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/*
* Copyright 2016 - 2017 Anton Tananaev (anton@traccar.org)
*
* 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.traccar.protocol;
import org.jboss.netty.buffer.ChannelBuffer;
import org.jboss.netty.buffer.ChannelBuffers;
import org.jboss.netty.channel.Channel;
import org.jboss.netty.channel.ChannelHandlerContext;
import org.jboss.netty.handler.codec.frame.FrameDecoder;
import java.nio.ByteOrder;
public class At2000FrameDecoder extends FrameDecoder {
private static final int BLOCK_LENGTH = 16;
private static final int ACK_LENGTH = 496;
private boolean firstPacket = true;
private void sendResponse(Channel channel) {
if (channel != null) {
ChannelBuffer response = ChannelBuffers.directBuffer(ByteOrder.LITTLE_ENDIAN, 2 * BLOCK_LENGTH);
response.writeByte(At2000ProtocolDecoder.MSG_ACKNOWLEDGEMENT);
response.writeMedium(ChannelBuffers.swapMedium(1));
response.writeByte(0x00); // success
response.writerIndex(2 * BLOCK_LENGTH);
channel.write(response);
}
}
@Override
protected Object decode(
ChannelHandlerContext ctx, Channel channel, ChannelBuffer buf) throws Exception {
if (buf.readableBytes() < 5) {
return null;
}
int length;
if (firstPacket) {
firstPacket = false;
length = buf.getUnsignedMedium(buf.readerIndex() + 2);
} else {
length = buf.getUnsignedMedium(buf.readerIndex() + 1);
}
length += BLOCK_LENGTH;
if (length % BLOCK_LENGTH != 0) {
length = (length / BLOCK_LENGTH + 1) * BLOCK_LENGTH;
}
if (buf.readableBytes() >= length || buf.readableBytes() % ACK_LENGTH == 0) {
sendResponse(channel);
}
if (buf.readableBytes() >= length) {
return buf.readBytes(length);
}
return null;
}
}
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