (info.absolute_is_monotonic)
+          return to_ns();
+        else
+          return system_ns();
+
+      case timestamp_mode::AudioFrame:
+        if constexpr (info.has_samples)
+          return samples;
+        else
+          return 0;
+
+      case timestamp_mode::Custom:
+        return configuration.get_timestamp(to_ns());
+    }
+  }
+  int64_t last_time_ns = 0;
+  bool first_message = true;
+};
+
+namespace midi1
+{
+struct input_state_machine : input_state_machine_base<input_configuration>
+{
+  using input_state_machine_base::input_state_machine_base;
+
+  void reset()
+  {
+    message.bytes.clear();
+    message.timestamp = {};
+    state = main;
+  }
+
   bool has_finished_sysex(std::span<const uint8_t> bytes) const noexcept
   {
     return (((bytes.front() == 0xF0) || (state == in_sysex)) && (bytes.back() == 0xF7));
@@ -46,6 +118,26 @@ struct input_state_machine
   // Function to process a byte stream which may contain multiple successive
   // MIDI events (CoreMIDI, ALSA Sequencer can work like this)
   void on_bytes_multi(std::span<const uint8_t> bytes, int64_t timestamp)
+  {
+    if (this->configuration.on_message)
+      on_bytes_multi_segmented(this->configuration.on_message, bytes, timestamp);
+    if (this->configuration.on_raw_data)
+      this->configuration.on_raw_data(bytes, timestamp);
+  }
+
+  // Function to process bytes corresponding to at most one midi event
+  // e.g. a midi channel event or a single sysex
+  void on_bytes(std::span<const uint8_t> bytes, int64_t timestamp)
+  {
+    if (this->configuration.on_message)
+      on_bytes_segmented(this->configuration.on_message, bytes, timestamp);
+    if (this->configuration.on_raw_data)
+      this->configuration.on_raw_data(bytes, timestamp);
+  }
+
+private:
+  void on_bytes_multi_segmented(
+      const message_callback& cb, std::span<const uint8_t> bytes, int64_t timestamp)
   {
     int64_t nBytes = bytes.size();
     int64_t iByte = 0;
@@ -54,7 +146,7 @@ struct input_state_machine
     switch (state)
     {
       case in_sysex: {
-        return on_continue_sysex(bytes, finished_sysex);
+        return on_continue_sysex(cb, bytes, finished_sysex);
       }
       case main: {
         while (iByte < nBytes)
@@ -150,7 +242,7 @@ struct input_state_machine
             message.assign(begin, begin + size);
             message.timestamp = timestamp;
 
-            this->configuration.on_message(std::move(message));
+            cb(std::move(message));
             message.clear();
 
             iByte += size;
@@ -160,7 +252,8 @@ struct input_state_machine
     }
   }
 
-  void on_continue_sysex(std::span<const uint8_t> bytes, bool finished_sysex)
+  void on_continue_sysex(
+      const message_callback& cb, std::span<const uint8_t> bytes, bool finished_sysex)
   {
     if (finished_sysex)
       state = main;
@@ -174,14 +267,16 @@ struct input_state_machine
       message.insert(message.end(), bytes.begin(), bytes.end());
       if (finished_sysex)
       {
-        this->configuration.on_message(std::move(message));
+        cb(std::move(message));
         message.clear();
       }
     }
     return;
   }
 
-  void on_main(std::span<const uint8_t> bytes, int64_t timestamp, bool finished_sysex)
+  void on_main(
+      const message_callback& cb, std::span<const uint8_t> bytes, int64_t timestamp,
+      bool finished_sysex)
   {
     switch (bytes[0])
     {
@@ -196,7 +291,7 @@ struct input_state_machine
           message.timestamp = timestamp;
           if (finished_sysex)
           {
-            this->configuration.on_message(std::move(message));
+            cb(std::move(message));
             message.clear();
           }
         }
@@ -222,13 +317,12 @@ struct input_state_machine
     message.assign(bytes.begin(), bytes.end());
     message.timestamp = timestamp;
 
-    this->configuration.on_message(std::move(message));
+    cb(std::move(message));
     message.clear();
   }
 
-  // Function to process bytes corresponding to at most one midi event
-  // e.g. a midi channel event or a single sysex
-  void on_bytes(std::span<const uint8_t> bytes, int64_t timestamp)
+  void
+  on_bytes_segmented(const message_callback& cb, std::span<const uint8_t> bytes, int64_t timestamp)
   {
     if (bytes.empty())
       return;
@@ -237,78 +331,135 @@ struct input_state_machine
     switch (state)
     {
       case in_sysex:
-        return on_continue_sysex(bytes, finished_sysex);
+        return on_continue_sysex(cb, bytes, finished_sysex);
 
       case main:
-        return on_main(bytes, timestamp, finished_sysex);
-    }
-  }
-
-  template <timestamp_backend_info info>
-  int64_t timestamp(auto to_ns, int64_t samples)
-  {
-    switch (configuration.timestamps)
-    {
-      default:
-      case timestamp_mode::NoTimestamp:
-        return 0;
-
-      case timestamp_mode::Relative: {
-        int64_t time_ns;
-
-        if constexpr (info.has_absolute_timestamps)
-          time_ns = to_ns();
-        else
-          time_ns = system_ns();
-
-        int64_t res;
-        if (first_message)
-        {
-          first_message = false;
-          res = 0;
-        }
-        else
-        {
-          res = time_ns - last_time_ns;
-        }
-
-        last_time_ns = time_ns;
-        return res;
-      }
-
-      case timestamp_mode::Absolute:
-        if constexpr (info.has_absolute_timestamps)
-          return to_ns();
-        else
-          return system_ns();
-
-      case timestamp_mode::SystemMonotonic:
-        if constexpr (info.absolute_is_monotonic)
-          return to_ns();
-        else
-          return system_ns();
-
-      case timestamp_mode::AudioFrame:
-        if constexpr (info.has_samples)
-          return samples;
-        else
-          return 0;
-
-      case timestamp_mode::Custom:
-        return configuration.get_timestamp(to_ns());
+        return on_main(cb, bytes, timestamp, finished_sysex);
     }
   }
 
+public:
   libremidi::message message;
 
-  int64_t last_time_ns = 0;
+private:
   enum
   {
     main,
     in_sysex
   } state{main};
+};
+}
 
-  bool first_message = true;
+namespace midi2
+{
+struct input_state_machine : input_state_machine_base<ump_input_configuration>
+{
+  using input_state_machine_base::input_state_machine_base;
+
+public:
+  void on_bytes_multi(std::span<const unsigned char> bytes, int64_t timestamp)
+  {
+    auto ptr = reinterpret_cast<const uint32_t*>(bytes.data());
+    auto sz = bytes.size() / 4;
+    return on_bytes_multi({ptr, sz}, timestamp);
+  }
+
+  void on_bytes_multi(std::span<const uint32_t> bytes, int64_t timestamp)
+  {
+    if (this->configuration.on_message)
+      on_bytes_multi_segmented(this->configuration.on_message, bytes, timestamp);
+    if (this->configuration.on_raw_data)
+      this->configuration.on_raw_data(bytes, timestamp);
+  }
+
+  void on_bytes(std::span<const uint32_t> bytes, int64_t timestamp)
+  {
+    if (this->configuration.on_message)
+      on_bytes_segmented(this->configuration.on_message, bytes, timestamp);
+    if (this->configuration.on_raw_data)
+      this->configuration.on_raw_data(bytes, timestamp);
+  }
+
+private:
+  // Function to process a byte stream which may contain multiple successive
+  // MIDI events (CoreMIDI, ALSA Sequencer can work like this)
+  void on_bytes_multi_segmented(
+      const ump_callback& cb, std::span<const uint32_t> bytes, int64_t timestamp)
+  {
+    auto count = bytes.size();
+    auto ump_stream = bytes.data();
+    while (count > 0)
+    {
+      // Handle NOOP (or padding)
+      while (count > 0 && ump_stream[0] == 0)
+      {
+        count--;
+        ump_stream++;
+      }
+
+      if (count == 0)
+        break;
+
+      const auto ump_uints = cmidi2_ump_get_num_bytes(ump_stream[0]) / 4;
+      on_bytes_segmented(cb, {ump_stream, ump_stream + ump_uints}, timestamp);
+
+      ump_stream += ump_uints;
+      count -= ump_uints;
+    }
+  }
+
+  // Function to process bytes corresponding to at most one midi event
+  void
+  on_bytes_segmented(const ump_callback& cb, std::span<const uint32_t> bytes, int64_t timestamp)
+  {
+    // Filter according to message type
+    switch(cmidi2_ump_get_message_type(bytes.data()))
+    {
+      case CMIDI2_MESSAGE_TYPE_UTILITY:
+      {
+        // All the utility messages are about timing
+        if (this->configuration.ignore_timing)
+          return;
+        break;
+      }
+
+      case CMIDI2_MESSAGE_TYPE_SYSTEM:
+      {
+        if (this->configuration.ignore_timing)
+        {
+          auto status = cmidi2_ump_get_system_message_byte2(bytes.data());
+          switch(status)
+          {
+            case CMIDI2_SYSTEM_STATUS_MIDI_TIME_CODE:
+            case CMIDI2_SYSTEM_STATUS_SONG_POSITION:
+            case CMIDI2_SYSTEM_STATUS_TIMING_CLOCK:
+              return;
+          }
+        }
+
+       if (this->configuration.ignore_sensing)
+       {
+         auto status = cmidi2_ump_get_system_message_byte2(bytes.data());
+         if(status == CMIDI2_SYSTEM_STATUS_ACTIVE_SENSING)
+           return;
+       }
+       break;
+      }
+
+      case CMIDI2_MESSAGE_TYPE_SYSEX7:
+      case CMIDI2_MESSAGE_TYPE_SYSEX8_MDS:
+      {
+        if (this->configuration.ignore_sysex)
+          return;
+        break;
+      }
+    }
+
+    libremidi::ump msg;
+    std::copy(bytes.begin(), bytes.end(), msg.data);
+    msg.timestamp = timestamp;
+    cb(std::move(msg));
+  }
 };
 }
 }

include/libremidi/detail/observer.hpp

@@ -2,6 +2,7 @@
 #include <libremidi/api.hpp>
 #include <libremidi/config.hpp>
 #include <libremidi/observer_configuration.hpp>
+#include <libremidi/error_handler.hpp>
 
 #include <memory>
 #include <vector>

include/libremidi/detail/ump_stream.hpp

@@ -1,5 +1,6 @@
 #pragma once
 #include <libremidi/cmidi2.hpp>
+#include <libremidi/error.hpp>
 
 #include <cinttypes>
 #include <cstdint>
@@ -17,7 +18,7 @@ enum class segmentation_error
  * Utility function to segment an ump stream into individual messages.
  * Used to send a stream to APIs that work message-by-message.
  */
-inline void
+inline stdx::error
 segment_ump_stream(const uint32_t* ump_stream, int64_t count, auto write_func, auto realloc_func)
 {
   while (count > 0)
@@ -35,24 +36,27 @@ segment_ump_stream(const uint32_t* ump_stream, int64_t count, auto write_func, a
     const auto ump_bytes = cmidi2_ump_get_num_bytes(ump_stream[0]);
 
