[GCM] Adding handling of the immediate ack to Chrome

If a message carries immediate_ack bit, stream ack will be sent
immediately upon receipt.

This patch also adds a test for that behavior.

BUG=548766

Review URL: https://codereview.chromium.org/1408403006

Cr-Commit-Position: refs/heads/master@{#356679}

5 files changed, 164 insertions, 133 deletions

diff --git a/google_apis/gcm/base/mcs_util.cc b/google_apis/gcm/base/mcs_util.cc
index 7dd9d7b..b5fb928 100644
--- a/google_apis/gcm/base/mcs_util.cc
+++ b/google_apis/gcm/base/mcs_util.cc
@@ -259,4 +259,12 @@ int GetTTL(const google::protobuf::MessageLite& protobuf) {
   return data_message->ttl();
 }
 
+bool IsImmediateAckRequested(const google::protobuf::MessageLite& protobuf) {
+  if (protobuf.GetTypeName() != kProtoNames[kDataMessageStanzaTag])
+    return false;
+  const mcs_proto::DataMessageStanza* data_message =
+      reinterpret_cast<const mcs_proto::DataMessageStanza*>(&protobuf);
+  return data_message->has_immediate_ack() && data_message->immediate_ack();
+}
+
 }  // namespace gcm
diff --git a/google_apis/gcm/base/mcs_util.h b/google_apis/gcm/base/mcs_util.h
index 95d97f2..e6fc1e0 100644
--- a/google_apis/gcm/base/mcs_util.h
+++ b/google_apis/gcm/base/mcs_util.h
@@ -89,6 +89,10 @@ GCM_EXPORT bool HasTTLExpired(const google::protobuf::MessageLite& protobuf,
                               base::Clock* clock);
 GCM_EXPORT int GetTTL(const google::protobuf::MessageLite& protobuf);
 
+// Returns whether the message was sent with an immediate ack request.
+GCM_EXPORT bool IsImmediateAckRequested(
+    const google::protobuf::MessageLite& protobuf);
+
 }  // namespace gcm
 
 #endif  // GOOGLE_APIS_GCM_BASE_MCS_UTIL_H_
diff --git a/google_apis/gcm/engine/mcs_client.cc b/google_apis/gcm/engine/mcs_client.cc
index f20d937..2e52ddb 100644
--- a/google_apis/gcm/engine/mcs_client.cc
+++ b/google_apis/gcm/engine/mcs_client.cc
@@ -681,8 +681,9 @@ void MCSClient::HandlePacketFromWire(
            << ", stream id " << stream_id_in_ << " and last stream id received "
            << last_stream_id_received;
 
-  if (unacked_server_ids_.size() > 0 &&
-      unacked_server_ids_.size() % kUnackedMessageBeforeStreamAck == 0) {
+  if ((unacked_server_ids_.size() > 0 &&
+       unacked_server_ids_.size() % kUnackedMessageBeforeStreamAck == 0) ||
+      IsImmediateAckRequested(*protobuf)) {
     SendMessage(MCSMessage(kIqStanzaTag, BuildStreamAck()));
   }
 
diff --git a/google_apis/gcm/engine/mcs_client_unittest.cc b/google_apis/gcm/engine/mcs_client_unittest.cc
index 6c7ea72..961c36d 100644
--- a/google_apis/gcm/engine/mcs_client_unittest.cc
+++ b/google_apis/gcm/engine/mcs_client_unittest.cc
@@ -41,6 +41,13 @@ const int kAckLimitSize = 10;
 // TTL value for reliable messages.
 const int kTTLValue = 5 * 60;  // 5 minutes.
 
