Fix the generation mismatch assertion error.

talk/app/webrtc/webrtcsession.cc

 /*
  * libjingle
  * Copyright 2012 Google Inc.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are met:
  *
  *  1. Redistributions of source code must retain the above copyright notice,
  *     this list of conditions and the following disclaimer.
  *  2. Redistributions in binary form must reproduce the above copyright notice,
@@ skipping 414 matching lines @@
   bool Get() const {
     return ice_restart_;
   }
 
   void Reset() {
     if (ice_restart_) {
       ice_restart_ = false;
     }
   }
 
-  void CheckForRemoteIceRestart(
-      const SessionDescriptionInterface* old_desc,
-      const SessionDescriptionInterface* new_desc) {
+  bool CheckForRemoteIceRestart(const SessionDescriptionInterface* old_desc,
+                                const SessionDescriptionInterface* new_desc) {
     if (!old_desc || new_desc->type() != SessionDescriptionInterface::kOffer) {
-      return;
+      return false;
     }
     const SessionDescription* new_sd = new_desc->description();
     const SessionDescription* old_sd = old_desc->description();
     const ContentInfos& contents = new_sd->contents();
     for (size_t index = 0; index < contents.size(); ++index) {
       const ContentInfo* cinfo = &contents[index];
       if (cinfo->rejected) {
         continue;
       }
       // If the content isn't rejected, check if ufrag and password has
       // changed.
       const cricket::TransportDescription* new_transport_desc =
           new_sd->GetTransportDescriptionByName(cinfo->name);
       const cricket::TransportDescription* old_transport_desc =
           old_sd->GetTransportDescriptionByName(cinfo->name);
       if (!new_transport_desc || !old_transport_desc) {
         // No transport description exist. This is not an ice restart.
         continue;
       }
       if (cricket::IceCredentialsChanged(old_transport_desc->ice_ufrag,
                                          old_transport_desc->ice_pwd,
                                          new_transport_desc->ice_ufrag,
                                          new_transport_desc->ice_pwd)) {
         LOG(LS_INFO) << "Remote peer request ice restart.";
         ice_restart_ = true;

[pthatcher1, 2015/07/29 21:09:42]

Instead of setting ice_restart_ here, can you move it to the place where
CheckForRemoteIceRestart is called?

Something like:

if (CheckForIceRestart(...) {
  ice_restart_ = true;
}

[honghaiz3, 2015/07/30 17:16:16]

It was called outside the class and we cannot set the member variable in this
class from that location. 

-        break;
+        return true;
       }
     }
+    return false;
   }
 
  private:
   bool ice_restart_;
 };
 
 WebRtcSession::WebRtcSession(
     cricket::ChannelManager* channel_manager,
     rtc::Thread* signaling_thread,
     rtc::Thread* worker_thread,
@@ skipping 353 matching lines @@
   }
 
   // Update remote MediaStreams.
   mediastream_signaling_->OnRemoteDescriptionChanged(desc);
   if (local_description() && !UseCandidatesInSessionDescription(desc)) {
     return BadRemoteSdp(desc->type(), kInvalidCandidates, err_desc);
   }
 
   // Copy all saved candidates.
   CopySavedCandidates(desc);
-  // We retain all received candidates.
-  WebRtcSessionDescriptionFactory::CopyCandidatesFromSessionDescription(
-      remote_desc_.get(), desc);
+
   // Check if this new SessionDescription contains new ice ufrag and password
   // that indicates the remote peer requests ice restart.
-  ice_restart_latch_->CheckForRemoteIceRestart(remote_desc_.get(),
-                                               desc);
+  bool ice_restart =
+      ice_restart_latch_->CheckForRemoteIceRestart(remote_desc_.get(), desc);
+  // We retain all received candidates unless ICE is restarted;

[pthatcher1, 2015/07/29 21:09:42]

Can you expand the comment to explain in more detail why we don't keep
candidates during an ICE restart?

[honghaiz3, 2015/07/30 17:16:16]

Done.

+  if (!ice_restart) {
+    WebRtcSessionDescriptionFactory::CopyCandidatesFromSessionDescription(
+        remote_desc_.get(), desc);
+  }
+
   remote_desc_.reset(desc_temp.release());
 
   rtc::SSLRole role;
   if (data_channel_type_ == cricket::DCT_SCTP && GetSslRole(&role)) {
     mediastream_signaling_->OnDtlsRoleReadyForSctp(role);
   }
 
   if (error() != cricket::BaseSession::ERROR_NONE) {
     return BadRemoteSdp(desc->type(), GetSessionErrorMsg(), err_desc);
   }
@@ skipping 641 matching lines @@
     }
   }
   return content_found;
 }
 
 bool WebRtcSession::UseCandidatesInSessionDescription(
     const SessionDescriptionInterface* remote_desc) {
   if (!remote_desc)
     return true;
   bool ret = true;
-
   for (size_t m = 0; m < remote_desc->number_of_mediasections(); ++m) {
     const IceCandidateCollection* candidates = remote_desc->candidates(m);
     for  (size_t n = 0; n < candidates->count(); ++n) {
       const IceCandidateInterface* candidate = candidates->at(n);
       bool valid = false;
       if (!ReadyToUseRemoteCandidate(candidate, remote_desc, &valid)) {
         if (valid) {
           LOG(LS_INFO) << "UseCandidatesInSessionDescription: Candidate saved.";
           saved_candidates_.push_back(
               new JsepIceCandidate(candidate->sdp_mid(),
                                    candidate->sdp_mline_index(),
                                    candidate->candidate()));
         }
         continue;
       }
-
       ret = UseCandidate(candidate);
       if (!ret)
         break;
     }
   }
   return ret;
 }
 
 bool WebRtcSession::UseCandidate(
     const IceCandidateInterface* candidate) {
@@ skipping 424 matching lines @@
 
   if (!srtp_cipher.empty()) {
     metrics_observer_->AddHistogramSample(srtp_name, srtp_cipher);
   }
   if (!ssl_cipher.empty()) {
     metrics_observer_->AddHistogramSample(ssl_name, ssl_cipher);
   }
 }
 
 }  // namespace webrtc