     // FIXME std::expected, propagate the error back to caller?
-    switch (write_func(ump_stream, ump_bytes))
+    switch (int err = static_cast<int>(write_func(ump_stream, ump_bytes)))
     {
-      case segmentation_error::no_error:
+      case 0:
         break;
-      case segmentation_error::need_space:
+      case -ENOMEM:
+      case ENOMEM:
         // Try again if we didn't have enough space in the OS queue
         realloc_func();
-        if (write_func(ump_stream, ump_bytes) != segmentation_error::no_error)
-          return;
+        if (auto err = write_func(ump_stream, ump_bytes); err != std::errc{})
+          return std::make_error_code(err);
         break;
-      case segmentation_error::other:
-        return;
+      default:
+        return from_errc(err);
     }
 
     const auto ump_uints = ump_bytes / 4;
     ump_stream += ump_uints;
     count -= ump_uints;
   }
+
+  return stdx::error{};
 }
 
 }

include/libremidi/error.hpp

@@ -1,82 +1,37 @@
 #pragma once
 #include <libremidi/config.hpp>
 
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wmissing-field-initializers"
+#pragma GCC diagnostic ignored "-Wunused-parameter"
+#include <libremidi/system_error2.hpp>
+#pragma GCC diagnostic pop
+
 #include <functional>
-#include <stdexcept>
 #include <string_view>
+#include <version>
+
+#if __has_include(<source_location>) && (__cpp_lib_source_location >= 201907L)
+  #include <source_location>
+namespace libremidi { using source_location = std::source_location; }
+#else
+namespace libremidi {
+struct source_location {
+  static source_location current() noexcept { return {}; }
+  int line() const noexcept { return -1; }
+  int offset() const noexcept { return -1; }
+  const char* function_name() const noexcept { return "(unknown)"; }
+  const char* file_name() const noexcept { return "(unknown)"; }
+};
+}
+#endif
 
 namespace libremidi
 {
-//! Defines various error types.
-enum midi_error
+inline auto from_errc(int ret) noexcept
 {
-  WARNING,           /*!< A non-critical error. */
-  UNSPECIFIED,       /*!< The default, unspecified error type. */
-  NO_DEVICES_FOUND,  /*!< No devices found on system. */
-  INVALID_DEVICE,    /*!< An invalid device ID was specified. */
-  MEMORY_ERROR,      /*!< An error occured during memory allocation. */
-  INVALID_PARAMETER, /*!< An invalid parameter was specified to a function. */
-  INVALID_USE,       /*!< The function was called incorrectly. */
-  DRIVER_ERROR,      /*!< A system driver error occured. */
-  SYSTEM_ERROR,      /*!< A system error occured. */
-  THREAD_ERROR       /*!< A thread error occured. */
-};
-
-//! Base exception class for MIDI problems
-struct LIBREMIDI_EXPORT midi_exception : public std::runtime_error
-{
-  using std::runtime_error::runtime_error;
-  ~midi_exception() override;
-};
-
-struct LIBREMIDI_EXPORT no_devices_found_error final : public midi_exception
-{
-  static constexpr auto code = midi_error::NO_DEVICES_FOUND;
-  using midi_exception::midi_exception;
-  ~no_devices_found_error() override;
-};
-struct LIBREMIDI_EXPORT invalid_device_error final : public midi_exception
-{
-  static constexpr auto code = midi_error::INVALID_DEVICE;
-  using midi_exception::midi_exception;
-  ~invalid_device_error() override;
-};
-struct LIBREMIDI_EXPORT memory_error final : public midi_exception
-{
-  static constexpr auto code = midi_error::MEMORY_ERROR;
-  using midi_exception::midi_exception;
-  ~memory_error() override;
-};
-struct LIBREMIDI_EXPORT invalid_parameter_error final : public midi_exception
-{
-  static constexpr auto code = midi_error::INVALID_PARAMETER;
-  using midi_exception::midi_exception;
-  ~invalid_parameter_error() override;
-};
-struct LIBREMIDI_EXPORT invalid_use_error final : public midi_exception
-{
-  static constexpr auto code = midi_error::INVALID_USE;
-  using midi_exception::midi_exception;
-  ~invalid_use_error() override;
-};
-struct LIBREMIDI_EXPORT driver_error final : public midi_exception
-{
-  static constexpr auto code = midi_error::DRIVER_ERROR;
-  using midi_exception::midi_exception;
-  ~driver_error() override;
-};
-struct LIBREMIDI_EXPORT system_error final : public midi_exception
-{
-  static constexpr auto code = midi_error::SYSTEM_ERROR;
-  using midi_exception::midi_exception;
-  ~system_error() override;
-};
-struct LIBREMIDI_EXPORT thread_error final : public midi_exception
-{
-  static constexpr auto code = midi_error::THREAD_ERROR;
-  using midi_exception::midi_exception;
-  ~thread_error() override;
-};
+  return static_cast<std::errc>(-ret);
+}
 
 /*! \brief Error callback function
     \param type Type of error.
@@ -85,5 +40,25 @@ struct LIBREMIDI_EXPORT thread_error final : public midi_exception
     Note that class behaviour is undefined after a critical error (not
     a warning) is reported.
  */
-using midi_error_callback = std::function<void(midi_error type, std::string_view errorText)>;
+using midi_error_callback = std::function<void(std::string_view errorText, const source_location&)>;
+using midi_warning_callback = std::function<void(std::string_view errorText, const source_location&)>;
 }
+
+#if !defined(LIBREMIDI_LOG)
+  #if !defined(__LIBREMIDI_DEBUG__)
+    #define LIBREMIDI_LOG(...) \
+      do                       \
+      {                        \
+      } while (0)
+  #else
+    #include <iostream>
+    #define LIBREMIDI_LOG(...)        \
+      do                              \
+      {                               \
+        [](auto&&... args) {          \
+          (std::cerr << ... << args); \
+          std::cerr << std::endl;     \
+        }(__VA_ARGS__);               \
+      } while (0)
+  #endif
+#endif

include/libremidi/error_handler.hpp

@@ -0,0 +1,63 @@
+#pragma once
+#include <libremidi/api.hpp>
+#include <libremidi/config.hpp>
+#include <libremidi/error.hpp>
+#include <libremidi/observer_configuration.hpp>
+#include <libremidi/input_configuration.hpp>
+#include <libremidi/output_configuration.hpp>
+
+#include <string_view>
+
+namespace libremidi
+{
+struct error_handler
+{
+  //! Error reporting function for libremidi classes.
+  void error_impl(
+      const midi_error_callback& callback, std::string_view errorString,
+      const source_location& location) const
+  {
+    if (callback)
+    {
+      if (first_error)
+        return;
+
+      first_error = true;
+      callback(errorString, location);
+      first_error = false;
+    }
+    else
+    {
+      LIBREMIDI_LOG(errorString, " (", location.function_name(), ":", location.line(), ")");
+    }
+  }
+
+  //! Warning reporting function for libremidi classes.
+  void warning_impl(
+      const midi_warning_callback& callback, std::string_view errorString,
+      const source_location& location) const
+  {
+    if (callback)
+    {
+      if (first_warning)
+        return;
+
+      first_warning = true;
+      callback(errorString, location);
+      first_warning = false;
+    }
+    else
+    {
+      LIBREMIDI_LOG(errorString, " (", location.function_name(), ":", location.line(), ")");
+    }
+  }
+
+  // To prevent infinite error loops
+  mutable bool first_error{};
+  mutable bool first_warning{};
+};
+
+// Needed as apple still doesn't support source_location in xcode 15.3
+#define libremidi_handle_error(config, str) error_impl(config.on_error, str, libremidi::source_location::current())
+#define libremidi_handle_warning(config, str) warning_impl(config.on_warning, str, libremidi::source_location::current())
+}

include/libremidi/input_configuration.hpp

@@ -5,7 +5,6 @@
 #include <libremidi/ump.hpp>
 
 #include <functional>
-#include <string>
 
 namespace libremidi
 {
@@ -41,19 +40,23 @@ enum timestamp_mode
 
 using timestamp = int64_t;
 using message_callback = std::function<void(message&& message)>;
-using raw_callback = std::function<void(std::span<uint8_t>, timestamp)>;
+using raw_callback = std::function<void(std::span<const uint8_t>, timestamp)>;
 using timestamp_callback = std::function<timestamp(timestamp)>;
 struct input_configuration
 {
   //! Set a callback function to be invoked for incoming MIDI messages.
-  //! Mandatory!
-  message_callback on_message;
+  //! Either this or on_raw_message must be set
+  message_callback on_message{};
+
+  //! Invoked for incoming MIDI bytes. No transformation, no filtering, no packetization,
+  //! just the MIDI data straight from the source.
+  raw_callback on_raw_data{};
 
   //! Set a custom callback function to be invoked for timestamping MIDI messages.
   //! Input: the API provided timestamp in nanoseconds, if available, for reference.
   //! (e.g. the same as "Absolute").
   //! Mandatory if timestamps == timestamp_mode::Custom, unused otherwise.
-  timestamp_callback get_timestamp;
+  timestamp_callback get_timestamp{};
 
   //! Set an error callback function to be invoked when an error has occured.
   /*!
@@ -61,7 +64,7 @@ struct input_configuration
     best to set the error callback function before opening a port.
   */
   midi_error_callback on_error{};
-  midi_error_callback on_warning{};
+  midi_warning_callback on_warning{};
 
   //! Specify whether certain MIDI message types should be queued or ignored
   //! during input.
@@ -81,16 +84,22 @@ struct input_configuration
 };
 
 using ump_callback = std::function<void(ump&&)>;
+using raw_ump_callback = std::function<void(std::span<const uint32_t>, timestamp)>;
 struct ump_input_configuration
 {
   //! Set a callback function to be invoked for incoming UMP messages.
-  ump_callback on_message;
+  //! Either this or on_raw_message must be set
+  ump_callback on_message{};
+
+  //! Invoked for incoming UMP bytes. No transformation, no filtering, no packetization,
+  //! just the UMP data straight from the source.
+  raw_ump_callback on_raw_data{};
 
   //! Set a custom callback function to be invoked for timestamping MIDI messages.
   //! Input: the API provided timestamp in nanoseconds, if available, for reference.
   //! (e.g. the same as "Absolute").
   //! Mandatory if timestamps == timestamp_mode::Custom, unused otherwise.
-  timestamp_callback get_timestamp;
+  timestamp_callback get_timestamp{};
 
   //! Set an error callback function to be invoked when an error has occured.
   /*!
@@ -98,7 +107,7 @@ struct ump_input_configuration
     best to set the error callback function before opening a port.
   */
   midi_error_callback on_error{};
-  midi_error_callback on_warning{};
+  midi_warning_callback on_warning{};
 
   //! Specify whether certain MIDI message types should be queued or ignored
   //! during input.

