UDP winsock服务器C++

Question

我正在使用 UDP 连接进行一些套接字编程。我已经编写了我的服务器（它也为 NTP 服务器提供了一个偏移量），但是当我对其进行单元测试时，它在 recvfrom 函数中失败了。我是 Winsock 编程和一般网络编程的新手，所以我不确定从这里去哪里。这是我的代码：

NtpServer::NtpServer(u_short portnum, const std::chrono::nanoseconds desiredOffset) : portnum(0), client_length(0), bytes_received(0), current_time(0), desiredOffset(0)
{
    WORD wVersionRequested;
    wVersionRequested = MAKEWORD(2, 2);
    WSADATA wsaData;

    int iResult = WSAStartup(MAKEWORD(2, 2), &wsaData);
    if (WSAStartup(wVersionRequested, &wsaData) != 0)
    {

        std::cerr << "Could not open Windows connection" << std::endl;
        exit(0);
    }

    sd = socket(AF_INET, SOCK_DGRAM, 0);
    if (sd == INVALID_SOCKET)
    {
        std::cerr << "Could not create socket." << std::endl;
        WSACleanup();
        exit(0);
    }

    //blocking enabled
    u_long iMode = 0;

    iResult = ioctlsocket(sd, FIONBIO, &iMode);
    if (iResult != NO_ERROR)
        std::cerr << "ioctlsocket failed with error: " << iResult << std::endl;


    memset((void *)&server, '\0', sizeof(struct sockaddr_in));
    server.sin_family = AF_INET;
    server.sin_addr.s_addr = htonl(INADDR_ANY);
    server.sin_port = htons(portnum);


    if (bind(sd, reinterpret_cast<SOCKADDR *>(&server),
        sizeof(server)) == -1)
    {
        std::cerr << "Could not bind name to socket" << std::endl;
        closesocket(sd);
        WSACleanup();
        exit(0);
    }
    getResult(desiredOffset);
}

和getResult函数：

void NtpServer::getResult(const std::chrono::nanoseconds desiredOffset)
{
    ntp_data ntpData = ntp_data();
    //struct for timeout
    struct timeval tv;
    tv.tv_sec = 10;  // 10 Secs Timeout 
    setsockopt(sd, SOL_SOCKET, SO_RCVTIMEO, (char *)&tv, sizeof(struct timeval));

    while (1)
    {
        client_length = (int)sizeof(struct sockaddr_in);

        /* Receive bytes from client */
        bytes_received = recvfrom(sd, sendBuffer, NTP_PACKET_MAX, 0, (struct sockaddr *)&client, &client_length);
        if (bytes_received < NTP_PACKET_MIN)
        {
            std::cerr << "Could not receive datagram." << std::endl;
            closesocket(sd);
            WSACleanup();
            exit(0);
        }



        /* Check for time request */
        if (strcmp(readBuffer, "GET TIME\r\n") == 0)
        {
            /* Get current time */
            system_clock::time_point now = std::chrono::system_clock::now();
            auto timepointoffset = (now + desiredOffset).time_since_epoch();
            double current_value = std::chrono::duration_cast<std::chrono::duration<double>>(timepointoffset).count();

            unpack_ntp(&ntpData, (unsigned char*)readBuffer, bytes_received);
            make_packet(&ntpData, NTP_CLIENT, current_value);
            pack_ntp((unsigned char *)sendBuffer, NTP_PACKET_MIN, &ntpData);


            /* Send data back */
            if (sendto(sd, sendBuffer,
                (int)sizeof(sendBuffer), 0,
                (struct sockaddr *)&client, client_length) !=
                (int)sizeof(current_time))
            {
                std::cerr << "Error sending datagram." << std::endl;
                closesocket(sd);
                WSACleanup();
                exit(0);
            }
        }
    }
        closesocket(sd);
        WSACleanup();


}

Answer 1

您必须测试来自recvfrom() 的错误——您正在设置 SO_RCVTIMEO，因此您可以预期接收超时。

您真的要启用读取超时吗？如果是这样，当你设置 SO_RCVTIMEO 时，设置tv.tv_usec = 0。你让它未初始化。如果 tv_usec 恰好是一个无效值（小于 0 或大于 999,999），那么 setsockopt() 调用应该会失败。