bridge_simple: Improve renegotiation success rate.

When making channels compatible the bridge_simple module
will renegotiate one to better match the other. Some
endpoints incorrectly terminate the call if this process
fails.

To better handle this scenario the audio streams present
on the new requested topology will include any existing
negotiated formats that happen to exist on the first
valid audio stream. This ensures formats are persent that
are known to be acceptable to the remote endpoint.

ASTERISK-27259

Change-Id: I8fc0cc03e8bcfd0be8302f13b9f32d8268977f43

bridges/bridge_simple.c

@@ -113,6 +113,58 @@ static struct ast_bridge_technology simple_bridge = {
 	.stream_topology_changed = simple_bridge_stream_topology_changed,
 };
 
+static void simple_bridge_request_stream_topology_change(struct ast_channel *chan,
+	struct ast_stream_topology *requested_topology)
+{
+	struct ast_stream_topology *existing_topology = ast_channel_get_stream_topology(chan);
+	struct ast_stream *stream;
+	struct ast_format_cap *audio_formats = NULL;
+	struct ast_stream_topology *new_topology;
+	int i;
+
+	/* We find an existing stream with negotiated audio formats that we can place into
+	 * any audio streams in the new topology to ensure that negotiation succeeds. Some
+	 * endpoints incorrectly terminate the call if SDP negotiation fails.
+	 */
+	for (i = 0; i < ast_stream_topology_get_count(existing_topology); ++i) {
+		stream = ast_stream_topology_get_stream(existing_topology, i);
+
+		if (ast_stream_get_type(stream) != AST_MEDIA_TYPE_AUDIO ||
+			ast_stream_get_state(stream) == AST_STREAM_STATE_REMOVED) {
+			continue;
+		}
+
+		audio_formats = ast_stream_get_formats(stream);
+		break;
+	}
+
+	if (!audio_formats) {
+		ast_channel_request_stream_topology_change(chan, requested_topology, &simple_bridge);
+		return;
+	}
+
+	new_topology = ast_stream_topology_clone(requested_topology);
+	if (!new_topology) {
+		ast_channel_request_stream_topology_change(chan, requested_topology, &simple_bridge);
+		return;
+	}
+
+	for (i = 0; i < ast_stream_topology_get_count(new_topology); ++i) {
+		stream = ast_stream_topology_get_stream(new_topology, i);
+
+		if (ast_stream_get_type(stream) != AST_MEDIA_TYPE_AUDIO ||
+			ast_stream_get_state(stream) == AST_STREAM_STATE_REMOVED) {
+			continue;
+		}
+
+		ast_format_cap_append_from_cap(ast_stream_get_formats(stream), audio_formats, AST_MEDIA_TYPE_AUDIO);
+	}
+
+	ast_channel_request_stream_topology_change(chan, new_topology, &simple_bridge);
+
+	ast_stream_topology_free(new_topology);
+}
+
 static void simple_bridge_stream_topology_changed(struct ast_bridge *bridge,
 		struct ast_bridge_channel *bridge_channel)
 {
@@ -135,9 +187,9 @@ static void simple_bridge_stream_topology_changed(struct ast_bridge *bridge,
 
 	/* Align topologies according to size or first channel to join */
 	if (ast_stream_topology_get_count(t0) < ast_stream_topology_get_count(t1)) {
-		ast_channel_request_stream_topology_change(c0, t1, &simple_bridge);
+		simple_bridge_request_stream_topology_change(c0, t1);
 	} else {
-		ast_channel_request_stream_topology_change(c1, t0, &simple_bridge);
+		simple_bridge_request_stream_topology_change(c1, t0);
 	}
 }