include/libremidi/libremidi-c.cpp

@@ -0,0 +1,507 @@
+// clang-format off
+#include <libremidi/libremidi-c.h>
+#include <libremidi/libremidi.hpp>
+#include <libremidi/backends.hpp>
+// clang-format on
+
+#include <cerrno>
+#include <cstdlib>
+#include <cstring>
+#include <limits>
+
+struct libremidi_midi_observer_handle
+{
+  libremidi::observer self;
+};
+
+struct libremidi_midi_in_handle
+{
+  libremidi::midi_in self;
+};
+
+struct libremidi_midi_out_handle
+{
+  libremidi::midi_out self;
+};
+
+namespace libremidi
+{
+
+static void assign_error_callback(const auto& src, auto& dst)
+{
+  if (src.callback)
+  {
+    dst = [src](std::string_view errorText, const source_location& loc) {
+      src.callback(src.context, errorText.data(), errorText.size(), &loc);
+    };
+  }
+}
+}
+
+extern "C" {
+const char* libremidi_get_version(void)
+{
+  return LIBREMIDI_VERSION;
+}
+
+void libremidi_available_midi1_apis(void* ctx, void (*cb)(void* ctx, libremidi_api))
+{
+  if (!cb)
+    return;
+  libremidi::midi1::for_all_backends([=](auto b) { cb(ctx, b.API); });
+}
+
+void libremidi_available_midi2_apis(void* ctx, void (*cb)(void* ctx, libremidi_api))
+{
+  if (!cb)
+    return;
+  libremidi::midi2::for_all_backends([=](auto b) { cb(ctx, b.API); });
+}
+
+const char* libremidi_api_identifier(libremidi_api api)
+{
+  return libremidi::get_api_name(api).data();
+}
+
+const char* libremidi_api_display_name(libremidi_api api)
+{
+  return libremidi::get_api_display_name(api).data();
+}
+
+libremidi_api libremidi_get_compiled_api_by_identifier(const char* name)
+{
+  libremidi_api ret = libremidi_api::UNSPECIFIED;
+  libremidi::midi_any::for_all_backends([&](auto& b) {
+    if (name == b.name)
+      ret = b.API;
+  });
+  return ret;
+}
+
+int libremidi_midi_api_configuration_init(libremidi_api_configuration* conf)
+{
+  memset(conf, 0, sizeof(*conf));
+  return 0;
+}
+
+int libremidi_midi_observer_configuration_init(libremidi_observer_configuration* conf)
+{
+  memset(conf, 0, sizeof(*conf));
+  return 0;
+}
+
+int libremidi_midi_configuration_init(libremidi_midi_configuration* conf)
+{
+  memset(conf, 0, sizeof(*conf));
+  return 0;
+}
+
+int libremidi_midi_in_port_clone(const libremidi_midi_in_port* port, libremidi_midi_in_port** dst)
+{
+  if (!port || !dst)
+    return -EINVAL;
+
+  auto copied = new libremidi::input_port{*reinterpret_cast<const libremidi::input_port*>(port)};
+  *dst = reinterpret_cast<libremidi_midi_in_port*>(copied);
+  return 0;
+}
+
+int libremidi_midi_in_port_free(libremidi_midi_in_port* port)
+{
+  delete reinterpret_cast<libremidi::input_port*>(port);
+  return 0;
+}
+
+int libremidi_midi_in_port_name(const libremidi_midi_in_port* port, const char** name, size_t* len)
+{
+  if (!port || !name || !len)
+    return -EINVAL;
+
+  auto& p = *reinterpret_cast<const libremidi::input_port*>(port);
+  *name = p.port_name.data();
+  *len = p.port_name.size();
+  return 0;
+}
+
+int libremidi_midi_out_port_clone(
+    const libremidi_midi_out_port* port, libremidi_midi_out_port** dst)
+{
+  if (!port || !dst)
+    return -EINVAL;
+
+  auto copied = new libremidi::output_port{*reinterpret_cast<const libremidi::output_port*>(port)};
+  *dst = reinterpret_cast<libremidi_midi_out_port*>(copied);
+  return 0;
+}
+
+int libremidi_midi_out_port_free(libremidi_midi_out_port* port)
+{
+  delete reinterpret_cast<libremidi::output_port*>(port);
+  return 0;
+}
+
+int libremidi_midi_out_port_name(
+    const libremidi_midi_out_port* port, const char** name, size_t* len)
+{
+  if (!port || !name || !len)
+    return -EINVAL;
+
+  auto& p = *reinterpret_cast<const libremidi::output_port*>(port);
+  *name = p.port_name.data();
+  *len = p.port_name.size();
+  return 0;
+}
+
+int libremidi_midi_observer_new(
+    const libremidi_observer_configuration* c, libremidi_api_configuration* api,
+    libremidi_midi_observer_handle** out)
+{
+  if (!out || !c)
+    return -EINVAL;
+
+  libremidi::observer_configuration conf;
+  libremidi::assign_error_callback(c->on_error, conf.on_error);
+  libremidi::assign_error_callback(c->on_warning, conf.on_warning);
+
+  conf.track_hardware = c->track_hardware;
+  conf.track_virtual = c->track_virtual;
+  conf.track_any = c->track_any;
+  conf.notify_in_constructor = c->notify_in_constructor;
+
+  auto api_conf = libremidi::observer_configuration_for(static_cast<libremidi::API>(api->api));
+
+  if (c->input_added.callback)
+  {
+    conf.input_added = [cb = c->input_added](const auto& port) {
+      cb.callback(cb.context, reinterpret_cast<const libremidi_midi_in_port*>(&port));
+    };
+  }
+  if (c->input_removed.callback)
+  {
+    conf.input_removed = [cb = c->input_removed](const auto& port) {
+      cb.callback(cb.context, reinterpret_cast<const libremidi_midi_in_port*>(&port));
+    };
+  }
+  if (c->output_added.callback)
+  {
+    conf.output_added = [cb = c->output_added](const auto& port) {
+      cb.callback(cb.context, reinterpret_cast<const libremidi_midi_out_port*>(&port));
+    };
+  }
+  if (c->output_removed.callback)
+  {
+    conf.output_removed = [cb = c->output_removed](const auto& port) {
+      cb.callback(cb.context, reinterpret_cast<const libremidi_midi_out_port*>(&port));
+    };
+  }
+
+  try
+  {
+    auto ptr = new libremidi_midi_observer_handle{
+        libremidi::observer{std::move(conf), std::move(api_conf)}};
+    *out = ptr;
+    return 0;
+  }
+  catch (...)
+  {
+    return -EINVAL;
+  }
+}
+
+int libremidi_midi_observer_enumerate_input_ports(
+    libremidi_midi_observer_handle* ptr, void* context,
+    void (*cb)(void* ctx, const libremidi_midi_in_port*))
+{
+  if (!ptr || !cb)
+    return -EINVAL;
+
+  for (const auto& port : ptr->self.get_input_ports())
+  {
+    cb(context, reinterpret_cast<const libremidi_midi_in_port*>(&port));
+  }
+
+  return 0;
+}
+
+int libremidi_midi_observer_enumerate_output_ports(
+    libremidi_midi_observer_handle* ptr, void* context,
+    void (*cb)(void* ctx, const libremidi_midi_out_port*))
+{
+  if (!ptr || !cb)
+    return -EINVAL;
+
+  for (const auto& port : ptr->self.get_output_ports())
+  {
+    cb(context, reinterpret_cast<const libremidi_midi_out_port*>(&port));
+  }
+
+  return 0;
+}
+
+int libremidi_midi_observer_free(libremidi_midi_observer_handle* ptr)
+{
+  delete ptr;
+  return 0;
+}
+
+int libremidi_midi_in_new(
+    const libremidi_midi_configuration* c, const libremidi_api_configuration* api,
+    libremidi_midi_in_handle** out)
+{
+  if (!out || !c)
+    return -EINVAL;
+  if (!c->virtual_port && !c->in_port)
+    return -EINVAL;
+
+  *out = nullptr;
+
+  auto api_conf = libremidi::midi_in_configuration_for(static_cast<libremidi::API>(api->api));
+
+  // Create the MIDI object
+  switch (c->version)
+  {
+    case libremidi_midi_configuration::MIDI1:
+    case libremidi_midi_configuration::MIDI1_RAW: {
+      libremidi::input_configuration conf;
+      libremidi::assign_error_callback(c->on_error, conf.on_error);
+      libremidi::assign_error_callback(c->on_warning, conf.on_warning);
+      conf.ignore_sensing = c->ignore_sensing;
+      conf.ignore_sysex = c->ignore_sysex;
+      conf.ignore_timing = c->ignore_timing;
+      conf.timestamps = c->timestamps;
+
+      if (c->get_timestamp.callback)
+      {
+        conf.get_timestamp
+            = [cb = c->get_timestamp](int64_t msg) { return cb.callback(cb.context, msg); };
+      }
+
+      if (c->on_midi1_message.callback)
+        conf.on_message = [cb = c->on_midi1_message](const libremidi::message& msg) {
+          cb.callback(cb.context, msg.timestamp, msg.bytes.data(), msg.size());
+        };
+      else if (c->on_midi1_raw_data.callback)
+      {
+        conf.on_raw_data = [cb = c->on_midi1_raw_data](std::span<const uint8_t> msg, int64_t ts) {
+          cb.callback(cb.context, ts, msg.data(), msg.size());
+        };
+      }
+      else
+      {
+        return -EINVAL;
+      }
+
+      try
+      {
+        auto ptr = new libremidi_midi_in_handle{
+            libremidi::midi_in{std::move(conf), std::move(api_conf)}};
+        *out = ptr;
+      }
+      catch (...)
+      {
+        return -EINVAL;
+      }
+      break;
+    }
+    case libremidi_midi_configuration::MIDI2:
+    case libremidi_midi_configuration::MIDI2_RAW: {
+      libremidi::ump_input_configuration conf;
+      libremidi::assign_error_callback(c->on_error, conf.on_error);
+      libremidi::assign_error_callback(c->on_warning, conf.on_warning);
+      conf.ignore_sensing = c->ignore_sensing;
+      conf.ignore_sysex = c->ignore_sysex;
+      conf.ignore_timing = c->ignore_timing;
+      conf.timestamps = c->timestamps;
+
+      if (c->get_timestamp.callback)
+      {
+        conf.get_timestamp
+            = [cb = c->get_timestamp](int64_t msg) { return cb.callback(cb.context, msg); };
+      }
+
+      if (c->on_midi2_message.callback)
+        conf.on_message = [cb = c->on_midi2_message](const libremidi::ump& msg) {
+          cb.callback(cb.context, msg.timestamp, msg.data, msg.size());
+        };
+      else if (c->on_midi2_raw_data.callback)
+      {
+        conf.on_raw_data = [cb = c->on_midi2_raw_data](std::span<const uint32_t> msg, int64_t ts) {
+          cb.callback(cb.context, ts, msg.data(), msg.size());
+        };
+      }
+      else
+      {
+        return -EINVAL;
+      }
+
+      try
+      {
+        auto ptr = new libremidi_midi_in_handle{
+            libremidi::midi_in{std::move(conf), std::move(api_conf)}};
+        *out = ptr;
+      }
+      catch (...)
+      {
+        return -EINVAL;
+      }
+      break;
+    }
+    default:
+      return -EINVAL;
+  }
+
+  // Open the port
+  auto ptr = *out;
+  if (!ptr)
+    return -EINVAL;
+
+  if (c->virtual_port)
+  {
+    if (auto ret = ptr->self.open_virtual_port(c->port_name); ret != stdx::error{})
+    {
+      *out = nullptr;
+      delete ptr;
+      return -EIO;
+    }
+  }
+  else
+  {
+    auto port = reinterpret_cast<const libremidi::input_port*>(c->in_port);
+    if (auto ret = ptr->self.open_port(*port); ret != stdx::error{})
+    {
+      *out = nullptr;
+      delete ptr;
+      return -EIO;
+    }
+  }
+
+  return 0;
+}
+int libremidi_midi_in_is_connected(const libremidi_midi_in_handle* in)
+{
+  if (!in)
+    return -EINVAL;
+  return in->self.is_port_connected() ? 1 : 0;
+}
+
+libremidi_timestamp libremidi_midi_in_absolute_timestamp(libremidi_midi_in_handle* in)
+{
+  if (!in)
+    return -EINVAL;
+  return in->self.absolute_timestamp();
+}
+
+int libremidi_midi_in_free(libremidi_midi_in_handle* ptr)
+{
+  delete ptr;
+  return 0;
+}
+
+int libremidi_midi_out_new(
+    const libremidi_midi_configuration* c, const libremidi_api_configuration* api,
+    libremidi_midi_out_handle** out)
+{
+  if (!out || !c)
+    return -EINVAL;
+  if (!c->virtual_port && !c->out_port)
+    return -EINVAL;
+
+  *out = nullptr;
+
+  auto api_conf = libremidi::midi_out_configuration_for(static_cast<libremidi::API>(api->api));
+
+  // Create the MIDI object
+  libremidi::output_configuration conf;
+  libremidi::assign_error_callback(c->on_error, conf.on_error);
+  libremidi::assign_error_callback(c->on_warning, conf.on_warning);
+  conf.timestamps = c->timestamps;
+  try
+  {
+    auto ptr
+        = new libremidi_midi_out_handle{libremidi::midi_out{std::move(conf), std::move(api_conf)}};
+    *out = ptr;
+  }
+  catch (...)
+  {
+    return -EINVAL;
+  }
+
+  // Open the port
+  auto ptr = *out;
+  if (!ptr)
+    return -EINVAL;
+
+  if (c->virtual_port)
+  {
+    if (auto ret = ptr->self.open_virtual_port(c->port_name); ret != stdx::error{})
+    {
+      *out = nullptr;
+      delete ptr;
+      return -EIO;
+    }
+  }
+  else
+  {
+    auto port = reinterpret_cast<const libremidi::output_port*>(c->in_port);
+    if (auto ret = ptr->self.open_port(*port); ret != stdx::error{})
+    {
+      *out = nullptr;
+      delete ptr;
+      return -EIO;
+    }
+  }
+  return 0;
+}
+
+int libremidi_midi_out_is_connected(const libremidi_midi_out_handle* out)
+{
+  if (!out)
+    return -EINVAL;
+  return out->self.is_port_connected() ? 1 : 0;
+}
+
+int libremidi_midi_out_send_message(
+    libremidi_midi_out_handle* out, const libremidi_midi1_symbol* msg, size_t sz)
+{
+  if (!out || !msg || sz > std::numeric_limits<int32_t>::max())
+    return -EINVAL;
+
+  auto res = out->self.send_message(msg, sz);
+  return res != stdx::error{} ? -EIO : 0;
+}
+
+int libremidi_midi_out_send_ump(libremidi_midi_out_handle* out, const libremidi_midi2_symbol* msg, size_t sz)
+{
+  if (!out || !msg || sz > std::numeric_limits<int32_t>::max())
+    return -EINVAL;
+
+  auto res = out->self.send_ump(msg, sz);
+  return res != stdx::error{} ? -EIO : 0;
+}
+
+int libremidi_midi_out_schedule_message(
+    libremidi_midi_out_handle* out, int64_t ts, const libremidi_midi1_symbol* msg, size_t sz)
+{
+  if (!out || !msg || sz > std::numeric_limits<int32_t>::max())
+    return -EINVAL;
+
+  auto res = out->self.schedule_message(ts, msg, sz);
+  return res != stdx::error{} ? -EIO : 0;
+}
+
+int libremidi_midi_out_schedule_ump(
+    libremidi_midi_out_handle* out, int64_t ts, const libremidi_midi2_symbol* msg, size_t sz)
+{
+  if (!out || !msg || sz > std::numeric_limits<int32_t>::max())
+    return -EINVAL;
+
+  auto res = out->self.schedule_ump(ts, msg, sz);
+  return res != stdx::error{} ? -EIO : 0;
+}
+
+int libremidi_midi_out_free(libremidi_midi_out_handle* ptr)
+{
+  delete ptr;
+  return 0;
+}
+}

