/*

 * 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.

 */



import java.io.*;

import java.net.*;

import java.util.*;



/**

 * This class is a generic Framework for a flexible, multi-threaded server.

 * It listens on any number of specified ports, and, when it receives a 

 * connection on a port, passes input and output streams to a specified Service

 * object which provides the actual service.  It can limit the number of

 * concurrent connections, and logs activity to a specified stream.

 **/

public class Server {

    /**

     * A main() method for running the server as a standalone program.  The

     * command-line arguments to the program should be pairs of servicenames

     * and port numbers.  For each pair, the program will dynamically load the

     * named Service class, instantiate it, and tell the server to provide

     * that Service on the specified port.  The special -control argument

     * should be followed by a password and port, and will start special

     * server control service running on the specified port, protected by the

     * specified password.

     **/

    public static void main(String[] args) {

        try {

            if (args.length < 2)  // Check number of arguments

                throw new IllegalArgumentException("Must specify a service");

            

            // Create a Server object that uses standard out as its log and

            // has a limit of ten concurrent connections at once.

            Server s = new Server(System.out, 10);



            // Parse the argument list

            int i = 0;

            while(i < args.length) {

                if (args[i].equals("-control")) {  // Handle the -control arg

                    i++;

                    String password = args[i++];

                    int port = Integer.parseInt(args[i++]);

      // add control service

                    s.addService(new Control(s, password), port);

                } 

                else {

                    // Otherwise start a named service on the specified port.

                    // Dynamically load and instantiate a Service class

                    String serviceName = args[i++];

                    Class serviceClass = Class.forName(serviceName); 

                    Service service = (Service)serviceClass.newInstance();

                    int port = Integer.parseInt(args[i++]);

                    s.addService(service, port);

                }

            }

        }

        catch (Exception e) { // Display a message if anything goes wrong

            System.err.println("Server: " + e);

            System.err.println("Usage: java Server " +

          "[-control  ] " +

          "[  ... ]");

            System.exit(1);

        }

    }



    // This is the state for the server

    Map services;                   // Hashtable mapping ports to Listeners

    Set connections;                // The set of current connections

    int maxConnections;             // The concurrent connection limit

    ThreadGroup threadGroup;        // The threadgroup for all our threads

    PrintWriter logStream;          // Where we send our logging output to



    /**

     * This is the Server() constructor.  It must be passed a stream 

     * to send log output to (may be null), and the limit on the number of

     * concurrent connections.  

     **/

    public Server(OutputStream logStream, int maxConnections) { 

        setLogStream(logStream);

        log("Starting server");

        threadGroup = new ThreadGroup(Server.class.getName());

 this.maxConnections = maxConnections;

        services = new HashMap();

 connections = new HashSet(maxConnections);

    }

    

    /** 

     * A public method to set the current logging stream.  Pass null

     * to turn logging off

     **/

    public synchronized void setLogStream(OutputStream out) {

        if (out != null) logStream = new PrintWriter(out);

        else logStream = null;

    }



    /** Write the specified string to the log */

    protected synchronized void log(String s) { 

        if (logStream != null) {

            logStream.println("[" + new Date() + "] " + s);

            logStream.flush();

        }

    }

    /** Write the specified object to the log */

    protected void log(Object o) { log(o.toString()); }

    

    /**

     * This method makes the server start providing a new service.

     * It runs the specified Service object on the specified port.

     **/

    public synchronized void addService(Service service, int port)

 throws IOException

    {

        Integer key = new Integer(port);  // the hashtable key

        // Check whether a service is already on that port

        if (services.get(key) != null) 

            throw new IllegalArgumentException("Port " + port +

            " already in use.");

        // Create a Listener object to listen for connections on the port

        Listener listener = new Listener(threadGroup, port, service);

        // Store it in the hashtable

        services.put(key, listener);

        // Log it

        log("Starting service " + service.getClass().getName() + 

     " on port " + port);

        // Start the listener running.

        listener.start();

    }

    

    /**

     * This method makes the server stop providing a service on a port.

