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sdp: answer with spec msid when msid support is unknown

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this removes the reliance on the no-longer-spec a=msid-semantic lines
in case the offer did not signal any msid. Endpoints not supporting
msid should silently ignore the resulting a=msid: line. This also changes behavior such that a "legacy" offer without msid-semantic
line will be responded to with both msid-semantic and msid for any tracks present.
Plan-B ssrc-specific msid attributes are not signalled in that case.

See https://datatracker.ietf.org/doc/html/rfc8829#section-5.3.1
which includes it in the answer depending on the transceiver direction
but not if and only if the offer signalled a msid.

This also avoids recreating the stream and changing the SSRC
which could happen if the answer object was serialized to SDP
(which most unit tests do not do)

BUG=chromium:328522463

Change-Id: Id2f890b7756721d7c50460359950826d392483ae
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/346741
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Reviewed-by: Florent Castelli <orphis@webrtc.org>
Commit-Queue: Philipp Hancke <phancke@meta.com>
Cr-Commit-Position: refs/heads/main@{#42237}
This commit is contained in:
Philipp Hancke 2024-04-15 16:36:38 -07:00 committed by WebRTC LUCI CQ
parent 1e5f88c5be
commit 3f10f65713
2 changed files with 72 additions and 43 deletions
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24
pc/media_session.cc
View file

@ -1713,23 +1713,27 @@ MediaSessionDescriptionFactory::CreateAnswerOrError(
// a=msid.
answer->set_msid_signaling(cricket::kMsidSignalingSemantic |
cricket::kMsidSignalingMediaSection);
} else if (msid_signaling == cricket::kMsidSignalingSemantic) {
} else if (msid_signaling == (cricket::kMsidSignalingSemantic |
cricket::kMsidSignalingSsrcAttribute) ||
msid_signaling == cricket::kMsidSignalingSsrcAttribute) {
// If only a=ssrc MSID signaling method was used, we're probably talking
// to a Plan B endpoint so respond with just a=ssrc MSID.
answer->set_msid_signaling(cricket::kMsidSignalingSemantic |
cricket::kMsidSignalingSsrcAttribute);
} else {
// We end up here in one of three cases:
// 1. An empty offer. We'll reply with an empty answer so it doesn't
// matter what we pick here.
// 2. A data channel only offer. We won't add any MSIDs to the answer so
// it also doesn't matter what we pick here.
// 3. Media that's either sendonly or inactive from the remote endpoint.
// 3. Media that's either recvonly or inactive from the remote point of
// view.
// We don't have any information to say whether the endpoint is Plan B
// or Unified Plan, so be conservative and send both.
// or Unified Plan. Since plan-b is obsolete, do not respond with it.
// We assume that endpoints not supporting MSID will silently ignore
// the a=msid lines they do not understand.
answer->set_msid_signaling(cricket::kMsidSignalingSemantic |
cricket::kMsidSignalingMediaSection |
cricket::kMsidSignalingSsrcAttribute);
} else {
// Otherwise, it's clear which method the offerer is using so repeat that
// back to them. This includes the case where the msid-semantic line is
// not included.
answer->set_msid_signaling(msid_signaling);
cricket::kMsidSignalingMediaSection);
}
} else {
// Plan B always signals MSID using a=ssrc lines.