include/libremidi/libremidi-c.h

@@ -0,0 +1,275 @@
+#pragma once
+#include <libremidi/api-c.h>
+
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+
+#if defined(LIBREMIDI_EXPORTS)
+  #if defined(_MSC_VER)
+    #define LIBREMIDI_EXPORT __declspec(dllexport)
+  #elif defined(__GNUC__) || defined(__clang__)
+    #define LIBREMIDI_EXPORT __attribute__((visibility("default")))
+  #endif
+#else
+  #define LIBREMIDI_EXPORT
+#endif
+
+#if __cplusplus
+extern "C" {
+#endif
+typedef unsigned char libremidi_midi1_symbol;
+typedef libremidi_midi1_symbol* libremidi_midi1_message;
+
+typedef uint32_t libremidi_midi2_symbol;
+typedef libremidi_midi2_symbol* libremidi_midi2_message;
+
+typedef int64_t libremidi_timestamp;
+
+typedef struct libremidi_midi_in_port libremidi_midi_in_port;
+typedef struct libremidi_midi_out_port libremidi_midi_out_port;
+typedef struct libremidi_midi_in_handle libremidi_midi_in_handle;
+typedef struct libremidi_midi_out_handle libremidi_midi_out_handle;
+typedef struct libremidi_midi_observer_handle libremidi_midi_observer_handle;
+
+typedef struct libremidi_api_configuration libremidi_api_configuration;
+
+enum libremidi_timestamp_mode
+{
+  NoTimestamp,
+
+  Relative,
+  Absolute,
+  SystemMonotonic,
+  AudioFrame,
+  Custom
+};
+
+typedef struct libremidi_api_configuration
+{
+  enum libremidi_api api;
+  enum
+  {
+    Observer,
+    Input,
+    Output
+  } configuration_type;
+
+  void* data;
+} libremidi_api_configuration;
+
+typedef struct libremidi_observer_configuration
+{
+  struct
+  {
+    void* context;
+    void (*callback)(void* ctx, const char* error, size_t error_len, const void* source_location);
+  } on_error;
+  struct
+  {
+    void* context;
+    void (*callback)(void* ctx, const char* error, size_t error_len, const void* source_location);
+  } on_warning;
+
+  struct
+  {
+    void* context;
+    void (*callback)(void* ctx, const libremidi_midi_in_port*);
+  } input_added;
+  struct
+  {
+    void* context;
+    void (*callback)(void* ctx, const libremidi_midi_in_port*);
+  } input_removed;
+  struct
+  {
+    void* context;
+    void (*callback)(void* ctx, const libremidi_midi_out_port*);
+  } output_added;
+  struct
+  {
+    void* context;
+    void (*callback)(void* ctx, const libremidi_midi_out_port*);
+  } output_removed;
+
+  bool track_hardware;
+  bool track_virtual;
+  bool track_any;
+  bool notify_in_constructor;
+} libremidi_observer_configuration;
+
+typedef struct libremidi_midi1_callback
+{
+  void* context;
+  void (*callback)(void* ctx, libremidi_timestamp, const libremidi_midi1_symbol*, size_t len);
+} libremidi_midi1_callback;
+
+typedef struct libremidi_midi2_callback
+{
+  void* context;
+  void (*callback)(void* ctx, libremidi_timestamp, const libremidi_midi2_symbol*, size_t len);
+} libremidi_midi2_callback;
+
+typedef struct libremidi_midi_configuration
+{
+  // Indicates the kind of callback requested, e.g. set MIDI1_RAW if you use the on_midi1_raw_data
+  enum
+  {
+    MIDI1 = (1 << 1),
+    MIDI1_RAW = (1 << 2),
+    MIDI2 = (1 << 3),
+    MIDI2_RAW = (1 << 4)
+  } version;
+
+  union
+  {
+    libremidi_midi_in_port* in_port;
+    libremidi_midi_out_port* out_port;
+  };
+
+  union
+  {
+    libremidi_midi1_callback on_midi1_message;
+    libremidi_midi1_callback on_midi1_raw_data;
+    libremidi_midi2_callback on_midi2_message;
+    libremidi_midi2_callback on_midi2_raw_data;
+  };
+
+  struct
+  {
+    void* context;
+    libremidi_timestamp (*callback)(void* ctx, libremidi_timestamp);
+  } get_timestamp;
+
+  struct
+  {
+    void* context;
+    void (*callback)(void* ctx, const char* error, size_t error_len, const void* source_location);
+  } on_error;
+  struct
+  {
+    void* context;
+    void (*callback)(void* ctx, const char* error, size_t error_len, const void* source_location);
+  } on_warning;
+
+  const char* port_name;
+  bool virtual_port;
+
+  bool ignore_sysex;
+  bool ignore_timing;
+  bool ignore_sensing;
+
+  enum libremidi_timestamp_mode timestamps;
+} libremidi_midi_configuration;
+
+/// API utilities
+LIBREMIDI_EXPORT
+const char* libremidi_get_version(void);
+
+LIBREMIDI_EXPORT
+void libremidi_midi1_available_apis(void* ctx, void (*)(void*, libremidi_api));
+LIBREMIDI_EXPORT
+void libremidi_midi2_available_apis(void* ctx, void (*)(void*, libremidi_api));
+LIBREMIDI_EXPORT
+const char* libremidi_api_identifier(libremidi_api);
+LIBREMIDI_EXPORT
+const char* libremidi_api_display_name(libremidi_api);
+LIBREMIDI_EXPORT
+libremidi_api libremidi_get_compiled_api_by_identifier(const char*);
+
+/// Create configurations
+LIBREMIDI_EXPORT
+int libremidi_midi_api_configuration_init(libremidi_api_configuration*);
+
+LIBREMIDI_EXPORT
+int libremidi_midi_observer_configuration_init(libremidi_observer_configuration*);
+
+LIBREMIDI_EXPORT
+int libremidi_midi_configuration_init(libremidi_midi_configuration*);
+
+/// Read information about port objects
+LIBREMIDI_EXPORT
+int libremidi_midi_in_port_clone(const libremidi_midi_in_port* port, libremidi_midi_in_port** dst);
+
+LIBREMIDI_EXPORT
+int libremidi_midi_in_port_free(libremidi_midi_in_port* port);
+
+LIBREMIDI_EXPORT
+int libremidi_midi_in_port_name(
+    const libremidi_midi_in_port* port, const char** name, size_t* len);
+
+LIBREMIDI_EXPORT
+int libremidi_midi_out_port_clone(
+    const libremidi_midi_out_port* port, libremidi_midi_out_port** dst);
+
+LIBREMIDI_EXPORT
+int libremidi_midi_out_port_free(libremidi_midi_out_port* port);
+
+LIBREMIDI_EXPORT
+int libremidi_midi_out_port_name(
+    const libremidi_midi_out_port* port, const char** name, size_t* len);
+
+/// Observer API
+LIBREMIDI_EXPORT
+int libremidi_midi_observer_new(
+    const libremidi_observer_configuration*, libremidi_api_configuration*,
+    libremidi_midi_observer_handle**);
+
+LIBREMIDI_EXPORT
+int libremidi_midi_observer_enumerate_input_ports(
+    libremidi_midi_observer_handle*, void* context,
+    void (*)(void* ctx, const libremidi_midi_in_port*));
+
+LIBREMIDI_EXPORT
+int libremidi_midi_observer_enumerate_output_ports(
+    libremidi_midi_observer_handle*, void* context,
+    void (*)(void* ctx, const libremidi_midi_out_port*));
+
+LIBREMIDI_EXPORT
+int libremidi_midi_observer_free(libremidi_midi_observer_handle*);
+
+/// MIDI input API (read MIDI messages)
+LIBREMIDI_EXPORT
+int libremidi_midi_in_new(
+    const libremidi_midi_configuration*, const libremidi_api_configuration*,
+    libremidi_midi_in_handle**);
+
+LIBREMIDI_EXPORT
+int libremidi_midi_in_is_connected(const libremidi_midi_in_handle*);
+
+LIBREMIDI_EXPORT
+libremidi_timestamp libremidi_midi_in_absolute_timestamp(libremidi_midi_in_handle*);
+
+LIBREMIDI_EXPORT
+int libremidi_midi_in_free(libremidi_midi_in_handle*);
+
+/// MIDI output API (send MIDI messages)
+LIBREMIDI_EXPORT
+int libremidi_midi_out_new(
+    const libremidi_midi_configuration*, const libremidi_api_configuration*,
+    libremidi_midi_out_handle**);
+
+LIBREMIDI_EXPORT
+int libremidi_midi_out_is_connected(const libremidi_midi_out_handle*);
+
+LIBREMIDI_EXPORT
+int libremidi_midi_out_send_message(
+    libremidi_midi_out_handle*, const libremidi_midi1_symbol*, size_t);
+
+LIBREMIDI_EXPORT
+int libremidi_midi_out_send_ump(libremidi_midi_out_handle*, const libremidi_midi2_symbol*, size_t);
+
+LIBREMIDI_EXPORT
+int libremidi_midi_out_schedule_message(
+    libremidi_midi_out_handle*, int64_t ts, const libremidi_midi1_symbol*, size_t);
+
+LIBREMIDI_EXPORT
+int libremidi_midi_out_schedule_ump(
+    libremidi_midi_out_handle*, int64_t ts, const libremidi_midi2_symbol*, size_t);
+
+LIBREMIDI_EXPORT
+int libremidi_midi_out_free(libremidi_midi_out_handle*);
+
+#if __cplusplus
+}
+#endif

