时间获取程序客户端 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.如果 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.保存服务器套接字地址结构

*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 套接字和服务器套接字地址结构

sockfd = Udp_client(argv[1], argv[2], (void **) &sa, &salen);

//2.显示服务器地址

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);

}