Message: Add Clone method. (#804)

* Message: Add Clone method.

Packet cloning is done only inside ip6.cpp right now, but this method
might be useful for MPL and CoAP retransmissions in order to not repeat the same
code.

src/core/common/message.cpp

@@ -455,6 +455,32 @@ int Message::CopyTo(uint16_t aSourceOffset, uint16_t aDestinationOffset, uint16_
     return bytesCopied;
 }
 
+Message *Message::Clone(void) const
+{
+    ThreadError error = kThreadError_None;
+    Message *messageCopy;
+
+    VerifyOrExit((messageCopy = GetMessagePool()->New(GetType(), GetReserved())) != NULL, error = kThreadError_NoBufs);
+    SuccessOrExit(error = messageCopy->SetLength(GetLength()));
+    CopyTo(0, 0, GetLength(), *messageCopy);
+
+    // Copy selected message information.
+    messageCopy->SetOffset(GetOffset());
+    messageCopy->SetInterfaceId(GetInterfaceId());
+    messageCopy->SetSubType(GetSubType());
+    messageCopy->SetLinkSecurityEnabled(IsLinkSecurityEnabled());
+
+exit:
+
+    if (error != kThreadError_None && messageCopy != NULL)
+    {
+        messageCopy->Free();
+        messageCopy = NULL;
+    }
+
+    return messageCopy;
+}
+
 uint16_t Message::GetDatagramTag(void) const
 {
     return mInfo.mDatagramTag;

src/core/common/message.hpp

@@ -384,6 +384,14 @@ public:
      */
     int CopyTo(uint16_t aSourceOffset, uint16_t aDestinationOffset, uint16_t aLength, Message &aMessage) const;
 
+    /**
+     * This method creates a copy of the current Message. It allocates the new one
+     * from the same Message Poll as the original Message.
+     *
+     * @returns A pointer to the message or NULL if insufficient message buffers are available.
+     */
+    Message *Clone(void) const;
+
     /**
      * This method returns the datagram tag used for 6LoWPAN fragmentation.
      *
@@ -559,7 +567,7 @@ public:
     uint16_t UpdateChecksum(uint16_t aChecksum, uint16_t aOffset, uint16_t aLength) const;
 
 private:
-    MessagePool *GetMessagePool(void) { return mInfo.mMessagePool; }
+    MessagePool *GetMessagePool(void) const { return mInfo.mMessagePool; }
 
     void SetMessagePool(MessagePool *aMessagePool) { mInfo.mMessagePool = aMessagePool; }
 

src/core/net/ip6.cpp

@@ -412,20 +412,10 @@ ThreadError Ip6::ProcessReceiveCallback(const Message &aMessage, const MessageIn
     }
 
     // make a copy of the datagram to pass to host
-    VerifyOrExit((messageCopy = NewMessage(0)) != NULL, error = kThreadError_NoBufs);
-    SuccessOrExit(error = messageCopy->SetLength(aMessage.GetLength()));
-    aMessage.CopyTo(0, 0, aMessage.GetLength(), *messageCopy);
-    messageCopy->SetLinkSecurityEnabled(aMessage.IsLinkSecurityEnabled());
-
+    VerifyOrExit((messageCopy = aMessage.Clone()) != NULL, error = kThreadError_NoBufs);
     mReceiveIp6DatagramCallback(messageCopy, mReceiveIp6DatagramCallbackContext);
 
 exit:
-
-    if (error != kThreadError_None && messageCopy != NULL)
-    {
-        messageCopy->Free();
-    }
-
     return error;
 }