how is this supposed to work in 3.0.0, my private file descriptors are none of Pidgin's business!

gistfile1.c

/**
 * Starts a file transfer.
 *
 * Either @a fd must be specified <i>or</i> @a ip and @a port on a
 * file receive transfer. On send, @a fd must be specified, and
 * @a ip and @a port are ignored.
 *
 * Prior to libpurple 2.6.0, passing '0' to @a fd was special-cased to
 * allow the protocol plugin to facilitate the file transfer itself. As of
 * 2.6.0, this is supported (for backward compatibility), but will be
 * removed in libpurple 3.0.0. If a prpl detects that the running libpurple
 * is running 2.6.0 or higher, it should use the invalid fd '-1'.
 *
 * @param xfer The file transfer.
 * @param fd   The file descriptor for the socket.
 * @param ip   The IP address to connect to.
 * @param port The port to connect to.
 */
void purple_xfer_start(PurpleXfer *xfer, int fd, const char *ip,
					 unsigned int port);