PacketDecoder.java

/*
 * This file is part of the OdinMS Maple Story Server Copyright (C) 2008 ~ 2010
 * Patrick Huy <patrick.huy@frz.cc> Matthias Butz <matze@odinms.de> Jan
 * Christian Meyer <vimes@odinms.de>
 * 
 * This program is free software: you can redistribute it and/or modify it under
 * the terms of the GNU Affero General Public License version 3 as published by
 * the Free Software Foundation. You may not use, modify or distribute this
 * program under any other version of the GNU Affero General Public License.
 * 
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
 * FOR A PARTICULAR PURPOSE. See the GNU Affero General Public License for more
 * details.
 * 
 * You should have received a copy of the GNU Affero General Public License
 * along with this program. If not, see <http://www.gnu.org/licenses/>.
 */
package javastory.server.handling;

import javastory.channel.ChannelClient;
import javastory.client.GameClient;
import javastory.cryptography.AesTransform;
import javastory.cryptography.CustomEncryption;

import org.apache.mina.core.buffer.IoBuffer;
import org.apache.mina.core.session.IoSession;
import org.apache.mina.filter.codec.CumulativeProtocolDecoder;
import org.apache.mina.filter.codec.ProtocolDecoderOutput;

public class PacketDecoder extends CumulativeProtocolDecoder {

	public static final String DECODER_STATE_KEY = PacketDecoder.class.getName() + ".STATE";

	public static class DecoderState {

		public int packetLength = -1;
	}

	@Override
	protected boolean doDecode(final IoSession session, final IoBuffer buffer, final ProtocolDecoderOutput out) throws Exception {
		final DecoderState decoderState = (DecoderState) session.getAttribute(DECODER_STATE_KEY);

		final ChannelClient client = (ChannelClient) session.getAttribute(GameClient.CLIENT_KEY);

		if (decoderState.packetLength == -1) {
			if (buffer.remaining() < 4) {
				return false;
			}

			final byte[] header = new byte[4];
			buffer.get(header);
			if (!client.getClientCrypto().validateHeader(header)) {
				session.close(true);
				return false;
			}
			decoderState.packetLength = AesTransform.getPacketLength(header);
		}

		if (buffer.remaining() < decoderState.packetLength) {
			return false;
		}

		final byte decryptedPacket[] = new byte[decoderState.packetLength];
		buffer.get(decryptedPacket, 0, decoderState.packetLength);
		decoderState.packetLength = -1;

		client.getClientCrypto().transform(decryptedPacket);
		CustomEncryption.decrypt(decryptedPacket);

		out.write(decryptedPacket);
		return true;
	}
}