udpwrite.c

unix网络编程卷1：套接口API的全书源码

#include	"udpcksum.h"

/* include open_output_raw */
int		rawfd;			/* raw socket to write on */

void
open_output(void)
{
	int	on=1;
	/*
	 * Need a raw socket to write our own IP datagrams to.
	 * Process must have superuser privileges to create this socket.
	 * Also must set IP_HDRINCL so we can write our own IP headers.
	 */

	rawfd = Socket(dest->sa_family, SOCK_RAW, 0);

	Setsockopt(rawfd, IPPROTO_IP, IP_HDRINCL, &on, sizeof(on));
}
/* end open_output_raw */

/*
 * "buf" points to an empty IP/UDP header,
 * followed by "ulen" bytes of user data.
 */

/* include udp_write */
void
udp_write(char *buf, int userlen)
{
	struct udpiphdr		*ui;
	struct ip			*ip;

		/* 4fill in and checksum UDP header */
	ip = (struct ip *) buf;
	ui = (struct udpiphdr *) buf;
	bzero(ui, sizeof(*ui));
			/* 8add 8 to userlen for pseudoheader length */
	ui->ui_len = htons((uint16_t) (sizeof(struct udphdr) + userlen));
			/* 8then add 28 for IP datagram length */
	userlen += sizeof(struct udpiphdr);

	ui->ui_pr = IPPROTO_UDP;
	ui->ui_src.s_addr = ((struct sockaddr_in *) local)->sin_addr.s_addr;
	ui->ui_dst.s_addr = ((struct sockaddr_in *) dest)->sin_addr.s_addr;
	ui->ui_sport = ((struct sockaddr_in *) local)->sin_port;
	ui->ui_dport = ((struct sockaddr_in *) dest)->sin_port;
	ui->ui_ulen = ui->ui_len;
	if (zerosum == 0) {
#if 1	/* change to if 0 for Solaris 2.x, x < 6 */
		if ( (ui->ui_sum = in_cksum((u_int16_t *) ui, userlen)) == 0)
			ui->ui_sum = 0xffff;
#else
		ui->ui_sum = ui->ui_len;
#endif
	}

		/* 4fill in rest of IP header; */
		/* 4ip_output() calcuates & stores IP header checksum */
	ip->ip_v = IPVERSION;
	ip->ip_hl = sizeof(struct ip) >> 2;
	ip->ip_tos = 0;
#if defined(linux) || defined(__OpenBSD__)
	ip->ip_len = htons(userlen);	/* network byte order */
#else
	ip->ip_len = userlen;			/* host byte order */
#endif
	ip->ip_id = 0;			/* let IP set this */
	ip->ip_off = 0;			/* frag offset, MF and DF flags */
	ip->ip_ttl = TTL_OUT;

	Sendto(rawfd, buf, userlen, 0, dest, destlen);
}
/* end udp_write */