Optional Bluetooth LE advertisement for BLE-MIDI

doc/bluealsa.8.rst

@@ -6,7 +6,7 @@ bluealsa
 Bluetooth Audio ALSA Backend
 ----------------------------
 
-:Date: July 2023
+:Date: January 2024
 :Manual section: 8
 :Manual group: System Manager's Manual
 :Version: $VERSION$
@@ -20,7 +20,7 @@ DESCRIPTION
 ===========
 
 **bluealsa** is a Linux daemon to give applications access to Bluetooth audio
-streams using the Bluetooth A2DP, HFP and/or HSP profiles.
+streams using the Bluetooth A2DP, HFP, HSP and/or BLE-MIDI profiles.
 It provides a D-Bus API to applications, and can be used by ALSA applications
 via libasound plugins (see **bluealsa-plugins(7)** for details).
 
@@ -246,6 +246,9 @@ OPTIONS
     - **standard** - standard quality (44.1 kHz: 606 kbps, 48 kHz: 660 kbps)
     - **high** - high quality (44.1 kHz: 909 kbps, 48 kHz: 990 kbps)
 
+--midi-advertisement
+    Advertise BLE-MIDI service using Bluetooth LE advertising.
+
 --xapl-resp-name=NAME
     Set the product name send in the XAPL response message.
     By default, the name is set as "BlueALSA".
@@ -260,10 +263,12 @@ Profiles
 --------
 
 **bluealsa** provides support for Bluetooth Advanced Audio Distribution Profile
-(A2DP), Hands-Free Profile (HFP) and Headset Profile (HSP).
+(A2DP), Hands-Free Profile (HFP), Headset Profile (HSP) and Bluetooth Low
+Energy MIDI (BLE-MIDI).
 A2DP profile is dedicated for streaming music (i.e., stereo, 48 kHz or more
 sampling frequency), while HFP and HSP for two-way voice transmission (mono, 8
-kHz or 16 kHz sampling frequency).
+kHz or 16 kHz sampling frequency). BLE-MIDI, on the other hand, is used for
+transmitting MIDI messages over Bluetooth LE.
 
 The Bluetooth audio profiles are not peer-to-peer; they each have a source or
 gateway role (a2dp-source, hfp-ag, or hsp-ag) and a sink or target role
@@ -314,13 +319,15 @@ The list of profile *NAME*-s accepted by the ``--profile=NAME`` option:
 - **hfp-hf** - Hands-Free
 - **hsp-ag** Headset Audio Gateway
 - **hsp-hs** - Headset
+- **midi** - Bluetooth LE MIDI
 
-The **hfp-ofono** is available only when **bluealsa** was compiled with oFono
-support. Enabling HFP over oFono will automatically disable **hfp-hf** and
-**hfp-ag**.
+The **hfp-ofono** and **midi** profiles are available only when **bluealsa**
+was compiled respectively with oFono and BLE-MIDI support.
 
-BlueZ permits only one service to register the HSP and HFP profiles, and that
-service is automatically registered with every HCI device.
+Enabling HFP over oFono will automatically disable **hfp-hf** and **hfp-ag**.
+Also, it is important to note that BlueZ permits only one service to register
+the HFP profile, and that service is automatically registered with every HCI
+device.
 
 For the A2DP profile, BlueZ allows each HCI device to be registered to a
 different service, so it is possible to have multiple instances of
@@ -452,7 +459,7 @@ Please add following lines to the BlueALSA D-Bus policy:
 COPYRIGHT
 =========
 
-Copyright (c) 2016-2023 Arkadiusz Bokowy.
+Copyright (c) 2016-2024 Arkadiusz Bokowy.
 
 The bluez-alsa project is licensed under the terms of the MIT license.
 

src/bluealsa-config.h

@@ -1,6 +1,6 @@
 /*
  * BlueALSA - bluealsa-config.h
- * Copyright (c) 2016-2023 Arkadiusz Bokowy
+ * Copyright (c) 2016-2024 Arkadiusz Bokowy
  *
  * This file is a part of bluez-alsa.
  *
@@ -128,6 +128,13 @@ struct ba_config {
 
 	} a2dp;
 
