[GCM] Add basic collapse key support for upstream

google_apis/gcm/engine/mcs_client.h

Index: google_apis/gcm/engine/mcs_client.h
diff --git a/google_apis/gcm/engine/mcs_client.h b/google_apis/gcm/engine/mcs_client.h
index 340f9c1aa14c957f1373765f5e18fd28d6a767a8..3cd00425f83e0e28ad8ccf5345cb5eeb6df69ea9 100644
--- a/google_apis/gcm/engine/mcs_client.h
+++ b/google_apis/gcm/engine/mcs_client.h
@@ -36,6 +36,7 @@ class LoginRequest;
 namespace gcm {
 
 class ConnectionFactory;
+class CollapseKey;

[jianli, 2014/02/04 22:55:14]

nit: sort

[Nicolas Zea, 2014/02/12 23:35:46]

Done.

 struct ReliablePacketInfo;
 
 // An MCS client. This client is in charge of all communications with an
@@ -218,6 +219,9 @@ class GCM_EXPORT MCSClient {
   std::deque<MCSPacketInternal> to_send_;
   std::deque<MCSPacketInternal> to_resend_;
 
+  // Map of collapse keys to their pending messages.
+  std::map<CollapseKey, ReliablePacketInfo*> collapse_key_map_;

[jianli, 2014/02/04 22:55:14]

It seems that the value "ReliablePacketInfo*" is owned by to_send_ and
to_resend_. If the packet is removed from to_send_ and we forget to update
collapse_key_map_, we will get the crash. This might happen when we call
SendMessage and then ResetStateAndBuildLoginRequest.

[Nicolas Zea, 2014/02/12 23:35:46]

Good catch. Note that to_resend_ will never share packets with the
collapse_key_map_, only to_send_. I've gone ahead and added the
PopMessageForSend helper to ensure the collapse key map is always updated if
necessary. 

+
   // Last device_to_server stream id acknowledged by the server.
   StreamId last_device_to_server_stream_id_received_;
   // Last server_to_device stream id acknowledged by this device.