bridge_softmix: Use removed stream spots when renegotiating.

Streams are never truly removed in SDP, they still occupy
a location within the SDP. This location can be reused by
another stream if it so chooses.

This change takes advantage of this such that if a new stream
is needing to be added for a new participant any removed streams
are instead replaced first. This reduces the size of the SDP
and the number of streams.

ASTERISK-27134

Change-Id: I95cdcfd55cf47e02ea52abb5d94008db3fb68b1d

1 files changed, 18 insertions, 1 deletions

diff --git a/bridges/bridge_softmix.c b/bridges/bridge_softmix.c
index ae877eb6e..3801ccbec 100644
--- a/bridges/bridge_softmix.c
+++ b/bridges/bridge_softmix.c
@@ -524,15 +524,32 @@ static int append_all_streams(struct ast_stream_topology *dest,
 	const struct ast_stream_topology *source)
 {
 	int i;
+	int dest_index = 0;
 
 	for (i = 0; i < ast_stream_topology_get_count(source); ++i) {
 		struct ast_stream *clone;
+		int added = 0;
 
 		clone = ast_stream_clone(ast_stream_topology_get_stream(source, i), NULL);
 		if (!clone) {
 			return -1;
 		}
-		if (ast_stream_topology_append_stream(dest, clone) < 0) {
+
+		/* If we can reuse an existing removed stream then do so */
+		while (dest_index < ast_stream_topology_get_count(dest)) {
+			struct ast_stream *stream = ast_stream_topology_get_stream(dest, dest_index);
+
+			dest_index++;
+
+			if (ast_stream_get_state(stream) == AST_STREAM_STATE_REMOVED) {
+				ast_stream_topology_set_stream(dest, dest_index - 1, clone);
+				added = 1;
+				break;
+			}
+		}
+
+		/* If no removed stream exists that we took the place of append the stream */
+		if (!added && ast_stream_topology_append_stream(dest, clone) < 0) {
 			ast_stream_free(clone);
 			return -1;
 		}