GetDefaultLocalAddress should return the bestIP

webrtc/base/network.cc

Index: webrtc/base/network.cc
diff --git a/webrtc/base/network.cc b/webrtc/base/network.cc
index 4780e2f88d463ce9a9862e9da9b74a8c04e324d7..bbec317298bf2ee78055e5560ebcafa78bc7d9eb 100644
--- a/webrtc/base/network.cc
+++ b/webrtc/base/network.cc
@@ -361,12 +361,30 @@ bool NetworkManagerBase::GetDefaultLocalAddress(int family,
     *ipaddr = default_local_ipv4_address_;
     return true;
   } else if (family == AF_INET6 && !default_local_ipv6_address_.IsNil()) {
-    *ipaddr = default_local_ipv6_address_;
+    // Using the best IP on the same network as the default IPv6 address
+    // prevents potential IP leaking.
+    Network* network = GetNetworkFromAddress(default_local_ipv6_address_);

[pthatcher1, 2016/03/30 17:25:06]

I think this could be a little more clear:

*ipaddr = default_local_ipv6_address_;
Network* default_ipv6_network =
GetNetworkFromAddress(default_local_ipv6_address_);
if (default_ipv6_network) {
  // The default ipv6 network's BestIP is different than
default_local_ipv6_address_, use it instead.
  // This is to prevent potential IP address leakage. See WebRTC bug 5376. 
  *ipaddr = network->GetBestIP();
} 
return true;

[honghaiz3, 2016/03/30 18:02:59]

Revised. 1. we don't need to assign *ipaddr twice in some cases. 2. ipv6_network
need not be prefixed withe default. 

+    *ipaddr = (network != nullptr) ? network->GetBestIP()

[pthatcher1, 2016/03/30 17:25:06]

How do we know that GetBestIP() will return an ipv6 address?  Is a Network
guaranteed to only return IP addresses of either ipv4 or ipv6, but not both? 
Should we check that it's ipv6?

[honghaiz3, 2016/03/30 18:02:59]

IPv6 address and IPv4 address will be contained in different networks. 
Network includes the interface name, the prefix and the length of the prefix. 

+                                   : default_local_ipv6_address_;
     return true;
   }
   return false;
 }
 
+Network* NetworkManagerBase::GetNetworkFromAddress(
+    const rtc::IPAddress& ip) const {
+  for (Network* network : networks_) {
+    const auto& ips = network->GetIPs();
+    if (std::find_if(ips.begin(), ips.end(),
+                     [ip](const InterfaceAddress& existing_ip) {
+                       return ip == static_cast<rtc::IPAddress>(existing_ip);
+                     }) != ips.end()) {
+      return network;
+    }
+  }
+  return nullptr;
+}
+
 BasicNetworkManager::BasicNetworkManager()
     : thread_(NULL), sent_first_update_(false), start_count_(0),
       ignore_non_default_routes_(false) {