res_pjsip_session/_sdp_rtp: Handling of 'msid' is incorrect

Currently, the handling of the msid attribute is not quite right. According to
the spec the msid's between the offer/answer are not dependent upon one another.
Meaning the same msid's given in an offer do not have to be returned in the
answer for a given stream. And they probably shouldn't be (copied/reused) since
this can potentially cause some browser side confusion.

This patch generates new msids when both an offer and answer are sent from
Asterisk. However, Asterisk does reuse the original msid it sent out for a
reinvite. Also audio+video streams are paired together by sharing the same
stream id, but a different track id.

ASTERISK-27179 #close

Change-Id: Ifaec06dc7e65ad841633a24ebec8c8a9302d6643

include/asterisk/res_pjsip_session.h

@@ -105,8 +105,10 @@ struct ast_sip_session_media {
 	int bundle_group;
 	/*! \brief Whether this stream is currently bundled or not */
 	unsigned int bundled;
-	/*! \brief RTP/Media streams association identifier */
-	char *msid;
+	/*! \brief Media stream label */
+	char mslabel[AST_UUID_STR_LEN];
+	/*! \brief Track label */
+	char label[AST_UUID_STR_LEN];
 };
 
 /*!

res/res_pjsip_sdp_rtp.c

@@ -1025,44 +1025,46 @@ static void process_ssrc_attributes(struct ast_sip_session *session, struct ast_
 	}
 }
 
-static void process_msid_attribute(struct ast_sip_session *session,
-	struct ast_sip_session_media *session_media, pjmedia_sdp_media *media)
+static void add_msid_to_stream(struct ast_sip_session *session,
+	struct ast_sip_session_media *session_media, pj_pool_t *pool, pjmedia_sdp_media *media,
+	struct ast_stream *stream)
 {
+	pj_str_t stmp;
 	pjmedia_sdp_attr *attr;
+	char msid[(AST_UUID_STR_LEN * 2) + 2];
 
 	if (!session->endpoint->media.webrtc) {
 		return;
 	}
 
-	attr = pjmedia_sdp_media_find_attr2(media, "msid", NULL);
-	if (attr) {
-		ast_free(session_media->msid);
-		ast_copy_pj_str2(&session_media->msid, &attr->value);
-	}
-}
+	if (ast_strlen_zero(session_media->mslabel)) {
+		if (ast_sip_session_is_pending_stream_default(session, stream)) {
+			int index;
 
-static void add_msid_to_stream(struct ast_sip_session *session,
-	struct ast_sip_session_media *session_media, pj_pool_t *pool, pjmedia_sdp_media *media)
-{
-	pj_str_t stmp;
-	pjmedia_sdp_attr *attr;
+			/* If this is a default stream we group them together under the same stream, but as different tracks */
+			for (index = 0; index < AST_VECTOR_SIZE(&session->pending_media_state->sessions); ++index) {
+				struct ast_sip_session_media *other_session_media = AST_VECTOR_GET(&session->pending_media_state->sessions, index);
 
-	if (!session->endpoint->media.webrtc) {
-		return;
-	}
+				if (session_media == other_session_media) {
+					continue;
+				}
 
-	if (ast_strlen_zero(session_media->msid)) {
-		char uuid1[AST_UUID_STR_LEN], uuid2[AST_UUID_STR_LEN];
+				ast_copy_string(session_media->mslabel, other_session_media->mslabel, sizeof(session_media->mslabel));
+				break;
+			}
+		}
 
-		if (ast_asprintf(&session_media->msid, "{%s} {%s}",
-			ast_uuid_generate_str(uuid1, sizeof(uuid1)),
-			ast_uuid_generate_str(uuid2, sizeof(uuid2))) < 0) {
-			session_media->msid = NULL;
-			return;
+		if (ast_strlen_zero(session_media->mslabel)) {
+			ast_uuid_generate_str(session_media->mslabel, sizeof(session_media->mslabel));
 		}
 	}
 
-	attr = pjmedia_sdp_attr_create(pool, "msid", pj_cstr(&stmp, session_media->msid));
+	if (ast_strlen_zero(session_media->label)) {
+		ast_uuid_generate_str(session_media->label, sizeof(session_media->label));
+	}
+
+	snprintf(msid, sizeof(msid), "%s %s", session_media->mslabel, session_media->label);
+	attr = pjmedia_sdp_attr_create(pool, "msid", pj_cstr(&stmp, msid));
 	pjmedia_sdp_attr_add(&media->attr_count, media->attr, attr);
 }
 
@@ -1127,7 +1129,6 @@ static int negotiate_incoming_sdp_stream(struct ast_sip_session *session,
 	}
 
 	process_ssrc_attributes(session, session_media, stream);
-	process_msid_attribute(session, session_media, stream);
 	session_media_transport = ast_sip_session_media_get_transport(session, session_media);
 
 	if (session_media_transport == session_media || !session_media->bundled) {
@@ -1586,7 +1587,7 @@ static int create_outgoing_sdp_stream(struct ast_sip_session *session, struct as
 	}
 
 	add_ssrc_to_stream(session, session_media, pool, media);
-	add_msid_to_stream(session, session_media, pool, media);
+	add_msid_to_stream(session, session_media, pool, media, stream);
 	add_rtcp_fb_to_stream(session, session_media, pool, media);
 
 	/* Add the media stream to the SDP */

res/res_pjsip_session.c

@@ -395,7 +395,6 @@ static void session_media_dtor(void *obj)
 	}
 
 	ast_free(session_media->mid);
-	ast_free(session_media->msid);
 }
 
 struct ast_sip_session_media *ast_sip_session_media_state_add(struct ast_sip_session *session,