[message] add clone methods to MessageAllocator (#12704)

This commit adds `CloneMessage()`, `CloneMessageWithoutFooter()`,
and `CloneMessageWithout<Footer>()` methods to the `MessageAllocator`
class. These methods simplify creating copies of messages by
automatically applying the correct `kReservedHeader` size. It also
updates existing code in `CoapBase`, `Dns::Client`, `Sntp::Client`,
and `Mle` to utilize these new methods.

Additionally, this commit updates the `Clone()` method in `Message`
to be a template method, accepting a `CloneMode` to specify whether
the cloned message should retain the reserved header or have no
reserved header. The documentation for the clone methods has also
been updated to clarify which message fields are copied during the
cloning process.

tests/nexus/platform/nexus_infra_if.cpp

@@ -335,7 +335,7 @@ void InfraIf::SendUdp(const Ip6::Address &aSrcAddress,
 
     if (aDestAddress.IsMulticast())
     {
-        Message *loopbackMessage = aPayload.Clone();
+        Message *loopbackMessage = aPayload.Clone<kNoReservedHeader>();
 
         VerifyOrQuit(loopbackMessage != nullptr);
         Receive(GetNode(), *loopbackMessage);
@@ -396,7 +396,7 @@ void InfraIf::Receive(Node &aSrcNode, Message &aMessage)
         if (headers.GetDestinationAddress().IsMulticast() || node.mInfraIf.HasAddress(headers.GetDestinationAddress()))
         {
             Mdns::AddressInfo senderAddress;
-            Message          *payload = aMessage.Clone();
+            Message          *payload = aMessage.Clone<kNoReservedHeader>();
 
             VerifyOrQuit(payload != nullptr);
             payload->RemoveHeader(sizeof(Ip6::Header) + sizeof(Ip6::Udp::Header));
@@ -432,7 +432,7 @@ void InfraIf::Receive(Node &aSrcNode, Message &aMessage)
         VerifyOrExit(updatedHeader.GetHopLimit() > 1);
         updatedHeader.SetHopLimit(updatedHeader.GetHopLimit() - 1);
 
-        messagePtr.Reset(aMessage.Clone());
+        messagePtr.Reset(aMessage.Clone<kNoReservedHeader>());
         VerifyOrQuit(messagePtr != nullptr);
 
         messagePtr->Write(0, updatedHeader);

tests/nexus/platform/nexus_mdns.cpp

@@ -140,7 +140,7 @@ void Mdns::Receive(Instance &aInstance, Message &aMessage, bool aIsUnicast, cons
         VerifyOrExit(aSenderAddress.mPort == kUdpPort);
     }
 
-    message = aMessage.Clone();
+    message = aMessage.Clone<kNoReservedHeader>();
     VerifyOrQuit(message != nullptr);
 
     otPlatMdnsHandleReceive(&aInstance, message, aIsUnicast, &aSenderAddress);

tests/nexus/test_border_admitter.cpp

@@ -361,14 +361,14 @@ bool HandleResource(void *aContext, Uri aUri, Coap::Msg &aMsg)
         SuccessOrQuit(Tlv::Find<MeshCoP::JoinerIidTlv>(aMsg.mMessage, joinerIid));
         Log("  Received `RelayRx` from joiner - port:%u iid:%s", joinerPort, joinerIid.ToString().AsCString());
 
-        msgClone = aMsg.mMessage.Clone();
+        msgClone = aMsg.mMessage.Clone<kNoReservedHeader>();
         VerifyOrQuit(msgClone != nullptr);
         recvContext->mRelayRxMsgs.Enqueue(*msgClone);
         break;
 
     case kUriProxyRx:
         Log("  Received `ProxyRx`");
-        msgClone = aMsg.mMessage.Clone();
+        msgClone = aMsg.mMessage.Clone<kNoReservedHeader>();
         VerifyOrQuit(msgClone != nullptr);
         recvContext->mProxyRxMsgs.Enqueue(*msgClone);
         break;

tests/nexus/test_dtls.cpp

@@ -333,7 +333,7 @@ void TestDtlsSingleSession(void)
         {
             OwnedPtr<Message> msg(PrepareMessage(node0));
 
-            SuccessOrQuit(dtls0.Send(*msg->Clone()));
+            SuccessOrQuit(dtls0.Send(*msg->Clone<kNoReservedHeader>()));
             nexus.AdvanceTime(100);
 
             VerifyOrQuit(sDtlsLastReceive[node1.GetId()].GetLength() == msg->GetLength());
@@ -347,7 +347,7 @@ void TestDtlsSingleSession(void)
         {
             OwnedPtr<Message> msg(PrepareMessage(node1));
 
-            SuccessOrQuit(dtls1.Send(*msg->Clone()));
+            SuccessOrQuit(dtls1.Send(*msg->Clone<kNoReservedHeader>()));
             nexus.AdvanceTime(100);
 
             VerifyOrQuit(sDtlsLastReceive[node0.GetId()].GetLength() == msg->GetLength());

tests/unit/test_aes.cpp

@@ -218,7 +218,7 @@ void TestInPlaceAesCcmProcessing(void)
             SuccessOrQuit(message->Append<uint8_t>(i & 0xff));
         }
 
-        messageClone = message->Clone();
+        messageClone = message->Clone<kNoReservedHeader>();
         VerifyOrQuit(messageClone != nullptr);
         VerifyOrQuit(messageClone->GetLength() == msgLength);
 

tests/unit/test_message.cpp

@@ -379,7 +379,7 @@ public:
         message->SetOrigin(Message::kOriginHostUntrusted);
 
         // Test 1: Default cloning
-        clone = message->Clone();
+        clone = message->Clone<kSameReservedHeader>();
         VerifyOrQuit(clone != nullptr);
 
         VerifyOrQuit(clone->GetLength() == message->GetLength());
@@ -397,7 +397,7 @@ public:
         clone->Free();
 
         // Test 2: Cloning with shorter length
-        clone = message->Clone(kLength / 2);
+        clone = message->Clone<kSameReservedHeader>(kLength / 2);
         VerifyOrQuit(clone != nullptr);
 
         VerifyOrQuit(clone->GetLength() == kLength / 2);
@@ -411,12 +411,12 @@ public:
         // Test 3: Cloning with shorter length, offset change
         message->SetOffset(80);
 
-        clone = message->Clone(kLength / 2);
+        clone = message->Clone<kNoReservedHeader>(kLength / 2);
         VerifyOrQuit(clone != nullptr);
 
         VerifyOrQuit(clone->GetLength() == kLength / 2);
         VerifyOrQuit(clone->GetPriority() == message->GetPriority());
-        VerifyOrQuit(clone->GetReserved() == message->GetReserved());
+        VerifyOrQuit(clone->GetReserved() == 0);
         VerifyOrQuit(clone->GetOffset() == 50); // Offset should be updated
         VerifyOrQuit(clone->CompareBytes(0, buffer, kLength / 2));