/*
 * Copyright (c) 2000 David Flanagan.  All rights reserved.
 * This code is from the book Java Examples in a Nutshell, 2nd Edition.
 * It is provided AS-IS, WITHOUT ANY WARRANTY either expressed or implied.
 * You may study, use, and modify it for any non-commercial purpose.
 * You may distribute it non-commercially as long as you retain this notice.
 * For a commercial use license, or to purchase the book (recommended),
 * visit http://www.davidflanagan.com/javaexamples2.
 */
package com.davidflanagan.examples.net;
import java.io.*;
import java.net.*;

/**
 * This class uses the Server class to provide a multi-threaded server 
 * framework for a relatively simple proxy service.  The main() method
 * starts up the server.  The nested Proxy class implements the 
 * Server.Service interface and provides the proxy service.
 **/
public class ProxyServer {
    /** 
     * Create a Server object, and add Proxy service objects to it to provide
     * proxy service as specified by the command-line arguments.
     **/
    public static void main(String[] args) {
        try {
            // Check number of args.  Must be a multiple of 3 and > 0.
            if ((args.length == 0) || (args.length % 3 != 0))
                throw new IllegalArgumentException("Wrong number of args");
	    
            // Create the Server object
            Server s = new Server(null, 12); // log stream, max connections
	    
            // Loop through the arguments parsing (host, remoteport, localport)
            // tuples.  For each, create a Proxy, and add it to the server.
            int i = 0;
            while(i < args.length) {
                String host = args[i++];
                int remoteport = Integer.parseInt(args[i++]);
                int localport = Integer.parseInt(args[i++]);
                s.addService(new Proxy(host, remoteport), localport);
            }
        }
        catch (Exception e) {  // Print an error message if anything goes wrong
            System.err.println(e);
            System.err.println("Usage: java ProxyServer " +
			       "<host> <remoteport> <localport> ...");
            System.exit(1);
        }
    }
    
    /**
     * This is the class that implements the proxy service.  The serve() method
     * will be called when the client has connected.  At that point, it must
     * establish a connection to the server, and then transfer bytes back and
     * forth between client and server.  For symmetry, this class implements
     * two very similar threads as anonymous classes.  One thread copies bytes
     * from client to server, and the other copies them from server to client.
     * The thread that invoke the serve() method creates and starts these 
     * threads, then just sits and waits for them to exit.
     **/
    public static class Proxy implements Server.Service {
        String host;
        int port;
	
        /** Remember the host and port we are a proxy for */
        public Proxy(String host, int port) {
            this.host = host;
            this.port = port;
        }
	
        /** The server invokes this method when a client connects. */
        public void serve(InputStream in, OutputStream out) {
            // These are some sockets we'll use.  They are final so they can
            // be used by the anonymous classes defined below.
            final InputStream from_client = in;
            final OutputStream to_client = out;
            final InputStream from_server;
            final OutputStream to_server;

            // Try to establish a connection to the specified server and port
            // and get sockets to talk to it.  Tell our client if we fail.
            final Socket server;
            try { 
                server = new Socket(host, port); 
                from_server = server.getInputStream();
                to_server = server.getOutputStream();
            }
            catch (Exception e) {
                PrintWriter pw = new PrintWriter(new OutputStreamWriter(out));
                pw.print("Proxy server could not connect to " + host +
			 ":" + port + "\n");
                pw.flush();
                pw.close();
                try { in.close(); } catch (IOException ex) {}
                return;
            }
	    
            // Create an array to hold two Threads.  It is declared final so
            // that it can be used by the anonymous classes below.  We use an
            // array instead of two variables because given the structure of
            // this program two variables would not work if declared final.
            final Thread[] threads = new Thread[2];
	    
            // Define and create a thread to copy bytes from client to server
            Thread c2s = new Thread() {
		    public void run() {
			// Copy bytes 'till EOF from client
			byte[] buffer = new byte[2048];
			int bytes_read;
			try {
			    while((bytes_read=from_client.read(buffer))!=-1) {
				to_server.write(buffer, 0, bytes_read);
				to_server.flush();
			    }
			}
			catch (IOException e) {}
			finally {
			    // When the thread is done
			    try {
				server.close();     // close the server socket
				to_client.close();  // and the client streams
				from_client.close();
			    }
			    catch (IOException e) {}
			}
		    }
		};

            // Define and create a thread to copy bytes from server to client.
	    // This thread works just like the one above.
            Thread s2c = new Thread() {
		    public void run() {
			byte[] buffer = new byte[2048];
			int bytes_read;
			try {
			    while((bytes_read=from_server.read(buffer))!=-1) {
				to_client.write(buffer, 0, bytes_read);
				to_client.flush();
			    }
			}
			catch (IOException e) {}
			finally {
			    try {
				server.close(); // close down 
				to_client.close();
				from_client.close();
			    } catch (IOException e) {}
			}
		    }
		};
	    
            // Store the threads into the final threads[] array, so that the 
            // anonymous classes can refer to each other.
            threads[0] = c2s; threads[1] = s2c;
	    
            // start the threads
            c2s.start(); s2c.start();
	    
            // Wait for them to exit
            try { c2s.join(); s2c.join(); } catch (InterruptedException e) {}
        }
    }
}