policy-node: make streams follow default sink/src changes

The motivation is to have both existing and new streams that have been
created without explicit target node, to be directed to the same devices
at all times. To achieve this:

Consider what find_node returns as the "default node".

Consider streams that auto+reconnect and don't have an explicit target,
as following default.  In rescan, if the default node has changed,
relink such streams to the new default.

Remove the old code that explicitly moved streams when the default.*
metadata changed, as it implements a similar thing but in a less robust
way (may fail to do what's intended, because the default device
metadata is commonly unset, or the metadata callback comes before
session_create has seen the new nodes).

Enable this feature based on "policy-node.streams-follow-default"
property. Allow setting the property also by loading the
streams-follow-default module. Enable it by default only for the
with-pulseaudio module group.

src/daemon/media-session.d/media-session.conf

@@ -30,6 +30,7 @@ modules = {
         #default-nodes		# restore default nodes
         #default-profile	# restore default profiles 
         #default-routes		# restore default route
+        #streams-follow-default	# move streams when default changes
         #alsa-seq		# alsa seq midi support
         #alsa-monitor		# alsa udev detection
         #bluez5			# bluetooth support
@@ -53,5 +54,6 @@ modules = {
         with-audio
         bluez5
         restore-stream
+        streams-follow-default
     ]
 }

src/examples/media-session/media-session.c

@@ -84,6 +84,7 @@ int sm_default_nodes_start(struct sm_media_session *sess);
 int sm_default_profile_start(struct sm_media_session *sess);
 int sm_default_routes_start(struct sm_media_session *sess);
 int sm_restore_stream_start(struct sm_media_session *sess);
+int sm_streams_follow_default_start(struct sm_media_session *sess);
 int sm_alsa_midi_start(struct sm_media_session *sess);
 int sm_v4l2_monitor_start(struct sm_media_session *sess);
 int sm_libcamera_monitor_start(struct sm_media_session *sess);
@@ -2227,6 +2228,7 @@ static const struct {
 	{ "default-profile", "restore default profiles", sm_default_profile_start, NULL },
 	{ "default-routes", "restore default route", sm_default_routes_start, NULL },
 	{ "restore-stream", "restore stream settings", sm_restore_stream_start, NULL },
+	{ "streams-follow-default", "move streams when default changes", sm_streams_follow_default_start, NULL },
 	{ "alsa-seq", "alsa seq midi support", sm_alsa_midi_start, NULL },
 	{ "alsa-monitor", "alsa card udev detection", sm_alsa_monitor_start, NULL },
 	{ "v4l2", "video for linux udev detection", sm_v4l2_monitor_start, NULL },

src/examples/media-session/policy-node.c

@@ -64,6 +64,8 @@ struct impl {
 	uint32_t default_audio_sink;
 	uint32_t default_audio_source;
 	uint32_t default_video_source;
+
+	bool streams_follow_default;
 };
 
 struct node {
@@ -560,6 +562,7 @@ static int rescan_node(struct impl *impl, struct node *n)
 	struct node *peer;
 	struct sm_object *obj;
 	uint32_t path_id;
+	bool follows_default;
 
 	if (!n->active) {
 		pw_log_debug(NAME " %p: node %d is not active", impl, n->id);
@@ -580,14 +583,23 @@ static int rescan_node(struct impl *impl, struct node *n)
 		return 0;
 	}
 
-	if (n->peer != NULL) {
+	info = n->obj->info;
+	props = info->props;
+
+	str = spa_dict_lookup(props, PW_KEY_NODE_DONT_RECONNECT);
+	reconnect = str ? !pw_properties_parse_bool(str) : true;
+
+	follows_default = (impl->streams_follow_default &&
+	                   n->type == NODE_TYPE_STREAM &&
+	                   reconnect &&
+	                   n->obj->target_node == NULL &&
+	                   spa_dict_lookup(props, PW_KEY_NODE_TARGET) == NULL);
+
+	if (n->peer != NULL && !follows_default) {
 		pw_log_debug(NAME " %p: node %d is already linked", impl, n->id);
 		return 0;
 	}
 
-	info = n->obj->info;
-	props = info->props;
-
 	if ((str = spa_dict_lookup(props, PW_KEY_STREAM_DONT_REMIX)) != NULL)
 		n->dont_remix = pw_properties_parse_bool(str);
 
@@ -627,9 +639,6 @@ static int rescan_node(struct impl *impl, struct node *n)
 	find.target = n;
 	find.exclusive = exclusive;
 
-	str = spa_dict_lookup(props, PW_KEY_NODE_DONT_RECONNECT);
-	reconnect = str ? !pw_properties_parse_bool(str) : true;
-
 	/* we always honour the target node asked for by the client */
 	path_id = SPA_ID_INVALID;
 	if ((str = spa_dict_lookup(props, PW_KEY_NODE_TARGET)) != NULL)
@@ -637,8 +646,22 @@ static int rescan_node(struct impl *impl, struct node *n)
 	if (path_id == SPA_ID_INVALID && n->obj->target_node != NULL)
 		path_id = find_device_for_name(impl, n->obj->target_node);
 
