socket.BeginReceive() 导致打印机无响应

Question

我一直在开发一个应用程序，该应用程序可以在 PDF 文件到达时自动在特定网络打印机上打印并监视 @PJL USTATUS JOB 消息。但是，每当我启动应用程序并且代码命中 socket.BeginReceive() 时，打印机无法从任何工作站接收任何打印作业，这也意味着永远不会调用回调。但是，如果我关闭应用程序或仅关闭套接字，打印机将再次开始工作。

我错过了什么吗？喜欢阻塞/非阻塞或同步或异步套接字？

public class SocketData {
    public Socket socket;
    public byte[] dataBuffer = new byte[1024];
}

public void Start() {
    // start the thread that checks the printer status
    thread = new Thread(new ThreadStart(ConnectAndListen));
    thread.Priority = ThreadPriority.Lowest;
    thread.Start();

    // start the file listener
    listener = new FileSystemWatcher(this.WatchPath);
    listener.Created += new FileSystemEventHandler(listener_Created);
    listener.EnableRaisingEvents = true;
}

public void ConnectAndListen() {
        ipEndPoint = new IPEndPoint(Dns.GetHostEntry(this.IPAddress).AddressList[0], 9100);
        socket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
        socket.Connect(ipEndPoint);

        //socket.Send(Encoding.ASCII.GetBytes("\x1B%-12345X@PJL USTATUS DEVICE = ON\r\n\x1B%-12345X\r\n"));
        //socket.Send(Encoding.ASCII.GetBytes("\x1B%-12345X@PJL USTATUS JOB = ON\r\n\x1B%-12345X\r\n"));
        socket.Send(Encoding.ASCII.GetBytes("\x1B%-12345X@PJL USTATUS PAGE = ON\r\n\x1B%-12345X\r\n"));
        //socket.Send(Encoding.ASCII.GetBytes("\x1B%-12345X@PJL USTATUS TIMED = 0\r\n\x1B%-12345X\r\n"));

        ListenForPrinterReadBack(socket);
}

public void ListenForPrinterReadBack(Socket socket) {
    if (DataRecievedCallBack == null) {
        DataRecievedCallBack = new AsyncCallback(OnDataReceived);
    }

    SocketData socketData = new SocketData();
    socketData.socket = socket;

    m_asynResult = socket.BeginReceive(socketData.dataBuffer, 0, socketData.dataBuffer.Length, SocketFlags.None, DataRecievedCallBack, socketData);
}

public void OnDataReceived(IAsyncResult asyn) {
    SocketData socketData = (SocketData)asyn.AsyncState;

    int result = socketData.socket.EndReceive(asyn);

    char[] chars = new char[result + 1];
    Decoder d = Encoding.UTF8.GetDecoder(); //creating object for decoding
    int charLen = d.GetChars(socketData.dataBuffer, 0, result, chars, 0);
    String recievedData = new String(chars);

    this.Status = recievedData;

    ListenForPrinterReadBack(socketData.socket);
}

我知道我可以进行轮询，但我无法接收未经请求的打印机消息。

提前致谢！

更新： 我感觉打印机上只允许一个套接字连接。由于 socket.BeginReceive() 仅在套接字已连接时才能工作，因此无法发送任何其他请求，因为该套接字已被使用。也许还有另一种方法来处理未经请求的打印机读回？

Answer 1

Send 是否报告所有字节已发送（检查其返回值）？我无法发现任何会阻止另一端接收您的消息的错误。您是否 100% 确定您发送的字符串是正确的？

Answer 2

您好，我在使用打印机时发现与您相同的问题，

首先：确保打印机处于“双向”模式并尝试此代码：

  private void SendCommand(byte[] data, string ip, int port)
    {
        var socket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
        socket.NoDelay = true;

        var ipAddress = IPAddress.Parse(ip);
        IPEndPoint remoteEP = new IPEndPoint(ipAddress, port);

        socket.Connect(remoteEP);
        socket.Send(data);
        socket.Close();
    }

它会正常工作。

此致