[mle] use newly added Netif::IterateExternalMulticastAddresses (#5286)

This commit updates `Mle` class to use the newly added `Netif`
iterator for external multicast addresses. It also adds a helper
method in `Netif` to indicate if it is subscribed to any external
multicast address.

src/core/net/netif.hpp

@@ -219,12 +219,21 @@ public:
          * @param[in] aNetif  A reference to the Netif instance.
          *
          */
-        explicit ExternalMulticastAddressIterator(Netif &aNetif)
+        explicit ExternalMulticastAddressIterator(const Netif &aNetif)
             : mNetif(aNetif)
         {
             AdvanceFrom(mNetif.GetMulticastAddresses());
         }
 
+        /**
+         * This method indicates whether the iterator has reached end of the list.
+         *
+         * @retval TRUE   There are no more entries in the list (reached end of the list).
+         * @retval FALSE  The current address entry is valid.
+         *
+         */
+        bool IsDone(void) const { return mCurrent != nullptr; }
+
         /**
          * This method overloads `++` operator (pre-increment) to advance the iterator.
          *
@@ -298,7 +307,7 @@ public:
             kEndIterator,
         };
 
-        ExternalMulticastAddressIterator(Netif &aNetif, IteratorType)
+        ExternalMulticastAddressIterator(const Netif &aNetif, IteratorType)
             : mNetif(aNetif)
             , mCurrent(nullptr)
         {
@@ -315,7 +324,7 @@ public:
                 const_cast<ExternalNetifMulticastAddress *>(static_cast<const ExternalNetifMulticastAddress *>(aAddr));
         }
 
-        Netif &                        mNetif;
+        const Netif &                  mNetif;
         ExternalNetifMulticastAddress *mCurrent;
     };
 
@@ -569,6 +578,15 @@ public:
         return ExternalMulticastAddressIteratorBuilder(*this);
     }
 
+    /**
+     * This method indicates whether or not the network interfaces is subscribed to any external multicast address.
+     *
+     * @retval TRUE  The network interface is subscribed to at least one external multicast address.
+     * @retval FALSE The network interface is not subscribed to any external multicast address.
+     *
+     */
+    bool HasAnyExternalMulticastAddress(void) const { return !ExternalMulticastAddressIterator(*this).IsDone(); }
+
 protected:
     /**
      * This method subscribes the network interface to the realm-local all MPL forwarders, link-local, and realm-local
@@ -595,7 +613,7 @@ private:
     class ExternalMulticastAddressIteratorBuilder
     {
     public:
-        ExternalMulticastAddressIteratorBuilder(Netif &aNetif)
+        ExternalMulticastAddressIteratorBuilder(const Netif &aNetif)
             : mNetif(aNetif)
         {
         }
@@ -607,7 +625,7 @@ private:
         }
 
     private:
-        Netif &mNetif;
+        const Netif &mNetif;
     };
 
     LinkedList<NetifUnicastAddress>   mUnicastAddresses;

src/core/thread/mle.cpp

@@ -1235,14 +1235,7 @@ bool Mle::HasUnregisteredAddress(void)
         // For sleepy end-device, we register any external multicast
         // addresses.
 
-        for (const Ip6::NetifMulticastAddress *address = Get<ThreadNetif>().GetMulticastAddresses(); address != nullptr;
-             address                                   = address->GetNext())
-        {
-            if (Get<ThreadNetif>().IsMulticastAddressExternal(*address))
-            {
-                ExitNow(retval = true);
-            }
-        }
+        retval = Get<ThreadNetif>().HasAnyExternalMulticastAddress();
     }
 
 exit:
@@ -1341,25 +1334,19 @@ otError Mle::AppendAddressRegistration(Message &aMessage, AddressRegistrationMod
 #endif
     )
     {
-        for (const Ip6::NetifMulticastAddress *addr = Get<ThreadNetif>().GetMulticastAddresses(); addr != nullptr;
-             addr                                   = addr->GetNext())
+        for (const Ip6::NetifMulticastAddress &addr : Get<ThreadNetif>().IterateExternalMulticastAddresses())
         {
-            if (!Get<ThreadNetif>().IsMulticastAddressExternal(*addr))
-            {
-                continue;
-            }
-
 #if (OPENTHREAD_CONFIG_THREAD_VERSION >= OT_THREAD_VERSION_1_2)
             // For Thread 1.2 MED, skip multicast address with scope not
             // larger than realm local when registering.
-            if (IsRxOnWhenIdle() && !addr->GetAddress().IsMulticastLargerThanRealmLocal())
+            if (IsRxOnWhenIdle() && !addr.GetAddress().IsMulticastLargerThanRealmLocal())
             {
                 continue;
             }
 #endif
 
             entry.SetUncompressed();
-            entry.SetIp6Address(addr->GetAddress());
+            entry.SetIp6Address(addr.GetAddress());
             SuccessOrExit(error = aMessage.Append(&entry, entry.GetLength()));
             length += entry.GetLength();