Add network cost as part of the connection comparison.

talk/app/webrtc/webrtcsdp.cc

 /*
  * libjingle
  * Copyright 2011 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 125 matching lines @@
 static const char kSSrcAttributeLabel[] = "label";
 static const char kAttributeSsrcGroup[] = "ssrc-group";
 static const char kAttributeCrypto[] = "crypto";
 static const char kAttributeCandidate[] = "candidate";
 static const char kAttributeCandidateTyp[] = "typ";
 static const char kAttributeCandidateRaddr[] = "raddr";
 static const char kAttributeCandidateRport[] = "rport";
 static const char kAttributeCandidateUfrag[] = "ufrag";
 static const char kAttributeCandidatePwd[] = "pwd";
 static const char kAttributeCandidateGeneration[] = "generation";
+static const char kAttributeCandidateCost[] = "cost";
 static const char kAttributeFingerprint[] = "fingerprint";
 static const char kAttributeSetup[] = "setup";
 static const char kAttributeFmtp[] = "fmtp";
 static const char kAttributeRtpmap[] = "rtpmap";
 static const char kAttributeSctpmap[] = "sctpmap";
 static const char kAttributeRtcp[] = "rtcp";
 static const char kAttributeIceUfrag[] = "ice-ufrag";
 static const char kAttributeIcePwd[] = "ice-pwd";
 static const char kAttributeIceLite[] = "ice-lite";
 static const char kAttributeIceOption[] = "ice-options";
@@ skipping 916 matching lines @@
     }
   }
 
   // Extension
   // Though non-standard, we support the ICE ufrag and pwd being signaled on
   // the candidate to avoid issues with confusing which generation a candidate
   // belongs to when trickling multiple generations at the same time.
   std::string username;
   std::string password;
   uint32_t generation = 0;
+  uint32_t cost = 0;
   for (size_t i = current_position; i + 1 < fields.size(); ++i) {
     // RFC 5245
     // *(SP extension-att-name SP extension-att-value)
     if (fields[i] == kAttributeCandidateGeneration) {
       if (!GetValueFromString(first_line, fields[++i], &generation, error)) {
         return false;
       }
     } else if (fields[i] == kAttributeCandidateUfrag) {
       username = fields[++i];
     } else if (fields[i] == kAttributeCandidatePwd) {
       password = fields[++i];
+    } else if (fields[i] == kAttributeCandidateCost) {
+      if (!GetValueFromString(first_line, fields[++i], &cost, error)) {
+        return false;
+      }
     } else {
       // Skip the unknown extension.
       ++i;
     }
   }
 
   *candidate = Candidate(component_id, cricket::ProtoToString(protocol),
                          address, priority, username, password, candidate_type,
                          generation, foundation);
   candidate->set_related_address(related_address);
   candidate->set_tcptype(tcptype);
+  candidate->set_network_cost(std::min(cost, cricket::kMaxNetworkCost));

[pthatcher1, 2016/02/04 23:16:20]

I think we should pick "cost" or "network cost" but not both.  I'd say just go
with "cost".  A client might choose to use this for TURN vs. not as well.

[honghaiz3, 2016/02/05 01:36:46]

Discussed in other comments.

[honghaiz3, 2016/02/11 21:12:28]

I think it might be good to put "cost" on the signaling to save a few bytes. For
the rest, I am using NetworkCost. 

   return true;
 }
 
 bool ParseIceOptions(const std::string& line,
                      std::vector<std::string>* transport_options,
                      SdpParseError* error) {
   std::string ice_options;
   if (!GetValue(line, kAttributeIceOption, &ice_options, error)) {
     return false;
   }
@@ skipping 654 matching lines @@
 
     if (it->protocol() == cricket::TCP_PROTOCOL_NAME) {
       os << kTcpCandidateType << " " << it->tcptype() << " ";
     }
 
     // Extensions
     os << kAttributeCandidateGeneration << " " << it->generation();
     if (include_ufrag && !it->username().empty()) {
       os << " " << kAttributeCandidateUfrag << " " << it->username();
     }
+    os << " " << kAttributeCandidateCost << " " << it->network_cost();
 
     AddLine(os.str(), message);
   }
 }
 
 void BuildIceOptions(const std::vector<std::string>& transport_options,
                      std::string* message) {
   if (!transport_options.empty()) {
     std::ostringstream os;
     InitAttrLine(kAttributeIceOption, &os);
@@ skipping 1286 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