使用setsockopt来控制connect超时

原来我们实现connect()超时基本上都使用unix网络编程一书的非阻塞方式（connect_nonb），今天在网上看到一篇文章，觉得很有意思，转载如下：

读Linux内核源码的时候偶然发现其connect的超时参数竟然和用SO_SNDTIMO操作的参数一致:
File: net/ipv4/af_inet.c

    559       timeo = sock_sndtimeo(sk, flags & O_NONBLOCK);
    560
    561       if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) {
    562           /* Error code is set above */
    563           if (!timeo || !inet_wait_for_connect(sk, timeo))
    564               goto out;
    565
    566           err = sock_intr_errno(timeo);
    567           if (signal_pending(current))
    568               goto out;
    569       }

这意味着：在Linux平台下，可以通过在connect之前设置SO_SNDTIMO来达到控制连接超时的目的。简单的写了份测试代码:

#include
#include
#include
#include
#include
#include
#include
#include
#include

int main(int argc, char *argv[])
{
        int fd;
        struct sockaddr_in addr;
        struct timeval timeo = {3, 0};
        socklen_t len = sizeof(timeo);

         fd = socket(AF_INET, SOCK_STREAM, 0);
         if (argc == 4)
                 timeo.tv_sec = atoi(argv[3]);

         setsockopt(fd, SOL_SOCKET, SO_SNDTIMEO, &timeo, len);
         addr.sin_family = AF_INET;
         addr.sin_addr.s_addr = inet_addr(argv[1]);
         addr.sin_port = htons(atoi(argv[2]));

        if (connect(fd, (struct sockaddr*)&addr, sizeof(addr)) == -1) {
                if (errno == EINPROGRESS) {
                        fprintf(stderr, "timeout\n");
                        return -1;
                }
                perror("connect");
                return 0;
        }
        printf("connected\n");

        return 0;
}

#include <stdlib.h> #include <stdio.h> #include <sys/types.h> #include <sys/socket.h> #include <netinet/in.h> #include <errno.h> #include <sys/socket.h> #include <netinet/in.h> #include <arpa/inet.h> int main(int argc, char *argv[]) { int fd; struct sockaddr_in addr; struct timeval timeo = {3, 0}; socklen_t len = sizeof(timeo); fd = socket(AF_INET, SOCK_STREAM, 0); if (argc == 4) timeo.tv_sec = atoi(argv[3]); setsockopt(fd, SOL_SOCKET, SO_SNDTIMEO, &timeo, len); addr.sin_family = AF_INET; addr.sin_addr.s_addr = inet_addr(argv[1]); addr.sin_port = htons(atoi(argv[2])); if (connect(fd, (struct sockaddr*)&addr, sizeof(addr)) == -1) { if (errno == EINPROGRESS) { fprintf(stderr, "timeout\n"); return -1; } perror("connect"); return 0; } printf("connected\n"); return 0; }

使用 ./cmd  ip地址  端口  超时秒数   

(测试的ip和端口必须是不存在的，或者是ip的机器是死掉的，才会出现，否则机器存在而端口不存在会立即返回的)