command.java

使用Java语言编写模拟路由器程序

/* File: Command.java
 *
 * Author: Venkata Sastry Malladi
 *
 * This file contains the code for the class Command
 * that represents the Command program. It sends the commands in the
 * Event File to the active routers in the network and logs their responses
 *
 * Preferred Editor: emacs
 */
import java.util.*;
import java.io.*;
import java.net.*;

public class Command {

	// a list of commands
	LinkedList commands;

	// the list of routers
	RouterLocation rl;

	// currently active routers
	HashSet activeRouters;

	// the log file
	String logfile;

	/*
	 * Constructor
	 * 
	 * @eventfile: The file containing the events/commands @locationfile: The
	 * Router Location File @logfile: The log file @topologyfile: The Topology
	 * Configuration file
	 * 
	 * Use: To read the set of events and router locations
	 */
	public Command(String eventfile, String locationfile, String logfile,
			String topologyfile) {
		// create a new list of commands
		commands = new LinkedList();

		// read the Router Location File
		rl = new RouterLocation(locationfile);

		// get the list of initially active routers
		Topology t = new Topology(topologyfile);
		activeRouters = t.getRouterIds();

		this.logfile = logfile;

		BufferedReader in = null;

		try {
			// open the Event File
			in = new BufferedReader(new FileReader(eventfile));
		} catch (IOException e) {
			System.out.println("Unable to open file: " + eventfile);
			System.out.println("Quitting.");
			System.exit(1);
		}

		try {
			String line;
			int linenumber = 1;

			// read a command
			line = in.readLine();

			while (line != null) {
				if (line.equals("") != true) {
					// add it to the list of commands
					commands.add(line);
				}

				linenumber++;

				line = in.readLine();
			}

			in.close();
		} catch (IOException ioe) {
			System.out
					.println("I/O error occured while reading from the file: "
							+ eventfile);
			System.out.println("Quitting.");

			System.exit(1);
		}

		return;
	}

	/*
	 * Method Name: addRouter
	 * 
	 * @args: the arguments to the addRouter command
	 * 
	 * Use: to add a router to the list of active routers
	 */

	String addRouter(String args) {
		int routerId;
		Socket s;

		try {
			// get the id of the router to be added
			routerId = Integer.parseInt(args);

			if (rl.contains(routerId) == false) {
				return ("Router with ID " + args + " not found in the Router Location Table");
			}

			// open a connection to the router
			s = new Socket(rl.getIp(routerId), rl.getCommandPort(routerId));

			ObjectInputStream ois;
			ObjectOutputStream oos;

			// open the streams associated with the connection
			ois = new ObjectInputStream(s.getInputStream());
			oos = new ObjectOutputStream(s.getOutputStream());

			// probe whether the router is up
			oos.writeObject("addRouter");
			String result = (String) ois.readObject();
			ois.close();
			oos.close();
			s.close();

			// if it is up, add it to the list of currently active routers
			if (result.equals("true"))
				activeRouters.add(new Integer(routerId));
			return (result);
		} catch (NumberFormatException nfe) {
			return ("Invalid Router ID" + args);
		} catch (Exception ioe) {
			return ("An I/O error occured while communication with Router " + args);
		}
	}

	/*
	 * Method Name: getPackets
	 * 
	 * @args: the arguments to the packets command
	 * 
	 * Use: to get the number of distance vector packets received by a router
	 */
	String getPackets(String args) {
		int routerId;
		Socket s;

		try {
			// get the id of the router

			routerId = Integer.parseInt(args);

			if (rl.contains(routerId) == false) {
				return ("Router with ID " + args + " not found in the Router Location Table");
			}
			if (activeRouters.contains(new Integer(routerId)) == false) {
				return ("Router with ID " + routerId + " not in the list of currently active routers");
			}

			// open a connection to the router
			s = new Socket(rl.getIp(routerId), rl.getCommandPort(routerId));

			ObjectInputStream ois;
			ObjectOutputStream oos;

			ois = new ObjectInputStream(s.getInputStream());
			oos = new ObjectOutputStream(s.getOutputStream());

			// send the command
			oos.writeObject("packets");

			// receive the number of packets
			String result = (String) ois.readObject();
			ois.close();
			oos.close();
			s.close();
			return (result);
		} catch (NumberFormatException nfe) {
			return ("Invalid Router ID" + args);
		} catch (Exception ioe) {
			return ("An I/O error occured while communication with Router " + args);
		}
	}

	/*
	 * Method Name: displayRoutingTable
	 * 
	 * @args: the arguments to the display command
	 * 
	 * Use: to display the routing table
	 */
	String displayRoutingTable(String args) {
		int routerId;
		Socket s;

		try {
			// get the id of the router
			routerId = Integer.parseInt(args);

			if (rl.contains(routerId) == false) {
				return ("Router with ID " + args + " not found in the Router Location Table");
			}

			if (activeRouters.contains(new Integer(routerId)) == false) {
				return ("Router with ID " + routerId + " not in the list of currently active routers");
			}

