[mle] evicts delayed MLE Data Request when sending a newer one (#6996)

This commit evicts delayed MLE Data Requests whenever the device is
sending a newer one.

src/core/common/message.hpp

@@ -291,6 +291,7 @@ public:
         kSubTypeMleChildUpdateRequest  = 8,  ///< MLE Child Update Request
         kSubTypeMleDataResponse        = 9,  ///< MLE Data Response
         kSubTypeMleChildIdRequest      = 10, ///< MLE Child ID Request
+        kSubTypeMleDataRequest         = 11, ///< MLE Data Request
     };
 
     enum Priority : uint8_t

src/core/thread/mle.cpp

@@ -1964,7 +1964,7 @@ void Mle::HandleDelayedResponseTimer(void)
             mDelayedResponses.Dequeue(*message);
             metadata.RemoveFrom(*message);
 
-            if (metadata.mAppendTimestamps)
+            if (message->GetSubType() == Message::kSubTypeMleDataRequest)
             {
                 error = AppendActiveTimestamp(*message);
                 error = (error == kErrorNone) ? AppendPendingTimestamp(*message) : error;
@@ -2021,6 +2021,25 @@ void Mle::RemoveDelayedDataResponseMessage(void)
     }
 }
 
+void Mle::RemoveDelayedDataRequestMessage(const Ip6::Address &aDestination)
+{
+    for (Message *message = mDelayedResponses.GetHead(); message != nullptr; message = message->GetNext())
+    {
+        DelayedResponseMetadata metadata;
+
+        metadata.ReadFrom(*message);
+
+        if (message->GetSubType() == Message::kSubTypeMleDataRequest && metadata.mDestination == aDestination)
+        {
+            mDelayedResponses.DequeueAndFree(*message);
+            Log(kMessageRemoveDelayed, kTypeDataRequest, metadata.mDestination);
+
+            // no more than one MLE Data Request for the destination in Delayed Message Queue.
+            break;
+        }
+    }
+}
+
 Error Mle::SendParentRequest(ParentRequestType aType)
 {
     Error        error = kErrorNone;
@@ -2160,7 +2179,10 @@ Error Mle::SendDataRequest(const Ip6::Address &aDestination,
     Error    error = kErrorNone;
     Message *message;
 
+    RemoveDelayedDataRequestMessage(aDestination);
+
     VerifyOrExit((message = NewMleMessage()) != nullptr, error = kErrorNoBufs);
+    message->SetSubType(Message::kSubTypeMleDataRequest);
     SuccessOrExit(error = AppendHeader(*message, kCommandDataRequest));
     SuccessOrExit(error = AppendTlvRequest(*message, aTlvs, aTlvsLength));
 
@@ -2171,7 +2193,7 @@ Error Mle::SendDataRequest(const Ip6::Address &aDestination,
 
     if (aDelay)
     {
-        SuccessOrExit(error = AddDelayedResponse(*message, aDestination, aDelay, /* aAppendTimestamps */ true));
+        SuccessOrExit(error = AddDelayedResponse(*message, aDestination, aDelay));
         Log(kMessageDelay, kTypeDataRequest, aDestination);
     }
     else
@@ -2662,17 +2684,13 @@ exit:
     return error;
 }
 
-Error Mle::AddDelayedResponse(Message &           aMessage,
-                              const Ip6::Address &aDestination,
-                              uint16_t            aDelay,
-                              bool                aAppendTimestamps)
+Error Mle::AddDelayedResponse(Message &aMessage, const Ip6::Address &aDestination, uint16_t aDelay)
 {
     Error                   error = kErrorNone;
     DelayedResponseMetadata metadata;
 
-    metadata.mSendTime         = TimerMilli::GetNow() + aDelay;
-    metadata.mDestination      = aDestination;
-    metadata.mAppendTimestamps = aAppendTimestamps;
+    metadata.mSendTime    = TimerMilli::GetNow() + aDelay;
+    metadata.mDestination = aDestination;
 
     SuccessOrExit(error = metadata.AppendTo(aMessage));
     mDelayedResponses.Enqueue(aMessage);

src/core/thread/mle.hpp

@@ -1445,16 +1445,12 @@ protected:
      * @param[in]  aMessage             The message to transmit after given delay.
      * @param[in]  aDestination         The IPv6 address of the recipient of the message.
      * @param[in]  aDelay               The delay in milliseconds before transmission of the message.
-     * @param[in]  aAppendTimestamps    Whether or not to append Active and Pending Timestamps before sending.
      *
      * @retval kErrorNone     Successfully queued the message to transmit after the delay.
      * @retval kErrorNoBufs   Insufficient buffers to queue the message.
      *
      */
-    Error AddDelayedResponse(Message &           aMessage,
-                             const Ip6::Address &aDestination,
-                             uint16_t            aDelay,
-                             bool                aAppendTimestamps = false);
+    Error AddDelayedResponse(Message &aMessage, const Ip6::Address &aDestination, uint16_t aDelay);
 
 #if (OPENTHREAD_CONFIG_LOG_LEVEL >= OT_LOG_LEVEL_INFO) && (OPENTHREAD_CONFIG_LOG_MLE == 1)
     /**
@@ -1671,9 +1667,8 @@ private:
         void  ReadFrom(const Message &aMessage);
         void  RemoveFrom(Message &aMessage) const;
 
-        Ip6::Address mDestination;          // IPv6 address of the message destination.
-        TimeMilli    mSendTime;             // Time when the message shall be sent.
-        bool         mAppendTimestamps : 1; // Append Active Timestamp and Pending Timestamp before sending.
+        Ip6::Address mDestination; // IPv6 address of the message destination.
+        TimeMilli    mSendTime;    // Time when the message shall be sent.
     };
 
     OT_TOOL_PACKED_BEGIN
@@ -1818,6 +1813,7 @@ private:
     bool     PrepareAnnounceState(void);
     void     SendAnnounce(uint8_t aChannel, AnnounceMode aMode);
     void     SendAnnounce(uint8_t aChannel, const Ip6::Address &aDestination, AnnounceMode aMode = kNormalAnnounce);
+    void     RemoveDelayedDataRequestMessage(const Ip6::Address &aDestination);
 #if OPENTHREAD_CONFIG_MLE_LINK_METRICS_SUBJECT_ENABLE
     Error SendLinkMetricsManagementResponse(const Ip6::Address &aDestination, LinkMetrics::Status aStatus);
 #endif