Add a flag to filter out high-cost networks.

webrtc/base/network.h

 /*
  *  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 19 matching lines @@
 namespace rtc {
 
 extern const char kPublicIPv4Host[];
 extern const char kPublicIPv6Host[];
 
 class IfAddrsConverter;
 class Network;
 class NetworkMonitorInterface;
 class Thread;
 
+static const uint16_t kMaxNetworkCost = 999;
+static const uint16_t kNetworkCostForUnknownType = 10;

[pthatcher1, 2016/05/17 20:44:28]

I think kNetworkCostMax and kNetworkCostUnknown  would be a good pair of names. 

[honghaiz3, 2016/05/18 05:55:02]

Done.

 
 // By default, ignore loopback interfaces on the host.
 const int kDefaultNetworkIgnoreMask = ADAPTER_TYPE_LOOPBACK;
 
 // Makes a string key for this network. Used in the network manager's maps.
 // Network objects are keyed on interface name, network prefix and the
 // length of that prefix.
 std::string MakeNetworkKey(const std::string& name, const IPAddress& prefix,
                            int prefix_length);
 
@@ skipping 289 matching lines @@
   void set_scope_id(int id) { scope_id_ = id; }
 
   // Indicates whether this network should be ignored, perhaps because
   // the IP is 0, or the interface is one we know is invalid.
   bool ignored() const { return ignored_; }
   void set_ignored(bool ignored) { ignored_ = ignored; }
 
   AdapterType type() const { return type_; }
   void set_type(AdapterType type) { type_ = type; }
 
+  uint16_t GetCost() const {
+    switch (type_) {
+      case rtc::ADAPTER_TYPE_UNKNOWN:
+        return kNetworkCostForUnknownType;
+      case rtc::ADAPTER_TYPE_CELLULAR:
+        return kMaxNetworkCost;

[pthatcher1, 2016/05/17 20:44:28]

Should we use kNetworkCostHigh == 900 or so just in case later we want something
with even higher cost?

[honghaiz3, 2016/05/18 05:55:02]

Done.
I initially chose cellular network cost to be the maximum cost 999 so that one
side can not choose a higher value (say 901) than the other side (choosing 900)
to use the other-side's cellular more often (when both cell-wifi and wifi-cell
connections exist). That may rarely happen because in most cases, we (webrtc)
control both sides. If you think that may still be an issue, let me know. I can
change it back. 

[honghaiz3, 2016/05/18 05:55:02]

Done.

+      default:
+        return 0;

[pthatcher1, 2016/05/17 20:44:28]

Would a kNetworkCostMin be a good constant?

[pthatcher1, 2016/05/17 20:44:28]

Wouldn't it be better to have the default be "unknown", with something like
this?

case rtc::ADAPTER_TYPE_CELLULAR:
   return kNetworkCostHigh;
case rtc::ADAPTER_TYPE_WIFI:
   return kNetworkCostLow;
case rtc::ADAPTER_TYPE_ETHERNET:
     return kNetworkCostMin;
default:
     return kNetworkCostUnknown;

[honghaiz3, 2016/05/18 05:55:02]

Done. I just listed all types we may have now. 

[honghaiz3, 2016/05/18 05:55:02]

Done.

+    }

[pthatcher1, 2016/05/17 20:44:28]

Would it make sense to make WiFi kNetworkCostLow == 1 an Ethernet
kNetworkCostMin so we slightly prefer Ethernet over WiFi?

[honghaiz3, 2016/05/18 05:55:02]

I choose Wifi cost to be 10 to have slightly more difference, although it won't
matter for now.
May be easier in the future if we need to add rtt as part of the cost.

+  }
+
   // A unique id assigned by the network manager, which may be signaled
   // to the remote side in the candidate.
   uint16_t id() const { return id_; }
   void set_id(uint16_t id) { id_ = id; }
 
   int preference() const { return preference_; }
   void set_preference(int preference) { preference_ = preference; }
 
   // When we enumerate networks and find a previously-seen network is missing,
   // we do not remove it (because it may be used elsewhere). Instead, we mark
@@ skipping 26 matching lines @@
   int preference_;
   bool active_ = true;
   uint16_t id_ = 0;
 
   friend class NetworkManager;
 };
 
 }  // namespace rtc
 
 #endif  // WEBRTC_BASE_NETWORK_H_