sdp: document existing mid backfill cornercases
mids get backfilled starting with 0 which means they are always
present in the answer (even though JSEP says otherwise) and may
even be backfilled in a manner compatible with their usage in a
BUNDLE group. Those cases are ok-ish but should be documented by
tests.
BUG=None
Change-Id: I69f0475c279da5022109a56f0006169dbc2de147
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/349380
Reviewed-by: Florent Castelli <orphis@webrtc.org>
Commit-Queue: Philipp Hancke <phancke@meta.com>
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#42234}
diff --git a/pc/sdp_offer_answer_unittest.cc b/pc/sdp_offer_answer_unittest.cc
index e4324fa..536c712 100644
--- a/pc/sdp_offer_answer_unittest.cc
+++ b/pc/sdp_offer_answer_unittest.cc
@@ -1242,4 +1242,75 @@
EXPECT_TRUE(pc->SetLocalDescription(std::move(answer)));
}
+TEST_F(SdpOfferAnswerTest, MidBackfillAnswer) {
+ auto pc = CreatePeerConnection();
+ // An offer without a mid backfills the mid. This is currently
+ // done with a per-peerconnection counter that starts from 0.
+ // JSEP says to only include the mid in the answer if it was in the offer
+ // but due to backfill it is always present.
+ // TODO: https://issues.webrtc.org/issues/338529222 - don't respond with mid.
+ 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=setup:actpass\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 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=mid:0\r\n"
+ "a=rtcp-mux\r\n";
+ auto desc = CreateSessionDescription(SdpType::kOffer, sdp);
+ ASSERT_NE(desc, nullptr);
+ RTCError error;
+ pc->SetRemoteDescription(std::move(desc), &error);
+ EXPECT_TRUE(error.ok());
+ auto offer_contents =
+ pc->pc()->remote_description()->description()->contents();
+ ASSERT_EQ(offer_contents.size(), 1u);
+ EXPECT_EQ(offer_contents[0].mid(), "0");
+ auto answer = pc->CreateAnswerAndSetAsLocal();
+ auto answer_contents = answer->description()->contents();
+ ASSERT_EQ(answer_contents.size(), 1u);
+ EXPECT_EQ(answer_contents[0].mid(), offer_contents[0].mid());
+}
+
+TEST_F(SdpOfferAnswerTest, MidBackfillDoesNotCheckAgainstBundleGroup) {
+ auto pc = CreatePeerConnection();
+ // An offer with a BUNDLE group specifying a mid that is not present
+ // in the offer. This is not rejected due to the mid being backfilled
+ // starting at 0.
+ // TODO: https://issues.webrtc.org/issues/338528603 - reject this.
+ 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=setup:actpass\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"
+ "a=group:BUNDLE 0\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=mid:0\r\n"
+ "a=rtcp-mux\r\n";
+ auto desc = CreateSessionDescription(SdpType::kOffer, sdp);
+ ASSERT_NE(desc, nullptr);
+ RTCError error;
+ pc->SetRemoteDescription(std::move(desc), &error);
+ EXPECT_TRUE(error.ok());
+ EXPECT_TRUE(pc->CreateAnswerAndSetAsLocal());
+}
+
} // namespace webrtc
