[core] use AppendBytesFromMessage() to copy bytes between messages (#8686)

This commit updates multiple core modules to use the `Message` helper
method `AppendBytesFromMessage()` to append bytes read from one
message at a given offset and length to the end of another message.

src/core/common/message.cpp

@@ -40,6 +40,7 @@
 #include "common/instance.hpp"
 #include "common/locator_getters.hpp"
 #include "common/log.hpp"
+#include "common/num_utils.hpp"
 #include "common/numeric_limits.hpp"
 #include "net/checksum.hpp"
 #include "net/ip6.hpp"
@@ -678,10 +679,10 @@ Message *Message::Clone(uint16_t aLength) const
     Settings settings(IsLinkSecurityEnabled() ? kWithLinkSecurity : kNoLinkSecurity, GetPriority());
     uint16_t offset;
 
+    aLength     = Min(GetLength(), aLength);
     messageCopy = GetMessagePool()->Allocate(GetType(), GetReserved(), settings);
     VerifyOrExit(messageCopy != nullptr, error = kErrorNoBufs);
-    SuccessOrExit(error = messageCopy->SetLength(aLength));
-    CopyTo(0, 0, aLength, *messageCopy);
+    SuccessOrExit(error = messageCopy->AppendBytesFromMessage(*this, 0, aLength));
 
     // Copy selected message information.
     offset = GetOffset() < aLength ? GetOffset() : aLength;

src/core/meshcop/border_agent.cpp

@@ -272,8 +272,7 @@ template <> void BorderAgent::HandleTmf<kUriProxyTx>(Coap::Message &aMessage, co
     VerifyOrExit(udpEncapHeader.GetSourcePort() > 0 && udpEncapHeader.GetDestinationPort() > 0, error = kErrorDrop);
 
     VerifyOrExit((message = Get<Ip6::Udp>().NewMessage(0)) != nullptr, error = kErrorNoBufs);
-    SuccessOrExit(error = message->SetLength(length));
-    aMessage.CopyTo(/* aSroOffset */ offset, /* aDestOffset */ 0, length, /* aDestMsg */ *message);
+    SuccessOrExit(error = message->AppendBytesFromMessage(aMessage, offset, length));
 
     messageInfo.SetSockPort(udpEncapHeader.GetSourcePort());
     messageInfo.SetSockAddr(mCommissionerAloc.GetAddress());
@@ -312,7 +311,6 @@ bool BorderAgent::HandleUdpReceive(const Message &aMessage, const Ip6::MessageIn
     {
         ExtendedTlv               extTlv;
         UdpEncapsulationTlvHeader udpEncapHeader;
-        uint16_t                  offset;
         uint16_t                  udpLength = aMessage.GetLength() - aMessage.GetOffset();
 
         extTlv.SetType(Tlv::kUdpEncapsulation);
@@ -322,11 +320,7 @@ bool BorderAgent::HandleUdpReceive(const Message &aMessage, const Ip6::MessageIn
         udpEncapHeader.SetSourcePort(aMessageInfo.GetPeerPort());
         udpEncapHeader.SetDestinationPort(aMessageInfo.GetSockPort());
         SuccessOrExit(error = message->Append(udpEncapHeader));
-
-        offset = message->GetLength();
-        SuccessOrExit(error = message->SetLength(offset + udpLength));
-        aMessage.CopyTo(/* aSrcOffset */ aMessage.GetOffset(), /* aDestOffset */ offset, udpLength,
-                        /* aDestMsg */ *message);
+        SuccessOrExit(error = message->AppendBytesFromMessage(aMessage, aMessage.GetOffset(), udpLength));
     }
 
     SuccessOrExit(error = Tlv::Append<Ip6AddressTlv>(*message, aMessageInfo.GetPeerAddr()));
@@ -368,13 +362,10 @@ exit:
 
 Error BorderAgent::ForwardToCommissioner(Coap::Message &aForwardMessage, const Message &aMessage)
 {
-    Error    error  = kErrorNone;
-    uint16_t offset = 0;
-
-    offset = aForwardMessage.GetLength();
-    SuccessOrExit(error = aForwardMessage.SetLength(offset + aMessage.GetLength() - aMessage.GetOffset()));
-    aMessage.CopyTo(aMessage.GetOffset(), offset, aMessage.GetLength() - aMessage.GetOffset(), aForwardMessage);
+    Error error;
 
