#
/* udp_write.c */

/* EMACS_MODES: c !fill */


/* User Datagram Protocol layer for the UNIX network system.  The
 * following routines are included:
 *	udp_write	send a udp packet
 */


#include	<udp.h>


udp_write (fd, buf, datalen)

/* Write the specified packet out to the specified net connection.
 * The buf argument is a pointer to a packet buffer as allocated by
 * udp_alloc ().  The write routine assumes that the foreign address
 * (in the packet's internet header) and the local and foreign sockets
 * (in the udp header) have been filled by the caller.  It fills in the
 * rest of the udp header, including checksumming; then writes it out.
 * Returns the number of bytes written if successful; if not, returns
 * -1 and errno contains the error code.
 *
 * Arguments:
 */

int	fd;				/* the file descriptor  */
caddr_t	buf;				/* packet buffer */
int	datalen;			/* data length */
{
	struct	udpph	ph;		/* pseudo-header for checksum */
	reg	struct	udp	*pup;	/* udp packet */
	reg	struct	ip	*pip;	/* internet packet */
	reg	int	udplen;		/* udp packet length */
	caddr_t	pdata;			/* data portion of udp packet */
	extern	in_name	mymach;		/* my internet addr (from in layer) */
	
	pip = in_head(buf);		/* get internet */
	pup = in_data(pip);		/*   and udp headers */
	pup->ud_len = udplen = datalen + sizeof (struct udp);
	if (udplen & 1) {		/* goddam odd byte count */
		pdata = (char *)(pup);	/* pad to even byte count */
		pdata[udplen] = 0;
	}
	
#ifndef	BIGINDIAN
	udpswab (pup);			/* swap bytes if needed */
#endif
	
	ph.ph_src = mymach;		/* set up pseudo-header */
	ph.ph_dest = pip->ip_dest;
	ph.ph_zero = 0;
	ph.ph_prot = UDPPROT;
	ph.ph_len = pup->ud_len;
	pup->ud_cksum = cksum (&ph, sizeof (ph) >> 1, 0); /* slight kludge*/
	if (udplen > BIGCKSUM)		/* fast cksum routine better? */
		pup->ud_cksum = ~fcksum (pup, (udplen + 1) >> 1, 0);
	else
		pup->ud_cksum = ~cksum (pup, (udplen + 1) >> 1, 0);
	
	pip->ip_prot = UDPPROT;
	pip->ip_tsrv = IP_TSRV;
	return (in_write (fd, buf, udplen));
}