Enumerate devices on linux

launchpad_test.go

@@ -15,10 +15,7 @@ func TestLaunchpad(t *testing.T) {
 	// For the launchpad MIDI reference, see https://d19ulaff0trnck.cloudfront.net/sites/default/files/novation/downloads/4080/launchpad-programmers-reference.pdf
 	// t.SkipNow()
 
-	device := &Device{
-		Name:      "hw:0,0,0",
-		QueueSize: 0,
-	}
+	device := &Device{ID: "hw:0"}
 	if err := device.Open(); err != nil {
 		t.Fatal(err)
 	}

list_test.go

@@ -0,0 +1,19 @@
+package midi
+
+import (
+	"fmt"
+	"testing"
+)
+
+func TestDevices(t *testing.T) {
+	devices, err := Devices()
+	if err != nil {
+		t.Fatal(err)
+	}
+	for i, d := range devices {
+		if d == nil {
+			continue
+		}
+		fmt.Printf("device %d: %#v\n", i, *d)
+	}
+}

midi_linux.c

@@ -1,6 +1,5 @@
 // +build cgo
 #include <assert.h>
-#include <errno.h>
 #include <stddef.h>
 
 #include <alsa/asoundlib.h>

midi_linux.go

@@ -2,6 +2,7 @@
 // package for talking to midi devices in Go.
 package midi
 
+// #include <alsa/asoundlib.h>
 // #include <stddef.h>
 // #include <stdlib.h>
 // #include "midi_linux.h"
@@ -11,25 +12,41 @@ import "C"
 import (
 	"fmt"
 	"os"
+	"unsafe"
 
 	"github.com/pkg/errors"
 )
 
 // Packet is a MIDI packet.
 type Packet [3]byte
 
+// DeviceType is a flag that says if a device is an input, an output, or duplex.
+type DeviceType int
+
+const (
+	DeviceInput DeviceType = iota
+	DeviceOutput
+	DeviceDuplex
+)
+
 // Device provides an interface for MIDI devices.
 type Device struct {
+	ID        string
 	Name      string
 	QueueSize int
+	Type      DeviceType
 
 	conn C.Midi
-	buf  []byte
 }
 
 // Open opens a MIDI device.
 func (d *Device) Open() error {
-	result := C.Midi_open(C.CString(d.Name))
+	var (
+		id     = C.CString(d.ID)
+		result = C.Midi_open(id)
+	)
+	defer C.free(unsafe.Pointer(id))
+
 	if result.error != 0 {
 		return errors.Errorf("error opening device %d", result.error)
 	}
@@ -75,6 +92,160 @@ func (d *Device) Read(buf []byte) (int, error) {
 
