How to check whether a port is open at client's network/firewall?

Question

This is solved at last with \"timeout\" attribute of jQuery AJAX (and JSONP). See my own answer !

Please see the updated part, I

Answer 1

Here is a Java code as an Applet to test server/port connectivity:

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

public class ConnectionTestApplet extends Applet {
    public void start() {
        boolean portAvailable = false;
        int delay = 1000; // 1 s
        try {
            Socket socket = new Socket();
            socket.connect(new InetSocketAddress("server.domain.com", 1935), delay);
            portAvailable = socket.isConnected();
            socket.close();
        } catch (UnknownHostException uhe) {
            uhe.printStackTrace();
        } catch (IOException ioe) {
            ioe.printStackTrace();
        }
        System.out.println("Connection possible: " + portAvailable);
    }
}

You still have to get the information out of the applet to do something else with that result. The easiest way is to redirect the browser thanks to getAppletContext().showDocument(url)