网络编程学习笔记(udp_server函数)

#include <netdb.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <errno.h>
#include <string.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>

#define MAXLINE 128

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

bzero(&hints, sizeof(hints));
hints.ai_flags = AI_PASSIVE;
hints.ai_family = AF_UNSPEC;
hints.ai_socktype = SOCK_DGRAM;

if ((n = getaddrinfo(host, serv, &hints, &res)) != 0) {
printf("udp_server error for %s,%s:%s\n", host, serv, gai_strerror(n));
return -1;
}

ressave = res;

do {
sockfd = socket(res->ai_family, res->ai_socktype, res->ai_protocol);
if (sockfd < 0) continue;

if (bind(sockfd, res->ai_addr, res->ai_addrlen) == 0) break;

close(sockfd);
} while ((res = res->ai_next) != NULL);

if (res == NULL) {
printf("udp_server error for %s,%s\n", host, serv);
return -1;
}

freeaddrinfo(ressave);
if (addrlenp) *addrlenp = res->ai_addrlen;
return sockfd;

}

char *sock_ntop(const struct sockaddr* sa, socklen_t len)
{
char portstr[7];
static char str[MAXLINE + 1];

switch (sa->sa_family) {
case AF_INET:
{
struct sockaddr_in *sin = (struct sockaddr_in*)sa;
if (inet_ntop(AF_INET, &sin->sin_addr, str, sizeof(str)) == NULL) return NULL;

if (ntohs(sin->sin_port) != 0) {
snprintf(portstr, sizeof(portstr), ":%d", ntohs(sin->sin_port));
strcat(str, portstr);
}
return str;
}
}

return NULL;
}

int main(int argc, char **argv)
{
int sockfd;
ssize_t n;
char buff[MAXLINE];
time_t ticks;
socklen_t addrlen, len;
struct sockaddr *cliaddr;

if (argc == 2) sockfd = udp_server(NULL, argv[1], &addrlen);
else if (argc == 3) sockfd = udp_server(argv[1], argv[2], &addrlen);
else {
printf("usage:exename [<host>] <service or port>\n");
return -1;
}

cliaddr = malloc(addrlen);
for (;;) {
len = addrlen;
n = recvfrom(sockfd, buff, MAXLINE, 0, cliaddr, &len);
printf("datagram form %s\n", sock_ntop(cliaddr, len));
ticks = time(NULL);
snprintf(buff, sizeof(buff), "%.24s\r\n", ctime(&ticks));
sendto(sockfd, buff, strlen(buff), 0, cliaddr, len);
}
}