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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);
}