-	pw_log_info("trying to link node %d exclusive:%d reconnect:%d target:%d", n->id,
+	pw_log_info("trying to link node %d exclusive:%d reconnect:%d target:%d follows-default:%d", n->id,
-			exclusive, reconnect, path_id);
+	            exclusive, reconnect, path_id, follows_default);
+
+	if (n->peer != NULL) {
+		spa_list_for_each(peer, &impl->node_list, link)
+			find_node(&find, peer);
+
+		if (follows_default && find.node != NULL && find.node != n->peer) {
+			pw_log_debug(NAME " %p: node %d follows default, changed (%d -> %d)", impl, n->id,
+			             n->peer->id, find.node->id);
+			unlink_nodes(n, n->peer);
+		} else {
+			pw_log_debug(NAME " %p: node %d already linked (not changing)", impl, n->id);
+			return 0;
+		}
+	}
 
 	if (path_id != SPA_ID_INVALID) {
 		pw_log_debug(NAME " %p: target:%d", impl, path_id);
@@ -660,8 +683,11 @@ static int rescan_node(struct impl *impl, struct node *n)
 				path_id, reconnect);
 	}
 	if (path_id == SPA_ID_INVALID && (reconnect || n->connect_count == 0)) {
-		spa_list_for_each(peer, &impl->node_list, link)
+		if (find.node == NULL)
-			find_node(&find, peer);
+			spa_list_for_each(peer, &impl->node_list, link)
+				find_node(&find, peer);
+	} else {
+		find.node = NULL;
 	}
 
 	if (find.node == NULL) {
@@ -751,44 +777,6 @@ static int do_move_node(struct node *n, struct node *src, struct node *dst)
 	return 0;
 }
 
-static int move_node(struct impl *impl, uint32_t source, uint32_t target)
-{
-	struct node *n, *src_node, *dst_node;
-	const char *str;
-
-	if (source == SPA_ID_INVALID || target == SPA_ID_INVALID)
-		return 0;
-
-	/* find source and dest node */
-	if ((src_node = find_node_by_id(impl, source)) == NULL)
-		return -ENOENT;
-	if ((dst_node = find_node_by_id(impl, target)) == NULL)
-		return -ENOENT;
-
-	if (src_node == dst_node)
-		return 0;
-
-	pw_log_info("move %d -> %d", src_node->id, dst_node->id);
-
-	/* unlink all nodes from source and link to target */
-	spa_list_for_each(n, &impl->node_list, link) {
-		struct pw_node_info *info;
-
-		if (n->peer != src_node)
-			continue;
-
-		if ((info = n->obj->info) == NULL)
-			continue;
-
-		if ((str = spa_dict_lookup(info->props, PW_KEY_NODE_DONT_RECONNECT)) != NULL &&
-		    pw_properties_parse_bool(str))
-			continue;
-
-		do_move_node(n, src_node, dst_node);
-	}
-	return 0;
-}
-
 static int handle_move(struct impl *impl, struct node *src_node, struct node *dst_node)
 {
 	const char *str;
@@ -825,18 +813,26 @@ static int metadata_property(void *object, uint32_t subject,
 	uint32_t val = (key && value) ? (uint32_t)atoi(value) : SPA_ID_INVALID;
 
 	if (subject == PW_ID_CORE) {
+		bool changed = false;
+
 		if (key == NULL || strcmp(key, "default.audio.sink") == 0) {
-			move_node(impl, impl->default_audio_sink, val);
+			if (impl->default_audio_sink != val)
+				changed = true;
 			impl->default_audio_sink = val;
 		}
 		if (key == NULL || strcmp(key, "default.audio.source") == 0) {
-			move_node(impl, impl->default_audio_source, val);
+			if (impl->default_audio_source != val)
+				changed = true;
 			impl->default_audio_source = val;
 		}
 		if (key == NULL || strcmp(key, "default.video.source") == 0) {
-			move_node(impl, impl->default_video_source, val);
+			if (impl->default_video_source != val)
+				changed = true;
 			impl->default_video_source = val;
 		}
+
+		if (changed && impl->streams_follow_default)
+			sm_media_session_schedule_rescan(impl->session);
 	} else {
 		if (val != SPA_ID_INVALID && strcmp(key, "target.node") == 0) {
 			struct node *src_node, *dst_node;
@@ -859,6 +855,7 @@ static const struct pw_metadata_events metadata_events = {
 int sm_policy_node_start(struct sm_media_session *session)
 {
 	struct impl *impl;
+	const char *flag;
 
 	impl = calloc(1, sizeof(struct impl));
 	if (impl == NULL)
@@ -872,6 +869,9 @@ int sm_policy_node_start(struct sm_media_session *session)
 	impl->default_audio_source = SPA_ID_INVALID;
 	impl->default_video_source = SPA_ID_INVALID;
 
+	flag = pw_properties_get(session->props, NAME ".streams-follow-default");
+	impl->streams_follow_default = (flag != NULL && pw_properties_parse_bool(flag));
+
 	spa_list_init(&impl->node_list);
 
 	sm_media_session_add_listener(impl->session,

src/examples/media-session/streams-follow-default.c

@@ -0,0 +1,46 @@
+/* PipeWire
+ *
+ * Copyright © 2021 Pauli Virtanen
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ */
+
+/*
+ * Instruct policy-node to move streams when the default sink/sources (either explicitly set
+ * via metadata, or determined from priority) changes, and the stream does not have an
+ * explicitly specified target node.
+ *
+ * This is done by just setting a session property flag, and policy-node does the rest.
+ */
+
+#include "config.h"
+
+#include "pipewire/pipewire.h"
+#include "extensions/metadata.h"
+
+#include "media-session.h"
+
+#define KEY_NAME	"policy-node.streams-follow-default"
+
+int sm_streams_follow_default_start(struct sm_media_session *session)
+{
+	pw_properties_set(session->props, KEY_NAME, "true");
+	return 0;
+}

src/examples/meson.build

@@ -85,6 +85,7 @@ if alsa_dep.found()
     'media-session/restore-stream.c',
     'media-session/policy-ep.c',
     'media-session/policy-node.c',
+    'media-session/streams-follow-default.c',
     'media-session/v4l2-monitor.c',
     'media-session/v4l2-endpoint.c',
     'media-session/libcamera-monitor.c',