+#if ENABLE_MIDI
+	struct {
+		/* advertise BLE-MIDI via LE advertisement */
+		bool advertise;
+	} midi;
+#endif
+
 	/* BlueALSA supports 5 SBC qualities: low, medium, high, XQ and XQ+. The XQ
 	 * mode uses 44.1 kHz sampling rate, dual channel mode with bitpool 38, 16
 	 * blocks in frame, 8 frequency bands and allocation method Loudness, which

src/bluez-iface.h

@@ -1,6 +1,6 @@
 /*
  * BlueALSA - bluez-iface.h
- * Copyright (c) 2016-2023 Arkadiusz Bokowy
+ * Copyright (c) 2016-2024 Arkadiusz Bokowy
  *
  * This file is a part of bluez-alsa.
  *
@@ -69,6 +69,14 @@ OrgBluezGattService1Skeleton *org_bluez_gatt_service1_skeleton_new(
 		const GDBusInterfaceSkeletonVTable *vtable, void *userdata,
 		GDestroyNotify userdata_free_func);
 
+typedef struct {
+	GDBusInterfaceSkeletonEx parent;
+} OrgBluezLeadvertisement1Skeleton;
+
+OrgBluezLeadvertisement1Skeleton *org_bluez_leadvertisement1_skeleton_new(
+		const GDBusInterfaceSkeletonVTable *vtable, void *userdata,
+		GDestroyNotify userdata_free_func);
+
 #endif
 
 typedef struct {

src/bluez-iface.xml

@@ -1,5 +1,5 @@
 <!-- BlueALSA - bluez-iface.xml
-     Copyright (c) 2016-2023 Arkadiusz Bokowy
+     Copyright (c) 2016-2024 Arkadiusz Bokowy
 
      This file is a part of bluez-alsa.
 
@@ -40,6 +40,16 @@
 		<property name="Primary" type="b" access="read"/>
 	</interface>
 
+	<interface name="org.bluez.LEAdvertisement1">
+		<annotation name="org.gtk.GDBus.CPP.if" value="ENABLE_MIDI"/>
+		<method name="Release">
+		</method>
+		<property name="Type" type="s" access="read"/>
+		<property name="ServiceUUIDs" type="as" access="read"/>
+		<property name="Discoverable" type="b" access="read"/>
+		<property name="Includes" type="as" access="read"/>
+	</interface>
+
 	<interface name="org.bluez.MediaEndpoint1">
 		<method name="SelectConfiguration">
 			<arg direction="in" type="ay" name="capabilities"/>

src/bluez-midi.c

@@ -50,6 +50,7 @@
 struct bluez_midi_app {
 	/* D-Bus object registration paths */
 	char path[64];
+	char path_adv[64 + 8];
 	char path_service[64 + 8];
 	char path_char[64 + 16];
 	/* associated adapter */
@@ -69,14 +70,6 @@ struct bluez_midi_app {
  * D-Bus unique name of the BlueZ daemon. */
 static char bluez_dbus_unique_name[64] = "";
 
-static GVariant *variant_new_midi_service_uuid(void) {
-	return g_variant_new_string(BT_UUID_MIDI);
-}
-
-static GVariant *variant_new_midi_characteristic_uuid(void) {
-	return g_variant_new_string(BT_UUID_MIDI_CHAR);
-}
-
 static struct bluez_midi_app *bluez_midi_app_ref(struct bluez_midi_app *app) {
 	atomic_fetch_add_explicit(&app->ref_count, 1, memory_order_relaxed);
 	return app;
@@ -128,12 +121,69 @@ static struct ba_transport *bluez_midi_transport_new(
 	return t;
 }
 
+static void bluez_midi_advertisement_release(
+		GDBusMethodInvocation *inv, G_GNUC_UNUSED void *userdata) {
+	debug("Releasing MIDI LE advertisement: %s", ((struct bluez_midi_app *)userdata)->path);
+	g_object_unref(inv);
+}
+
+static GVariant *bluez_midi_advertisement_iface_get_property(
+		const char *property, G_GNUC_UNUSED GError **error, void *userdata) {
+	(void)userdata;
+
+	if (strcmp(property, "Type") == 0)
+		return g_variant_new_string("peripheral");
+	if (strcmp(property, "ServiceUUIDs") == 0) {
+		static const char *uuids[] = { BT_UUID_MIDI };
+		return g_variant_new_strv(uuids, ARRAYSIZE(uuids));
+	}
+	if (strcmp(property, "Discoverable") == 0)
+		/* advertise as general discoverable LE-only device */
+		return g_variant_new_boolean(TRUE);
+	if (strcmp(property, "Includes") == 0) {
+		const char *values[] = { "local-name" };
+		return g_variant_new_strv(values, ARRAYSIZE(values));
+	}
+
+	g_assert_not_reached();
+	return NULL;
+}
+
+static GDBusObjectSkeleton *bluez_midi_advertisement_skeleton_new(
+		struct bluez_midi_app *app) {
+
+	static const GDBusMethodCallDispatcher dispatchers[] = {
+		{ .method = "Release",
+			.sender = bluez_dbus_unique_name,
+			.handler = bluez_midi_advertisement_release },
+		{ 0 },
+	};
+
+	static const GDBusInterfaceSkeletonVTable vtable = {
+		.dispatchers = dispatchers,
+		.get_property = bluez_midi_advertisement_iface_get_property,
+	};
+
+	OrgBluezLeadvertisement1Skeleton *ifs_gatt_adv;
+	if ((ifs_gatt_adv = org_bluez_leadvertisement1_skeleton_new(&vtable,
+					app, (GDestroyNotify)bluez_midi_app_unref)) == NULL)
+		return NULL;
+
+	GDBusInterfaceSkeleton *ifs = G_DBUS_INTERFACE_SKELETON(ifs_gatt_adv);
+	GDBusObjectSkeleton *skeleton = g_dbus_object_skeleton_new(app->path_adv);
+	g_dbus_object_skeleton_add_interface(skeleton, ifs);
+	g_object_unref(ifs_gatt_adv);
+
+	bluez_midi_app_ref(app);
+	return skeleton;
+}
+
 static GVariant *bluez_midi_service_iface_get_property(
 		const char *property, G_GNUC_UNUSED GError **error,
 		G_GNUC_UNUSED void *userdata) {
 