     * It does not terminate any pending connections to that service, merely

     * causes the server to stop accepting new connections

     **/

    public synchronized void removeService(int port) {

        Integer key = new Integer(port);  // hashtable key

        // Look up the Listener object for the port in the hashtable

        final Listener listener = (Listener) services.get(key);

        if (listener == null) return;

        // Ask the listener to stop

        listener.pleaseStop();

        // Remove it from the hashtable

        services.remove(key);

        // And log it.

        log("Stopping service " + listener.service.getClass().getName() + 

     " on port " + port);

    }

    

    /** 

     * This nested Thread subclass is a "listener".  It listens for

     * connections on a specified port (using a ServerSocket) and when it gets

     * a connection request, it calls the servers addConnection() method to

     * accept (or reject) the connection.  There is one Listener for each

     * Service being provided by the Server.

     **/

    public class Listener extends Thread {

        ServerSocket listen_socket;    // The socket to listen for connections

        int port;                      // The port we're listening on

        Service service;               // The service to provide on that port

        volatile boolean stop = false; // Whether we've been asked to stop



        /**

  * The Listener constructor creates a thread for itself in the

  * threadgroup.  It creates a ServerSocket to listen for connections

  * on the specified port.  It arranges for the ServerSocket to be

  * interruptible, so that services can be removed from the server.

  **/

        public Listener(ThreadGroup group, int port, Service service) 

     throws IOException

 {

            super(group, "Listener:" + port);      

            listen_socket = new ServerSocket(port);

            // give it a non-zero timeout so accept() can be interrupted

            listen_socket.setSoTimeout(600000);

            this.port = port;

            this.service = service;

        }



        /** 

  * This is the polite way to get a Listener to stop accepting

  * connections

  ***/

        public void pleaseStop() {

            this.stop = true;              // Set the stop flag

            this.interrupt();              // Stop blocking in accept()

     try { listen_socket.close(); } // Stop listening.

     catch(IOException e) {}

        }

        

        /**

  * A Listener is a Thread, and this is its body.

  * Wait for connection requests, accept them, and pass the socket on

  * to the addConnection method of the server.

  **/

        public void run() {

            while(!stop) {      // loop until we're asked to stop.

                try {

                    Socket client = listen_socket.accept();

                    addConnection(client, service);

                } 

                catch (InterruptedIOException e) {} 

                catch (IOException e) {log(e);}

            }

        }

    }

 

    /**

     * This is the method that Listener objects call when they accept a

     * connection from a client.  It either creates a Connection object 

     * for the connection and adds it to the list of current connections,

     * or, if the limit on connections has been reached, it closes the 

     * connection. 

     **/

    protected synchronized void addConnection(Socket s, Service service) {

 // If the connection limit has been reached

 if (connections.size() >= maxConnections) {

     try {

  // Then tell the client it is being rejected.

  PrintWriter out = new PrintWriter(s.getOutputStream());

  out.print("Connection refused; " +

     "the server is busy; please try again later.\n");

  out.flush();

  // And close the connection to the rejected client.

  s.close();

  // And log it, of course

  log("Connection refused to " +

      s.getInetAddress().getHostAddress() +

      ":" + s.getPort() + ": max connections reached.");

     } catch (IOException e) {log(e);}

 }

 else {  // Otherwise, if the limit has not been reached

     // Create a Connection thread to handle this connection

     Connection c = new Connection(s, service);

     // Add it to the list of current connections

     connections.add(c);

     // Log this new connection

     log("Connected to " + s.getInetAddress().getHostAddress() +

  ":" + s.getPort() + " on port " + s.getLocalPort() +

  " for service " + service.getClass().getName());

     // And start the Connection thread to provide the service

     c.start();

 }

    }



    /**

     * A Connection thread calls this method just before it exits.  It removes

     * the specified Connection from the set of connections.

