UNIX网络编程卷1 时间获取程序client UDP 协议无关

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/**
* UDP。协议无关，调用 getaddrinfo 和 udp_client
**/
#include	"unp.h"


int
udp_client(const char *host, const char *serv, SA **saptr, socklen_t *lenp)
{
	int				sockfd, n;
	struct addrinfo	hints, *res, *ressave;


	//1.调用 getaddrinfo
	//协议地址族为 AF_UNSPEC ，套接字类型为 SOCK_DGRAM
	bzero(&hints, sizeof(struct addrinfo));
	hints.ai_family = AF_UNSPEC;
	hints.ai_socktype = SOCK_DGRAM;


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


	//2.尝试每一个 addrinfo 结构直到成功或到达链表尾
	do {
	    // 创建套接字
		sockfd = socket(res->ai_family, res->ai_socktype, res->ai_protocol);
		if (sockfd >= 0)
			break;		/* success */
	} while ( (res = res->ai_next) != NULL);


	//3.假设 getaddrinfo 失败或创建套接字不成功。本函数将终止
	if (res == NULL)	/* errno set from final socket() */
		err_sys("udp_client error for %s, %s", host, serv);


	//4.保存server套接字地址结构	
	*saptr = Malloc(res->ai_addrlen);
	memcpy(*saptr, res->ai_addr, res->ai_addrlen);
	*lenp = res->ai_addrlen;


	//5.调用 freeaddrinfo 清理由 getaddrinfo 返回的动态存储空间
	freeaddrinfo(ressave);


	//6.返回套接字
	return(sockfd);
}
/* end udp_client */


int
Udp_client(const char *host, const char *serv, SA **saptr, socklen_t *lenptr)
{
	return(udp_client(host, serv, saptr, lenptr));
}

/**
* UDP，协议无关。调用 getaddrinfo 和 udp_client
**/
#include	"unp.h"


int
main(int argc, char **argv)
{
	int				sockfd, n;
	char			recvline[MAXLINE + 1];
	socklen_t		salen;
	struct sockaddr	*sa;


	if (argc != 3)
		err_quit("usage: daytimeudpcli1 <hostname/IPaddress> <service/port#>");


	//1.利用 Udp_client 获得 UDP 套接字和server套接字地址结构
	sockfd = Udp_client(argv[1], argv[2], (void **) &sa, &salen);


	//2.显示server地址
	printf("sending to %s\n", Sock_ntop_host(sa, salen));


	//3.发送1字节的数据报
	Sendto(sockfd, "", 1, 0, sa, salen);	/* send 1-byte datagram */


	//4.读取并显示应答数据报
	n = Recvfrom(sockfd, recvline, MAXLINE, 0, NULL, NULL);
	recvline[n] = '\0';	/* null terminate */
	Fputs(recvline, stdout);


	exit(0);
}