[message] introduce RemoveFooter() (#10012)

src/core/coap/coap_message.cpp

@@ -97,7 +97,7 @@ void Message::Finish(void)
 
     if (GetHelpData().mPayloadMarkerSet && (GetHelpData().mHeaderLength == GetLength()))
     {
-        IgnoreError(SetLength(GetLength() - 1));
+        RemoveFooter(sizeof(uint8_t));
     }
 
     WriteBytes(0, &GetHelpData().mHeader, GetOptionStart());

src/core/common/message.cpp

@@ -547,6 +547,8 @@ exit:
     return error;
 }
 
+void Message::RemoveFooter(uint16_t aLength) { IgnoreError(SetLength(GetLength() - Min(aLength, GetLength()))); }
+
 void Message::GetFirstChunk(uint16_t aOffset, uint16_t &aLength, Chunk &aChunk) const
 {
     // This method gets the first message chunk (contiguous data

src/core/common/message.hpp

@@ -666,6 +666,17 @@ public:
      */
     Error InsertHeader(uint16_t aOffset, uint16_t aLength);
 
+    /**
+     * Removes footer bytes from the end of the message.
+     *
+     * The caller should ensure the message contains the bytes to be removed, otherwise as many bytes as available
+     * will be removed.
+     *
+     * @param[in] aLength   Number of footer bytes to remove from end of the `Message`.
+     *
+     */
+    void RemoveFooter(uint16_t aLength);
+
     /**
      * Appends bytes to the end of the message.
      *

src/core/net/dnssd_server.cpp

@@ -974,10 +974,7 @@ void Server::ProxyQueryInfo::ReadFrom(const ProxyQuery &aQuery)
     SuccessOrAssert(aQuery.Read(aQuery.GetLength() - sizeof(ProxyQueryInfo), *this));
 }
 
-void Server::ProxyQueryInfo::RemoveFrom(ProxyQuery &aQuery) const
-{
-    SuccessOrAssert(aQuery.SetLength(aQuery.GetLength() - sizeof(ProxyQueryInfo)));
-}
+void Server::ProxyQueryInfo::RemoveFrom(ProxyQuery &aQuery) const { aQuery.RemoveFooter(sizeof(ProxyQueryInfo)); }
 
 void Server::ProxyQueryInfo::UpdateIn(ProxyQuery &aQuery) const
 {

src/core/net/ip6_mpl.cpp

@@ -465,10 +465,7 @@ void Mpl::Metadata::ReadFrom(const Message &aMessage)
     IgnoreError(aMessage.Read(length - sizeof(*this), *this));
 }
 
-void Mpl::Metadata::RemoveFrom(Message &aMessage) const
-{
-    SuccessOrAssert(aMessage.SetLength(aMessage.GetLength() - sizeof(*this)));
-}
+void Mpl::Metadata::RemoveFrom(Message &aMessage) const { aMessage.RemoveFooter(sizeof(*this)); }
 
 void Mpl::Metadata::UpdateIn(Message &aMessage) const { aMessage.Write(aMessage.GetLength() - sizeof(*this), *this); }
 

src/core/thread/mle.cpp

@@ -2397,7 +2397,7 @@ Error Mle::ProcessMessageSecurity(Crypto::AesCcm::Mode    aMode,
     if (aMode == Crypto::AesCcm::kDecrypt)
     {
         // Skip decrypting the message under fuzz build mode
-        IgnoreError(aMessage.SetLength(aMessage.GetLength() - kMleSecurityTagSize));
+        aMessage.RemoveFooter(kMleSecurityTagSize);
         ExitNow();
     }
 #endif
@@ -2412,7 +2412,7 @@ Error Mle::ProcessMessageSecurity(Crypto::AesCcm::Mode    aMode,
     else
     {
         VerifyOrExit(aMessage.Compare(aMessage.GetLength() - kMleSecurityTagSize, tag), error = kErrorSecurity);
-        IgnoreError(aMessage.SetLength(aMessage.GetLength() - kMleSecurityTagSize));
+        aMessage.RemoveFooter(kMleSecurityTagSize);
     }
 
 exit:
@@ -4423,10 +4423,7 @@ void Mle::DelayedResponseMetadata::ReadFrom(const Message &aMessage)
     IgnoreError(aMessage.Read(length - sizeof(*this), *this));
 }
 
-void Mle::DelayedResponseMetadata::RemoveFrom(Message &aMessage) const
-{
-    SuccessOrAssert(aMessage.SetLength(aMessage.GetLength() - sizeof(*this)));
-}
+void Mle::DelayedResponseMetadata::RemoveFrom(Message &aMessage) const { aMessage.RemoveFooter(sizeof(*this)); }
 
 //---------------------------------------------------------------------------------------------------------------------
 // TxMessage