网络编程学习笔记(tcp_connect函数)

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

#define MAXLINE 128
#define MAXSOCKADDR sizeof(struct sockaddr)

struct addrinfo *host_serv(char *host, const char *serv, int family, int socktype)
{
int n;
struct addrinfo hints, *res;

bzero(&hints, sizeof(hints));
hints.ai_flags = AI_CANONNAME;
hints.ai_family = family;
hints.ai_socktype = socktype;

if ((n = getaddrinfo(host, serv, &hints, &res)) != 0) return NULL;

return res;
}

int tcp_connect(const char *hostname, const char *serv)
{
int sockfd, n;

struct addrinfo hints, *res, *ressave;
bzero(&hints, sizeof(hints));
hints.ai_family = AF_INET;
hints.ai_socktype = SOCK_STREAM;

if ((n = getaddrinfo(hostname, serv, &hints, &res)) != 0) {
printf("tcp connect error for %s, %s:%s\n", hostname, 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 (connect(sockfd, res->ai_addr, res->ai_addrlen) == 0) break;
close(sockfd);
} while ((res = res->ai_next) != NULL);

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

freeaddrinfo(ressave);

return sockfd;
}

char *sock_ntop(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, n;
char recvline[MAXLINE + 1];
socklen_t len;
struct sockaddr *sa;

if (argc != 3) {
printf("usage: exename <hostname/ipaddress> <service/port>\n");
return -1;
}

sockfd = tcp_connect(argv[1], argv[2]);
if (sockfd < 0) {
//printf("tcp_connect error\n");
return -1;
}

sa = malloc(MAXSOCKADDR);
len = MAXSOCKADDR;

if (getpeername(sockfd, sa, &len) < 0) {
printf("getpeername error:%s\n", strerror(errno));
close(sockfd);
return -1;
}

printf("connected to %s\n", sock_ntop(sa, len));
while ((n = read(sockfd, recvline, MAXLINE)) > 0) {
recvline
= 0;
fputs(recvline, stdout);
}
return 0;
}