+// Specifies whether immediate ACK should be requested.
+enum RequestImmediateAck {
+  IMMEDIATE_ACK_IGNORE,  // Ignores the field and does not set it.
+  IMMEDIATE_ACK_NO,      // Sets the field to false.
+  IMMEDIATE_ACK_YES      // Sets the field to true.
+};
+
 // Helper for building arbitrary data messages.
 MCSMessage BuildDataMessage(const std::string& from,
                             const std::string& category,
@@ -51,7 +58,8 @@ MCSMessage BuildDataMessage(const std::string& from,
                             uint64 sent,
                             int queued,
                             const std::string& token,
-                            const uint64& user_id) {
+                            const uint64& user_id,
+                            RequestImmediateAck immediate_ack) {
   mcs_proto::DataMessageStanza data_message;
   data_message.set_id(message_id);
   data_message.set_from(from);
@@ -64,6 +72,9 @@ MCSMessage BuildDataMessage(const std::string& from,
   data_message.set_queued(queued);
   data_message.set_token(token);
   data_message.set_device_user_id(user_id);
+  if (immediate_ack != IMMEDIATE_ACK_IGNORE) {
+    data_message.set_immediate_ack(immediate_ack == IMMEDIATE_ACK_YES);
+  }
   return MCSMessage(kDataMessageStanzaTag, data_message);
 }
 
@@ -342,8 +353,8 @@ TEST_F(MCSClientTest, SendMessageNoRMQ) {
   BuildMCSClient();
   InitializeClient();
   LoginClient(std::vector<std::string>());
-  MCSMessage message(
-      BuildDataMessage("from", "category", "X", 1, "", 0, 1, 0, "", 0));
+  MCSMessage message(BuildDataMessage("from", "category", "X", 1, "", 0, 1, 0,
+                                      "", 0, IMMEDIATE_ACK_NO));
   GetFakeHandler()->ExpectOutgoingMessage(message);
   mcs_client()->SendMessage(message);
   EXPECT_TRUE(GetFakeHandler()->AllOutgoingMessagesReceived());
@@ -356,8 +367,8 @@ TEST_F(MCSClientTest, SendMessageNoRMQWhileDisconnected) {
   InitializeClient();
 
   EXPECT_TRUE(sent_message_id().empty());
-  MCSMessage message(
-      BuildDataMessage("from", "category", "X", 1, "", 0, 1, 0, "", 0));
+  MCSMessage message(BuildDataMessage("from", "category", "X", 1, "", 0, 1, 0,
+                                      "", 0, IMMEDIATE_ACK_NO));
   mcs_client()->SendMessage(message);
 
   // Message sent callback should be invoked, but no message should actually
@@ -372,8 +383,9 @@ TEST_F(MCSClientTest, SendMessageRMQ) {
   BuildMCSClient();
   InitializeClient();
   LoginClient(std::vector<std::string>());
-  MCSMessage message(BuildDataMessage(
-      "from", "category", "X", 1, "1", kTTLValue, 1, 0, "", 0));
+  MCSMessage message(BuildDataMessage("from", "category", "X", 1, "1",
+                                      kTTLValue, 1, 0, "", 0,
+                                      IMMEDIATE_ACK_NO));
   GetFakeHandler()->ExpectOutgoingMessage(message);
   mcs_client()->SendMessage(message);
   EXPECT_TRUE(GetFakeHandler()->AllOutgoingMessagesReceived());
@@ -386,8 +398,9 @@ TEST_F(MCSClientTest, SendMessageRMQWhileDisconnected) {
   InitializeClient();
   LoginClient(std::vector<std::string>());
   GetFakeHandler()->set_fail_send(true);
-  MCSMessage message(BuildDataMessage(
-      "from", "category", "X", 1, "1", kTTLValue, 1, 0, "", 0));
+  MCSMessage message(BuildDataMessage("from", "category", "X", 1, "1",
+                                      kTTLValue, 1, 0, "", 0,
+                                      IMMEDIATE_ACK_NO));
 