 // Write writes data to a MIDI device.
 func (d *Device) Write(buf []byte) (int, error) {
-	n, err := C.Midi_write(d.conn, C.CString(string(buf)), C.size_t(len(buf)))
+	cs := C.CString(string(buf))
+	n, err := C.Midi_write(d.conn, cs, C.size_t(len(buf)))
+	C.free(unsafe.Pointer(cs))
 	return int(n), err
 }
+
+type Stream struct {
+	Name string
+}
+
+func Devices() ([]*Device, error) {
+	var card C.int = -1
+
+	if rc := C.snd_card_next(&card); rc != 0 {
+		return nil, alsaMidiError(rc)
+	}
+	if card < 0 {
+		return nil, errors.New("no sound card found")
+	}
+	devices := []*Device{}
+
+	for {
+		cardDevices, err := getCardDevices(card)
+		if err != nil {
+			return nil, err
+		}
+		if rc := C.snd_card_next(&card); rc != 0 {
+			return nil, alsaMidiError(rc)
+		}
+		if card < 0 {
+			break
+		}
+		devices = append(devices, cardDevices...)
+	}
+	return devices, nil
+}
+
+func getCardDevices(card C.int) ([]*Device, error) {
+	var (
+		ctl  *C.snd_ctl_t
+		name = C.CString(fmt.Sprintf("hw:%d", card))
+	)
+	defer C.free(unsafe.Pointer(name))
+
+	if rc := C.snd_ctl_open(&ctl, name, 0); rc != 0 {
+		return nil, alsaMidiError(rc)
+	}
+	var (
+		cardDevices       = []*Device{}
+		device      C.int = -1
+	)
+	for {
+		if rc := C.snd_ctl_rawmidi_next_device(ctl, &device); rc != 0 {
+			return nil, alsaMidiError(rc)
+		}
+		if device < 0 {
+			break
+		}
+		deviceDevices, err := getDeviceDevices(ctl, card, C.uint(device))
+		if err != nil {
+			return nil, err
+		}
+		cardDevices = append(cardDevices, deviceDevices...)
+	}
+	if rc := C.snd_ctl_close(ctl); rc != 0 {
+		return nil, alsaMidiError(rc)
+	}
+	return cardDevices, nil
+}
+
+func getDeviceDevices(ctl *C.snd_ctl_t, card C.int, device C.uint) ([]*Device, error) {
+	var info *C.snd_rawmidi_info_t
+	C.snd_rawmidi_info_malloc(&info)
+	C.snd_rawmidi_info_set_device(info, device)
+
+	defer C.snd_rawmidi_info_free(info)
+
+	// Get inputs.
+	var subsIn C.uint
+	C.snd_rawmidi_info_set_stream(info, C.SND_RAWMIDI_STREAM_INPUT)
+	if rc := C.snd_ctl_rawmidi_info(ctl, info); rc != 0 {
+		return nil, alsaMidiError(rc)
+	}
+	subsIn = C.snd_rawmidi_info_get_subdevices_count(info)
+
+	// Get outputs.
+	var subsOut C.uint
+	C.snd_rawmidi_info_set_stream(info, C.SND_RAWMIDI_STREAM_OUTPUT)
+	if rc := C.snd_ctl_rawmidi_info(ctl, info); rc != 0 {
+		return nil, alsaMidiError(rc)
+	}
+	subsOut = C.snd_rawmidi_info_get_subdevices_count(info)
+
+	// List subdevices.
+	var subs C.uint
+	if subsIn > subsOut {
+		subs = subsIn
+	} else {
+		subs = subsOut
+	}
+	if subs == C.uint(0) {
+		return nil, errors.New("no streams")
+	}
+	devices := []*Device{}
+
+	for sub := C.uint(0); sub < subs; sub++ {
+		subDevice, err := getSubdevice(ctl, info, card, device, sub, subsIn, subsOut)
+		if err != nil {
+			return nil, err
+		}
+		devices = append(devices, subDevice)
+	}
+	return devices, nil
+}
+
+func getSubdevice(ctl *C.snd_ctl_t, info *C.snd_rawmidi_info_t, card C.int, device, sub, subsIn, subsOut C.uint) (*Device, error) {
+	if sub < subsIn {
+		C.snd_rawmidi_info_set_stream(info, C.SND_RAWMIDI_STREAM_INPUT)
+	} else {
+		C.snd_rawmidi_info_set_stream(info, C.SND_RAWMIDI_STREAM_OUTPUT)
+	}
+	C.snd_rawmidi_info_set_subdevice(info, sub)
+	if rc := C.snd_ctl_rawmidi_info(ctl, info); rc != 0 {
+		return nil, alsaMidiError(rc)
+	}
+	var (
+		name    = C.GoString(C.snd_rawmidi_info_get_name(info))
+		subName = C.GoString(C.snd_rawmidi_info_get_subdevice_name(info))
+	)
+	var dt DeviceType
+	if sub < subsIn && sub >= subsOut {
+		dt = DeviceInput
+	} else if sub >= subsIn && sub < subsOut {
+		dt = DeviceOutput
+	} else {
+		dt = DeviceDuplex
+	}
+	if sub == 0 && len(subName) > 0 && subName[0] == 0 {
+		return &Device{
+			ID:   fmt.Sprintf("hw:%d,%d", card, device),
+			Name: name,
+			Type: dt,
+		}, nil
+	}
+	return &Device{
+		ID:   fmt.Sprintf("hw:%d,%d,%d", card, device, sub),
+		Name: subName,
+		Type: dt,
+	}, nil
+}
+
+func alsaMidiError(code C.int) error {
+	if code == C.int(0) {
+		return nil
+	}
+	return errors.New(C.GoString(C.snd_strerror(code)))
+}