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Network communication library for solver-aggregator connections.
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/*
 * Owl Platform Solver-Aggregator Library for Java
 * Copyright (C) 2012 Robert Moore and the Owl Platform
 * 
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation; either version 2.1 of the License, or
 * (at your option) any later version.
 *  
 * 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 Lesser General Public License for more details.
 *  
 * You should have received a copy of the GNU Lesser General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */

package com.owlplatform.solver.protocol.codec;

import org.apache.mina.core.buffer.IoBuffer;
import org.apache.mina.core.session.IoSession;
import org.apache.mina.filter.codec.ProtocolEncoderOutput;
import org.apache.mina.filter.codec.demux.MessageEncoder;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.owlplatform.solver.protocol.messages.HandshakeMessage;

/**
 * Encoder for the {@code HandshakeMessage} according to the Solver-Aggregator protocol.
 * @author Robert Moore
 *
 */
public class HandshakeEncoder implements MessageEncoder {

	/**
	 * Logger for this class.
	 */
	private static final Logger log = LoggerFactory
			.getLogger(HandshakeEncoder.class);

	/**
	 * Key to track connection state.
	 */
	private static final String CONN_STATE_KEY = HandshakeEncoder.class
			.getName()
			+ ".STATE";

	/**
	 * Connection state class.  Used to determine if a handshake was already exchanged.
	 * @author Robert Moore
	 *
	 */
	private static final class HubConnectionState {
	  /**
	   * Flag to indicate if a handshake was previously encoded.
	   */
		boolean handshakeSent = false;
		
		/**
		 * Creates a new {@code HubConnectionState} with the handshake flag set to false.
		 */
		public HubConnectionState(){
		  super();
		}
	}

	@Override
	public void encode(IoSession session, HandshakeMessage message,
			ProtocolEncoderOutput out) throws Exception {
		HubConnectionState connState = (HubConnectionState) session
				.getAttribute(CONN_STATE_KEY);
		if (connState == null) {
			connState = new HubConnectionState();
			connState.handshakeSent = false;
			session.setAttribute(CONN_STATE_KEY, connState);
		}

		log.debug("Sending handshake message.");

		if (connState.handshakeSent) {
			log.warn("Handshake already sent.");
			return;
		}

		IoBuffer buffer = IoBuffer.allocate(HandshakeMessage.MESSAGE_LENGTH);

		buffer.putInt(message.getStringLength());
		buffer.put(message.getProtocolString().getBytes("ASCII"));
		buffer.put(message.getVersionNumber());
		buffer.put(message.getReservedBits());

		buffer.flip();

		out.write(buffer);

		connState.handshakeSent = true;

	}

}