content: /*******************************************************************************
   * Copyright 2011 Albin Theander
   * 
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   * 
   *   http://www.apache.org/licenses/LICENSE-2.0
   * 
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   ******************************************************************************/
  package org.meqantt.netty;
  
  import java.io.ByteArrayInputStream;
  
  import org.jboss.netty.buffer.ChannelBuffer;
  import org.jboss.netty.channel.Channel;
  import org.jboss.netty.channel.ChannelHandlerContext;
  import org.jboss.netty.handler.codec.frame.FrameDecoder;
  import org.meqantt.message.Message;
  import org.meqantt.message.MessageInputStream;
  
  
  public class MqttMessageDecoder extends FrameDecoder {
  
  	@Override
  	protected Object decode(ChannelHandlerContext ctx, Channel channel,
  			ChannelBuffer buf) throws Exception {
  		if (buf.readableBytes() < 2) {
  			return null;
  		}
  		buf.markReaderIndex();
  		buf.readByte(); // read away header
  		int msgLength = 0;
  		int multiplier = 1;
  		int digit;
  		int lengthSize = 0;
  		do {
  			lengthSize++;
  			digit = buf.readByte();
  			msgLength += (digit & 0x7f) * multiplier;
  			multiplier *= 128;
  			if ((digit & 0x80) > 0 && !buf.readable()) {
  				buf.resetReaderIndex();
  				return null;
  			}
  		} while ((digit & 0x80) > 0);
  		if (buf.readableBytes() < msgLength) {
  			buf.resetReaderIndex();
  			return null;
  		}
  		byte[] data = new byte[1 + lengthSize + msgLength];
  		buf.resetReaderIndex();
  		buf.readBytes(data);
  		MessageInputStream mis = new MessageInputStream(
  				new ByteArrayInputStream(data));
  		Message msg = mis.readMessage();
  		return msg;
  	}
  
  }
  