			// open a connection to the router
			s = new Socket(rl.getIp(routerId), rl.getCommandPort(routerId));

			ObjectInputStream ois;
			ObjectOutputStream oos;

			ois = new ObjectInputStream(s.getInputStream());
			oos = new ObjectOutputStream(s.getOutputStream());

			// send the command
			oos.writeObject("display");

			// receive the routing table
			String result = (String) ois.readObject();
			ois.close();
			oos.close();
			s.close();
			return (result);
		} catch (NumberFormatException nfe) {
			return ("Invalid Router ID: " + args);
		} catch (Exception ioe) {
			return ("An I/O error occured while communication with Router " + args);
		}
	}

	/*
	 * Method Name: getRoute
	 * 
	 * @args: the arguments to the route command
	 * 
	 * Use: to get the route between two routers
	 */

	String getRoute(String args) {
		int router1;
		int router2;
		String[] fields;
		String result = new String("");
		Socket s;
		int ttl = 16;

		try {
			// get the source and destination router ids
			fields = args.split(",");

			if (fields.length != 2) {
				return ("Invalid arguments: " + args);
			}

			router1 = Integer.parseInt(fields[0]);
			router2 = Integer.parseInt(fields[1]);

			// until the destination is reached
			do {
				if ((rl.contains(router1) == false)
						|| (rl.contains(router2) == false)) {
					return ("One of the routers " + router1 + " or " + router2 + " not found in the Router Location Table");
				}

				if (activeRouters.contains(new Integer(router1)) == false) {
					return ("Router with ID " + router1 + " not in the list of currently active routers");
				}

				if (activeRouters.contains(new Integer(router2)) == false) {
					return ("Router with ID " + router2 + " not in the list of currently active routers");
				}

				// open a connection to the current source
				s = new Socket(rl.getIp(router1), rl.getCommandPort(router1));

				ObjectInputStream ois;
				ObjectOutputStream oos;

				ois = new ObjectInputStream(s.getInputStream());
				oos = new ObjectOutputStream(s.getOutputStream());

				// send the command
				oos.writeObject("route:" + router2);

				// receive the next hop
				String reply = (String) ois.readObject();

				if (reply.equals("error")) {
					ois.close();
					oos.close();
					s.close();

					return ("Router " + router2 + " not found in " + router1 + "'s Routing Table");
				}

				else if (reply.equals("inf")) {
					ois.close();
					oos.close();
					s.close();
					return ("Router " + router1
							+ " does not have a route to Router " + router2);
				}

				else {
					// current source = next hop
					result = result + router1 + "->";
					router1 = Integer.parseInt(reply);
				}

				--ttl;
				// continue till the destination is reached or a routing loop is
				// encountered
			} while ((router1 != router2) && (ttl != 0));

			if (ttl != 0) {
				result = result + router2;
			}

			else {
				result = result + "<ttl expired>";
			}

			return (result);
		} catch (NumberFormatException nfe) {
			return ("Invalid Router ID received in the process");
		} catch (Exception ioe) {
			return ("An I/O error occured while communication ");
		}
	}

	/*
	 * Method Name: step
	 * 
	 * @args: the arguments to the step command
	 * 
	 * Use: to trigger the distance vector exchange between the routers
	 */
	String step(String args) {
		int routerId = -1;
		String result = new String("");
		Socket s;

		try {
			// if the command is step:*, send the command to all the active
			// routers
			if (args.equals("*")) {
				Iterator i = activeRouters.iterator();

				// for each active router
				while (i.hasNext()) {
					routerId = ((Integer) i.next()).intValue();

					if (rl.contains(routerId) == false) {
						result = result
								+ ("router with ID " + routerId + " (currently in the list of active routers) not found in the Router Location Table\n");
					}

					// open a connection
					s = new Socket(rl.getIp(routerId), rl
							.getCommandPort(routerId));

					ObjectInputStream ois;
					ObjectOutputStream oos;

					ois = new ObjectInputStream(s.getInputStream());
					oos = new ObjectOutputStream(s.getOutputStream());

					// send the command
					oos.writeObject("step");

					// read the response
					result = result + routerId + ": "
							+ (String) ois.readObject() + "\n";

					ois.close();
					oos.close();
					s.close();
				}
			}

			// if the command is step:x, send step to router x
			else {
				// get router id
				routerId = Integer.parseInt(args);

				if (rl.contains(routerId) == false) {
					return ("Router with ID " + routerId + " not found in the Router Location Table");
				}

				// open a connection
				s = new Socket(rl.getIp(routerId), rl.getCommandPort(routerId));