91
pc/sdp_offer_answer_unittest.cc
View file

@ -1052,6 +1052,64 @@ TEST_F(SdpOfferAnswerTest, MsidSignalingInSubsequentOfferAnswer) {
EXPECT_NE(std::string::npos, sdp.find("a=msid:- audio_track\r\n"));
}
// Regression test for crbug.com/328522463
// where the stream parameters got recreated which changed the ssrc.
TEST_F(SdpOfferAnswerTest, MsidSignalingUnknownRespondsWithMsidAndKeepsSsrc) {
auto pc = CreatePeerConnection();
pc->AddAudioTrack("audio_track", {"default"});
std::string sdp =
"v=0\r\n"
"o=- 0 3 IN IP4 127.0.0.1\r\n"
"s=-\r\n"
"t=0 0\r\n"
"a=group:BUNDLE 0\r\n"
// "a=msid-semantic: WMS *\r\n"
"a=ice-ufrag:ETEn\r\n"
"a=ice-pwd:OtSK0WpNtpUjkY4+86js7Z/l\r\n"
"a=fingerprint:sha-1 "
"4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB\r\n"
"a=setup:actpass\r\n"
"m=audio 9 UDP/TLS/RTP/SAVPF 111\r\n"
"c=IN IP4 0.0.0.0\r\n"
"a=rtcp:9 IN IP4 0.0.0.0\r\n"
"a=recvonly\r\n"
"a=rtcp-mux\r\n"
"a=mid:0\r\n"
"a=rtpmap:111 opus/48000/2\r\n";
auto offer = CreateSessionDescription(SdpType::kOffer, sdp);
EXPECT_TRUE(pc->SetRemoteDescription(std::move(offer)));
auto first_transceiver = pc->pc()->GetTransceivers()[0];
EXPECT_TRUE(first_transceiver
->SetDirectionWithError(RtpTransceiverDirection::kSendOnly)
.ok());
// Check the generated *serialized* SDP.
auto answer = pc->CreateAnswer();
const auto& answer_contents = answer->description()->contents();
ASSERT_EQ(answer_contents.size(), 1u);
auto answer_streams = answer_contents[0].media_description()->streams();
ASSERT_EQ(answer_streams.size(), 1u);
std::string first_stream_serialized = answer_streams[0].ToString();
uint32_t first_ssrc = answer_contents[0].media_description()->first_ssrc();
answer->ToString(&sdp);
EXPECT_TRUE(
pc->SetLocalDescription(CreateSessionDescription(SdpType::kAnswer, sdp)));
auto reoffer = pc->CreateOffer();
const auto& offer_contents = reoffer->description()->contents();
ASSERT_EQ(offer_contents.size(), 1u);
auto offer_streams = offer_contents[0].media_description()->streams();
ASSERT_EQ(offer_streams.size(), 1u);
std::string second_stream_serialized = offer_streams[0].ToString();
uint32_t second_ssrc = offer_contents[0].media_description()->first_ssrc();
EXPECT_EQ(first_ssrc, second_ssrc);
EXPECT_EQ(first_stream_serialized, second_stream_serialized);
EXPECT_TRUE(pc->SetLocalDescription(std::move(reoffer)));
}
// Test variant with boolean order for audio-video and video-audio.
class SdpOfferAnswerShuffleMediaTypes
: public SdpOfferAnswerTest,
@ -1182,39 +1240,6 @@ TEST_F(SdpOfferAnswerTest, OfferWithNoCompatibleCodecsIsRejectedInAnswer) {
EXPECT_EQ(answer_contents[1].rejected, true);
}
TEST_F(SdpOfferAnswerTest,
OfferWithNoMsidSemanticYieldsAnswerWithoutMsidSemantic) {
auto pc = CreatePeerConnection();
// An offer with no msid-semantic line. The answer should not add one.
std::string sdp =
"v=0\r\n"
"o=- 0 3 IN IP4 127.0.0.1\r\n"
"s=-\r\n"
"t=0 0\r\n"
"a=fingerprint:sha-1 "
"4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB\r\n"
"a=setup:actpass\r\n"
"a=ice-ufrag:ETEn\r\n"
"a=ice-pwd:OtSK0WpNtpUjkY4+86js7Z/l\r\n"
"m=audio 9 RTP/SAVPF 111\r\n"
"c=IN IP4 0.0.0.0\r\n"
"a=sendrecv\r\n"
"a=rtpmap:111 opus/48000/2\r\n"
"a=rtcp-mux\r\n";
auto desc = CreateSessionDescription(SdpType::kOffer, sdp);
ASSERT_NE(desc, nullptr);
EXPECT_EQ(desc->description()->msid_signaling(),
cricket::kMsidSignalingNotUsed);
RTCError error;
pc->SetRemoteDescription(std::move(desc), &error);
EXPECT_TRUE(error.ok());
auto answer = pc->CreateAnswer();
EXPECT_EQ(answer->description()->msid_signaling(),
cricket::kMsidSignalingNotUsed);
}
TEST_F(SdpOfferAnswerTest, OfferWithRejectedMlineWithoutFingerprintIsAccepted) {
auto pc = CreatePeerConnection();
// A rejected m-line without fingerprint.