include/libremidi/libremidi.cpp

@@ -7,9 +7,6 @@
 
 #include <cmath>
 
-#include <array>
-#include <thread>
-
 namespace libremidi
 {
 
@@ -56,17 +53,20 @@ LIBREMIDI_INLINE libremidi::API get_compiled_api_by_name(std::string_view name)
   midi2::for_all_backends([&](auto b) { apis.push_back(b.API); });
   return apis;
 }
-
-LIBREMIDI_INLINE midi_exception::~midi_exception() = default;
-LIBREMIDI_INLINE no_devices_found_error::~no_devices_found_error() = default;
-LIBREMIDI_INLINE invalid_device_error::~invalid_device_error() = default;
-LIBREMIDI_INLINE memory_error::~memory_error() = default;
-LIBREMIDI_INLINE invalid_parameter_error::~invalid_parameter_error() = default;
-LIBREMIDI_INLINE invalid_use_error::~invalid_use_error() = default;
-LIBREMIDI_INLINE driver_error::~driver_error() = default;
-LIBREMIDI_INLINE system_error::~system_error() = default;
-LIBREMIDI_INLINE thread_error::~thread_error() = default;
-
+LIBREMIDI_INLINE
+libremidi::API midi_api(const std::any& conf)
+{
+  libremidi::API ret = libremidi::API::UNSPECIFIED;
+  midi_any::for_all_backends([&]<typename T>(T) {
+    if (std::any_cast<typename T::midi_in_configuration>(&conf)
+        || std::any_cast<typename T::midi_out_configuration>(&conf)
+        || std::any_cast<typename T::midi_observer_configuration>(&conf))
+    {
+      ret = T::API;
+    }
+  });
+  return ret;
+}
 LIBREMIDI_INLINE
 std::any midi_in_configuration_for(libremidi::API api)
 {

include/libremidi/libremidi.hpp

@@ -69,7 +69,6 @@
   #include <midi/universal_packet.h>
 #endif
 #include <any>
-#include <optional>
 
 namespace libremidi
 {
@@ -132,19 +131,20 @@ public:
   [[nodiscard]] libremidi::API get_current_api() const noexcept;
 
   //! Open a MIDI input connection
-  void open_port(const input_port& pt, std::string_view local_port_name = "libremidi input");
+  stdx::error
+  open_port(const input_port& pt, std::string_view local_port_name = "libremidi input");
 
   //! Create a virtual input port, with optional name, to allow software
   //! connections.
   //!
   //! \param portName An optional name for the application port that is
   //!                 used to connect to portId can be specified.
-  void open_virtual_port(std::string_view portName = "libremidi virtual port");
+  stdx::error open_virtual_port(std::string_view portName = "libremidi virtual port");
 
-  void set_port_name(std::string_view portName);
+  stdx::error set_port_name(std::string_view portName);
 
   //! Close an open MIDI connection (if one exists).
-  void close_port();
+  stdx::error close_port();
 
   //! Returns true if a port has been opened successfully with open_port or open_virtual_port
   [[nodiscard]] bool is_port_open() const noexcept;
@@ -182,11 +182,11 @@ public:
   [[nodiscard]] libremidi::API get_current_api() const noexcept;
 
   //! Open a MIDI output connection.
-  void
+  stdx::error
   open_port(const output_port& pt, std::string_view local_port_name = "libremidi output") const;
 
   //! Close an open MIDI connection (if one exists).
-  void close_port() const;
+  stdx::error close_port() const;
 
   //! Returns true if a port has been opened successfully with open_port or open_virtual_port
   [[nodiscard]] bool is_port_open() const noexcept;
@@ -200,48 +200,56 @@ public:
   //!
   //! \param portName An optional name for the application port that is
   //!                 used to connect to portId can be specified.
-  void open_virtual_port(std::string_view portName = "libremidi virtual port") const;
+  stdx::error open_virtual_port(std::string_view portName = "libremidi virtual port") const;
 
-  void set_port_name(std::string_view portName) const;
+  stdx::error set_port_name(std::string_view portName) const;
 
   //! Immediately send a single message out an open MIDI output port.
   /*!
       An exception is thrown if an error occurs during output or an
       output connection was not previously established.
   */
-  void send_message(const libremidi::message& message) const;
+  stdx::error send_message(const libremidi::message& message) const;
 
   //! Immediately send a single message to an open MIDI output port.
-  void send_message(const unsigned char* message, size_t size) const;
-  void send_message(std::span<const unsigned char>) const;
-  void send_message(unsigned char b0) const;
-  void send_message(unsigned char b0, unsigned char b1) const;
-  void send_message(unsigned char b0, unsigned char b1, unsigned char b2) const;
+  stdx::error send_message(const unsigned char* message, size_t size) const;
+  stdx::error send_message(std::span<const unsigned char>) const;
+  stdx::error send_message(unsigned char b0) const;
+  stdx::error send_message(unsigned char b0, unsigned char b1) const;
+  stdx::error send_message(unsigned char b0, unsigned char b1, unsigned char b2) const;
+
+  // Avoid silly mistakes:
+  stdx::error send_message(auto* message) const noexcept = delete;
+  stdx::error send_message(const auto* message) const noexcept = delete;
 
   //! Current time in the timestamp referential
   int64_t current_time();
 
   //! Try to schedule a message later in time if the underlying API supports it
   //! (currently not implemented anywhere)
-  void schedule_message(int64_t timestamp, const unsigned char* message, size_t size);
+  stdx::error schedule_message(int64_t timestamp, const unsigned char* message, size_t size) const;
 
   //! Immediately send a single UMP packet to an open MIDI output port.
-  void send_ump(const uint32_t* message, size_t size) const;
-  void send_ump(const libremidi::ump&) const;
-  void send_ump(std::span<const uint32_t>) const;
-  void send_ump(uint32_t b0) const;
-  void send_ump(uint32_t b0, uint32_t b1) const;
-  void send_ump(uint32_t b0, uint32_t b1, uint32_t b2) const;
-  void send_ump(uint32_t b0, uint32_t b1, uint32_t b2, uint32_t b3) const;
+  stdx::error send_ump(const uint32_t* message, size_t size) const;
+  stdx::error send_ump(const libremidi::ump&) const;
+  stdx::error send_ump(std::span<const uint32_t>) const;
+  stdx::error send_ump(uint32_t b0) const;
+  stdx::error send_ump(uint32_t b0, uint32_t b1) const;
+  stdx::error send_ump(uint32_t b0, uint32_t b1, uint32_t b2) const;
+  stdx::error send_ump(uint32_t b0, uint32_t b1, uint32_t b2, uint32_t b3) const;
+  // Better compat with cmidi2
+  stdx::error send_ump(int32_t b0) const;
+  stdx::error send_ump(int64_t b01) const;
+  stdx::error send_ump(uint64_t b01) const;
 
 // Interop with ni-midi2
 #if LIBREMIDI_NI_MIDI2_COMPAT
-  void send_ump(const midi::universal_packet& pkt) const { send_ump(pkt.data, pkt.size()); }
-  void send_ump(const midi::sysex7& msg, int group = 0)
+  stdx::error send_ump(const midi::universal_packet& pkt) const { send_ump(pkt.data, pkt.size()); }
+  stdx::error send_ump(const midi::sysex7& msg, int group = 0)
   {
     midi::send_sysex7(msg, group, [&](const midi::sysex7_packet& x) { send_ump(x.data); });
   }
-  void send_ump(const midi::sysex8& msg, int stream, int group = 0)
+  stdx::error send_ump(const midi::sysex8& msg, int stream, int group = 0)
   {
     midi::send_sysex8(msg, stream, group, [&](const midi::sysex8_packet& x) { send_ump(x.data); });
   }
@@ -249,7 +257,7 @@ public:
 
