[indirect-sender] convert queued child messages when mode changes (#4001)

This commit ensures all queued messages for a child are accordingly
converted (indirect to direct transmission) when a child switches its
mode from sleepy to non-sleepy.

src/core/thread/indirect_sender.cpp

@@ -41,6 +41,7 @@
 #include "common/logging.hpp"
 #include "common/message.hpp"
 #include "thread/mesh_forwarder.hpp"
+#include "thread/mle_tlvs.hpp"
 #include "thread/topology.hpp"
 
 namespace ot {
@@ -163,6 +164,45 @@ exit:
     return;
 }
 
+void IndirectSender::HandleChildModeChange(Child &aChild, uint8_t aOldMode)
+{
+    bool wasRxOnWhenIdle = ((aOldMode & Mle::ModeTlv::kModeRxOnWhenIdle) != 0);
+
+    if (!aChild.IsRxOnWhenIdle() && (aChild.GetState() == Neighbor::kStateValid))
+    {
+        SetChildUseShortAddress(aChild, true);
+    }
+
+    // On sleepy to non-sleepy mode change, convert indirect messages in
+    // the send queue destined to the child to direct.
+
+    if (!wasRxOnWhenIdle && aChild.IsRxOnWhenIdle() && (aChild.GetIndirectMessageCount() > 0))
+    {
+        uint8_t childIndex = Get<ChildTable>().GetChildIndex(aChild);
+
+        for (Message *message = Get<MeshForwarder>().mSendQueue.GetHead(); message; message = message->GetNext())
+        {
+            if (message->GetChildMask(childIndex))
+            {
+                message->ClearChildMask(childIndex);
+                message->SetDirectTransmission();
+            }
+        }
+
+        aChild.SetIndirectMessage(NULL);
+        mSourceMatchController.ResetMessageCount(aChild);
+
+        mDataPollHandler.RequestFrameChange(DataPollHandler::kPurgeFrame, aChild);
+    }
+
+    // Since the queuing delays for direct transmissions are expected to
+    // be relatively small especially when compared to indirect, for a
+    // non-sleepy to sleepy mode change, we allow any direct message
+    // (for the child) already in the send queue to remain as is. This
+    // is equivalent to dropping the already queued messages in this
+    // case.
+}
+
 Message *IndirectSender::FindIndirectMessage(Child &aChild)
 {
     Message *message;

src/core/thread/indirect_sender.hpp

@@ -186,6 +186,15 @@ public:
      */
     void SetChildUseShortAddress(Child &aChild, bool aUseShortAddress);
 
+    /**
+     * This method handles a child mode change and updates any queued messages for the child accordingly.
+     *
+     * @param[in]  aChild    The child whose device mode was changed.
+     * @param[in]  aOldMode  The old device mode of the child.
+     *
+     */
+    void HandleChildModeChange(Child &aChild, uint8_t aOldMode);
+
 private:
     enum
     {

src/core/thread/mle_router.cpp

@@ -2225,6 +2225,7 @@ otError MleRouter::HandleChildUpdateRequest(const Message &         aMessage,
     LeaderDataTlv   leaderData;
     TimeoutTlv      timeout;
     Child *         child;
+    uint8_t         oldMode;
     TlvRequestTlv   tlvRequest;
     uint8_t         tlvs[kMaxResponseTlvs];
     uint8_t         tlvslength                = 0;
@@ -2257,23 +2258,8 @@ otError MleRouter::HandleChildUpdateRequest(const Message &         aMessage,
         ExitNow();
     }
 
-    if (child->GetDeviceMode() != mode.GetMode())
-    {
-        otLogNoteMle("Child 0x%04x mode change 0x%02x -> 0x%02x [rx-on:%s, sec-data-req:%s, ftd:%s, full-netdata:%s]",
-                     child->GetRloc16(), child->GetDeviceMode(), mode.GetMode(),
-                     (mode.GetMode() & ModeTlv::kModeRxOnWhenIdle) ? "yes" : " no",
-                     (mode.GetMode() & ModeTlv::kModeSecureDataRequest) ? "yes" : " no",
-                     (mode.GetMode() & ModeTlv::kModeFullThreadDevice) ? "yes" : "no",
-                     (mode.GetMode() & ModeTlv::kModeFullNetworkData) ? "yes" : "no");
-
-        child->SetDeviceMode(mode.GetMode());
-        childDidChange = true;
-
-        if (!(mode.GetMode() & ModeTlv::kModeRxOnWhenIdle) && (child->GetState() == Neighbor::kStateValid))
-        {
-            Get<IndirectSender>().SetChildUseShortAddress(*child, true);
-        }
-    }
+    oldMode = child->GetDeviceMode();
+    child->SetDeviceMode(mode.GetMode());
 
     tlvs[tlvslength++] = Tlv::kMode;
 
@@ -2337,6 +2323,25 @@ otError MleRouter::HandleChildUpdateRequest(const Message &         aMessage,
 
     child->SetLastHeard(TimerMilli::GetNow());
 
+    if (oldMode != child->GetDeviceMode())
+    {
+        otLogNoteMle("Child 0x%04x mode change 0x%02x -> 0x%02x [rx-on:%s, sec-data-req:%s, ftd:%s, full-netdata:%s]",
+                     child->GetRloc16(), oldMode, mode.GetMode(),
+                     (mode.GetMode() & ModeTlv::kModeRxOnWhenIdle) ? "yes" : "no",
+                     (mode.GetMode() & ModeTlv::kModeSecureDataRequest) ? "yes" : "no",
+                     (mode.GetMode() & ModeTlv::kModeFullThreadDevice) ? "yes" : "no",
+                     (mode.GetMode() & ModeTlv::kModeFullNetworkData) ? "yes" : "no");
+
+        childDidChange = true;
+
+        // The `IndirectSender::HandleChildModeChange()` needs to happen
+        // after "Child Update" message is fully parsed to ensure that
+        // any registered IPv6 addresses included in the "Child Update"
+        // are added to the child.
+
+        Get<IndirectSender>().HandleChildModeChange(*child, oldMode);
+    }
+
     if (child->IsStateRestoring())
     {
         SetChildStateToValid(*child);