PeerNAPSTER.java

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

public class PeerNAPSTER
    {
    public static void main(String[] args) throws Exception
        {
        switch(args[0])
            {
            case "client": search(); break;
            case "server": download(); break;
            default: break;
            }
        }

    /* client mode: searches for a file */
    static void search()
        {
        /* connection to server */
        Socket clientSocket = new Socket("serverID", 4445);

        /* opening buffers */
        BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
        BufferedReader inputStream = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
        DataOutputStream outputStream = new DataOutputStream(clientSocket.getOutputStream());

        /* search */
        in.readLine(); // the first line is the mode: "client" or "server", and should be skipped
        String user = in.readLine();
        String pwd = in.readLine();
        String searchID = in.readLine();
        byte[] data;
        /* converts user, pwd, and searchID into a packet to be sent to the server */
        outputStream.writeBytes(data);

        /* reads result from server */
        String result = inputStream.readLine();
        /* processes result; it contains the IP of the peer that has the file which we call "String IP" */
        /* connects to peer */
        InetAddress IPAddress = InetAddress.getByName(IP);
        Socket peerSocket = new Socket(IPAddress, 4446);
        /* repeats the same steps used to connect to the server, except that with peers user and pwd are not needed */
        peerSocket.close();

        clientSocket.close();
        }

    /* server mode: provides a file to the peer requesting it */
    static void download()
        {
        /* opening connection */
        ServerSocket serverSocket = new ServerSocket(4445);

        while(true)
            {
            Socket clientSocket = serverSocket.accept();

            /* opening buffers */
            BufferedReader inputStream = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
            DataOutputStream outputStream = new DataOutputStream(clientSocket.getOutputStream());

            String clientInput = inputStream.readLine();
            /* processes the request sent by the client and packs the data into a "byte[] data" */
            outputStream.writeBytes(data);

            clientSocket.close();
            }

        serverSocket.close();
        }
    }