Ignore "b=AS:-1" instead of treating as a hard error.

webrtc/pc/webrtcsdp.cc

 /*
  *  Copyright 2011 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 2701 matching lines @@
     if (IsLineType(line, kLineTypeSessionBandwidth)) {
       std::string bandwidth;
       if (HasAttribute(line, kApplicationSpecificMaximum)) {
         if (!GetValue(line, kApplicationSpecificMaximum, &bandwidth, error)) {
           return false;
         } else {
           int b = 0;
           if (!GetValueFromString(line, bandwidth, &b, error)) {
             return false;
           }
+          // TODO(deadbeef): Historically, applications may be setting a value
+          // of -1 to mean "unset any previously set bandwidth limit", even
+          // though ommitting the "b=AS" entirely will do just that. Once we've
+          // transitioned applications to doing the right thing, it would be
+          // better to treat this as a hard error instead of just ignoring it.
+          if (b == -1) {
+            LOG(LS_WARNING) << "Ignoring \"b=AS:-1\"; will be treated as \"no "
+                               "bandwidth limit\".";
+            continue;
+          }
           if (b < 0) {
             return ParseFailed(line, "b=AS value can't be negative.", error);

[Zhi Huang, 2017/08/03 23:37:40]

"b=AS value can't be negative other than -1"?

[Taylor Brandstetter, 2017/08/04 00:10:20]

Technically, but I don't want to encourage people to do that. :)

           }
           // We should never use more than the default bandwidth for RTP-based
           // data channels. Don't allow SDP to set the bandwidth, because
           // that would give JS the opportunity to "break the Internet".
           // See: https://code.google.com/p/chromium/issues/detail?id=280726
           if (media_type == cricket::MEDIA_TYPE_DATA && IsRtp(protocol) &&
               b > cricket::kDataMaxBandwidth / 1000) {
             std::ostringstream description;
             description << "RTP-based data channels may not send more than "
                         << cricket::kDataMaxBandwidth / 1000 << "kbps.";
@@ skipping 583 matching lines @@
     UpdateCodec<AudioContentDescription, cricket::AudioCodec>(
         media_desc, payload_type, feedback_param);
   } else if (media_type == cricket::MEDIA_TYPE_VIDEO) {
     UpdateCodec<VideoContentDescription, cricket::VideoCodec>(
         media_desc, payload_type, feedback_param);
   }
   return true;
 }
 
 }  // namespace webrtc