sdp: parse a=msid:<stream_id> w/o msid-appdata

parse
  a=msid:<stream_id>
since JSEP stipulates sending this syntax as track identifers
have become meaningless. The track id will be set to a random string.

  a=msid:<stream_id> <track_id>
remains supported for backward compability.

BUG=webrtc:14729

Change-Id: I86c073eb97cd613324271125de18a773235fc79d
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/285783
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Reviewed-by: Florent Castelli <orphis@webrtc.org>
Commit-Queue: Philipp Hancke <phancke@microsoft.com>
Cr-Commit-Position: refs/heads/main@{#38814}

pc/webrtc_sdp.cc

@@ -2333,33 +2333,46 @@ static bool ParseMsidAttribute(absl::string_view line,
                                std::vector<std::string>* stream_ids,
                                std::string* track_id,
                                SdpParseError* error) {
-  // https://datatracker.ietf.org/doc/draft-ietf-mmusic-msid/16/
+  // https://datatracker.ietf.org/doc/rfc8830/
-  // a=msid:<stream id> <track id>
+  // a=msid:<msid-value>
   // msid-value = msid-id [ SP msid-appdata ]
   // msid-id = 1*64token-char ; see RFC 4566
   // msid-appdata = 1*64token-char  ; see RFC 4566
-  std::string field1;
+  // Note that JSEP stipulates not sending msid-appdata so
-  std::string new_stream_id;
+  // a=msid:<stream id> <track id>
-  std::string new_track_id;
+  // is supported for backward compability reasons only.
-  if (!rtc::tokenize_first(line.substr(kLinePrefixLength),
+  std::vector<std::string> fields;
-                           kSdpDelimiterSpaceChar, &field1, &new_track_id)) {
+  size_t num_fields = rtc::tokenize(line.substr(kLinePrefixLength),
-    const size_t expected_fields = 2;
+                                    kSdpDelimiterSpaceChar, &fields);
-    return ParseFailedExpectFieldNum(line, expected_fields, error);
+  if (num_fields < 1 || num_fields > 2) {
+    return ParseFailed(line, "Expected a stream ID and optionally a track ID",
+                       error);
   }
+  if (num_fields == 1) {
+    if (line.back() == kSdpDelimiterSpaceChar) {
+      return ParseFailed(line, "Missing track ID in msid attribute.", error);
+    }
+    if (!track_id->empty()) {
+      fields.push_back(*track_id);
+    } else {
+      // Ending with an empty string track will cause a random track id
+      // to be generated later in the process.
+      fields.push_back("");
+    }
+  }
+  RTC_DCHECK_EQ(fields.size(), 2);
 
-  if (new_track_id.empty()) {
-    return ParseFailed(line, "Missing track ID in msid attribute.", error);
-  }
   // All track ids should be the same within an m section in a Unified Plan SDP.
-  if (!track_id->empty() && new_track_id.compare(*track_id) != 0) {
+  if (!track_id->empty() && track_id->compare(fields[1]) != 0) {
     return ParseFailed(
         line, "Two different track IDs in msid attribute in one m= section",
         error);
   }
-  *track_id = new_track_id;
+  *track_id = fields[1];
 
   // msid:<msid-id>
-  if (!GetValue(field1, kAttributeMsid, &new_stream_id, error)) {
+  std::string new_stream_id;
+  if (!GetValue(fields[0], kAttributeMsid, &new_stream_id, error)) {
     return false;
   }
   if (new_stream_id.empty()) {
@@ -3330,6 +3343,10 @@ bool ParseContent(absl::string_view message,
     // still create a track. This isn't done for data media types because
     // StreamParams aren't used for SCTP streams, and RTP data channels don't
     // support unsignaled SSRCs.
+    // If track id was not specified, create a random one.
+    if (track_id.empty()) {
+      track_id = rtc::CreateRandomString(8);
+    }
     CreateTrackWithNoSsrcs(stream_ids, track_id, send_rids, &tracks);
   }
 

pc/webrtc_sdp_unittest.cc

@@ -4073,6 +4073,72 @@ TEST_F(WebRtcSdpTest, DeserializeMsidAttributeWithMissingTrackId) {
   EXPECT_FALSE(SdpDeserialize(kSdpWithMissingTrackId, &jdesc_output));
 }
 
