[Unified Plan] Support legacy endpoints that do not use a=mid
These legacy endpoints were supported with Plan B since the SDP
parser would fill in default MID values if a=mid was absent that
happened to match the default offered MIDs.
With Unified Plan, these default MIDs changed so the autofilled
MIDs do not match any more.
This CL adds information to the SessionDescription struct to
indicate whether or not a=mid was present and modified
PeerConnection::SetRemoteDescription to copy MIDs from the local
description if the a=mid lines are not present.
Bug: webrtc:9540
Change-Id: Ibf923b4ad59edb0facd06ddbd01cc10c62fc48e6
Reviewed-on: https://webrtc-review.googlesource.com/c/114820
Commit-Queue: Steve Anton <steveanton@webrtc.org>
Reviewed-by: Amit Hilbuch <amithi@webrtc.org>
Reviewed-by: Seth Hampson <shampson@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#26054}diff --git a/pc/peerconnection.cc b/pc/peerconnection.cc
index 06fbae1..da34cc2 100644
--- a/pc/peerconnection.cc
+++ b/pc/peerconnection.cc
@@ -649,6 +649,25 @@
return DataMessageType::kControl;
}
+// Find a new MID that is not already in |used_mids|, then add it to |used_mids|
+// and return a reference to it.
+// Generated MIDs should be no more than 3 bytes long to take up less space in
+// the RTP packet.
+const std::string& AllocateMid(std::set<std::string>* used_mids) {
+ RTC_DCHECK(used_mids);
+ // We're boring: just generate MIDs 0, 1, 2, ...
+ size_t i = 0;
+ std::set<std::string>::iterator it;
+ bool inserted;
+ do {
+ std::string mid = rtc::ToString(i++);
+ auto insert_result = used_mids->insert(mid);
+ it = insert_result.first;
+ inserted = insert_result.second;
+ } while (!inserted);
+ return *it;
+}
+
} // namespace
// Upon completion, posts a task to execute the callback of the
@@ -2234,6 +2253,56 @@
return RTCError::OK();
}
+// The SDP parser used to populate these values by default for the 'content
+// name' if an a=mid line was absent.
+static absl::string_view GetDefaultMidForPlanB(cricket::MediaType media_type) {
+ switch (media_type) {
+ case cricket::MEDIA_TYPE_AUDIO:
+ return cricket::CN_AUDIO;
+ case cricket::MEDIA_TYPE_VIDEO:
+ return cricket::CN_VIDEO;
+ case cricket::MEDIA_TYPE_DATA:
+ return cricket::CN_DATA;
+ }
+ RTC_NOTREACHED();
+ return "";
+}
+
+void PeerConnection::FillInMissingRemoteMids(
+ cricket::SessionDescription* remote_description) {
+ RTC_DCHECK(remote_description);
+ const cricket::ContentInfos& local_contents =
+ (local_description() ? local_description()->description()->contents()
+ : cricket::ContentInfos());
+ std::set<std::string> used_mids = seen_mids_;
+ for (size_t i = 0; i < remote_description->contents().size(); ++i) {
+ cricket::ContentInfo& content = remote_description->contents()[i];
+ if (!content.name.empty()) {
+ continue;
+ }
+ absl::string_view new_mid;
+ absl::string_view source_explanation;
+ if (IsUnifiedPlan()) {
+ if (i < local_contents.size()) {
+ new_mid = local_contents[i].name;
+ source_explanation = "from the matching local media section";
+ } else {
+ new_mid = AllocateMid(&used_mids);
+ source_explanation = "generated just now";
+ }
+ } else {
+ new_mid = GetDefaultMidForPlanB(content.media_description()->type());
+ source_explanation = "to match pre-existing behavior";
+ }
+ content.name = std::string(new_mid);
+ remote_description->transport_infos()[i].content_name =
+ std::string(new_mid);
+ RTC_LOG(LS_INFO) << "SetRemoteDescription: Remote media section at i=" << i
+ << " is missing an a=mid line. Filling in the value '"
+ << new_mid << "' " << source_explanation << ".";
+ }
+}
+
void PeerConnection::SetRemoteDescription(
SetSessionDescriptionObserver* observer,
SessionDescriptionInterface* desc) {
@@ -2274,6 +2343,10 @@
ReportSdpFormatReceived(*desc);
}
+ // Handle remote descriptions missing a=mid lines for interop with legacy end
+ // points.
+ FillInMissingRemoteMids(desc->description());
+
RTCError error = ValidateSessionDescription(desc.get(), cricket::CS_REMOTE);
if (!error.ok()) {
std::string error_message = GetSetDescriptionErrorMessage(
@@ -3919,25 +3992,6 @@
offer_answer_options.num_simulcast_layers);
}
-// Find a new MID that is not already in |used_mids|, then add it to |used_mids|
-// and return a reference to it.
-// Generated MIDs should be no more than 3 bytes long to take up less space in
-// the RTP packet.
-static const std::string& AllocateMid(std::set<std::string>* used_mids) {
- RTC_DCHECK(used_mids);
- // We're boring: just generate MIDs 0, 1, 2, ...
- size_t i = 0;
- std::set<std::string>::iterator it;
- bool inserted;
- do {
- std::string mid = rtc::ToString(i++);
- auto insert_result = used_mids->insert(mid);
- it = insert_result.first;
- inserted = insert_result.second;
- } while (!inserted);
- return *it;
-}
-
static cricket::MediaDescriptionOptions
GetMediaDescriptionOptionsForTransceiver(
rtc::scoped_refptr<RtpTransceiverProxyWithInternal<RtpTransceiver>>
@@ -6099,6 +6153,17 @@
return content->media_description()->rtcp_mux();
}
+static RTCError ValidateMids(const cricket::SessionDescription& description) {
+ std::set<std::string> mids;
+ for (const cricket::ContentInfo& content : description.contents()) {
+ if (!mids.insert(content.name).second) {
+ LOG_AND_RETURN_ERROR(RTCErrorType::INVALID_PARAMETER,
+ "Duplicate a=mid value '" + content.name + "'.");
+ }
+ }
+ return RTCError::OK();
+}
+
RTCError PeerConnection::ValidateSessionDescription(
const SessionDescriptionInterface* sdesc,
cricket::ContentSource source) {
@@ -6118,6 +6183,11 @@
"Called in wrong state: " + GetSignalingStateString(signaling_state()));
}
+ RTCError error = ValidateMids(*sdesc->description());
+ if (!error.ok()) {
+ return error;
+ }
+
// Verify crypto settings.
std::string crypto_error;
if (webrtc_session_desc_factory_->SdesPolicy() == cricket::SEC_REQUIRED ||