 	if (strcmp(property, "UUID") == 0)
-		return variant_new_midi_service_uuid();
+		return g_variant_new_string(BT_UUID_MIDI);
 	if (strcmp(property, "Primary") == 0)
 		return g_variant_new_boolean(TRUE);
 
@@ -198,7 +248,7 @@ static void bluez_midi_characteristic_acquire_write(
 	}
 
 	int fds[2];
-	if (socketpair(AF_LOCAL, SOCK_SEQPACKET | SOCK_CLOEXEC | SOCK_NONBLOCK, 0, fds) == -1) {
+	if (socketpair(AF_UNIX, SOCK_SEQPACKET | SOCK_CLOEXEC | SOCK_NONBLOCK, 0, fds) == -1) {
 		error("Couldn't create BLE-MIDI char write socket pair: %s", strerror(errno));
 		goto fail;
 	}
@@ -258,7 +308,7 @@ static void bluez_midi_characteristic_acquire_notify(
 	}
 
 	int fds[2];
-	if (socketpair(AF_LOCAL, SOCK_SEQPACKET | SOCK_CLOEXEC | SOCK_NONBLOCK, 0, fds) == -1) {
+	if (socketpair(AF_UNIX, SOCK_SEQPACKET | SOCK_CLOEXEC | SOCK_NONBLOCK, 0, fds) == -1) {
 		error("Couldn't create BLE-MIDI char notify socket pair: %s", strerror(errno));
 		goto fail;
 	}
@@ -294,7 +344,7 @@ static GVariant *bluez_midi_characteristic_iface_get_property(
 	struct bluez_midi_app *app = userdata;
 
 	if (strcmp(property, "UUID") == 0)
-		return variant_new_midi_characteristic_uuid();
+		return g_variant_new_string(BT_UUID_MIDI_CHAR);
 	if (strcmp(property, "Service") == 0)
 		return g_variant_new_object_path(app->path_service);
 	if (strcmp(property, "WriteAcquired") == 0)
@@ -371,6 +421,59 @@ static void bluez_midi_app_register_finish(
 
 }
 
+static void bluez_midi_app_register(
+		struct ba_adapter *adapter, struct bluez_midi_app *app) {
+
+	GDBusMessage *msg;
+	msg = g_dbus_message_new_method_call(BLUEZ_SERVICE, adapter->bluez_dbus_path,
+			BLUEZ_IFACE_GATT_MANAGER, "RegisterApplication");
+
+	g_dbus_message_set_body(msg, g_variant_new("(oa{sv})", app->path, NULL));
+
+	debug("Registering MIDI GATT application: %s", app->path);
+	g_dbus_connection_send_message_with_reply(config.dbus, msg,
+			G_DBUS_SEND_MESSAGE_FLAGS_NONE, -1, NULL, NULL,
+			bluez_midi_app_register_finish, NULL);
+
+	g_object_unref(msg);
+}
+
+static void bluez_midi_app_advertise_finish(
+		GObject *source, GAsyncResult *result, G_GNUC_UNUSED void *userdata) {
+
+	GError *err = NULL;
+	GDBusMessage *rep;
+
+	if ((rep = g_dbus_connection_send_message_with_reply_finish(
+					G_DBUS_CONNECTION(source), result, &err)) != NULL)
+		g_dbus_message_to_gerror(rep, &err);
+
+	if (rep != NULL)
+		g_object_unref(rep);
+	if (err != NULL) {
+		error("Couldn't advertise MIDI GATT application: %s", err->message);
+		g_error_free(err);
+	}
+
+}
+
+static void bluez_midi_app_advertise(
+		struct ba_adapter *adapter, struct bluez_midi_app *app) {
+
+	GDBusMessage *msg;
+	msg = g_dbus_message_new_method_call(BLUEZ_SERVICE, adapter->bluez_dbus_path,
+			BLUEZ_IFACE_LE_ADVERTISING_MANAGER, "RegisterAdvertisement");
+
+	g_dbus_message_set_body(msg, g_variant_new("(oa{sv})", app->path_adv, NULL));
+
+	debug("Registering MIDI LE advertisement: %s", app->path);
+	g_dbus_connection_send_message_with_reply(config.dbus, msg,
+			G_DBUS_SEND_MESSAGE_FLAGS_NONE, -1, NULL, NULL,
+			bluez_midi_app_advertise_finish, NULL);
+
+	g_object_unref(msg);
+}
+
 GDBusObjectManagerServer *bluez_midi_app_new(
 		struct ba_adapter *adapter, const char *path) {
 