     **/

    protected synchronized void endConnection(Connection c) {

 connections.remove(c);

 log("Connection to " + c.client.getInetAddress().getHostAddress() +

     ":" + c.client.getPort() + " closed.");

    }



    /** Change the current connection limit */

    public synchronized void setMaxConnections(int max) {

 maxConnections = max;

    }



    /**

     * This method displays status information about the server on the

     * specified stream.  It can be used for debugging, and is used by the

     * Control service later in this example.

     **/

    public synchronized void displayStatus(PrintWriter out) {

 // Display a list of all Services that are being provided

 Iterator keys = services.keySet().iterator();

 while(keys.hasNext()) {

     Integer port = (Integer) keys.next();

     Listener listener = (Listener) services.get(port);

     out.print("SERVICE " + listener.service.getClass().getName()

        + " ON PORT " + port + "\n");

 }

 

 // Display the current connection limit

 out.print("MAX CONNECTIONS: " + maxConnections + "\n");



 // Display a list of all current connections

 Iterator conns = connections.iterator();

 while(conns.hasNext()) {

     Connection c = (Connection)conns.next();

     out.print("CONNECTED TO " +

        c.client.getInetAddress().getHostAddress() +

        ":" + c.client.getPort() + " ON PORT " +

        c.client.getLocalPort() + " FOR SERVICE " +

        c.service.getClass().getName() + "\n");

 }

    }



    /**

     * This class is a subclass of Thread that handles an individual

     * connection between a client and a Service provided by this server.

     * Because each such connection has a thread of its own, each Service can

     * have multiple connections pending at once.  Despite all the other

     * threads in use, this is the key feature that makes this a

     * multi-threaded server implementation.

     **/

    public class Connection extends Thread {

        Socket client;     // The socket to talk to the client through

        Service service;   // The service being provided to that client

 

        /**

  * This constructor just saves some state and calls the superclass

  * constructor to create a thread to handle the connection.  Connection

  * objects are created by Listener threads.  These threads are part of

  * the server's ThreadGroup, so all Connection threads are part of that

  * group, too.

  **/

        public Connection(Socket client, Service service) {

            super("Server.Connection:" +

    client.getInetAddress().getHostAddress() +

    ":" + client.getPort());

            this.client = client;

            this.service = service;

        }

 

        /**

  * This is the body of each and every Connection thread.

  * All it does is pass the client input and output streams to the

  * serve() method of the specified Service object.  That method is

  * responsible for reading from and writing to those streams to

  * provide the actual service.  Recall that the Service object has

  * been passed from the Server.addService() method to a Listener

  * object to the addConnection() method to this Connection object, and

  * is now finally being used to provide the service.  Note that just

  * before this thread exits it always calls the endConnection() method

  * to remove itself from the set of connections

  **/

        public void run() {

            try { 

                InputStream in = client.getInputStream();

                OutputStream out = client.getOutputStream();

                service.serve(in, out);

            } 

            catch (IOException e) {log(e);}

            finally { endConnection(this); }

        }

    }

    

    /**

     * Here is the Service interface that we have seen so much of.  It defines

     * only a single method which is invoked to provide the service.  serve()

     * will be passed an input stream and an output stream to the client.  It

     * should do whatever it wants with them, and should close them before

     * returning.

     *

     * All connections through the same port to this service share a single

     * Service object.  Thus, any state local to an individual connection must

     * be stored in local variables within the serve() method.  State that

     * should be global to all connections on the same port should be stored

     * in instance variables of the Service class.  If the same Service is

     * running on more than one port, there will typically be different

     * Service instances for each port.  Data that should be global to all

     * connections on any port should be stored in static variables.

     *

     * Note that implementations of this interface must have a no-argument 

     * constructor if they are to be dynamically instantiated by the main()

     * method of the Server class.

     **/

    public interface Service {

        public void serve(InputStream in, OutputStream out) throws IOException;

    }



    /**

     * A very simple service.  It displays the current time on the server

     * to the client, and closes the connection.