   // The initial (failed) send.
   GetFakeHandler()->ExpectOutgoingMessage(message);
@@ -395,8 +408,9 @@ TEST_F(MCSClientTest, SendMessageRMQWhileDisconnected) {
   GetFakeHandler()->ExpectOutgoingMessage(MCSMessage(
       kLoginRequestTag, BuildLoginRequest(kAndroidId, kSecurityToken, "")));
   // The second (re)send.
-  MCSMessage message2(BuildDataMessage(
-      "from", "category", "X", 1, "1", kTTLValue, 1, kTTLValue - 1, "", 0));
+  MCSMessage message2(BuildDataMessage("from", "category", "X", 1, "1",
+                                       kTTLValue, 1, kTTLValue - 1, "", 0,
+                                       IMMEDIATE_ACK_NO));
   GetFakeHandler()->ExpectOutgoingMessage(message2);
   mcs_client()->SendMessage(message);
   PumpLoop();         // Wait for the queuing to happen.
@@ -427,8 +441,9 @@ TEST_F(MCSClientTest, SendMessageRMQOnRestart) {
   InitializeClient();
   LoginClient(std::vector<std::string>());
   GetFakeHandler()->set_fail_send(true);
-  MCSMessage message(BuildDataMessage(
-      "from", "category", "X", 1, "1", kTTLValue, 1, 0, "", 0));
+  MCSMessage message(BuildDataMessage("from", "category", "X", 1, "1",
+                                      kTTLValue, 1, 0, "", 0,
+                                      IMMEDIATE_ACK_NO));
 
   // The initial (failed) send.
   GetFakeHandler()->ExpectOutgoingMessage(message);
@@ -443,8 +458,9 @@ TEST_F(MCSClientTest, SendMessageRMQOnRestart) {
   InitializeClient();
 
   clock()->Advance(base::TimeDelta::FromSeconds(kTTLValue - 1));
-  MCSMessage message2(BuildDataMessage(
-      "from", "category", "X", 1, "1", kTTLValue, 1, kTTLValue - 1, "", 0));
+  MCSMessage message2(BuildDataMessage("from", "category", "X", 1, "1",
+                                       kTTLValue, 1, kTTLValue - 1, "", 0,
+                                       IMMEDIATE_ACK_NO));
   LoginClient(std::vector<std::string>());
   GetFakeHandler()->ExpectOutgoingMessage(message2);
   PumpLoop();
@@ -460,16 +476,9 @@ TEST_F(MCSClientTest, SendMessageRMQWithStreamAck) {
 
   // Send some messages.
   for (int i = 1; i <= kMessageBatchSize; ++i) {
-    MCSMessage message(BuildDataMessage("from",
-                                        "category",
-                                        "X",
-                                        1,
-                                        base::IntToString(i),
-                                        kTTLValue,
-                                        1,
-                                        0,
-                                        "",
-                                        0));
+    MCSMessage message(BuildDataMessage("from", "category", "X", 1,
+                                        base::IntToString(i), kTTLValue, 1, 0,
+                                        "", 0, IMMEDIATE_ACK_NO));
     GetFakeHandler()->ExpectOutgoingMessage(message);
     mcs_client()->SendMessage(message);
     PumpLoop();
@@ -501,16 +510,9 @@ TEST_F(MCSClientTest, SendMessageRMQAckOnReconnect) {
   std::vector<std::string> id_list;
   for (int i = 1; i <= kMessageBatchSize; ++i) {
     id_list.push_back(base::IntToString(i));
-    MCSMessage message(BuildDataMessage("from",
-                                        "category",
-                                        id_list.back(),
-                                        1,
-                                        id_list.back(),
-                                        kTTLValue,
-                                        1,
-                                        0,
-                                        "",
-                                        0));
+    MCSMessage message(BuildDataMessage("from", "category", id_list.back(), 1,
+                                        id_list.back(), kTTLValue, 1, 0, "", 0,
+                                        IMMEDIATE_ACK_NO));
     GetFakeHandler()->ExpectOutgoingMessage(message);
     mcs_client()->SendMessage(message);
     PumpLoop();
@@ -540,16 +542,9 @@ TEST_F(MCSClientTest, SendMessageRMQPartialAckOnReconnect) {
   std::vector<std::string> id_list;
   for (int i = 1; i <= kMessageBatchSize; ++i) {
     id_list.push_back(base::IntToString(i));
-    MCSMessage message(BuildDataMessage("from",
-                                        "category",
-                                        id_list.back(),
-                                        1,
-                                        id_list.back(),
-                                        kTTLValue,
-                                        1,
-                                        0,
-                                        "",
-                                        0));
+    MCSMessage message(BuildDataMessage("from", "category", id_list.back(), 1,
+                                        id_list.back(), kTTLValue, 1, 0, "", 0,
+                                        IMMEDIATE_ACK_NO));
     GetFakeHandler()->ExpectOutgoingMessage(message);
     mcs_client()->SendMessage(message);
     PumpLoop();
@@ -571,16 +566,9 @@ TEST_F(MCSClientTest, SendMessageRMQPartialAckOnReconnect) {
                        id_list.begin() + kMessageBatchSize / 2,
                        id_list.end());
   for (int i = 1; i <= kMessageBatchSize / 2; ++i) {
-    MCSMessage message(BuildDataMessage("from",
-                                        "category",
-                                        remaining_ids[i - 1],
-                                        2,
-                                        remaining_ids[i - 1],
-                                        kTTLValue,
-                                        1,
-                                        0,
-                                        "",
-                                        0));
+    MCSMessage message(BuildDataMessage(
+        "from", "category", remaining_ids[i - 1], 2, remaining_ids[i - 1],
+        kTTLValue, 1, 0, "", 0, IMMEDIATE_ACK_NO));
     GetFakeHandler()->ExpectOutgoingMessage(message);
   }
   scoped_ptr<mcs_proto::IqStanza> ack(BuildSelectiveAck(acked_ids));
@@ -600,16 +588,18 @@ TEST_F(MCSClientTest, SelectiveAckMidStream) {
 
