通过select 和状态EINPROGRESS 实现socket 连接超时判断

调用connect连接一般的超时时间是75s, 但是在程序中我们一般不希望等这么长时间采取采取动作。可以在调用connect之前设置套接字非阻塞,然后调用connect,此时connect会立刻返回, 如果连接成功则直接返回0（成功），如果没有连接成功，也会立即返回并且会设置errno为EINPROCESS,这并不是一个致命错误,仅仅是告知你已经在连接了,你只要判断是它就继续执行后面的逻辑就行了,比如select.通过select设置超时来达到为connect设定超时的目的. 下面的代码显示这个过程。

bool timeout_connect(const string& _host, uint16_t _port, uint32t _timeout, int32_t& _sockfd)

{
#define CLOSE_SOCK_AND_RETURN_FALSE(so)    close(so); return false;

   if (_sockfd != -1) return true;

   int sockfd;
   struct sockaddr_in serv_addr;

   memset(&serv_addr, 0, sizeof(serv_addr));
   serv_addr.sin_family = AF_INET;
   serv_addr.sin_port = htons(_port);
   serv_addr.sin_addr.s_addr = inet_addr(_host.c_str());

   if ((sockfd=socket(AF_INET, SOCK_STREAM, 0)) == -1)
   {
       return false;
   }
   // get origin sockfd flag
   int flags = fcntl(sockfd, F_GETFL);
   if (flags == -1)
   {
       CLOSE_SOCK_AND_RETURN_FALSE(sockfd);
   }

   // set sockfd to non-block mode
   int retcode = fcntl(sockfd, F_SETFL, flags|O_NONBLOCK);
   if (retcode == -1)
   {
       CLOSE_SOCK_AND_RETURN_FALSE(sockfd);
   }

   if (::connect(sockfd, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) == -1)
   {

if (errno == EINPROGRESS) // EINPROGRESS means connection is in progress, normally the socket connecting timeout is 75s. after the socket fd is ready to read.

// means the connecting of the socket fd is established.

       {
           int err;
           int len = sizeof(int);
           fd_set wds;
           struct timeval tm;
           tm.tv_sec = _timeout;
           tm.tv_usec = 0;
           FD_ZERO(&wds);
           FD_SET(sockfd, &wds);
           if (select(sockfd + 1, NULL, &wds, NULL, &tm) > 0) // ">0" means sockfd ready to read, "=0" means timeout cause retrun, "<0" means error.
           {
               retcode = getsockopt(sockfd, SOL_SOCKET, SO_ERROR, &err, (socklen_t *)&len);
               if (retcode == -1 || err != 0)
               {
                   CLOSE_SOCK_AND_RETURN_FALSE(sockfd);
               }
           }
           else
           {
               CLOSE_SOCK_AND_RETURN_FALSE(sockfd);
           }
       }
       else
       {
           CLOSE_SOCK_AND_RETURN_FALSE(sockfd);
       }
   }
   retcode = fcntl(sockfd, F_SETFL, flags); // trun back the mode of sockfd to block.
   if (retcode == -1)
   {
       CLOSE_SOCK_AND_RETURN_FALSE(sockfd);
   }

   struct timeval readtimeout;
   readtimeout.tv_sec = _timeout;
   readtimeout.tv_usec = 0;
   retcode = setsockopt(sockfd, SOL_SOCKET, SO_RCVTIMEO, (void *)&readtimeout, sizeof(readtimeout)); // set socket read timeout.
   if (retcode == -1)
   {
       CLOSE_SOCK_AND_RETURN_FALSE(sockfd);
   }

#undef CLOSE_SOCK_AND_RETURN_FALSE
   _sockfd = sockfd;
   return true;

}

通过SO_RCVTIMEO 设置连接超时

SO_RCVTIMEO和SO_SNDTIMEO套接口选项可以给套接口的读和写,来设置超时时间,

一、在unix网络编程中,说是他们只能用于读和写,而像 accept和connect都不能用他们来设置.

可是我在阅读内核源码的过程中看到,在linux中,accept和connect可以分别用 SO_RCVTIMEO和SO_SNDTIMEO套接口来设置超时,这里他们的超时时间也就是sock的sk_rcvtimeo和sk_sndtimeo 域.accept和connect的相关代码我前面都介绍过了,这里再提一下.其中accept的相关部分在inet_csk_accept中,会调用 sock_rcvtimeo来取得超时时间(如果是非阻塞则忽略超时间).而connect的相关代码在inet_stream_connect中通过调用sock_sndtimeo来取得超时时间(如果非阻塞则忽略超时时间).

SO_RCVTIMEO和SO_SNDTIMEO ，它们分别用来设置socket接收数据超时时间和发送数据超时时间。
因此，这两个选项仅对与数据收发相关的系统调用有效，这些系统调用包括：send, sendmsg, recv, recvmsg, accept, connect 。
这两个选项设置后，若超时，返回-1，并设置errno为EAGAIN或EWOULDBLOCK.
其中connect超时的话，也是返回-1, 但errno设置为EINPROGRESS

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#include <stdio.h>
    #include <stdlib.h>
    #include <unistd.h>
    #include <string.h>
    #include <errno.h>
    #include <assert.h>
    #include <fcntl.h>
    #include <sys/types.h>
    #include <sys/socket.h>
    #include <netinet/in.h>
    #include <arpa/inet.h>

    //超时连接
    int timeout_connect(const char *ip, int port, int time);

    int main(int argc, char **argv)
    {
        if (argc != 3) {
            fprintf(stderr, "Usage: %s ip port\n", argv[0]);
            return 1;
        }

        const char *ip = argv[1];
        int port = atoi(argv[2]);

        int sockfd = timeout_connect(ip, port, 10);
        if (sockfd < 0)
            return 1;


        return 0;
    }

    int timeout_connect(const char *ip, int port, int time)
    {
        int ret = 0;
        int error;

        struct sockaddr_in address;
        bzero(&address, sizeof(address));
        address.sin_family = AF_INET;
        address.sin_port = htons(port);
        inet_pton(AF_INET, ip, &address.sin_addr);

        int sockfd = socket(PF_INET, SOCK_STREAM, 0);
        if (sockfd == -1)
            return -1;

        //超时时间
        struct timeval timeout;
        timeout.tv_sec = time;
        timeout.tv_usec = 0;

        socklen_t len = sizeof(timeout);
        ret = setsockopt(sockfd, SOL_SOCKET, SO_SNDTIMEO, &timeout, len);
        if (ret == -1) {
            error = errno;
            while ((close(sockfd) == -1) && (errno == EINTR));
            errno = error;
            return -1;
        }

        ret = connect(sockfd, (struct sockaddr*)&address, sizeof(address));
        if (ret == -1) {
            if (errno == EINPROGRESS) {
                printf("connecting timeout\n");
                return -1;
            }

            printf("error occur when connecting to server\n");
            return -1;
        }

        char buffer[1024];
        memset(buffer, '\0', 1024);
        ret = recv(sockfd, buffer, 1024, 0);

        printf("recv %d bytes, buf: %s\n", ret, buffer);

        return sockfd;
    }

通过select 和状态EINPROGRESS 实现socket 连接超时判断

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