     **/

    public static class Time implements Service {

        public void serve(InputStream i, OutputStream o) throws IOException {

            PrintWriter out = new PrintWriter(o);

            out.print(new Date() + "\n");

            out.close();

            i.close();

        }

    }

    

    /**

     * This is another example service.  It reads lines of input from the

     * client, and sends them back, reversed.  It also displays a welcome

     * message and instructions, and closes the connection when the user 

     * enters a '.' on a line by itself.

     **/

    public static class Reverse implements Service {

        public void serve(InputStream i, OutputStream o) throws IOException {

            BufferedReader in = new BufferedReader(new InputStreamReader(i));

            PrintWriter out = 

                new PrintWriter(new BufferedWriter(new OutputStreamWriter(o)));

            out.print("Welcome to the line reversal server.\n");

            out.print("Enter lines.  End with a '.' on a line by itself.\n");

            for(;;) {

                out.print("> ");

                out.flush();

                String line = in.readLine();

                if ((line == null) || line.equals(".")) break;

                for(int j = line.length()-1; j >= 0; j--)

                    out.print(line.charAt(j));

                out.print("\n");

            }

            out.close();

            in.close();

        }

    }

    

    /**

     * This service is an HTTP mirror, just like the HttpMirror class

     * implemented earlier in this chapter.  It echos back the client's

     * HTTP request

     **/

    public static class HTTPMirror implements Service {

        public void serve(InputStream i, OutputStream o) throws IOException {

            BufferedReader in = new BufferedReader(new InputStreamReader(i));

            PrintWriter out = new PrintWriter(o);

            out.print("HTTP/1.0 200 \n");

            out.print("Content-Type: text/plain\n\n");

            String line;

            while((line = in.readLine()) != null) {

                if (line.length() == 0) break;

                out.print(line + "\n");

            }

            out.close();

            in.close();

        }

    }

    

    /**

     * This service demonstrates how to maintain state across connections by

     * saving it in instance variables and using synchronized Access to those

     * variables.  It maintains a count of how many clients have connected and

     * tells each client what number it is

     **/

    public static class UniqueID implements Service {

        public int id=0;

        public synchronized int nextId() { return id++; }

        public void serve(InputStream i, OutputStream o) throws IOException {

            PrintWriter out = new PrintWriter(o);

            out.print("You are client #: " + nextId() + "\n");

            out.close();

            i.close();

        }

    }

    

    /**

     * This is a non-trivial service.  It implements a command-based protocol

     * that gives password-protected runtime control over the operation of the 

     * server.  See the main() method of the Server class to see how this

     * service is started.  

     *

     * The recognized commands are:

     *   password: give password; authorization is required for most commands

     *   add:      dynamically add a named service on a specified port

     *   remove:   dynamically remove the service running on a specified port

     *   max:      change the current maximum connection limit.

     *   status:   display current services, connections, and connection limit

     *   help:     display a help message

     *   quit:     disconnect

     *

     * This service displays a prompt, and sends all of its output to the user

     * in capital letters.  Only one client is allowed to connect to this 

     * service at a time.

     **/

    public static class Control implements Service {

        Server server;             // The server we control

        String password;           // The password we require

        boolean connected = false; // Whether a client is already connected

 

        /**

  * Create a new Control service.  It will control the specified Server

  * object, and will require the specified password for authorization

  * Note that this Service does not have a no argument constructor,

  * which means that it cannot be dynamically instantiated and added as

  * the other, generic services above can be.

  **/

        public Control(Server server, String password) {

            this.server = server;

            this.password = password;

        }



        /**

  * This is the serve method that provides the service.  It reads a

  * line the client, and uses java.util.StringTokenizer to parse it

  * into commands and arguments.  It does various things depending on

  * the command.