   // Server stream id 2 ("s1").
   // Acks client stream id 0 (login).
-  MCSMessage sMessage1(BuildDataMessage(
-      "from", "category", "X", 0, "s1", kTTLValue, 1, 0, "", 0));
+  MCSMessage sMessage1(BuildDataMessage("from", "category", "X", 0, "s1",
+                                        kTTLValue, 1, 0, "", 0,
+                                        IMMEDIATE_ACK_NO));
   GetFakeHandler()->ReceiveMessage(sMessage1);
   WaitForMCSEvent();
   PumpLoop();
 
   // Client stream id 1 ("1").
   // Acks server stream id 2 ("s1").
-  MCSMessage cMessage1(BuildDataMessage(
-      "from", "category", "Y", 2, "1", kTTLValue, 1, 0, "", 0));
+  MCSMessage cMessage1(BuildDataMessage("from", "category", "Y", 2, "1",
+                                        kTTLValue, 1, 0, "", 0,
+                                        IMMEDIATE_ACK_NO));
   GetFakeHandler()->ExpectOutgoingMessage(cMessage1);
   mcs_client()->SendMessage(cMessage1);
   PumpLoop();
@@ -618,16 +608,18 @@ TEST_F(MCSClientTest, SelectiveAckMidStream) {
   // Server stream id 3 ("s2").
   // Acks client stream id 1 ("1").
   // Confirms ack of server stream id 2 ("s1").
-  MCSMessage sMessage2(BuildDataMessage(
-      "from", "category", "X", 1, "s2", kTTLValue, 1, 0, "", 0));
+  MCSMessage sMessage2(BuildDataMessage("from", "category", "X", 1, "s2",
+                                        kTTLValue, 1, 0, "", 0,
+                                        IMMEDIATE_ACK_NO));
   GetFakeHandler()->ReceiveMessage(sMessage2);
   WaitForMCSEvent();
   PumpLoop();
 
   // Client Stream id 2 ("2").
   // Acks server stream id 3 ("s2").
-  MCSMessage cMessage2(BuildDataMessage(
-      "from", "category", "Y", 3, "2", kTTLValue, 1, 0, "", 0));
+  MCSMessage cMessage2(BuildDataMessage("from", "category", "Y", 3, "2",
+                                        kTTLValue, 1, 0, "", 0,
+                                        IMMEDIATE_ACK_NO));
   GetFakeHandler()->ExpectOutgoingMessage(cMessage2);
   mcs_client()->SendMessage(cMessage2);
   PumpLoop();
@@ -637,8 +629,9 @@ TEST_F(MCSClientTest, SelectiveAckMidStream) {
   // ack client message "1".
   // Client message "2" should be resent, acking server stream id 4 (selective
   // ack).
-  MCSMessage cMessage3(BuildDataMessage(
-      "from", "category", "Y", 4, "2", kTTLValue, 1, 0, "", 0));
+  MCSMessage cMessage3(BuildDataMessage("from", "category", "Y", 4, "2",
+                                        kTTLValue, 1, 0, "", 0,
+                                        IMMEDIATE_ACK_NO));
   GetFakeHandler()->ExpectOutgoingMessage(cMessage3);
   std::vector<std::string> acked_ids(1, "1");
   scoped_ptr<mcs_proto::IqStanza> ack(BuildSelectiveAck(acked_ids));
@@ -658,8 +651,9 @@ TEST_F(MCSClientTest, SelectiveAckMidStream) {
   acked_ids[0] = "s2";
   LoginClient(acked_ids);
 
