Question

I’m trying to write a small client server program. The Server is in C#, and the client is in Java.
Here are the codes:

Server:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Net;
using System.Net.Sockets;
using System.IO;

namespace Server
{
    class Program
    {
        private TcpListener tcpListener;
        public static void Main(string[] args)
        {
            Program program = new Program();
            program.StartServer();

            while (true) ;
        }

        private bool StartServer()
        {
            IPAddress ipAddress = Dns.GetHostEntry("localhost").AddressList[0];

            try
            {
                tcpListener = new TcpListener(ipAddress, 5678);
                tcpListener.Start();
                tcpListener.BeginAcceptTcpClient(new AsyncCallback(this.ProcessEvents), tcpListener);

                Console.WriteLine("Listing at Port {0}.", 5678);
            }
            catch (Exception e)
            {
                Console.WriteLine(e.ToString());
                return false;
            }

            return true;
        }

        private void ProcessEvents(IAsyncResult asyn)
        {
            try
            {
                TcpListener processListen = (TcpListener)asyn.AsyncState;
                TcpClient tcpClient = processListen.EndAcceptTcpClient(asyn);
                NetworkStream myStream = tcpClient.GetStream();
                if (myStream.CanRead)
                {
                    StreamReader readerStream = new StreamReader(myStream);
                    string myMessage = readerStream.ReadToEnd();
                    readerStream.Close();
                }
                myStream.Close();
                tcpClient.Close();
                tcpListener.BeginAcceptTcpClient(new AsyncCallback(this.ProcessEvents), tcpListener);
            }
            catch (Exception e)
            {
                Console.WriteLine(e.ToString());
            }
        }
    }
}

Client:

import java.io.PrintWriter;
import java.net.Socket;


public class Program {

    public static void main(String[] args) {
        Socket socket;
        try {
            socket = new Socket( "127.0.0.1", 5678);
            PrintWriter writer = new PrintWriter(socket.getOutputStream());
            writer.print("Hello world");
            writer.flush();
            writer.close();
            socket.close();
        } catch (Exception e) {
            e.printStackTrace();
        }

    }

}

But when I try to create a Socket in client, I get this exception:

java.net.ConnectException: Connection refused: connect
at java.net.DualStackPlainSocketImpl.connect0(Native Method)
at java.net.DualStackPlainSocketImpl.socketConnect(Unknown Source)
at java.net.AbstractPlainSocketImpl.doConnect(Unknown Source)
at java.net.AbstractPlainSocketImpl.connectToAddress(Unknown Source)
at java.net.AbstractPlainSocketImpl.connect(Unknown Source)
at java.net.PlainSocketImpl.connect(Unknown Source)
at java.net.SocksSocketImpl.connect(Unknown Source)
at java.net.Socket.connect(Unknown Source)
at java.net.Socket.connect(Unknown Source)
at java.net.Socket.<init>(Unknown Source)
at java.net.Socket.<init>(Unknown Source)
at Program.main(Program.java:10)

Can anyone tell me what I’m doing wrong here?

updated: I’m running x64 Windows 7 Ultimate, I don’t see anything firewall message pop up (I did saw it for server once, which I allowed and set to always allow). I can connect using telenet, no problem with that. Any other suggestion please.

Answer 1

I have finally figured out the problem myself.

The .Net server was by default using ipv6 address, and Java client was using the ipv4 address. To create a ipv4 address use:

TcpListener tcpListener = new TcpListener(IPAddress.Any, 5678);

instead of:

IPAddress ipAddress = Dns.GetHostEntry("localhost").AddressList[0];
TcpListener tcpListener = new TcpListener(ipAddress, 5678);