Question

When I open a websocket connection to my websocket server application from Java, the server sees two connections. The first one never sends any data and the second one sends all the proper headers, etc. Anyone know what the reason for this is?

Client side connection is:

var websocket = new WebSocket( "ws://192.168.1.19:3333/websession" );

On the server side, in a while loop I call “serverSocket.accept()” and this gets called twice. But one of them never sends any data (the in.read() simply times out eventually without returning anything).

JAVA SERVER CODE

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

public class WebListener {

    public static void main(String[] args) throws Exception {
        ServerSocket serverSocket = null;
        boolean listening = true;

        try {
            serverSocket = new ServerSocket(4444);
        } catch (IOException e) {
            System.err.println("Could not listen on port: 4444.");
            System.exit(-1);
        }

        while (listening) new ServerThread(serverSocket.accept()).start();

        serverSocket.close();
    }
}

class ServerThread extends Thread {
    private Socket socket = null;

    public ServerThread(Socket socket) {
        super("ServerThread");
        this.socket = socket;
    }

    public void run() {

        try {
            OutputStream outStream = null;
            PrintWriter out = new PrintWriter( outStream = socket.getOutputStream(), true);
            BufferedReader in = new BufferedReader( new InputStreamReader( socket.getInputStream()));

            String inputLine, outputLine;

            //Handle the headers first
            doHeaders( out, in );

            // ..elided..

            out.close();
            in.close();
            socket.close();

        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public void doHeaders(PrintWriter out, BufferedReader in) throws Exception {
        String inputLine = null;
        String key = null;

        //Read the headers
        while ( ( inputLine = in.readLine() ) != null ) {
            //Get the key
            if ( inputLine.startsWith( "Sec-WebSocket-Key" ) ) 
                key = inputLine.substring( "Sec-WebSocket-Key: ".length() );

            //They're done
            if ( inputLine.equals( "" ) ) break;
        }

        //We need a key to continue
        if ( key == null ) throw new Exception( "No Sec-WebSocket-Key was passed!" );

        //Send our headers
        out.println( "HTTP/1.1 101 Web Socket Protocol Handshake\r" );
        out.println( "Upgrade: websocket\r" );
        out.println( "Connection: Upgrade\r" );
        out.println( "Sec-WebSocket-Accept: " + createOK( key ) + "\r" );
        out.println( "\r" );
    }

    public String createOK(String key) throws NoSuchAlgorithmException, UnsupportedEncodingException, Exception {
        String uid = "258EAFA5-E914-47DA-95CA-C5AB0DC85B11";
        String text = key + uid;

        MessageDigest md = MessageDigest.getInstance( "SHA-1" );
        byte[] sha1hash = new byte[40];
        md.update( text.getBytes("iso-8859-1"), 0, text.length());
        sha1hash = md.digest();

        return new String( base64( sha1hash ) );
    }

    public byte[] base64(byte[] bytes) throws Exception {
        ByteArrayOutputStream out_bytes = new ByteArrayOutputStream();
        OutputStream out = new Base64.OutputStream(out_bytes); //Using http://iharder.net/base64
        out.write(bytes);
        out.close();

        return out_bytes.toByteArray();
    }

    private String convertToHex(byte[] data) { 
        StringBuffer buf = new StringBuffer();
        for (int i = 0; i < data.length; i++) { 
            int halfbyte = (data[i] >>> 4) & 0x0F;
            int two_halfs = 0;
            do { 
                if ((0 <= halfbyte) && (halfbyte <= 9)) 
                    buf.append((char) ('0' + halfbyte));
                else 
                    buf.append((char) ('a' + (halfbyte - 10)));
                halfbyte = data[i] & 0x0F;
            } while(two_halfs++ < 1);
        } 

        return buf.toString();
    } 
}

Answer 1

This looks to be a bug with Firefox. In Chrome it only opens one connection, while the same page in Firefox 15 opens two connections.