   //! Try to schedule an UMP packet later in time if the underlying API supports it
   //! (currently not implemented anywhere)
-  void schedule_ump(int64_t timestamp, const uint32_t* message, size_t size);
+  stdx::error schedule_ump(int64_t timestamp, const uint32_t* message, size_t size) const;
 
 private:
   std::unique_ptr<class midi_out_api> impl_;

include/libremidi/message.hpp

@@ -1,7 +1,12 @@
 #pragma once
 #include <libremidi/config.hpp>
 
+#include <algorithm>
 #include <span>
+#include <vector>
+#if defined(__cpp_exceptions)
+  #include <stdexcept>
+#endif
 
 namespace libremidi
 {
@@ -120,7 +125,7 @@ struct message
   {
 #if defined(__cpp_exceptions)
     if (channel <= 0 || channel > 16)
-      throw std::range_error("message::uses_channel: out of range");
+      throw std::range_error("out of range");
 #endif
     return ((bytes[0] & 0xF) == channel - 1) && ((bytes[0] & 0xF0) != 0xF0);
   }
@@ -240,7 +245,9 @@ struct meta_events
         static_cast<uint8_t>(mpqn)};
   }
 
-  static message time_signature(int numerator, int denominator)
+  static message time_signature(
+      int numerator, int denominator, int clocks_per_click = 1,
+      int notated_32nd_notes_per_beat = 96)
   {
     int n = 1;
     int powTwo = 0;
@@ -251,8 +258,14 @@ struct meta_events
       ++powTwo;
     }
 
-    return {0xff, 0x58, 0x04, static_cast<uint8_t>(numerator), static_cast<uint8_t>(powTwo),
-            1,    96};
+    return {
+        0xff,
+        0x58,
+        0x04,
+        static_cast<uint8_t>(numerator),
+        static_cast<uint8_t>(powTwo),
+        static_cast<uint8_t>(clocks_per_click),
+        static_cast<uint8_t>(notated_32nd_notes_per_beat)};
   }
 
   // Where key index goes from -7 (7 flats, C♭ Major) to +7 (7 sharps, C♯
@@ -261,7 +274,7 @@ struct meta_events
   {
 #if defined(__cpp_exceptions)
     if (keyIndex < -7 || keyIndex > 7)
-      throw std::range_error("meta_events::key_signature: out of range");
+      throw std::range_error("out of range");
 #endif
     return {
         0xff, 0x59, 0x02, static_cast<uint8_t>(keyIndex),

include/libremidi/midi_in.cpp

@@ -9,11 +9,63 @@
 
 namespace libremidi
 {
-LIBREMIDI_INLINE auto make_midi_in(auto base_conf, std::any api_conf, auto backends)
+
+static libremidi::ump_input_configuration
+convert_midi1_to_midi2_input_configuration(const input_configuration& base_conf) noexcept
+{
+  libremidi::ump_input_configuration c2;
+  c2.on_message = [cb = base_conf.on_message,
+                   converter = midi2_to_midi1{}](libremidi::ump&& msg) mutable -> void {
+    converter.convert(
+        msg.data, 1, msg.timestamp, [cb](const unsigned char* midi, std::size_t n, int64_t ts) {
+      cb(libremidi::message{{midi, midi + n}, ts});
+      return stdx::error{};
+    });
+  };
+  c2.get_timestamp = base_conf.get_timestamp;
+  c2.on_error = base_conf.on_error;
+  c2.on_warning = base_conf.on_warning;
+  c2.ignore_sysex = base_conf.ignore_sysex;
+  c2.ignore_timing = base_conf.ignore_timing;
+  c2.ignore_sensing = base_conf.ignore_sensing;
+  c2.timestamps = base_conf.timestamps;
+  return c2;
+}
+
+static libremidi::input_configuration
+convert_midi2_to_midi1_input_configuration(const ump_input_configuration& base_conf) noexcept
+{
+  libremidi::input_configuration c2;
+  c2.on_message = [cb = base_conf.on_message,
+                   converter = midi1_to_midi2{}](libremidi::message&& msg) mutable -> void {
+    converter.convert(
+        msg.bytes.data(), msg.bytes.size(), msg.timestamp,
+        [cb](const uint32_t* ump, std::size_t n, int64_t ts) {
+      if(n >= 4)
+      {
+        libremidi::ump u{ump[0],ump[1],ump[2],ump[3]};
+        u.timestamp = ts;
+        cb(std::move(u));
+      }
+      return stdx::error{};
+    });
+  };
+  c2.get_timestamp = base_conf.get_timestamp;
+  c2.on_error = base_conf.on_error;
+  c2.on_warning = base_conf.on_warning;
+  c2.ignore_sysex = base_conf.ignore_sysex;
+  c2.ignore_timing = base_conf.ignore_timing;
+  c2.ignore_sensing = base_conf.ignore_sensing;
+  c2.timestamps = base_conf.timestamps;
+  return c2;
+}
+
+static LIBREMIDI_INLINE std::unique_ptr<midi_in_api>
+make_midi_in(auto base_conf, std::any api_conf, auto backends)
 {
   std::unique_ptr<midi_in_api> ptr;
 
-  assert(base_conf.on_message);
+  assert(base_conf.on_message || base_conf.on_raw_data);
 
   auto from_api = [&]<typename T>(T& /*backend*/) mutable {
     if (auto conf = std::any_cast<typename T::midi_in_configuration>(&api_conf))
@@ -27,58 +79,199 @@ LIBREMIDI_INLINE auto make_midi_in(auto base_conf, std::any api_conf, auto backe
   return ptr;
 }
 
-LIBREMIDI_INLINE midi_in::midi_in(const input_configuration& base_conf) noexcept
+/// MIDI 1 helpers
+static LIBREMIDI_INLINE std::unique_ptr<midi_in_api>
+make_midi1_in(const input_configuration& base_conf)
 {
   for (const auto& api : available_apis())
   {
     try
     {
-      impl_ = make_midi_in(base_conf, midi_in_configuration_for(api), midi1::available_backends);
+      auto impl
+          = make_midi_in(base_conf, midi_in_configuration_for(api), midi1::available_backends);
+      if (impl)
+        return impl;
     }
     catch (const std::exception& e)
     {
     }
-
-    if (impl_)
-      return;
   }
-  if (!impl_)
-    impl_ = std::make_unique<midi_in_dummy>(input_configuration{}, dummy_configuration{});
+
+  // No MIDI 1 backend, try the MIDI 2 ones with a wrap:
+  {
+    auto c2 = convert_midi1_to_midi2_input_configuration(base_conf);
+    for (const auto& api : available_ump_apis())
+    {
+      try
+      {
+        auto impl = make_midi_in(c2, midi_in_configuration_for(api), midi2::available_backends);
+        if (impl)
+          return impl;
+      }
+      catch (const std::exception& e)
+      {
+      }
+    }
+  }
+
+  return std::make_unique<midi_in_dummy>(input_configuration{}, dummy_configuration{});
+}
+
+static LIBREMIDI_INLINE std::unique_ptr<midi_in_api>
+make_midi1_in(const input_configuration& base_conf, const std::any& api_conf, libremidi::API api)
+{
+  if (libremidi::is_midi1(api))
+  {
+    return make_midi_in(base_conf, api_conf, midi1::available_backends);
+  }
+  else if (libremidi::is_midi2(api))
+  {
+    auto c2 = convert_midi1_to_midi2_input_configuration(base_conf);
+    return make_midi_in(c2, api_conf, midi2::available_backends);
+  }
+  return {};
+}
+
+static LIBREMIDI_INLINE std::unique_ptr<midi_in_api>
+make_midi1_in(const input_configuration& base_conf, const std::any& api_conf)
+{
+  if (!api_conf.has_value())
+  {
+    return make_midi1_in(base_conf);
+  }
+  else if (auto api_p = std::any_cast<libremidi::API>(&api_conf))
+  {
+    if (*api_p == libremidi::API::UNSPECIFIED)
+    {
+      return make_midi1_in(base_conf);
+    }
+    else
+    {
+      return make_midi1_in(base_conf, midi_in_configuration_for(*api_p), *api_p);
+    }
+  }
+  else
+  {
+    if (auto api = libremidi::midi_api(api_conf); api == libremidi::API::UNSPECIFIED)
+      return {};
+    else
+      return make_midi1_in(base_conf, api_conf, libremidi::midi_api(api_conf));
+  }
+}
+
+/// MIDI 1 constructors
+LIBREMIDI_INLINE midi_in::midi_in(const input_configuration& base_conf) noexcept
+    : impl_{make_midi1_in(base_conf)}
+{
 }
 
 LIBREMIDI_INLINE
 midi_in::midi_in(input_configuration base_conf, std::any api_conf)
-    : impl_{make_midi_in(base_conf, api_conf, midi1::available_backends)}
+    : impl_{make_midi1_in(base_conf, api_conf)}
 {
   if (!impl_)
-    throw midi_exception("Could not open midi in for the given api");
+  {
+    error_handler e;
+    e.libremidi_handle_error(base_conf, "Could not open midi in for the given api");
+    impl_ = std::make_unique<midi_in_dummy>(input_configuration{}, dummy_configuration{});
+  }
 }
 
-LIBREMIDI_INLINE midi_in::midi_in(ump_input_configuration base_conf) noexcept
+/// MIDI 2 helpers
+static LIBREMIDI_INLINE std::unique_ptr<midi_in_api>
+make_midi2_in(const ump_input_configuration& base_conf)
 {
-  for (const auto& api : available_apis())
+  for (const auto& api : available_ump_apis())
   {
     try
     {
-      impl_ = make_midi_in(base_conf, midi_in_configuration_for(api), midi2::available_backends);
+      if (auto ret
+          = make_midi_in(base_conf, midi_in_configuration_for(api), midi2::available_backends))
+        return ret;
     }
     catch (const std::exception& e)
     {
     }
-
-    if (impl_)
-      return;
   }
-  if (!impl_)
-    impl_ = std::make_unique<midi_in_dummy>(input_configuration{}, dummy_configuration{});
+
+  // No MIDI 2 backend, try the MIDI 1 ones with a wrap:
+  {
+    auto c2 = convert_midi2_to_midi1_input_configuration(base_conf);
+    for (const auto& api : available_apis())
+    {
+      try
+      {
+        if (auto ret = make_midi_in(c2, midi_in_configuration_for(api), midi1::available_backends))
+          return ret;
+      }
+      catch (const std::exception& e)
+      {
+      }
+    }
+  }
+
+  return {};
+}
+
+static LIBREMIDI_INLINE std::unique_ptr<midi_in_api> make_midi2_in(
+    const ump_input_configuration& base_conf, const std::any& api_conf, libremidi::API api)
+{
+  if (is_midi2(api))
+  {
+    return make_midi_in(base_conf, api_conf, midi2::available_backends);
+  }
+  else if (is_midi1(api))
+  {
+    auto c2 = convert_midi2_to_midi1_input_configuration(base_conf);
+    return make_midi_in(c2, api_conf, midi1::available_backends);
+  }
+
+  return {};
+}
+
+static LIBREMIDI_INLINE std::unique_ptr<midi_in_api>
+make_midi2_in(const ump_input_configuration& base_conf, const std::any& api_conf)
+{
+  if (!api_conf.has_value())
+  {
+    return make_midi2_in(base_conf);
+  }
+  else if (auto api_p = std::any_cast<libremidi::API>(&api_conf))
+  {
+    if (*api_p == libremidi::API::UNSPECIFIED)
+    {
+      return make_midi2_in(base_conf);
+    }
+    else
+    {
+      return make_midi2_in(base_conf, midi_in_configuration_for(*api_p), *api_p);
+    }
+  }
+  else
+  {
+    if (auto api = libremidi::midi_api(api_conf); api == libremidi::API::UNSPECIFIED)
+      return {};
+    else
+      return make_midi2_in(base_conf, api_conf, libremidi::midi_api(api_conf));
+  }
+}
+
+/// MIDI 2 constructors
+LIBREMIDI_INLINE midi_in::midi_in(ump_input_configuration base_conf) noexcept
+    : impl_{make_midi2_in(base_conf)}
+{
 }
 