@@ -379,6 +482,7 @@ GDBusObjectManagerServer *bluez_midi_app_new(
 		return NULL;
 
 	snprintf(app->path, sizeof(app->path), "%s", path);
+	snprintf(app->path_adv, sizeof(app->path_adv), "%s/adv", path);
 	snprintf(app->path_service, sizeof(app->path_service), "%s/service", path);
 	snprintf(app->path_char, sizeof(app->path_char), "%s/char", app->path_service);
 	app->hci_dev_id = adapter->hci.dev_id;
@@ -404,19 +508,17 @@ GDBusObjectManagerServer *bluez_midi_app_new(
 	g_dbus_object_manager_server_export(manager, skeleton);
 	g_object_unref(skeleton);
 
-	g_dbus_object_manager_server_set_connection(manager, config.dbus);
-
-	GDBusMessage *msg;
-	msg = g_dbus_message_new_method_call(BLUEZ_SERVICE, adapter->bluez_dbus_path,
-			BLUEZ_IFACE_GATT_MANAGER, "RegisterApplication");
+	if (config.midi.advertise) {
+		skeleton = bluez_midi_advertisement_skeleton_new(app);
+		g_dbus_object_manager_server_export(manager, skeleton);
+		g_object_unref(skeleton);
+	}
 
-	g_dbus_message_set_body(msg, g_variant_new("(oa{sv})", path, NULL));
+	g_dbus_object_manager_server_set_connection(manager, config.dbus);
 
-	debug("Registering MIDI GATT application: %s", app->path);
-	g_dbus_connection_send_message_with_reply(config.dbus, msg,
-			G_DBUS_SEND_MESSAGE_FLAGS_NONE, -1, NULL, NULL,
-			bluez_midi_app_register_finish, NULL);
+	bluez_midi_app_register(adapter, app);
+	if (config.midi.advertise)
+		bluez_midi_app_advertise(adapter, app);
 
-	g_object_unref(msg);
 	return manager;
 }

src/main.c

@@ -179,6 +179,9 @@ int main(int argc, char **argv) {
 #if ENABLE_MP3LAME
 		{ "mp3-algorithm", required_argument, NULL, 12 },
 		{ "mp3-vbr-quality", required_argument, NULL, 13 },
+#endif
+#if ENABLE_MIDI
+		{ "midi-advertisement", no_argument, NULL, 22 },
 #endif
 		{ "xapl-resp-name", required_argument, NULL, 16 },
 		{ 0, 0, 0, 0 },
@@ -229,6 +232,9 @@ int main(int argc, char **argv) {
 #if ENABLE_MP3LAME
 					"  --mp3-algorithm=TYPE\t\tselect LAME encoder algorithm type\n"
 					"  --mp3-vbr-quality=MODE\tset LAME encoder VBR quality mode\n"
+#endif
+#if ENABLE_MIDI
+					"  --midi-advertisement\t\tenable LE advertisement for BLE-MIDI\n"
 #endif
 					"  --xapl-resp-name=NAME\t\tset product name used by XAPL\n"
 					"\nAvailable BT profiles:\n"
@@ -532,6 +538,12 @@ int main(int argc, char **argv) {
 		}
 #endif
 
+#if ENABLE_MIDI
+		case 22 /* --midi-advertisement */ :
+			config.midi.advertise = true;
+			break;
+#endif
+
 		case 16 /* --xapl-resp-name=NAME */ :
 			config.hfp.xapl_product_name = optarg;
 			break;