/* * Copyright 2021 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 org.traccar.BaseProtocolDecoder; import org.traccar.NetworkMessage; import org.traccar.Protocol; import org.traccar.helper.Checksum; import java.net.SocketAddress; import java.nio.charset.StandardCharsets; public class NavtelecomProtocolDecoder extends BaseProtocolDecoder { public NavtelecomProtocolDecoder(Protocol protocol) { super(protocol); } @Override protected Object decode( Channel channel, SocketAddress remoteAddress, Object msg) throws Exception { ByteBuf buf = (ByteBuf) msg; buf.skipBytes(4); // preamble int receiver = buf.readIntLE(); int sender = buf.readIntLE(); int length = buf.readUnsignedShortLE(); buf.readUnsignedByte(); // data checksum buf.readUnsignedByte(); // header checksum String sentence = buf.readCharSequence(length, StandardCharsets.US_ASCII).toString(); if (sentence.startsWith("*>S")) { String data = "*<S"; ByteBuf response = Unpooled.buffer(); response.writeCharSequence("@NTC", StandardCharsets.US_ASCII); response.writeIntLE(sender); response.writeIntLE(receiver); response.writeShortLE(data.length()); response.writeByte(Checksum.xor(data)); response.writeByte(Checksum.xor(response.nioBuffer())); response.writeCharSequence(data, StandardCharsets.US_ASCII); if (channel != null) { channel.writeAndFlush(new NetworkMessage(response, remoteAddress)); } } return null; } }