package net.sourceforge.jsocks.server;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.DatagramPacket;
import java.net.Socket;

import net.sourceforge.jsocks.ProxyMessage;

/**
 * Classes implementing this interface should provide socks server with
 * authentication and authorization of users.
 **/
public interface ServerAuthenticator {

	/**
	 * This method is called when datagram is received by the server.
	 * <p>
	 * Implementaions should decide wether it should be forwarded or dropped. It
	 * is expecteed that implementation will use datagram address and port
	 * information to make a decision, as well as anything else. Address and
	 * port of the datagram are always correspond to remote machine. It is
	 * either destination or source address. If out is true address is
	 * destination address, else it is a source address, address of the machine
	 * from which datagram have been received for the client.
	 * <p>
	 * Implementaions should return true if the datagram is to be forwarded, and
	 * false if the datagram should be dropped.
	 * <p>
	 * This method is called on the object returned from the startSession
	 * function.
	 * 
	 * @param out
	 *            If true the datagram is being send out(from the client),
	 *            otherwise it is an incoming datagram.
	 * @return True to forward datagram false drop it silently.
	 */
	boolean checkRequest(DatagramPacket dp, boolean out);

	/**
	 * This method is called when a request have been read.
	 * <p>
	 * Implementation should decide wether to grant request or not. Returning
	 * true implies granting the request, false means request should be
	 * rejected.
	 * <p>
	 * This method is called on the object returned from the startSession
	 * function.
	 * 
	 * @param msg
	 *            Request message.
	 * @return true to grant request, false to reject it.
	 */
	boolean checkRequest(ProxyMessage msg);

	/**
	 * This method is called when session is completed. Either due to normal
	 * termination or due to any error condition.
	 * <p>
	 * This method is called on the object returned from the startSession
	 * function.
	 */
	void endSession();

	/**
	 * This method should return input stream which should be used on the
	 * accepted socket.
	 * <p>
	 * SOCKSv5 allows to have multiple authentication methods, and these methods
	 * might require some kind of transformations being made on the data.
	 * <p>
	 * This method is called on the object returned from the startSession
	 * function.
	 */
	InputStream getInputStream();

	/**
	 * This method should return output stream to use to write to the accepted
	 * socket.
	 * <p>
	 * SOCKSv5 allows to have multiple authentication methods, and these methods
	 * might require some kind of transformations being made on the data.
	 * <p>
	 * This method is called on the object returned from the startSession
	 * function.
	 */
	OutputStream getOutputStream();

	/**
	 * This method is called when a new connection accepted by the server.
	 * <p>
	 * At this point no data have been extracted from the connection. It is
	 * responsibility of this method to ensure that the next byte in the stream
	 * after this method have been called is the first byte of the socks request
	 * message. For SOCKSv4 there is no authentication data and the first byte
	 * in the stream is part of the request. With SOCKSv5 however there is an
	 * authentication data first. It is expected that implementaions will
	 * process this authentication data.
	 * <p>
	 * If authentication was successful an instance of ServerAuthentication
	 * should be returned, it later will be used by the server to perform
	 * authorization and some other things. If authentication fails null should
	 * be returned, or an exception may be thrown.
	 * 
	 * @param s
	 *            Accepted Socket.
	 * @return An instance of ServerAuthenticator to be used for this connection
	 *         or null
	 */
	ServerAuthenticator startSession(Socket s) throws IOException;
}