 LIBREMIDI_INLINE
 midi_in::midi_in(ump_input_configuration base_conf, std::any api_conf)
-    : impl_{make_midi_in(base_conf, api_conf, midi2::available_backends)}
+    : impl_{make_midi2_in(base_conf, api_conf)}
 {
   if (!impl_)
-    throw midi_exception("Could not open midi in for the given api");
+  {
+    error_handler e;
+    e.libremidi_handle_error(base_conf, "Could not open midi in for the given api");
+    impl_ = std::make_unique<midi_in_dummy>(input_configuration{}, dummy_configuration{});
+  }
 }
 
 LIBREMIDI_INLINE midi_in::~midi_in() = default;
@@ -91,9 +284,12 @@ LIBREMIDI_INLINE midi_in::midi_in(midi_in&& other) noexcept
 }
 
 LIBREMIDI_INLINE
-void midi_in::set_port_name(std::string_view portName)
+stdx::error midi_in::set_port_name(std::string_view portName)
 {
-  impl_->set_port_name(portName);
+  if(impl_->is_port_open())
+    return impl_->set_port_name(portName);
+
+  return std::errc::not_connected;
 }
 
 LIBREMIDI_INLINE midi_in& midi_in::operator=(midi_in&& other) noexcept
@@ -111,37 +307,50 @@ libremidi::API midi_in::get_current_api() const noexcept
 }
 
 LIBREMIDI_INLINE
-void midi_in::open_port(const input_port& port, std::string_view portName)
+stdx::error midi_in::open_port(const input_port& port, std::string_view portName)
 {
-  if (impl_->is_port_open())
-    return;
+  if (auto err = impl_->is_client_open(); err != stdx::error{})
+    return std::errc::not_connected;
 
-  if (impl_->open_port(port, portName))
+  if (impl_->is_port_open())
+    return std::errc::operation_not_supported;
+
+  auto ret = impl_->open_port(port, portName);
+  if (ret == stdx::error{})
   {
     impl_->connected_ = true;
     impl_->port_open_ = true;
   }
+  return ret;
 }
 
 LIBREMIDI_INLINE
-void midi_in::open_virtual_port(std::string_view portName)
+stdx::error midi_in::open_virtual_port(std::string_view portName)
 {
+  if (auto err = impl_->is_client_open(); err != stdx::error{})
+    return std::errc::not_connected;
+
   if (impl_->is_port_open())
-    return;
+    return std::errc::operation_not_supported;
 
-  if (impl_->open_virtual_port(portName))
-  {
+  auto ret = impl_->open_virtual_port(portName);
+  if (ret == stdx::error{})
     impl_->port_open_ = true;
-  }
+  return ret;
 }
 
 LIBREMIDI_INLINE
-void midi_in::close_port()
+stdx::error midi_in::close_port()
 {
-  impl_->close_port();
+  if (auto err = impl_->is_client_open(); err != stdx::error{})
+    return std::errc::not_connected;
+
+  auto ret = impl_->close_port();
 
   impl_->connected_ = false;
   impl_->port_open_ = false;
+
+  return ret;
 }
 
 LIBREMIDI_INLINE

include/libremidi/midi_out.cpp

@@ -10,7 +10,8 @@
 
 namespace libremidi
 {
-LIBREMIDI_INLINE auto make_midi_out(auto base_conf, std::any api_conf)
+static LIBREMIDI_INLINE std::unique_ptr<midi_out_api>
+make_midi_out_impl(auto base_conf, std::any api_conf)
 {
   std::unique_ptr<midi_out_api> ptr;
   auto from_api = [&]<typename T>(T& /*backend*/) mutable {
@@ -26,23 +27,66 @@ LIBREMIDI_INLINE auto make_midi_out(auto base_conf, std::any api_conf)
   return ptr;
 }
 
-LIBREMIDI_INLINE midi_out::midi_out(const output_configuration& base_conf) noexcept
+static LIBREMIDI_INLINE std::unique_ptr<midi_out_api>
+make_midi_out(const output_configuration& base_conf)
 {
   for (const auto& api : available_apis())
   {
     try
     {
-      impl_ = make_midi_out(base_conf, midi_out_configuration_for(api));
+      if (auto ret = make_midi_out_impl(base_conf, midi_out_configuration_for(api)))
+        return ret;
     }
     catch (const std::exception& e)
     {
     }
-
-    if (impl_)
-      return;
   }
-  if (!impl_)
-    impl_ = std::make_unique<midi_out_dummy>(output_configuration{}, dummy_configuration{});
+
+  for (const auto& api : available_ump_apis())
+  {
+    try
+    {
+      if (auto ret = make_midi_out_impl(base_conf, midi_out_configuration_for(api)))
+        return ret;
+    }
+    catch (const std::exception& e)
+    {
+    }
+  }
+
+  return std::make_unique<midi_out_dummy>(output_configuration{}, dummy_configuration{});
+}
+
+static LIBREMIDI_INLINE std::unique_ptr<midi_out_api>
+make_midi_out(const output_configuration& base_conf, const std::any& api_conf)
+{
+  if (!api_conf.has_value())
+  {
+    return make_midi_out(base_conf);
+  }
+  else if (auto api_p = std::any_cast<libremidi::API>(&api_conf))
+  {
+    if (*api_p == libremidi::API::UNSPECIFIED)
+    {
+      return make_midi_out(base_conf);
+    }
+    else
+    {
+      return make_midi_out_impl(base_conf, midi_out_configuration_for(*api_p));
+    }
+  }
+  else
+  {
+    if (auto api = libremidi::midi_api(api_conf); api == libremidi::API::UNSPECIFIED)
+      return make_midi_out(base_conf);
+    else
+      return make_midi_out_impl(base_conf, api_conf);
+  }
+}
+
+LIBREMIDI_INLINE midi_out::midi_out(const output_configuration& base_conf) noexcept
+    : impl_{make_midi_out(base_conf)}
+{
 }
 
 LIBREMIDI_INLINE
@@ -50,7 +94,11 @@ midi_out::midi_out(output_configuration base_conf, std::any api_conf)
     : impl_{make_midi_out(base_conf, api_conf)}
 {
   if (!impl_)
-    throw midi_exception("Could not open midi out for the given api");
+  {
+    error_handler e;
+    e.libremidi_handle_error(base_conf, "Could not open midi out for the given api");
+    impl_ = std::make_unique<midi_out_dummy>(output_configuration{}, dummy_configuration{});
+  }
 }
 
 LIBREMIDI_INLINE midi_out::~midi_out() = default;
@@ -61,6 +109,7 @@ LIBREMIDI_INLINE midi_out::midi_out(midi_out&& other) noexcept
   other.impl_
       = std::make_unique<libremidi::midi_out_dummy>(output_configuration{}, dummy_configuration{});
 }
+
 LIBREMIDI_INLINE midi_out& midi_out::operator=(midi_out&& other) noexcept
 {
   this->impl_ = std::move(other.impl_);
@@ -70,9 +119,12 @@ LIBREMIDI_INLINE midi_out& midi_out::operator=(midi_out&& other) noexcept
 }
 
 LIBREMIDI_INLINE
-void midi_out::set_port_name(std::string_view portName) const
+stdx::error midi_out::set_port_name(std::string_view portName) const
 {
-  impl_->set_port_name(portName);
+  if(impl_->is_port_open())
+    return impl_->set_port_name(portName);
+
+  return std::errc::not_connected;
 }
 
 LIBREMIDI_INLINE
@@ -82,36 +134,48 @@ libremidi::API midi_out::get_current_api() const noexcept
 }
 
 LIBREMIDI_INLINE
-void midi_out::open_port(const output_port& port, std::string_view portName) const
+stdx::error midi_out::open_port(const output_port& port, std::string_view portName) const
 {
-  if (impl_->is_port_open())
-    return;
+  if (auto err = impl_->is_client_open(); err != stdx::error{})
+    return std::errc::not_connected;
 
-  if (impl_->open_port(port, portName))
+  if (impl_->is_port_open())
+    return std::errc::operation_not_supported;
+
+  auto ret = impl_->open_port(port, portName);
+  if (ret == stdx::error{})
   {
     impl_->connected_ = true;
     impl_->port_open_ = true;
   }
+  return ret;
 }
 
 LIBREMIDI_INLINE
-void midi_out::open_virtual_port(std::string_view portName) const
+stdx::error midi_out::open_virtual_port(std::string_view portName) const
 {
+  if (auto err = impl_->is_client_open(); err != stdx::error{})
+    return std::errc::not_connected;
+
   if (impl_->is_port_open())
-    return;
+    return std::errc::operation_not_supported;
 
-  if (impl_->open_virtual_port(portName))
-  {
+  auto ret = impl_->open_virtual_port(portName);
+  if (ret == stdx::error{})
     impl_->port_open_ = true;
-  }
+  return ret;
 }
 
 LIBREMIDI_INLINE
-void midi_out::close_port() const
+stdx::error midi_out::close_port() const
 {
-  impl_->close_port();
+  if (auto err = impl_->is_client_open(); err != stdx::error{})
+    return std::errc::not_connected;
+
+  auto ret = impl_->close_port();
   impl_->connected_ = false;
   impl_->port_open_ = false;
+  return ret;
 }
 
 LIBREMIDI_INLINE
@@ -127,89 +191,136 @@ bool midi_out::is_port_connected() const noexcept
 }
 
 LIBREMIDI_INLINE
-void midi_out::send_message(const libremidi::message& message) const
+stdx::error midi_out::send_message(const libremidi::message& message) const
 {
-  send_message(message.bytes.data(), message.bytes.size());
+  return send_message(message.bytes.data(), message.bytes.size());
 }
 
