Question

I have the following Java socket client app, that sends same string to socket server:

import java.net.*;
import java.io.*;

public class ServerClient {
public static void main(String[] args) throws IOException {
    System.out.println("Starting a socket server client...");
    Socket client = new Socket("XXX.X.XXX.XX", 12001);
    BufferedOutputStream stream = new BufferedOutputStream(client.getOutputStream());
    String message = "ABC";

    BufferedReader inputReader = new BufferedReader(new InputStreamReader(System.in));      
    String input = null;
    while ( true ) {
        System.out.print("Would you like to send a message to Server? ");
        input = inputReader.readLine();
        if ( !input.equals("Y") ) break;    

        System.out.println("Message to send: " + message);
        System.out.println("Message length is: " + message.length());

        byte[] messageBytes = message.getBytes("US-ASCII");
        stream.write(messageBytes, 0, messageBytes.length);
        stream.flush();
    }
    System.out.println("Shutting down socket server client...");        
    stream.close();
    client.close();
    inputReader.close();
}
}

The first time message is sent, server receives the message; however, every subsequent time I’m trying to send this message, server is not receiving anything. Message simply disappears. I am writing to the socket successfully (no exceptions) but nothing is coming on the other side of the pipe (or so I’m told).

I do not have access to the server app, logs or code, so I’m wondering if there is any approach you can recommend to figure out why server is not receiving subsequent messages. Any ideas would be greatly appreciated!

Clarification:

1. New lines are not expected by the server; otherwise, how would it even receive message the first time? As a trial and error, I did try sending ‘\n’ and “\r\n” and 0x00 characters at the end of the string – all without any luck.

2. I thought flushing was an issue, so I tried various outputstream classes (PrintStream, PrintWriter, FilterOutputStream), but was still running into same exact issues. Then, if “flushing” is an issue, how is it working the first time?

Answer 1

Other tests:

1 – use a network sniffer to see what is realy hapening on the network

2 – use some program like TCP Test Tool to send data to the server and simulate your program. (netcat can also be used, but it sends a newline after each line)