Bind a socket to a network if the network handle is set.

webrtc/base/networkmonitor.h

Index: webrtc/base/networkmonitor.h
diff --git a/webrtc/base/networkmonitor.h b/webrtc/base/networkmonitor.h
index c45c81704072774497facdbf7821121dbd5a76d9..15a75b15f2bc6356cc24e6dc641f50adcb295cd9 100644
--- a/webrtc/base/networkmonitor.h
+++ b/webrtc/base/networkmonitor.h
@@ -17,6 +17,27 @@
 #include "webrtc/base/thread.h"
 
 namespace rtc {
+
+class IPAddress;
+
+// Error values are negative.
+enum NetworkBindingResults {
+  OK = 0,           // No error
+  ERR_FAILED = -1,  // Generic error
+  ERR_NOT_IMPLEMENTED = -2,
+  ERR_ADDRESS_NOT_FOUND = -3,
+  ERR_NETWORK_CHANGED = -4
+};

[pthatcher1, 2016/01/15 19:56:11]

This should have more specific names, like:

NETWORK_BIND_SUCCESS
NETWORK_BIND_FAILURE
NETWORK_BIND_NOT_IMPLEMENTED
NETWORK_BIND_ADDRESS_NOT_FOUND
NETWORK_BIND_NETWORK_CHANGED

[honghaiz3, 2016/01/15 21:37:36]

Done.

+
+class NetworkBinderInterface {
+ public:
+  // Binds a socket to the network that is attached to |address| so that all
+  // packets on the socket |socket_fd| will be sent via that network.
+  // This is needed because some operating systems (like Android) require a
+  // special bind call to put packets on a non-default network interface.
+  virtual int BindSocketToNetwork(int socket_fd, const IPAddress& address) = 0;
+};
+
 /*
  * Receives network-change events via |OnNetworksChanged| and signals the
  * networks changed event.
@@ -36,7 +57,7 @@ namespace rtc {
  */
 // Generic network monitor interface. It starts and stops monitoring network
 // changes, and fires the SignalNetworksChanged event when networks change.
-class NetworkMonitorInterface {
+class NetworkMonitorInterface : public NetworkBinderInterface {

[pthatcher1, 2016/01/15 19:56:11]

Is it necessary to mandate that *every* NetworkMonitor is also a NetworkBinder? 
I think it's the case that on Android it happens to be that way.  I was hoping
we would be able to so something like this:

AndroidNetworkMonitor::Start() {
  // Yes, this is kind of magic behavior, but ... (explain further...).
  worker_thread()->socket_server()->set_network_binder(this);
  // ...
}

And then this whole "NetworkMonitor is a NetworkBinder that has private info
that is used by SocketServer to do an extra bind call" is mostly contained to
Android, and the main NetworkMonitorInterface doesn't need to be changed.

[honghaiz3, 2016/01/15 21:37:36]

Good point. Thanks!

  public:
   NetworkMonitorInterface();
   virtual ~NetworkMonitorInterface();
@@ -62,8 +83,11 @@ class NetworkMonitorBase : public NetworkMonitorInterface,
 
   void OnMessage(Message* msg) override;
 
+ protected:
+  Thread* worker_thread() { return worker_thread_; }
+
  private:
-  Thread* thread_;
+  Thread* worker_thread_;
 };
 
 /*