博客

int test_tcp_connect(const char* dst, unsigned short port)
{
    struct sockaddr_in addr;
    int flags;
    fd_set writefds;
    int nfds;
    struct timeval timeout;
    int result;
    int tcp_sd;

    if(NULL == dst)
        return -1;

    tcp_sd = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP); 
    if(tcp_sd < 0)
        return -2;

    addr.sin_family = AF_INET;
    addr.sin_addr.s_addr = net_inet_aton(dst);
    addr.sin_port = htons(port);
    printf("hilink tcp connect ip: %s port = %d\r\n",dst,port);
    /*Set as nonblocking*/
    flags = fcntl(tcp_sd, F_GETFL, 0);
    fcntl(tcp_sd, F_SETFL, flags | O_NONBLOCK);

    int    reuse = 1;
    if(setsockopt(tcp_sd, SOL_SOCKET, SO_REUSEADDR,(const char *) &reuse, sizeof( reuse ) ) != 0 )
    {
        close(tcp_sd);
        printf("tcp set SO_REUSEADDR failed\n");
        return -2;
    }
    if(connect(tcp_sd, (const struct sockaddr_in *)&addr, sizeof(addr)) != 0 \
        && errno != EINPROGRESS)
    {
        printf("dna_connect failed %d\n", tcp_sd);
        goto err;
    }

    nfds = tcp_sd + 1;
    timeout.tv_sec = 3; //Waiting 2s to connect to tcp server
    timeout.tv_usec = 0;

    FD_ZERO(&writefds);
    FD_SET(tcp_sd, &writefds);

    result = select(nfds, NULL, &writefds, NULL, &timeout);

    //dna_printf("hilink  tcp Result %d %d\r\n", result, FD_ISSET(tcp_sd, &writefds));
    if(result == 0)
        goto err;
    else if(result > 0)
    {
        if(FD_ISSET(tcp_sd, &writefds))
        {
            int   error   =   0; 
            int   len   =   sizeof   (error);
            result = getsockopt(tcp_sd,SOL_SOCKET,SO_ERROR,&error,  &len);
            printf( "getsockopt fail,result  =%d error=%d\r\n",result,error);
            if(result   <   0)
            {
                printf( "getsockopt fail,connected  fail \n");
                goto err;
            }

            if(error != 0)
            {
                printf("error = %d , connected fail \r\n",error);
                goto err;
            }

            return tcp_sd;

        }
    }


err:
    close(tcp_sd);
    return -2;
}

1 要设置为非阻塞的模式，阻塞模式connect 大多数设计都是75s

2 通过select 判断等待套接字可读或可写，如果可以读或写；再通过 getsockopt 处理SO_ERROR，如果小于0，则连接失败，考虑不同平台的兼容性，（Berkeley getsockopt 返回为0，错误在码SO_ERROR里，Solaris 则会返回-1），所以还需要进一步判断错误码，具体可以参考书籍《UNIX网络编程卷1：套接字API（第三版） p352》