The xs_msg_copy() function shall copy the message object referenced by src to the message object referenced by dest. The original content of dest, if any, shall be released.
The implementation may choose not to physically copy the message content, rather to share the underlying buffer between src and dest. Avoid modifying message content after a message has been copied with xs_msg_copy(), doing so can result in undefined behaviour. If what you need is an actual hard copy, allocate a new message using xs_msg_init_size() and copy the message content using memcpy().
Never access xs_msg_t members directly, instead always use the xs_msg family of functions.