Java客户机和python服务器套接字连接-接收消息时文件结束错误

Question

import java.io.DataOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.net.Socket;

public class Client {
    public static void main(String[] args) throws IOException {
        // need host and port, we want to connect to the ServerSocket at port 7777
        Socket socket = new Socket("localhost", 7777);
        System.out.println("Connected!");

        // get the output stream from the socket.
        OutputStream outputStream = socket.getOutputStream();
        // create a data output stream from the output stream so we can send data through it
        DataOutputStream dataOutputStream = new DataOutputStream(outputStream);

        System.out.println("Sending string to the ServerSocket");

        // write the message we want to send
        dataOutputStream.writeUTF("Hello from the other side!");
        dataOutputStream.flush(); // send the message
        dataOutputStream.close(); // close the output stream when we're done.

        System.out.println("Closing socket and terminating program.");
        socket.close();
    }
}

from multiprocessing.connection import Listener
address = ('localhost',7777)
while True:
    with Listener(address, authkey=None) as listener
        with listener.accept() as conn:
            print(conn.recv())

当我尝试执行此操作时，我在Python中得到以下错误：

OSError: got end of file during message

我做错了什么？

Answer 1

这里的问题是multiprocessing连接的recv*函数希望在消息中获得一个32位的前导码，该前导码指示正在传输的实际数据量。下面是Java部分需要的样子（我并没有考虑缓冲的IO--只是简单地介绍一下）：

import java.io.IOException;
import java.net.Socket;
import java.io.OutputStream;

public class Client {

    public static void main(String[] args) throws IOException {
        try (Socket socket = new Socket("localhost", 7777)) {
            OutputStream out = socket.getOutputStream();
            byte[] dts = "Hello from the other side!".getBytes();
            out.write(net(dts.length));
            out.write(dts);
        }
    }
    private static byte[] net(int n) {
        byte[] buffer = new byte[4];
        for (int i = 3; i >= 0; i -= 1) {
            buffer[i] = (byte)(n & 0xff);
            n >>>= 8;
        }
        return buffer;
    }
}

然后，您的Python服务器可以如下所示：

from multiprocessing.connection import Listener

def main():
    listener = Listener(address=('0.0.0.0', 7777), family='AF_INET', authkey=None)
    with listener.accept() as conn:
        print(conn.recv_bytes().decode())
            

if __name__ == '__main__':
    main()

因此，这意味着最初的问题是由于recv（）查看前4个字节并将其解释为传入数据的长度。但这将等同于比实际发送的要大得多的东西。