 LIBREMIDI_INLINE
-void midi_out::send_message(std::span<const unsigned char> message) const
+stdx::error midi_out::send_message(std::span<const unsigned char> message) const
 {
-  send_message(message.data(), message.size());
+  return send_message(message.data(), message.size());
 }
 
 LIBREMIDI_INLINE
-void midi_out::send_message(unsigned char b0) const
+stdx::error midi_out::send_message(unsigned char b0) const
 {
-  send_message(&b0, 1);
+  return send_message(&b0, 1);
 }
 
 LIBREMIDI_INLINE
-void midi_out::send_message(unsigned char b0, unsigned char b1) const
+stdx::error midi_out::send_message(unsigned char b0, unsigned char b1) const
 {
-  send_message(std::to_array({b0, b1}));
+  return send_message(std::to_array({b0, b1}));
 }
 
 LIBREMIDI_INLINE
-void midi_out::send_message(unsigned char b0, unsigned char b1, unsigned char b2) const
+stdx::error midi_out::send_message(unsigned char b0, unsigned char b1, unsigned char b2) const
 {
-  send_message(std::to_array({b0, b1, b2}));
+  return send_message(std::to_array({b0, b1, b2}));
 }
 
 LIBREMIDI_INLINE
-void midi_out::send_message(const unsigned char* message, size_t size) const
+stdx::error midi_out::send_message(const unsigned char* message, size_t size) const
 {
 #if defined(LIBREMIDI_ASSERTIONS)
   assert(size > 0);
 #endif
 
-  impl_->send_message(message, size);
+  return impl_->send_message(message, size);
 }
 
 LIBREMIDI_INLINE
-void midi_out::send_ump(const uint32_t* message, size_t size) const
+int64_t midi_out::current_time()
+{
+  return impl_->current_time();
+}
+
+LIBREMIDI_INLINE
+stdx::error midi_out::schedule_message(int64_t ts, const unsigned char* message, size_t size) const
+{
+#if defined(LIBREMIDI_ASSERTIONS)
+  assert(size > 0);
+#endif
+
+  return impl_->schedule_message(ts, message, size);
+}
+
+LIBREMIDI_INLINE
+stdx::error midi_out::send_ump(const uint32_t* message, size_t size) const
 {
 #if defined(LIBREMIDI_ASSERTIONS)
   assert(size > 0);
   assert(size <= 4);
 #endif
 
-  impl_->send_ump(message, size);
+  return impl_->send_ump(message, size);
 }
 LIBREMIDI_INLINE
-void midi_out::send_ump(const libremidi::ump& message) const
+stdx::error midi_out::send_ump(const libremidi::ump& message) const
 {
-  send_ump(message.data, message.size());
+  return send_ump(message.data, message.size());
 }
 
 LIBREMIDI_INLINE
-void midi_out::send_ump(std::span<const uint32_t> message) const
+stdx::error midi_out::send_ump(std::span<const uint32_t> message) const
 {
-  send_ump(message.data(), message.size());
+  return send_ump(message.data(), message.size());
 }
 
 LIBREMIDI_INLINE
-void midi_out::send_ump(uint32_t b0) const
+stdx::error midi_out::send_ump(uint32_t b0) const
 {
-  send_ump(&b0, 1);
+  return send_ump(&b0, 1);
 }
 
 LIBREMIDI_INLINE
-void midi_out::send_ump(uint32_t b0, uint32_t b1) const
+stdx::error midi_out::send_ump(uint32_t b0, uint32_t b1) const
 {
-  send_ump(std::to_array({b0, b1}));
+  return send_ump(std::to_array({b0, b1}));
 }
 
 LIBREMIDI_INLINE
-void midi_out::send_ump(uint32_t b0, uint32_t b1, uint32_t b2) const
+stdx::error midi_out::send_ump(uint32_t b0, uint32_t b1, uint32_t b2) const
 {
-  send_ump(std::to_array({b0, b1, b2}));
+  return send_ump(std::to_array({b0, b1, b2}));
 }
 
 LIBREMIDI_INLINE
-void midi_out::send_ump(uint32_t b0, uint32_t b1, uint32_t b2, uint32_t b3) const
+stdx::error midi_out::send_ump(uint32_t b0, uint32_t b1, uint32_t b2, uint32_t b3) const
 {
-  send_ump(std::to_array({b0, b1, b2, b3}));
+  return send_ump(std::to_array({b0, b1, b2, b3}));
 }
 
+LIBREMIDI_INLINE
+stdx::error midi_out::send_ump(int32_t b0) const
+{
+  return send_ump(reinterpret_cast<uint32_t*>(&b0), 1);
+}
+
+LIBREMIDI_INLINE
+stdx::error midi_out::send_ump(int64_t b01) const
+{
+  auto ptr = reinterpret_cast<uint32_t*>(&b01);
+  uint32_t msg[2]{ptr[1], ptr[0]};
+  return send_ump(msg, 2);
+}
+
+LIBREMIDI_INLINE
+stdx::error midi_out::send_ump(uint64_t b01) const
+{
+  auto ptr = reinterpret_cast<uint32_t*>(&b01);
+  uint32_t msg[2]{ptr[1], ptr[0]};
+  return send_ump(msg, 2);
+}
+
+LIBREMIDI_INLINE
+stdx::error midi_out::schedule_ump(int64_t ts, const uint32_t* message, size_t size) const
+{
+#if defined(LIBREMIDI_ASSERTIONS)
+  assert(size > 0);
+#endif
+
+  return impl_->schedule_ump(ts, message, size);
+}
 }

include/libremidi/observer.cpp

@@ -7,7 +7,37 @@
 
 namespace libremidi
 {
-LIBREMIDI_INLINE auto make_observer(auto base_conf, std::any api_conf)
+
+static LIBREMIDI_INLINE std::unique_ptr<observer_api> make_observer(auto base_conf)
+{
+  for (const auto& api : available_apis())
+  {
+    try
+    {
+      if (auto impl_ = make_observer(base_conf, observer_configuration_for(api)))
+        return impl_;
+    }
+    catch (const std::exception& e)
+    {
+    }
+  }
+
+  for (const auto& api : available_ump_apis())
+  {
+    try
+    {
+      if (auto impl_ = make_observer(base_conf, observer_configuration_for(api)))
+        return impl_;
+    }
+    catch (const std::exception& e)
+    {
+    }
+  }
+
+  return std::make_unique<observer_dummy>(observer_configuration{}, dummy_configuration{});
+}
+
+LIBREMIDI_INLINE auto make_observer_impl(auto base_conf, std::any api_conf)
 {
   std::unique_ptr<observer_api> ptr;
   auto from_api = [&]<typename T>(T& /*backend*/) mutable {
@@ -23,30 +53,46 @@ LIBREMIDI_INLINE auto make_observer(auto base_conf, std::any api_conf)
   return ptr;
 }
 
-LIBREMIDI_INLINE observer::observer(const observer_configuration& base_conf) noexcept
+LIBREMIDI_INLINE std::unique_ptr<observer_api> make_observer(auto base_conf, std::any api_conf)
 {
-  for (const auto& api : available_apis())
+  if (!api_conf.has_value())
   {
-    try
-    {
-      impl_ = make_observer(base_conf, observer_configuration_for(api));
+    return make_observer(base_conf);
   }
-    catch (const std::exception& e)
+  else if (auto api_p = std::any_cast<libremidi::API>(&api_conf))
   {
+    if (*api_p == libremidi::API::UNSPECIFIED)
+    {
+      return make_observer(base_conf);
     }
+    else
+    {
+      return make_observer_impl(base_conf, observer_configuration_for(*api_p));
+    }
+  }
+  else
+  {
+    if (auto api = libremidi::midi_api(api_conf); api == libremidi::API::UNSPECIFIED)
+      return {};
+    else
+      return make_observer_impl(base_conf, api_conf);
+  }
+}
 
-    if (impl_)
-      return;
-  }
-  if (!impl_)
-    impl_ = std::make_unique<observer_dummy>(observer_configuration{}, dummy_configuration{});
+LIBREMIDI_INLINE observer::observer(const observer_configuration& base_conf) noexcept
+    : impl_{make_observer(base_conf)}
+{
 }
 
 LIBREMIDI_INLINE observer::observer(observer_configuration base_conf, std::any api_conf)
     : impl_{make_observer(base_conf, api_conf)}
 {
   if (!impl_)
-    throw midi_exception("Could not open observer for the given API");
+  {
+    error_handler e;
+    e.libremidi_handle_error(base_conf, "Could not open observer for the given api");
+    impl_ = std::make_unique<observer_dummy>(observer_configuration{}, dummy_configuration{});
+  }
 }
 
 LIBREMIDI_INLINE observer::observer(observer&& other) noexcept

include/libremidi/observer_configuration.hpp

@@ -22,22 +22,22 @@ struct LIBREMIDI_EXPORT port_information
   // PipeWire: unused
   // WinMM: unused
   // WinUWP: unused
-  client_handle client;
+  client_handle client = static_cast<client_handle>(-1);
 
   // ALSA Raw: { uint16_t card, device, sub, padding; }
   // ALSA Seq: { uint32_t client, uint32_t port; }
-  // CoreMIDI: MidiObjectRef
+  // CoreMIDI: MidiObjectRef's kMIDIPropertyUniqueID (uint32_t)
   // WebMIDI: unused
   // JACK: jack_port_id_t
   // PipeWire: port.id
   // WinMM: unset, identified by port_name
   // WinUWP: unused
-  port_handle port;
+  port_handle port = static_cast<port_handle>(-1);
 
-  std::string manufacturer;
-  std::string device_name;
-  std::string port_name;
-  std::string display_name;
+  std::string manufacturer{};
+  std::string device_name{};
+  std::string port_name{};
+  std::string display_name{};
 
   bool operator==(const port_information& other) const noexcept = default;
   std::strong_ordering operator<=>(const port_information& other) const noexcept = default;
@@ -59,12 +59,12 @@ using output_port_callback = std::function<void(const output_port&)>;
 struct observer_configuration
 {
   midi_error_callback on_error{};
-  midi_error_callback on_warning{};
+  midi_warning_callback on_warning{};
 
-  input_port_callback input_added;
-  input_port_callback input_removed;
-  output_port_callback output_added;
-  output_port_callback output_removed;
+  input_port_callback input_added{};
+  input_port_callback input_removed{};
+  output_port_callback output_added{};
+  output_port_callback output_removed{};
 
   // Observe hardware ports
   uint32_t track_hardware : 1 = true;

include/libremidi/output_configuration.hpp

@@ -3,8 +3,6 @@
 #include <libremidi/error.hpp>
 #include <libremidi/input_configuration.hpp>
 
-#include <string>
-
 namespace libremidi
 {
 struct output_configuration
@@ -15,7 +13,7 @@ struct output_configuration
     best to set the error callback function before opening a port.
   */
   midi_error_callback on_error{};
-  midi_error_callback on_warning{};
+  midi_warning_callback on_warning{};
 
   //! Timestamp mode for the timestamps passed to schedule_message
   uint32_t timestamps : 3 = timestamp_mode::Absolute;