[mle] remove existing MLE Data Response in queues when there is newer Network Data (#2479)

This commit helps to reduce additional message exchanges when multiple network data updates
in short time.

src/core/common/message.cpp

@@ -366,6 +366,7 @@ bool Message::IsSubTypeMle(void) const
         mBuffer.mHead.mInfo.mSubType == kSubTypeMleDiscoverRequest ||
         mBuffer.mHead.mInfo.mSubType == kSubTypeMleDiscoverResponse ||
         mBuffer.mHead.mInfo.mSubType == kSubTypeMleChildUpdateRequest ||
+        mBuffer.mHead.mInfo.mSubType == kSubTypeMleDataResponse ||
         mBuffer.mHead.mInfo.mSubType == kSubTypeMleGeneral)
     {
         rval = true;

src/core/common/message.hpp

@@ -218,6 +218,7 @@ public:
         kSubTypeMleGeneral             = 6,  ///< General MLE
         kSubTypeJoinerFinalizeResponse = 7,  ///< Joiner Finalize Response
         kSubTypeMleChildUpdateRequest  = 8,  ///< MLE Child Update Request
+        kSubTypeMleDataResponse        = 9,  ///< MLE Data Response
     };
 
     enum

src/core/thread/mesh_forwarder.hpp

@@ -174,6 +174,12 @@ public:
      */
     void RemoveMessages(Child &aChild, uint8_t aSubType);
 
+    /**
+     * This method frees unicast/multicast MLE Data Responses from Send Message Queue if any.
+     *
+     */
+    void RemoveDataResponseMessages(void);
+
     /**
      * This method evicts the first indirect message in the indirect send queue.
      *

src/core/thread/mesh_forwarder_ftd.cpp

@@ -314,6 +314,43 @@ void MeshForwarder::RemoveMessages(Child &aChild, uint8_t aSubType)
     }
 }
 
+void MeshForwarder::RemoveDataResponseMessages(void)
+{
+    Ip6::Header ip6Header;
+
+    for (Message *message = mSendQueue.GetHead(); message; message = message->GetNext())
+    {
+        if (message->GetSubType() != Message::kSubTypeMleDataResponse)
+        {
+            continue;
+        }
+
+        message->Read(0, sizeof(ip6Header), &ip6Header);
+
+        if (!(ip6Header.GetDestination().IsMulticast()))
+        {
+            Child *children;
+            uint8_t numChildren;
+
+            children = GetNetif().GetMle().GetChildren(&numChildren);
+
+            for (uint8_t i = 0; i < numChildren; i++)
+            {
+                IgnoreReturnValue(RemoveMessageFromSleepyChild(*message, children[i]));
+            }
+        }
+
+        if (mSendMessage == message)
+        {
+            mSendMessage = NULL;
+        }
+
+        mSendQueue.Dequeue(*message);
+        LogIp6Message(kMessageDrop, *message, NULL, OT_ERROR_NONE);
+        message->Free();
+    }
+}
+
 otError MeshForwarder::GetIndirectTransmission(void)
 {
     otError error = OT_ERROR_NOT_FOUND;

src/core/thread/mle.cpp

@@ -1565,6 +1565,29 @@ void Mle::HandleDelayedResponseTimer(void)
     }
 }
 
+void Mle::RemoveDelayedDataResponseMessage(void)
+{
+    Message *message = mDelayedResponses.GetHead();
+    DelayedResponseHeader delayedResponse;
+
+    while (message != NULL)
+    {
+        delayedResponse.ReadFrom(*message);
+
+        if (message->GetSubType() == Message::kSubTypeMleDataResponse)
+        {
+            mDelayedResponses.Dequeue(*message);
+            message->Free();
+            LogMleMessage("Remove Delayed Data Response", delayedResponse.GetDestination());
+
+            // no more than one multicast MLE Data Response in Delayed Message Queue.
+            break;
+        }
+
+        message = message->GetNext();
+    }
+}
+
 otError Mle::SendParentRequest(void)
 {
     otError error = OT_ERROR_NONE;

src/core/thread/mle.hpp

@@ -937,6 +937,12 @@ public:
      */
     const MessageQueue &GetMessageQueue(void) const { return mDelayedResponses; }
 
+    /**
+     * This method frees multicast MLE Data Response from Delayed Message Queue if any.
+     *
+     */
+    void RemoveDelayedDataResponseMessage(void);
+
 protected:
     enum
     {

src/core/thread/mle_router.cpp

@@ -2198,6 +2198,7 @@ otError MleRouter::HandleChildIdRequest(const Message &aMessage, const Ip6::Mess
     // Remove existing MLE messages
     netif.GetMeshForwarder().RemoveMessages(*child, Message::kSubTypeMleGeneral);
     netif.GetMeshForwarder().RemoveMessages(*child, Message::kSubTypeMleChildUpdateRequest);
+    netif.GetMeshForwarder().RemoveMessages(*child, Message::kSubTypeMleDataResponse);
 
     // Link-Layer Frame Counter
     SuccessOrExit(error = Tlv::GetTlv(aMessage, Tlv::kLinkFrameCounter, sizeof(linkFrameCounter),
@@ -3131,6 +3132,7 @@ otError MleRouter::SendDataResponse(const Ip6::Address &aDestination, const uint
     }
 
     VerifyOrExit((message = NewMleMessage()) != NULL, error = OT_ERROR_NO_BUFS);
+    message->SetSubType(Message::kSubTypeMleDataResponse);
     SuccessOrExit(error = AppendHeader(*message, Header::kCommandDataResponse));
     SuccessOrExit(error = AppendSourceAddress(*message));
     SuccessOrExit(error = AppendLeaderData(*message));
@@ -3159,6 +3161,12 @@ otError MleRouter::SendDataResponse(const Ip6::Address &aDestination, const uint
 
     if (aDelay)
     {
+        // Remove MLE Data Responses from Send Message Queue.
+        GetNetif().GetMeshForwarder().RemoveDataResponseMessages();
+
+        // Remove multicast MLE Data Response from Delayed Message Queue.
+        RemoveDelayedDataResponseMessage();
+
         SuccessOrExit(error = AddDelayedResponse(*message, aDestination, aDelay));
         LogMleMessage("Delay Data Response", aDestination);
     }