Socket Exceptions not being generated, readLine not returning null

[jmlsteele]

I'm having a really weird problem that I can't for the life of me figure out. This is happening in a multi-client game I'm writing, but I've been able to reproduce it in significantly less code for posting here.

The way i understand BufferedReader is that readLine is supposed to block until it either reads a line OR the underlying stream has an error in which case it returns null. This is how it has been working for simple tests, but with the following code I can reproduce a case in which it fails to work properly, leaving a client connected that should actually be disconnected.

package sockettest;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;

class Client extends Thread{
    BufferedReader stdin;
    PrintWriter stdout;
    Socket s;
    int id;
    Client(Socket s, int id) throws IOException {
        this.s = s;
        this.id=id;
        stdin = new BufferedReader(new InputStreamReader(s.getInputStream()));
        stdout = new PrintWriter(s.getOutputStream());
        System.out.println("Client " + id + " connected.");
        this.start();
    }
    @Override
    public void run() {
        try {
            while(s.isConnected()) {
                String str = stdin.readLine();
                System.out.println("Client " + id + ": " + str);

                stdout.println(str.toUpperCase());
                stdout.flush();
            }
        } catch (IOException ex) {
            ex.printStackTrace();
        } finally {
            try {
                s.close();
                System.out.println("Client " + id + " disconnected.");
            } catch ( Exception e) {
                e.printStackTrace();
            }
        }
    }
}

public class Main {

    public static void main(String[] args) {
        try {
            ServerSocket s = new ServerSocket(4444);
            int count = 0;
            while(true) new Client(s.accept(),count++);
        } catch (IOException ex) {
            ex.printStackTrace();
        }
    }
}

Here's a log of what happens when the problem occurs. The remarks inside angle brackets are when I physically closed the connections, not something the program outputs.

Client 0 connected.
Client 0: A
Client 1 connected.
Client 1: B
<Client 0 closed telnet>
Client 1: C
Client 1: D
Client 1: E
<Client 1 closed telnet>
Client 1: null
Client 1 disconnected.
java.net.SocketException: Connection reset
Client 0 disconnected.
        at java.net.SocketInputStream.read(SocketInputStream.java:168)
        at sun.nio.cs.StreamDecoder.readBytes(StreamDecoder.java:264)
        at sun.nio.cs.StreamDecoder.implRead(StreamDecoder.java:306)
        at sun.nio.cs.StreamDecoder.read(StreamDecoder.java:158)
        at java.io.InputStreamReader.read(InputStreamReader.java:167)
        at java.io.BufferedReader.fill(BufferedReader.java:136)
        at java.io.BufferedReader.readLine(BufferedReader.java:299)
        at java.io.BufferedReader.readLine(BufferedReader.java:362)
        at sockettest.Client.run(Main.java:27)
Exception in thread "Thread-1" java.lang.NullPointerException
        at sockettest.Client.run(Main.java:29)
<Client 0 Closed Telnet>

As you can see when Client 0 closes telnet the server doesn't even notice it. It isn't until Client 1 closes his connection that the server notices that both Client 1 and Client 0 are closed.

I'm at a loss for what else I can test/check/do. If you want more information, or have a suggestion please feel free to ask/let me know. If this is a well known problem please point out to me where it is (I've been searching for a while and although I've found some related stuff, they don't solve this problem).

Thank you for your time.

Jody Steele

[jmlsteele]

*sigh*

Much to my expectations there ISN'T anything wrong with the code, or Java, it was with the manner I was testing it.

I was using PuTTY to connect to the server, and then instead of opening a brand new connection I simply used PuTTY's built in "Duplicate Session" feature.

Apparently there is a known bug with Duplicate Session where the Parent won't close its sockets until all of their children are gone.

Link: Google "PuTTY semi-bug dup-sessions-dont-close" (since I can't post URLs yet)