[mle] simplify signaling of DUA address change (#10296)

This commit simplifies how `ProcessAddressRegistrationTlv()` signals
DUA address changes. Signaling now occurs after all child addresses
are registered, using a new `SignalDuaAddressEvent()` method. This
method checks the old and new DUA addresses to determine the
appropriate event to signal.

Additionally, `Child::GetDomainUnicastAddress()` is updated to return
an `Error` and copy the DUA address into a provided `Ip6::Address`
reference.

src/core/thread/child.cpp

@@ -251,9 +251,9 @@ exit:
 }
 
 #if OPENTHREAD_FTD && OPENTHREAD_CONFIG_TMF_PROXY_DUA_ENABLE
-const Ip6::Address *Child::GetDomainUnicastAddress(void) const
+Error Child::GetDomainUnicastAddress(Ip6::Address &aAddress) const
 {
-    const Ip6::Address *addr = nullptr;
+    Error error = kErrorNotFound;
 
     for (const Ip6::Address &ip6Address : mIp6Address)
     {
@@ -261,12 +261,14 @@ const Ip6::Address *Child::GetDomainUnicastAddress(void) const
 
         if (Get<BackboneRouter::Leader>().IsDomainUnicast(ip6Address))
         {
-            ExitNow(addr = &ip6Address);
+            aAddress = ip6Address;
+            error    = kErrorNone;
+            ExitNow();
         }
     }
 
 exit:
-    return addr;
+    return error;
 }
 #endif
 

src/core/thread/child.hpp

@@ -325,10 +325,13 @@ public:
     /**
      * Retrieves the Domain Unicast Address registered by the child.
      *
-     * @returns A pointer to Domain Unicast Address registered by the child if there is.
+     * @param[out] aAddress    A reference to return the DUA address.
+     *
+     * @retval kErrorNone      Successfully retrieved the DUA address, @p aAddress is updated.
+     * @retval kErrorNotFound  Could not find any DUA address.
      *
      */
-    const Ip6::Address *GetDomainUnicastAddress(void) const;
+    Error GetDomainUnicastAddress(Ip6::Address &aAddress) const;
 #endif
 
     /**

src/core/thread/dua_manager.cpp

@@ -480,9 +480,8 @@ void DuaManager::PerformNextRegistration(void)
 #endif // OPENTHREAD_CONFIG_DUA_ENABLE
     {
 #if OPENTHREAD_FTD && OPENTHREAD_CONFIG_TMF_PROXY_DUA_ENABLE
-        uint32_t            lastTransactionTime;
-        const Ip6::Address *duaPtr = nullptr;
-        Child              *child  = nullptr;
+        uint32_t lastTransactionTime;
+        Child   *child = nullptr;
 
         OT_ASSERT(mChildIndexDuaRegistering == Mle::kMaxChildren);
 
@@ -497,12 +496,9 @@ void DuaManager::PerformNextRegistration(void)
             }
         }
 
-        child  = Get<ChildTable>().GetChildAtIndex(mChildIndexDuaRegistering);
-        duaPtr = child->GetDomainUnicastAddress();
+        child = Get<ChildTable>().GetChildAtIndex(mChildIndexDuaRegistering);
+        SuccessOrAssert(child->GetDomainUnicastAddress(dua));
 
-        OT_ASSERT(duaPtr != nullptr);
-
-        dua = *duaPtr;
         SuccessOrExit(error = Tlv::Append<ThreadTargetTlv>(*message, dua));
         SuccessOrExit(error = Tlv::Append<ThreadMeshLocalEidTlv>(*message, child->GetMeshLocalIid()));
 

src/core/thread/mle_router.cpp

@@ -1774,8 +1774,6 @@ Error MleRouter::ProcessAddressRegistrationTlv(RxInfo &aRxInfo, Child &aChild)
     uint8_t  count       = 0;
     uint8_t  storedCount = 0;
 #if OPENTHREAD_CONFIG_TMF_PROXY_DUA_ENABLE
-    bool         hasOldDua = false;
-    bool         hasNewDua = false;
     Ip6::Address oldDua;
 #endif
 #if OPENTHREAD_CONFIG_TMF_PROXY_MLR_ENABLE
@@ -1788,14 +1786,9 @@ Error MleRouter::ProcessAddressRegistrationTlv(RxInfo &aRxInfo, Child &aChild)
                       Tlv::FindTlvValueStartEndOffsets(aRxInfo.mMessage, Tlv::kAddressRegistration, offset, endOffset));
 