+    SuccessOrExit(error = aForwardMessage.AppendBytesFromMessage(aMessage, aMessage.GetOffset(),
+                                                                 aMessage.GetLength() - aMessage.GetOffset()));
     SuccessOrExit(error =
                       Get<Tmf::SecureAgent>().SendMessage(aForwardMessage, Get<Tmf::SecureAgent>().GetMessageInfo()));
 
@@ -443,7 +434,6 @@ template <> void BorderAgent::HandleTmf<kUriRelayTx>(Coap::Message &aMessage, co
     uint16_t         joinerRouterRloc;
     Coap::Message   *message = nullptr;
     Tmf::MessageInfo messageInfo(GetInstance());
-    uint16_t         offset = 0;
 
     VerifyOrExit(mState != kStateStopped);
 
@@ -454,9 +444,8 @@ template <> void BorderAgent::HandleTmf<kUriRelayTx>(Coap::Message &aMessage, co
     message = Get<Tmf::Agent>().NewPriorityNonConfirmablePostMessage(kUriRelayTx);
     VerifyOrExit(message != nullptr, error = kErrorNoBufs);
 
-    offset = message->GetLength();
-    SuccessOrExit(error = message->SetLength(offset + aMessage.GetLength() - aMessage.GetOffset()));
-    aMessage.CopyTo(aMessage.GetOffset(), offset, aMessage.GetLength() - aMessage.GetOffset(), *message);
+    SuccessOrExit(error = message->AppendBytesFromMessage(aMessage, aMessage.GetOffset(),
+                                                          aMessage.GetLength() - aMessage.GetOffset()));
 
     messageInfo.SetSockAddrToRlocPeerAddrTo(joinerRouterRloc);
     messageInfo.SetSockPortToTmf();
@@ -476,7 +465,6 @@ Error BorderAgent::ForwardToLeader(const Coap::Message &aMessage, const Ip6::Mes
     ForwardContext  *forwardContext = nullptr;
     Tmf::MessageInfo messageInfo(GetInstance());
     Coap::Message   *message  = nullptr;
-    uint16_t         offset   = 0;
     bool             petition = false;
     bool             separate = false;
 
@@ -508,9 +496,8 @@ Error BorderAgent::ForwardToLeader(const Coap::Message &aMessage, const Ip6::Mes
     message = Get<Tmf::Agent>().NewPriorityConfirmablePostMessage(aUri);
     VerifyOrExit(message != nullptr, error = kErrorNoBufs);
 
-    offset = message->GetLength();
-    SuccessOrExit(error = message->SetLength(offset + aMessage.GetLength() - aMessage.GetOffset()));
-    aMessage.CopyTo(aMessage.GetOffset(), offset, aMessage.GetLength() - aMessage.GetOffset(), *message);
+    SuccessOrExit(error = message->AppendBytesFromMessage(aMessage, aMessage.GetOffset(),
+                                                          aMessage.GetLength() - aMessage.GetOffset()));
 
     SuccessOrExit(error = messageInfo.SetSockAddrToRlocPeerAddrToLeaderAloc());
     messageInfo.SetSockPortToTmf();

src/core/meshcop/commissioner.cpp

@@ -1116,7 +1116,6 @@ Error Commissioner::SendRelayTransmit(Message &aMessage, const Ip6::MessageInfo
     Error            error = kErrorNone;
     ExtendedTlv      tlv;
     Coap::Message   *message;
-    uint16_t         offset;
     Tmf::MessageInfo messageInfo(GetInstance());
     Kek              kek;
 
@@ -1137,9 +1136,7 @@ Error Commissioner::SendRelayTransmit(Message &aMessage, const Ip6::MessageInfo
     tlv.SetType(Tlv::kJoinerDtlsEncapsulation);
     tlv.SetLength(aMessage.GetLength());
     SuccessOrExit(error = message->Append(tlv));
-    offset = message->GetLength();
-    SuccessOrExit(error = message->SetLength(offset + aMessage.GetLength()));
-    aMessage.CopyTo(0, offset, aMessage.GetLength(), *message);
+    SuccessOrExit(error = message->AppendBytesFromMessage(aMessage, 0, aMessage.GetLength()));
 
     messageInfo.SetSockAddrToRlocPeerAddrTo(mJoinerRloc);
 

src/core/meshcop/joiner_router.cpp

@@ -134,7 +134,6 @@ void JoinerRouter::HandleUdpReceive(Message &aMessage, const Ip6::MessageInfo &a
     Tmf::MessageInfo messageInfo(GetInstance());
     ExtendedTlv      tlv;
     uint16_t         borderAgentRloc;
-    uint16_t         offset;
 
