// Copyright MageLang Institute; Version $Id: //depot/main/src/edu/modules/RMI2/magercises/BootstrapHTTPServer/working/ClassServer.java#2 $

/*
 * Copyright (c) 1996, 1996, 1997 Sun Microsystems, Inc. All Rights Reserved.
 *
 * SUN MAKES NO REPRESENTATIONS OR WARRANTIES ABOUT THE SUITABILITY OF THE
 * SOFTWARE, EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
 * PURPOSE, OR NON-INFRINGEMENT. SUN SHALL NOT BE LIABLE FOR ANY DAMAGES
 * SUFFERED BY LICENSEE AS A RESULT OF USING, MODIFYING OR DISTRIBUTING
 * THIS SOFTWARE OR ITS DERIVATIVES.
 *
 * CopyrightVersion 1.1_beta
 */

//package examples.classServer;

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

/**
 * ClassServer is an abstract class that provides the
 * basic functionality of a mini-webserver, specialized
 * to load class files only. A ClassServer must be extended
 * and the concrete subclass should define the <b>getBytes</b>
 * method which is responsible for retrieving the bytecodes
 * for a class.<p>
 *
 * The ClassServer creates a thread that listens on a socket
 * and accepts  HTTP GET requests. The HTTP response contains the
 * bytecodes for the class that requested in the GET header. <p>
 *
 * For loading remote classes, an RMI application can use a concrete
 * subclass of this server in place of an HTTP server. <p>
 *
 * @see ClassFileServer
 */
public abstract class ClassServer

implements Runnable
{

    private ServerSocket server = null;
    private int port;

    /**
     * Constructs a ClassServer that listens on <b>port</b> and
     * obtains a class's bytecodes using the method <b>getBytes</b>.
     *
     * @param port the port number
     * @exception IOException if the ClassServer could not listen
     *            on <b>port</b>.
     */
    protected ClassServer(int port) throws IOException
    {
        this.port = port;
        server = new ServerSocket(port);
        newListener();
    }

    /**
     * Returns an array of bytes containing the bytecodes for
     * the class represented by the argument <b>path</b>.
     * The <b>path</b> is a dot separated class name with
     * the ".class" extension removed.
     *
     * @return the bytecodes for the class
     * @exception ClassNotFoundException if the class corresponding
     * to <b>path</b> could not be loaded.
     * @exception IOException if error occurs reading the class
     */
    public abstract byte[] getBytes(String path) throws IOException, ClassNotFoundException;

    /**
     * The "listen" thread that accepts a connection to the
     * server, parses the header to obtain the class file name
     * and sends back the bytecodes for the class (or error
     * if the class is not found or the response was malformed).
     */
    public void run()
    {
        Socket socket;

        // accept a connection
        try
        {
            socket = server.accept();
        }
        catch (IOException e)
        {
            System.out.println("Class Server died: " + e.getMessage());
            e.printStackTrace();
            return;
        }

        // create a new thread to accept the next connection
        newListener();

        try
        {
            DataOutputStream out =
                new DataOutputStream(socket.getOutputStream());
            try
            {
                // get path to class file from header
                BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
                String path = getPath(in);
                // retrieve bytecodes
                byte[] bytecodes = getBytes(path);
                // send bytecodes in response (assumes HTTP/1.0 or later)
                try
                {
                    out.writeBytes("HTTP/1.0 200 OK\r\n");
                    out.writeBytes("Content-Length: " + bytecodes.length + "\r\n");
                    out.writeBytes("Content-Type: application/java\r\n\r\n");
                    out.write(bytecodes);
                    out.flush();
                }
                catch (IOException ie)
                {
                    return;
                }

            }
            catch (Exception e)
            {
                // write out error response
                out.writeBytes("HTTP/1.0 400 " + e.getMessage() + "\r\n");
                out.writeBytes("Content-Type: text/html\r\n\r\n");
                out.flush();
            }

        }
        catch (IOException ex)
        {
            // eat exception (could log error to log file, but
            // write out to stdout for now).
            System.out.println("error writing response: " + ex.getMessage());
            ex.printStackTrace();

        }
        finally
        {
            try
            {
                socket.close();
            }
            catch (IOException e)
            {
            }
        }
    }

    /**
     * Create a new thread to listen.
     */
    private void newListener()
    {
        (new Thread(this)).start();
    }

    /**
     * Returns the path to the class file obtained from
     * parsing the HTML header.
     */
    private static String getPath(BufferedReader in)     throws IOException
    {
        String line = in.readLine();
        String path = "";

        // extract class from GET line
        if (line.startsWith("GET /"))
        {
            line = line.substring(5, line.length()-1).trim();

            int index = line.indexOf(".class ");
            if (index != -1)
            {
                path = line.substring(0, index).replace('/', '.');
            }
        }

        // eat the rest of header
        do
        {
            line = in.readLine();

        } while ((line.length() != 0) && (line.charAt(0) != '\r') && (line.charAt(0) != '\n'));

        if (path.length() != 0)
        {
            return path;
        }
        else
        {
            throw new IOException("Malformed Header");
        }
    }
}