tcp_connect.c

/* include tcp_connect */
#include	"unp.h"

int
tcp_connect(const char *host, const char *serv)
{
	int				sockfd, n;
	struct addrinfo	hints, *res, *ressave;

	bzero(&hints, sizeof(struct addrinfo));
	hints.ai_family = AF_UNSPEC;//会首先搜索AAAA记录，然后搜索A记录
	hints.ai_socktype = SOCK_STREAM;

	if ( (n = getaddrinfo(host, serv, &hints, &res)) != 0)
		err_quit("tcp_connect error for %s, %s: %s",
				 host, serv, gai_strerror(n));
	ressave = res;

	//对于同时支持IPv4和IPv6的主机，由于设置了AF_UNSPEC，所以首先会搜索AAAA
	//记录，连接成功后循环终止，可以通过指定带-4后缀的主机名来强制使用IPv4地址
	do {
		sockfd = socket(res->ai_family, res->ai_socktype, res->ai_protocol);
		if (sockfd < 0)
			continue;	/* ignore this one */

		if (connect(sockfd, res->ai_addr, res->ai_addrlen) == 0)
			break;		/* success */

		Close(sockfd);	/* ignore this one */
	} while ( (res = res->ai_next) != NULL);

	if (res == NULL)	/* errno set from final connect() */
		err_sys("tcp_connect error for %s, %s", host, serv);

	freeaddrinfo(ressave);

	return(sockfd);
}
/* end tcp_connect */

/*
 * We place the wrapper function here, not in wraplib.c, because some
 * XTI programs need to include wraplib.c, and it also defines
 * a Tcp_connect() function.
 */

int
Tcp_connect(const char *host, const char *serv)
{
	return(tcp_connect(host, serv));
}