[mle] prioritize equivalent pending dataset update over MLE announce (#10631)

Avoid processing announce messages with equivalent data that is stored
in a pending dataset update.

src/core/meshcop/dataset_manager.cpp

@@ -885,6 +885,35 @@ PendingDatasetManager::PendingDatasetManager(Instance &aInstance)
 {
 }
 
+Error PendingDatasetManager::ReadActiveTimestamp(Timestamp &aTimestamp) const
+{
+    Error   error = kErrorNotFound;
+    Dataset dataset;
+
+    SuccessOrExit(Read(dataset));
+
+    SuccessOrExit(dataset.Read<ActiveTimestampTlv>(aTimestamp));
+    error = kErrorNone;
+
+exit:
+    return error;
+}
+
+Error PendingDatasetManager::ReadRemainingDelay(uint32_t &aRemainingDelay) const
+{
+    Error     error = kErrorNone;
+    TimeMilli now   = TimerMilli::GetNow();
+
+    aRemainingDelay = 0;
+
+    VerifyOrExit(mDelayTimer.IsRunning(), error = kErrorNotFound);
+    VerifyOrExit(mDelayTimer.GetFireTime() > now);
+    aRemainingDelay = mDelayTimer.GetFireTime() - now;
+
+exit:
+    return error;
+}
+
 void PendingDatasetManager::StartDelayTimer(void)
 {
     Dataset dataset;

src/core/meshcop/dataset_manager.hpp

@@ -441,6 +441,28 @@ public:
      */
     explicit PendingDatasetManager(Instance &aInstance);
 
+    /**
+     * Reads the Active Timestamp in the Pending Operational Dataset.
+     *
+     * @param[out] aTimestamp A reference to return the read timestamp.
+     *
+     * @retval kErrorNone     The active timestamp was successfully fetched.
+     * @retval kErrorNotFound The pending dataset is not currently valid.
+     *
+     */
+    Error ReadActiveTimestamp(Timestamp &aTimestamp) const;
+
+    /**
+     * Reads the remaining delay time in ms.
+     *
+     * @param[out] aRemainingDelay A reference to return the remaining delay time.
+     *
+     * @retval kErrorNone     The remaining delay time was successfully fetched.
+     * @retval kErrorNotFound The pending dataset is not currently valid.
+     *
+     */
+    Error ReadRemainingDelay(uint32_t &aRemainingDelay) const;
+
 #if OPENTHREAD_FTD
     /**
      * Starts the Leader functions for maintaining the Active Operational Dataset.

src/core/thread/mle.cpp

@@ -3663,6 +3663,7 @@ void Mle::HandleAnnounce(RxInfo &aRxInfo)
     Error              error = kErrorNone;
     ChannelTlvValue    channelTlvValue;
     MeshCoP::Timestamp timestamp;
+    MeshCoP::Timestamp pendingActiveTimestamp;
     uint8_t            channel;
     uint16_t           panId;
     bool               isFromOrphan;
@@ -3707,6 +3708,24 @@ void Mle::HandleAnnounce(RxInfo &aRxInfo)
             VerifyOrExit(!channelAndPanIdMatch);
         }
 
+        if (Get<MeshCoP::PendingDatasetManager>().ReadActiveTimestamp(pendingActiveTimestamp) == kErrorNone)
+        {
+            // Ignore the Announce and take no action, if a pending
+            // dataset exists with an equal or more recent timestamp,
+            // and it will be applied soon.
+
+            if (pendingActiveTimestamp >= timestamp)
+            {
+                uint32_t remainingDelay;
+
+                if ((Get<MeshCoP::PendingDatasetManager>().ReadRemainingDelay(remainingDelay) == kErrorNone) &&
+                    (remainingDelay < kAnnounceBackoffForPendingDataset))
+                {
+                    ExitNow();
+                }
+            }
+        }
+
         if (mAttachState == kAttachStateProcessAnnounce)
         {
             VerifyOrExit(mAlternateTimestamp < timestamp.GetSeconds());

src/core/thread/mle.hpp

@@ -811,6 +811,7 @@ private:
     static constexpr uint32_t kMulticastRetxDelay             = 5000; // Base delay for MLE multicast retx
     static constexpr uint32_t kMulticastRetxDelayMin          = kMulticastRetxDelay * 9 / 10;  // 0.9 * base delay
     static constexpr uint32_t kMulticastRetxDelayMax          = kMulticastRetxDelay * 11 / 10; // 1.1 * base delay
+    static constexpr uint32_t kAnnounceBackoffForPendingDataset = 60000; // Max delay left to block Announce processing.
 
     static constexpr uint8_t kMaxTxCount                = 3; // Max tx count for MLE message
     static constexpr uint8_t kMaxCriticalTxCount        = 6; // Max tx count for critical MLE message