-  MCSMessage cMessage4(BuildDataMessage(
-      "from", "category", "Y", 1, "2", kTTLValue, 1, 0, "", 0));
+  MCSMessage cMessage4(BuildDataMessage("from", "category", "Y", 1, "2",
+                                        kTTLValue, 1, 0, "", 0,
+                                        IMMEDIATE_ACK_NO));
   GetFakeHandler()->ExpectOutgoingMessage(cMessage4);
   PumpLoop();
   EXPECT_TRUE(GetFakeHandler()->AllOutgoingMessagesReceived());
@@ -676,8 +670,9 @@ TEST_F(MCSClientTest, AckOnLogin) {
   std::vector<std::string> id_list;
   for (int i = 1; i <= kMessageBatchSize; ++i) {
     id_list.push_back(base::IntToString(i));
-    MCSMessage message(BuildDataMessage(
-        "from", "category", "X", 1, id_list.back(), kTTLValue, 1, 0, "", 0));
+    MCSMessage message(BuildDataMessage("from", "category", "X", 1,
+                                        id_list.back(), kTTLValue, 1, 0, "", 0,
+                                        IMMEDIATE_ACK_NO));
     GetFakeHandler()->ReceiveMessage(message);
     WaitForMCSEvent();
     PumpLoop();
@@ -701,31 +696,17 @@ TEST_F(MCSClientTest, AckOnSend) {
   std::vector<std::string> id_list;
   for (int i = 1; i <= kMessageBatchSize; ++i) {
     id_list.push_back(base::IntToString(i));
-    MCSMessage message(BuildDataMessage("from",
-                                        "category",
-                                        id_list.back(),
-                                        1,
-                                        id_list.back(),
-                                        kTTLValue,
-                                        1,
-                                        0,
-                                        "",
-                                        0));
+    MCSMessage message(BuildDataMessage("from", "category", id_list.back(), 1,
+                                        id_list.back(), kTTLValue, 1, 0, "", 0,
+                                        IMMEDIATE_ACK_NO));
     GetFakeHandler()->ReceiveMessage(message);
     PumpLoop();
   }
 
   // Trigger a message send, which should acknowledge via stream ack.
-  MCSMessage message(BuildDataMessage("from",
-                                      "category",
-                                      "X",
-                                      kMessageBatchSize + 1,
-                                      "1",
-                                      kTTLValue,
-                                      1,
-                                      0,
-                                      "",
-                                      0));
+  MCSMessage message(BuildDataMessage("from", "category", "X",
+                                      kMessageBatchSize + 1, "1", kTTLValue, 1,
+                                      0, "", 0, IMMEDIATE_ACK_NO));
   GetFakeHandler()->ExpectOutgoingMessage(message);
   mcs_client()->SendMessage(message);
   EXPECT_TRUE(GetFakeHandler()->AllOutgoingMessagesReceived());
@@ -747,16 +728,9 @@ TEST_F(MCSClientTest, AckWhenLimitReachedWithHeartbeat) {
   std::vector<std::string> id_list;
   for (int i = 1; i <= kAckLimitSize; ++i) {
     id_list.push_back(base::IntToString(i));
-    MCSMessage message(BuildDataMessage("from",
-                                        "category",
-                                        id_list.back(),
-                                        1,
-                                        id_list.back(),
-                                        kTTLValue,
-                                        1,
-                                        0,
-                                        "",
-                                        0));
+    MCSMessage message(BuildDataMessage("from", "category", id_list.back(), 1,
+                                        id_list.back(), kTTLValue, 1, 0, "", 0,
+                                        IMMEDIATE_ACK_NO));
     GetFakeHandler()->ReceiveMessage(message);
     WaitForMCSEvent();
     PumpLoop();
@@ -793,8 +767,9 @@ TEST_F(MCSClientTest, ExpiredTTLOnSend) {
   BuildMCSClient();
   InitializeClient();
   LoginClient(std::vector<std::string>());
-  MCSMessage message(BuildDataMessage(
-      "from", "category", "X", 1, "1", kTTLValue, 1, 0, "", 0));
+  MCSMessage message(BuildDataMessage("from", "category", "X", 1, "1",
+                                      kTTLValue, 1, 0, "", 0,
+                                      IMMEDIATE_ACK_NO));
 