+TEST_F(WebRtcSdpTest, DeserializeMsidAttributeWithoutAppData) {
+  static const char kSdpWithMissingStreamId[] =
+      "v=0\r\n"
+      "o=- 18446744069414584320 18446462598732840960 IN IP4 127.0.0.1\r\n"
+      "s=-\r\n"
+      "t=0 0\r\n"
+      "m=audio 9 RTP/SAVPF 111\r\n"
+      "c=IN IP4 0.0.0.0\r\n"
+      "a=rtpmap:111 opus/48000/2\r\n"
+      "a=msid:stream_id\r\n";
+
+  JsepSessionDescription jdesc_output(kDummyType);
+  EXPECT_TRUE(SdpDeserialize(kSdpWithMissingStreamId, &jdesc_output));
+}
+
+TEST_F(WebRtcSdpTest, DeserializeMsidAttributeWithoutAppDataTwoStreams) {
+  static const char kSdpWithMissingStreamId[] =
+      "v=0\r\n"
+      "o=- 18446744069414584320 18446462598732840960 IN IP4 127.0.0.1\r\n"
+      "s=-\r\n"
+      "t=0 0\r\n"
+      "m=audio 9 RTP/SAVPF 111\r\n"
+      "c=IN IP4 0.0.0.0\r\n"
+      "a=rtpmap:111 opus/48000/2\r\n"
+      "a=msid:stream_id\r\n"
+      "a=msid:stream_id2\r\n";
+
+  JsepSessionDescription jdesc_output(kDummyType);
+  EXPECT_TRUE(SdpDeserialize(kSdpWithMissingStreamId, &jdesc_output));
+}
+
+TEST_F(WebRtcSdpTest, DeserializeMsidAttributeWithoutAppDataDuplicate) {
+  static const char kSdpWithMissingStreamId[] =
+      "v=0\r\n"
+      "o=- 18446744069414584320 18446462598732840960 IN IP4 127.0.0.1\r\n"
+      "s=-\r\n"
+      "t=0 0\r\n"
+      "m=audio 9 RTP/SAVPF 111\r\n"
+      "c=IN IP4 0.0.0.0\r\n"
+      "a=rtpmap:111 opus/48000/2\r\n"
+      "a=msid:stream_id\r\n"
+      "a=msid:stream_id\r\n";
+
+  JsepSessionDescription jdesc_output(kDummyType);
+  // This is somewhat silly but accept it.
+  EXPECT_TRUE(SdpDeserialize(kSdpWithMissingStreamId, &jdesc_output));
+}
+
+TEST_F(WebRtcSdpTest, DeserializeMsidAttributeWithoutAppDataMixed) {
+  static const char kSdpWithMissingStreamId[] =
+      "v=0\r\n"
+      "o=- 18446744069414584320 18446462598732840960 IN IP4 127.0.0.1\r\n"
+      "s=-\r\n"
+      "t=0 0\r\n"
+      "m=audio 9 RTP/SAVPF 111\r\n"
+      "c=IN IP4 0.0.0.0\r\n"
+      "a=rtpmap:111 opus/48000/2\r\n"
+      "a=msid:stream_id\r\n"
+      "a=msid:stream_id track_id\r\n";
+
+  JsepSessionDescription jdesc_output(kDummyType);
+  // Mixing the syntax like this is not a good idea but we accept it
+  // and the result is the second track_id.
+  EXPECT_TRUE(SdpDeserialize(kSdpWithMissingStreamId, &jdesc_output));
+}
+
 TEST_F(WebRtcSdpTest, DeserializeMsidAttributeWithMissingStreamId) {
   static const char kSdpWithMissingStreamId[] =
       "v=0\r\n"