res_pjsip_session: Preserve stream name during renegotiation.

Stream names within Asterisk can have meaning so when an externally
initiated renegotiation occurs we need to preserve the name of
the stream if it already exists.

Change-Id: I29f50d0cc7f3238287d6d647777e76e1bdf8c596

res/res_pjsip_session.c

@@ -588,7 +588,14 @@ static int handle_incoming_sdp(struct ast_sip_session *session, const pjmedia_sd
 			stream = ast_stream_topology_get_stream(session->pending_media_state->topology, i);
 		}
 		if (!stream) {
-			stream = ast_stream_alloc(ast_codec_media_type2str(type), type);
+			struct ast_stream *existing_stream = NULL;
+
+			if (session->active_media_state->topology &&
+				(i < ast_stream_topology_get_count(session->active_media_state->topology))) {
+				existing_stream = ast_stream_topology_get_stream(session->active_media_state->topology, i);
+			}
+
+			stream = ast_stream_alloc(existing_stream ? ast_stream_get_name(existing_stream) : ast_codec_media_type2str(type), type);
 			if (!stream) {
 				return -1;
 			}
@@ -1626,6 +1633,7 @@ static int sdp_requires_deferral(struct ast_sip_session *session, const pjmedia_
 		char media[20];
 		struct ast_sip_session_sdp_handler *handler;
 		RAII_VAR(struct sdp_handler_list *, handler_list, NULL, ao2_cleanup);
+		struct ast_stream *existing_stream = NULL;
 		struct ast_stream *stream;
 		enum ast_media_type type;
 		struct ast_sip_session_media *session_media = NULL;
@@ -1634,8 +1642,13 @@ static int sdp_requires_deferral(struct ast_sip_session *session, const pjmedia_
 		/* We need a null-terminated version of the media string */
 		ast_copy_pj_str(media, &sdp->media[i]->desc.media, sizeof(media));
 
+		if (session->active_media_state->topology &&
+			(i < ast_stream_topology_get_count(session->active_media_state->topology))) {
+			existing_stream = ast_stream_topology_get_stream(session->active_media_state->topology, i);
+		}
+
 		type = ast_media_type_from_str(media);
-		stream = ast_stream_alloc(ast_codec_media_type2str(type), type);
+		stream = ast_stream_alloc(existing_stream ? ast_stream_get_name(existing_stream) : ast_codec_media_type2str(type), type);
 		if (!stream) {
 			return -1;
 		}