Java tutorial
/* * Copyright 2014 - 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 org.traccar.BaseFrameDecoder; import io.netty.buffer.ByteBuf; import io.netty.buffer.Unpooled; import io.netty.channel.Channel; import io.netty.channel.ChannelHandlerContext; public class UlbotechFrameDecoder extends BaseFrameDecoder { @Override protected Object decode(ChannelHandlerContext ctx, Channel channel, ByteBuf buf) throws Exception { if (buf.readableBytes() < 2) { return null; } if (buf.getUnsignedByte(buf.readerIndex()) == 0xF8) { int index = buf.indexOf(buf.readerIndex() + 1, buf.writerIndex(), (byte) 0xF8); if (index != -1) { ByteBuf result = Unpooled.buffer(index + 1 - buf.readerIndex()); while (buf.readerIndex() <= index) { int b = buf.readUnsignedByte(); if (b == 0xF7) { int ext = buf.readUnsignedByte(); if (ext == 0x00) { result.writeByte(0xF7); } else if (ext == 0x0F) { result.writeByte(0xF8); } } else { result.writeByte(b); } } return result; } } else { int index = buf.indexOf(buf.readerIndex(), buf.writerIndex(), (byte) '#'); if (index != -1) { return buf.readRetainedSlice(index + 1 - buf.readerIndex()); } } return null; } }