 #if OPENTHREAD_CONFIG_TMF_PROXY_DUA_ENABLE
+    if (aChild.GetDomainUnicastAddress(oldDua) != kErrorNone)
     {
-        const Ip6::Address *duaAddress = aChild.GetDomainUnicastAddress();
-
-        if (duaAddress != nullptr)
-        {
-            oldDua    = *duaAddress;
-            hasOldDua = true;
-        }
+        oldDua.Clear();
     }
 #endif
 
@@ -1888,34 +1881,6 @@ Error MleRouter::ProcessAddressRegistrationTlv(RxInfo &aRxInfo, Child &aChild)
                     address.ToString().AsCString(), aChild.GetRloc16());
         }
 
-#if OPENTHREAD_CONFIG_TMF_PROXY_DUA_ENABLE
-        if (Get<BackboneRouter::Leader>().IsDomainUnicast(address))
-        {
-            if (error == kErrorNone)
-            {
-                DuaManager::ChildDuaAddressEvent event;
-
-                hasNewDua = true;
-
-                if (hasOldDua)
-                {
-                    event = (oldDua != address) ? DuaManager::kAddressChanged : DuaManager::kAddressUnchanged;
-                }
-                else
-                {
-                    event = DuaManager::kAddressAdded;
-                }
-
-                Get<DuaManager>().HandleChildDuaAddressEvent(aChild, event);
-            }
-            else
-            {
-                // It cannot store DUA, then assume child does not have one.
-                hasNewDua = false;
-            }
-        }
-#endif
-
         if (address.IsMulticast())
         {
             continue;
@@ -1945,10 +1910,7 @@ Error MleRouter::ProcessAddressRegistrationTlv(RxInfo &aRxInfo, Child &aChild)
         Get<AddressResolver>().RemoveEntryForAddress(address);
     }
 #if OPENTHREAD_CONFIG_TMF_PROXY_DUA_ENABLE
-    if (hasOldDua && !hasNewDua)
-    {
-        Get<DuaManager>().HandleChildDuaAddressEvent(aChild, DuaManager::kAddressRemoved);
-    }
+    SignalDuaAddressEvent(aChild, oldDua);
 #endif
 
 #if OPENTHREAD_CONFIG_TMF_PROXY_MLR_ENABLE
@@ -1971,6 +1933,40 @@ exit:
     return error;
 }
 
+#if OPENTHREAD_CONFIG_TMF_PROXY_DUA_ENABLE
+void MleRouter::SignalDuaAddressEvent(const Child &aChild, const Ip6::Address &aOldDua) const
+{
+    DuaManager::ChildDuaAddressEvent event = DuaManager::kAddressUnchanged;
+    Ip6::Address                     newDua;
+
+    if (aChild.GetDomainUnicastAddress(newDua) == kErrorNone)
+    {
+        if (aOldDua.IsUnspecified())
+        {
+            event = DuaManager::kAddressAdded;
+        }
+        else if (aOldDua != newDua)
+        {
+            event = DuaManager::kAddressChanged;
+        }
+    }
+    else
+    {
+        // Child has no DUA address. If there was no old DUA, no need
+        // to signal.
+
+        VerifyOrExit(!aOldDua.IsUnspecified());
+
+        event = DuaManager::kAddressRemoved;
+    }
+
+    Get<DuaManager>().HandleChildDuaAddressEvent(aChild, event);
+
+exit:
+    return;
+}
+#endif // OPENTHREAD_CONFIG_TMF_PROXY_DUA_ENABLE
+
 void MleRouter::HandleChildIdRequest(RxInfo &aRxInfo)
 {
     Error              error = kErrorNone;

src/core/thread/mle_router.hpp

@@ -687,6 +687,9 @@ private:
     Error ProcessAddressRegistrationTlv(RxInfo &aRxInfo, Child &aChild);
     Error UpdateChildAddresses(const Message &aMessage, uint16_t aOffset, uint16_t aLength, Child &aChild);
     bool  HasNeighborWithGoodLinkQuality(void) const;
+#if OPENTHREAD_CONFIG_TMF_PROXY_DUA_ENABLE
+    void SignalDuaAddressEvent(const Child &aChild, const Ip6::Address &aOldDua) const;
+#endif
 
     static void HandleAddressSolicitResponse(void                *aContext,
                                              otMessage           *aMessage,