Home/ Questions/Q 7753275
In Process

The Archive Base Latest Questions

Editorial Team
  • 0
Asked: 2026-06-01T12:01:07+00:00

This is solved at last with timeout attribute of jQuery AJAX (and JSONP). See

  • 0

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

Please see the updated part, I have tried with applet too. And will not hesitate to accept your answer if you can give a solution with applet implementation.

I am working with a Java based web application. My requirement is to check whether a particular port (say 1935) is open or blocked at client’s end. I have implemented a “jsonp” (why ‘jsonp’ ? i found that ‘http’ request through AJAX cannot work for corssdomain for browsers ‘same origin policy’) AJAX call to one of my server containing particular port. And if the server returns xhr.status == 200 the port is open. Here is a drawback that I can’t make the execution-flow wait (synchronous) until the call completes. Here is the JavaScript function I am using.

Any alternative solution (must be a client-sided thing must be parallel with my application, please dont suggest python/php/other languages) is also welcome. Thanks for your time.

function checkURL() {

    var url = "http://10.0.5.255:1935/contextname" ;
    var isAccessible = false;

    $.ajax({
        url: url,
        type: "get",
        cache: false,
        dataType: 'jsonp',
        crossDomain : true,
        asynchronous : false,
        jsonpCallback: 'deadCode',
        complete : function(xhr, responseText, thrownError) {
            if(xhr.status == "200") {
                isAccessible = true;
                alert("Request complete, isAccessible==> " + isAccessible); // this alert does not come when port is blocked
            }
        }
    });

    alert("returning isAccessible=> "+ isAccessible); //this alert comes 2 times before and after the AJAX call when port is open
    return isAccessible;

}

function deadCode() {
    alert("Inside Deadcode"); // this does not execute in any cases
}

———————————————————UPDATE—————————————————————-

I have tried with Java Applet (thanks to Y Martin’s suggestion). This is working fine in appletviewer. But when I add the applet in HTML page, it is giving vulnerable results. Vulnerable in the sense, when I change the tab or resize the browser, the value of portAvailable is being altered in the printed message.

Applet Code :

import java.applet.Applet;
import java.awt.Graphics;
import java.net.InetSocketAddress;
import java.net.Socket;

public class ConnectionTestApplet extends Applet {
    private static boolean portAvailable;
    public void start() {
        int delay = 1000; // 1 s
        try {
            Socket socket = new Socket();
                /*****This is my tomcat5.5 which running on port 1935*************/
                /***I can view it with url--> http://101.220.25.76:1935/**********/
            socket.connect(new InetSocketAddress("101.220.25.76", 1935), delay);
            portAvailable = socket.isConnected();
            socket.close();
            System.out.println("init() giving--->  " + portAvailable);
        }
        catch (Exception e) {
            portAvailable = false;
            System.out.println("init() giving--->  " + portAvailable);
            System.out.println("Threw error---> " + e.getMessage());
        }

    }
    public void paint(Graphics g) {
        System.out.println("Connection possible---> " + portAvailable);
        String msg = "Connection possible---> " + portAvailable;
        g.drawString(msg, 10, 30);
    }
}

And this is my HTML page (I am hosting it on same computer with a different Tomcat 6 which runs on port 9090. I can view this page with url —> http://101.220.25.76:9090/test/):

<html>
<body>
        <applet code="ConnectionTestApplet" width=300 height=50>
        </applet>
</body>
</html>

And how I am doing the port 1935 blocking and openning ?

I have created firewall rule for both inbound and outbound for port 1935.
I check the port 1935 open/blocked scenario by disabling/enabling both rules.

This is my S.S.C.C.E. Now please help me 🙂

Share

Leave an answer

You must login to add an answer.

Need An Account,

1 Answer

  1. Editorial Team

    Gotcha !!! I have solved my problem with JSONP and jQuery AJAX call. I discovered the timeout attribute of jQuery AJAX and my code executed fluently when the port was blocked or opened. Here is the solution for future visitors. Thanks to all answerers for contribution.

    <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
    <head>
        <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
        <script type="text/javascript" src="jquery-1.7.2-min.js"></script>
    </head>
    <body>
        <script type"text/javascript">
            var isAccessible = null;
            function checkConnection() {
                var url = "http://101.212.33.60:1935/test/hello.html" ;
                $.ajax({
                    url: url,
                    type: "get",
                    cache: false,
                    dataType: 'jsonp', // it is for supporting crossdomain
                    crossDomain : true,
                    asynchronous : false,
                    jsonpCallback: 'deadCode',
                    timeout : 1500, // set a timeout in milliseconds
                    complete : function(xhr, responseText, thrownError) {
                        if(xhr.status == "200") {
                           isAccessible = true;
                           success(); // yes response came, esecute success()
                        }
                        else {
                           isAccessible = false;
                           failure(); // this will be executed after the request gets timed out due to blockage of ports/connections/IPs
                        }
                    }
               });
            }
            $(document).ready( function() {
                checkConnection(); // here I invoke the checking function
            });
        </script>
    </body>
</html>
    • 0