udpcksum.c

unix网络编程卷1：套接口API的全书源码

/* include sig_alrm */
#include	"udpcksum.h"
#include	<setjmp.h>

static sigjmp_buf	jmpbuf;
static int			canjump;

void
sig_alrm(int signo)
{
	if (canjump == 0)
		return;
	siglongjmp(jmpbuf, 1);
}
/* end sig_alrm */

/* include test_udp */
void
test_udp(void)
{
	volatile int	nsent = 0, timeout = 3;
	struct udpiphdr	*ui;

	Signal(SIGALRM, sig_alrm);

	if (sigsetjmp(jmpbuf, 1)) {
		if (nsent >= 3)
			err_quit("no response");
		printf("timeout\n");
		timeout *= 2;		/* exponential backoff: 3, 6, 12 */
	}
	canjump = 1;	/* siglongjmp is now OK */

	send_dns_query();
	nsent++;

	alarm(timeout);
	ui = udp_read();
	canjump = 0;
	alarm(0);

	if (ui->ui_sum == 0)
		printf("UDP checksums off\n");
	else
		printf("UDP checksums on\n");
	if (verbose)
		printf("received UDP checksum = %x\n", ntohs(ui->ui_sum));
}
/* end test_udp */