   // Advance time to after the TTL.
   clock()->Advance(base::TimeDelta::FromSeconds(kTTLValue + 2));
@@ -812,8 +787,9 @@ TEST_F(MCSClientTest, ExpiredTTLOnRestart) {
   InitializeClient();
   LoginClient(std::vector<std::string>());
   GetFakeHandler()->set_fail_send(true);
-  MCSMessage message(BuildDataMessage(
-      "from", "category", "X", 1, "1", kTTLValue, 1, 0, "", 0));
+  MCSMessage message(BuildDataMessage("from", "category", "X", 1, "1",
+                                      kTTLValue, 1, 0, "", 0,
+                                      IMMEDIATE_ACK_NO));
 
   // The initial (failed) send.
   GetFakeHandler()->ExpectOutgoingMessage(message);
@@ -840,12 +816,14 @@ TEST_F(MCSClientTest, ExpiredTTLOnRestart) {
 TEST_F(MCSClientTest, CollapseKeysSameApp) {
   BuildMCSClient();
   InitializeClient();
-  MCSMessage message(BuildDataMessage(
-      "from", "app", "message id 1", 1, "1", kTTLValue, 1, 0, "token", 0));
+  MCSMessage message(BuildDataMessage("from", "app", "message id 1", 1, "1",
+                                      kTTLValue, 1, 0, "token", 0,
+                                      IMMEDIATE_ACK_NO));
   mcs_client()->SendMessage(message);
 
-  MCSMessage message2(BuildDataMessage(
-      "from", "app", "message id 2", 1, "1", kTTLValue, 1, 0, "token", 0));
+  MCSMessage message2(BuildDataMessage("from", "app", "message id 2", 1, "1",
+                                       kTTLValue, 1, 0, "token", 0,
+                                       IMMEDIATE_ACK_NO));
   mcs_client()->SendMessage(message2);
 
   LoginClient(std::vector<std::string>());
@@ -858,20 +836,14 @@ TEST_F(MCSClientTest, CollapseKeysSameApp) {
 TEST_F(MCSClientTest, CollapseKeysDifferentApp) {
   BuildMCSClient();
   InitializeClient();
-  MCSMessage message(BuildDataMessage(
-      "from", "app", "message id 1", 1, "1", kTTLValue, 1, 0, "token", 0));
+  MCSMessage message(BuildDataMessage("from", "app", "message id 1", 1, "1",
+                                      kTTLValue, 1, 0, "token", 0,
+                                      IMMEDIATE_ACK_NO));
   mcs_client()->SendMessage(message);
 
-  MCSMessage message2(BuildDataMessage("from",
-                                       "app 2",
-                                       "message id 2",
-                                       1,
-                                       "2",
-                                       kTTLValue,
-                                       1,
-                                       0,
-                                       "token",
-                                       0));
+  MCSMessage message2(BuildDataMessage("from", "app 2", "message id 2", 1, "2",
+                                       kTTLValue, 1, 0, "token", 0,
+                                       IMMEDIATE_ACK_NO));
   mcs_client()->SendMessage(message2);
 
