Using a Java HTTP proxy with Firefox

Question

I am writing an HTTP proxy in Java which takes malformed HTTP request, corrects them, forwards them to a server, and then forwards the server's response back to the client. However, I'm having a lot of trouble testing it.

I am running the proxy on a virtual machine (of which I have root privilages) on a Red Hat server that I am sshing into and listening at port 12345. Then on my machine, in Firefox I am going to Options>Connection Settings>Manual Proxy Configuration and entering the IP address for the virtual machine and port 12345.

However, when I run the proxy on my virtual machine and try to go to a site in Firefox nothing happens. Here is my code:

package proxy;

import java.io.BufferedReader;
import java.io.DataOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.InetAddress;
import java.net.ServerSocket;
import java.net.Socket;
import java.net.UnknownHostException;

 public class WebProxy {

    public void run() {

            try {

                    toFromClient();
            }
            catch (IOException e) {
                    e.printStackTrace();
            }
    }

    public String requestNormalizer(String badRequest) {

            return badRequest.replace(badRequest.substring(0, badRequest.indexOf(" ")), badRequest.substring(0, badRequest.indexOf(" ")).toUpperCase());

    }

    public void toFromClient() throws IOException {

            ServerSocket welcome;
            Socket client;
            String request;
            String response;
            DataOutputStream outputToClient;
            BufferedReader inputFromClient;
            boolean listening = true;

            welcome = new ServerSocket(12345);

            while (listening) {

                    client = welcome.accept();


                    inputFromClient = new BufferedReader(new InputStreamReader(client.getInputStream()));

                    request = inputFromClient.readLine();

            //      request = requestNormalizer(request);
                    response = toFromServer(request);

                    outputToClient = new DataOutputStream(client.getOutputStream());

                    outputToClient.writeBytes(response);
            }
    }

    public String toFromServer(String request) throws UnknownHostException, IOException {

            Socket server;
            String response;
            DataOutputStream outputToServer;
            BufferedReader inputFromServer;

            if (!dnsQuery(request)[1].equals(""))
                    server = new Socket((InetAddress) dnsQuery(request)[0], (int) dnsQuery(request)[1]);
            else
                    server = new Socket((InetAddress) dnsQuery(request)[0], 80);  

            outputToServer = new DataOutputStream(server.getOutputStream());

            inputFromServer = new BufferedReader(new InputStreamReader(server.getInputStream()));

            outputToServer.writeBytes(request);

            response = inputFromServer.readLine();

            server.close();

            return response;
    }

    public Object[] dnsQuery(String request) throws UnknownHostException {

            Object[] addressPort = new Object[2];
            String hostname = request.substring(request.indexOf("host") + 6);
            hostname = hostname.substring(0, hostname.indexOf("\r"));

            if (hostname.contains(":")) {

                    hostname = hostname.substring(0, hostname.indexOf(":"));
                    addressPort[1] = hostname.substring(hostname.indexOf(":"));
            }
            else
                    addressPort[1] = "";

            addressPort[0] = InetAddress.getByName(hostname);

            return addressPort;
    }

    public static void main(String[] args) {

            WebProxy wp = new WebProxy();
            wp.run();
    }
}

I'm not worrying about fixing the HTTP request right now, so I have the call to requestNormalizer() in toFromClient() commented out.

I've determined (through print statments) that my code never gets past "client = welcome.accept();" in the toFromClient() method and idles until I stop it, so I'm guessing that my program is never receiving any connection when I try to connect to a webpage in Firefox. I've tried ports different than port 12345, and I've also been able to successfully set up a connection to port 12345 on my VM by listening on that port using Netcat, and then connecting to that port in a different console window, also using Netcat. Also I am unable to telnet to the VM from my own machine (the one I am using Firefox on, not the VM).

Does anyone have any idea what the issue could be? Is it the code, or is it some other issue like a firewall, etc.? Please let me know I have have failed to sufficiently clarify something or if anyone needs any additional information.

Thanks in advance!

Answer 1

Have you tried to connect to this proxy using links installed on the same machine? It could help you to figure out whenever there is something, which blocks communication between your vm and firefox.

You can install links(or elinks) by doing yum install links (sorry I do not have Red Hat near me right now).

In case if you are able to connect via links have a look at http://www.techotopia.com/index.php/Basic_RHEL_6_Firewall_Configuration