c++ - connect() 超时不工作

Question

我正在使用此代码连接到服务器，但它没有等待我设置的 10 秒超时。连接失败后立即返回。

BOOL Connect(string server, int port, int timeout)
{
    struct sockaddr_in RemoteHost;
    TIMEVAL Timeout;
    Timeout.tv_sec = timeout;
    Timeout.tv_usec = 0;
    int con_error = 0;

#ifdef W32
    WSADATA       wsd;
    if (WSAStartup(MAKEWORD(2, 2), &wsd) != 0)
    {
        DEBUG(L"Failed to load Winsock!\n");
        return FALSE;
    }
#endif

    //create socket if it is not already created
    if (s == SOCKET_ERROR)
    {
        //Create socket
        s = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
        if (s == SOCKET_ERROR)
        {
            DEBUG(L"Could not create socket");
            return FALSE;
        }
    }

    //setup address structure
    if (inet_addr(server.c_str()) == INADDR_NONE)
    {
        struct hostent *he;

        //resolve the hostname, its not an ip address
        if ((he = gethostbyname(server.c_str())) == NULL)
        {
            //gethostbyname failed
            DEBUG(L"gethostbyname() - Failed to resolve hostname\n");
            return FALSE;
        }
    }   
    else//plain ip address
    {
        RemoteHost.sin_addr.s_addr = inet_addr(server.c_str());
    }

    RemoteHost.sin_family = AF_INET;
    RemoteHost.sin_port = htons(port);

    //set the socket in non-blocking
    unsigned long iMode = 1;
    int iResult = ioctlsocket(s, FIONBIO, &iMode);
    if (iResult != NO_ERROR)
    {
        DEBUGP(L"ioctlsocket failed with error: %ld\n", iResult);
        return FALSE;
    }

    //Connect to remote server
    if ((con_error=connect(s, (struct sockaddr *)&RemoteHost, sizeof(RemoteHost))) < 0)
    {
        if (con_error != EINPROGRESS)
        {
            DEBUG(L"connect() failed");
            return FALSE;
        }       
    }

    // restart the socket mode
    iMode = 0;
    iResult = ioctlsocket(s, FIONBIO, &iMode);
    if (iResult != NO_ERROR)
    {
        DEBUGP(L"ioctlsocket failed with error: %ld\n", iResult);
        return FALSE;
    }

    fd_set Write, Err;
    FD_ZERO(&Write);
    FD_ZERO(&Err);
    FD_SET(s, &Write);
    FD_SET(s, &Err);

    // check if the socket is ready
    select(0, NULL, &Write, &Err, &Timeout);
    if (FD_ISSET(s, &Write))
    {
        return TRUE;
    }
    return FALSE;
}

Answer 1

当套接字在目标系统上不可用时，它可能会发回 an ICMP message indicating that the socket is not open并尝试连接失败。在这种情况下，winsock 函数将立即返回 - 这是设计使然。