   LoginClient(std::vector<std::string>());
@@ -885,20 +857,14 @@ TEST_F(MCSClientTest, CollapseKeysDifferentApp) {
 TEST_F(MCSClientTest, CollapseKeysDifferentUser) {
   BuildMCSClient();
   InitializeClient();
-  MCSMessage message(BuildDataMessage(
-      "from", "app", "message id 1", 1, "1", kTTLValue, 1, 0, "token", 0));
+  MCSMessage message(BuildDataMessage("from", "app", "message id 1", 1, "1",
+                                      kTTLValue, 1, 0, "token", 0,
+                                      IMMEDIATE_ACK_NO));
   mcs_client()->SendMessage(message);
 
-  MCSMessage message2(BuildDataMessage("from",
-                                       "app",
-                                       "message id 2",
-                                       1,
-                                       "2",
-                                       kTTLValue,
-                                       1,
-                                       0,
-                                       "token",
-                                       1));
+  MCSMessage message2(BuildDataMessage("from", "app", "message id 2", 1, "2",
+                                       kTTLValue, 1, 0, "token", 1,
+                                       IMMEDIATE_ACK_NO));
   mcs_client()->SendMessage(message2);
 
   LoginClient(std::vector<std::string>());
@@ -1175,6 +1141,42 @@ TEST_F(MCSClientTest, CustomHeartbeatIntervalRemoveShorterInterval) {
   EXPECT_EQ(interval_ms, hb_manager->GetClientHeartbeatIntervalMs());
 }
 
+// Receive a message with immediate ack request, which should trigger an
+// automatic stream ack.
+TEST_F(MCSClientTest, AckWhenImmediateAckRequested) {
+  BuildMCSClient();
+  InitializeClient();
+  LoginClient(std::vector<std::string>());
+
+  // The stream ack.
+  scoped_ptr<mcs_proto::IqStanza> ack = BuildStreamAck();
+  ack->set_last_stream_id_received(kAckLimitSize - 1);
+  GetFakeHandler()->ExpectOutgoingMessage(MCSMessage(kIqStanzaTag, ack.Pass()));
+
+  // Receive some messages.
+  for (int i = 1; i < kAckLimitSize - 2; ++i) {
+    std::string id(base::IntToString(i));
+    MCSMessage message(BuildDataMessage("from", "category", id, 1, id,
+                                        kTTLValue, 1, 0, "", 0,
+                                        IMMEDIATE_ACK_NO));
+    GetFakeHandler()->ReceiveMessage(message);
+    WaitForMCSEvent();
+    PumpLoop();
+  }
+  // This message expects immediate ACK, which means it will happen before the
+  // ACK limit size is reached. All of the preceding messages will be acked at
+  // the same time.
+  std::string ack_id(base::IntToString(kAckLimitSize - 1));
+  MCSMessage message(BuildDataMessage("from", "category", ack_id, 1, ack_id,
+                                      kTTLValue, 1, 0, "", 0,
+                                      IMMEDIATE_ACK_YES));
+  GetFakeHandler()->ReceiveMessage(message);
+  WaitForMCSEvent();
+  PumpLoop();
+
+  EXPECT_TRUE(GetFakeHandler()->AllOutgoingMessagesReceived());
+}
+
 } // namespace
 
 }  // namespace gcm
diff --git a/google_apis/gcm/protocol/mcs.proto b/google_apis/gcm/protocol/mcs.proto
index a1ea614..cba5845 100644
--- a/google_apis/gcm/protocol/mcs.proto
+++ b/google_apis/gcm/protocol/mcs.proto
@@ -253,6 +253,22 @@ message DataMessageStanza {
 
   // Optional field containing the binary payload of the message.
   optional bytes raw_data = 21;
+
+  // Not used.
+  // The maximum delay of the message, in seconds.
+  // optional int32 max_delay = 22;
+
+  // Not used.
+  // How long the message was delayed before it was sent, in seconds.
+  // optional int32 actual_delay = 23;
+
+  // If set the server requests immediate ack. Used for important messages and
+  // for testing.
+  optional bool immediate_ack = 24;
+
+  // Not used.
+  // Enables message receipts from MCS/GCM back to CCS clients
+  // optional bool delivery_receipt_requested = 25;
 }
 
 /**