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/*
* Copyright 2016 - 2018 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 io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.Channel;
import io.netty.channel.ChannelHandlerContext;
import org.traccar.BaseFrameDecoder;
import org.traccar.NetworkMessage;
public class At2000FrameDecoder extends BaseFrameDecoder {
private static final int BLOCK_LENGTH = 16;
private static final int ACK_LENGTH = 496;
private boolean firstPacket = true;
private ByteBuf currentBuffer;
private int acknowledgedBytes;
private void sendResponse(Channel channel) {
if (channel != null) {
ByteBuf response = Unpooled.buffer(2 * BLOCK_LENGTH);
response.writeByte(At2000ProtocolDecoder.MSG_ACKNOWLEDGEMENT);
response.writeMedium(1);
response.writeByte(0x00); // success
response.writerIndex(2 * BLOCK_LENGTH);
channel.writeAndFlush(new NetworkMessage(response, channel.remoteAddress()));
}
}
@Override
protected Object decode(
ChannelHandlerContext ctx, Channel channel, ByteBuf buf) throws Exception {
if (buf.readableBytes() < 5) {
return null;
}
int length;
if (firstPacket) {
firstPacket = false;
length = buf.getUnsignedMediumLE(buf.readerIndex() + 2);
} else {
length = buf.getUnsignedMediumLE(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)
&& (buf != currentBuffer || buf.readableBytes() > acknowledgedBytes)) {
sendResponse(channel);
currentBuffer = buf;
acknowledgedBytes = buf.readableBytes();
}
if (buf.readableBytes() >= length) {
return buf.readRetainedSlice(length);
}
return null;
}
}
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