  **/

        public void serve(InputStream i, OutputStream o) throws IOException {

            // Setup the streams

            BufferedReader in = new BufferedReader(new InputStreamReader(i));

            PrintWriter out = new PrintWriter(o);

            String line;  // For reading client input lines

     // Has the user has given the password yet?

            boolean authorized = false; 



            // If there is already a client connected to this service, display

            // a message to this client and close the connection.  We use a

            // synchronized block to prevent a race condition.

            synchronized(this) { 

                if (connected) { 

                    out.print("ONLY ONE CONTROL CONNECTION ALLOWED.\n");

                    out.close();

                    return;

                }

                else connected = true;

            }



     // This is the main loop: read a command, parse it, and handle it

            for(;;) {  // infinite loop

                out.print("> ");           // Display a prompt

                out.flush();               // Make it appear right away

                line = in.readLine();      // Get the user's input

                if (line == null) break;   // Quit if we get EOF.

                try {

                    // Use a StringTokenizer to parse the user's command

                    StringTokenizer t = new StringTokenizer(line);

                    if (!t.hasMoreTokens()) continue;  // if input was empty

                    // Get first word of the input and convert to lower case

                    String command = t.nextToken().toLowerCase(); 

                    // Now compare to each of the possible commands, doing the

                    // appropriate thing for each command

                    if (command.equals("password")) {  // Password command

                        String p = t.nextToken();      // Get the next word

                        if (p.equals(this.password)) { // Is it the password?

                            out.print("OK\n");         // Say so

                            authorized = true;         // Grant authorization

                        }

                        else out.print("INVALID PASSWORD\n"); // Otherwise fail

                    }

                    else if (command.equals("add")) {  // Add Service command

                        // Check whether password has been given

                        if (!authorized) out.print("PASSWORD REQUIRED\n"); 

                        else {

                            // Get the name of the service and try to

                            // dynamically load and instantiate it.

                            // Exceptions will be handled below

                            String serviceName = t.nextToken();

                            Class serviceClass = Class.forName(serviceName);

                            Service service;

                            try {

    service = (Service)serviceClass.newInstance();

       }

                            catch (NoSuchMethodError e) {

                                throw new IllegalArgumentException(

             "Service must have a " +

      "no-argument constructor");

                            }

                            int port = Integer.parseInt(t.nextToken());

                            // If no exceptions occurred, add the service

                            server.addService(service, port);

                            out.print("SERVICE ADDED\n");    // acknowledge

                        }

                    }

                    else if (command.equals("remove")) { // Remove service

                        if (!authorized) out.print("PASSWORD REQUIRED\n");

                        else {

                            int port = Integer.parseInt(t.nextToken()); 

                            server.removeService(port); // remove the service

                            out.print("SERVICE REMOVED\n"); // acknowledge

                        }

                    }

                    else if (command.equals("max")) { // Set connection limit

                        if (!authorized) out.print("PASSWORD REQUIRED\n");

                        else {

                            int max = Integer.parseInt(t.nextToken()); 

                            server.setMaxConnections(max); 

                            out.print("MAX CONNECTIONS CHANGED\n");

                        }

                    }

                    else if (command.equals("status")) { // Status Display

                        if (!authorized) out.print("PASSWORD REQUIRED\n");

   else server.displayStatus(out);

                    }

                    else if (command.equals("help")) {  // Help command

                        // Display command syntax.  Password not required

                        out.print("COMMANDS:\n" + 

      "\tpassword \n" +

      "\tadd  \n" +

      "\tremove \n" +

      "\tmax \n" +

      "\tstatus\n" +

      "\thelp\n" + 

      "\tquit\n");

                    }

                    else if (command.equals("quit")) break; // Quit command.

                    else out.print("UNRECOGNIZED COMMAND\n"); // Error

  }

                catch (Exception e) {

                    // If an exception occurred during the command, print an

                    // error message, then output details of the exception.

                    out.print("ERROR WHILE PARSING OR EXECUTING COMMAND:\n" +

         e + "\n");

                }

            }

            // Finally, when the loop command loop ends, close the streams

            // and set our connected flag to false so that other clients can

            // now connect.

            connected = false;

            out.close();

            in.close();

        }    

    }

}