     LogInfo("JoinerRouter::HandleUdpReceive");
 
@@ -150,9 +149,7 @@ void JoinerRouter::HandleUdpReceive(Message &aMessage, const Ip6::MessageInfo &a
     tlv.SetType(Tlv::kJoinerDtlsEncapsulation);
     tlv.SetLength(aMessage.GetLength() - aMessage.GetOffset());
     SuccessOrExit(error = message->Append(tlv));
-    offset = message->GetLength();
-    SuccessOrExit(error = message->SetLength(offset + tlv.GetLength()));
-    aMessage.CopyTo(aMessage.GetOffset(), offset, tlv.GetLength(), *message);
+    SuccessOrExit(error = message->AppendBytesFromMessage(aMessage, aMessage.GetOffset(), tlv.GetLength()));
 
     messageInfo.SetSockAddrToRlocPeerAddrTo(borderAgentRloc);
 
@@ -189,8 +186,7 @@ template <> void JoinerRouter::HandleTmf<kUriRelayTx>(Coap::Message &aMessage, c
 
     VerifyOrExit((message = mSocket.NewMessage(0, settings)) != nullptr, error = kErrorNoBufs);
 
-    SuccessOrExit(error = message->SetLength(length));
-    aMessage.CopyTo(offset, 0, length, *message);
+    SuccessOrExit(error = message->AppendBytesFromMessage(aMessage, offset, length));
 
     messageInfo.GetPeerAddr().SetToLinkLocalAddress(joinerIid);
     messageInfo.SetPeerPort(joinerPort);

src/core/net/dns_client.cpp

@@ -833,24 +833,10 @@ exit:
 
 Error Client::AppendNameFromQuery(const Query &aQuery, Message &aMessage)
 {
-    Error    error = kErrorNone;
-    uint16_t offset;
-    uint16_t length;
+    // The name is encoded and included after the `Info` in `aQuery`
+    // starting at `kNameOffsetInQuery`.
 
-    // The name is encoded and included after the `Info` in `aQuery`. We
-    // first calculate the encoded length of the name, then grow the
-    // message, and finally copy the encoded name bytes from `aQuery`
-    // into `aMessage`.
-
-    length = aQuery.GetLength() - kNameOffsetInQuery;
-
-    offset = aMessage.GetLength();
-    SuccessOrExit(error = aMessage.SetLength(offset + length));
-
-    aQuery.CopyTo(/* aSourceOffset */ kNameOffsetInQuery, /* aDestOffset */ offset, length, aMessage);
-
-exit:
-    return error;
+    return aMessage.AppendBytesFromMessage(aQuery, kNameOffsetInQuery, aQuery.GetLength() - kNameOffsetInQuery);
 }
 
 void Client::FinalizeQuery(Query &aQuery, Error aError)

src/core/net/icmp6.cpp

@@ -182,7 +182,7 @@ Error Icmp::HandleEchoRequest(Message &aRequestMessage, const MessageInfo &aMess
     Header      icmp6Header;
     Message    *replyMessage = nullptr;
     MessageInfo replyMessageInfo;
-    uint16_t    payloadLength;
+    uint16_t    dataOffset;
 
     // always handle Echo Request destined for RLOC or ALOC
     VerifyOrExit(ShouldHandleEchoRequest(aMessageInfo) || aMessageInfo.GetSockAddr().GetIid().IsLocator());
@@ -198,12 +198,11 @@ Error Icmp::HandleEchoRequest(Message &aRequestMessage, const MessageInfo &aMess
         ExitNow();
     }
 
-    payloadLength = aRequestMessage.GetLength() - aRequestMessage.GetOffset() - Header::kDataFieldOffset;
-    SuccessOrExit(error = replyMessage->SetLength(Header::kDataFieldOffset + payloadLength));
+    dataOffset = aRequestMessage.GetOffset() + Header::kDataFieldOffset;
 
-    replyMessage->WriteBytes(0, &icmp6Header, Header::kDataFieldOffset);
-    aRequestMessage.CopyTo(aRequestMessage.GetOffset() + Header::kDataFieldOffset, Header::kDataFieldOffset,
-                           payloadLength, *replyMessage);
+    SuccessOrExit(error = replyMessage->AppendBytes(&icmp6Header, Header::kDataFieldOffset));
+    SuccessOrExit(error = replyMessage->AppendBytesFromMessage(aRequestMessage, dataOffset,
+                                                               aRequestMessage.GetLength() - dataOffset));
 
     replyMessageInfo.SetPeerAddr(aMessageInfo.GetPeerAddr());