Use the same draft version in SDP data channel answers as used in the offer.

webrtc/pc/mediasession.cc

 /*
  *  Copyright 2004 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 1978 matching lines @@
           sdes_policy,
           GetCryptos(GetFirstDataContentDescription(current_description)),
           RtpHeaderExtensions(),
           current_streams,
           add_legacy_,
           bundle_enabled,
           data_answer.get())) {
     return false;  // Fails the session setup.
   }
 
+  // Respond with sctmap if the offer uses sctmap.

[Taylor Brandstetter, 2017/02/17 02:10:56]

Missing a 'p'

[Zach Stein, 2017/02/17 21:29:17]

Done.

+  const DataContentDescription* offer_data_description =
+      static_cast<const DataContentDescription*>(data_content->description);
+  bool offer_uses_sctpmap = offer_data_description->use_sctpmap();
+  data_answer->set_use_sctpmap(offer_uses_sctpmap);
+
   bool rejected = !options.has_data() || data_content->rejected ||
       !IsMediaProtocolSupported(MEDIA_TYPE_DATA,
                                 data_answer->protocol(),
                                 data_transport->secure());
   if (!rejected) {
     data_answer->set_bandwidth(options.data_bandwidth);
     if (!AddTransportAnswer(data_content->name, *(data_transport.get()),
                             answer)) {
       return false;
     }
@@ skipping 160 matching lines @@
       GetFirstMediaContentDescription(sdesc, MEDIA_TYPE_VIDEO));
 }
 
 DataContentDescription* GetFirstDataContentDescription(
     SessionDescription* sdesc) {
   return static_cast<DataContentDescription*>(
       GetFirstMediaContentDescription(sdesc, MEDIA_TYPE_DATA));
 }
 
 }  // namespace cricket