* File transfer receive callback prototype. This function is called by the core upon an incoming File transfer is started. This function may be call several time for the same file in case of large file.
* @param room #LinphoneChatRoom object
* @param message #LinphoneChatMessage message from which the body is received.
* @param content #LinphoneContent incoming content information
* @param buffer #LinphoneBuffer holding the received data. Empty buffer means end of file.
* File transfer send callback prototype. This function is called by the core when an outgoing file transfer is started. This function is called until size is set to 0.
* @param room #LinphoneChatRoom object
* @param message #LinphoneChatMessage message from which the body is received.