Java tutorial
/* * Copyright 2013 - 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.channel.Channel; import io.netty.channel.ChannelHandlerContext; import org.traccar.BaseFrameDecoder; public class MeiligaoFrameDecoder extends BaseFrameDecoder { private static final int MESSAGE_HEADER = 4; @Override protected Object decode(ChannelHandlerContext ctx, Channel channel, ByteBuf buf) throws Exception { // Strip not '$' (0x24) bytes from the beginning while (buf.isReadable() && buf.getUnsignedByte(buf.readerIndex()) != 0x24) { buf.readByte(); } // Check length and return buffer if (buf.readableBytes() >= MESSAGE_HEADER) { int length = buf.getUnsignedShort(buf.readerIndex() + 2); if (buf.readableBytes() >= length) { return buf.readRetainedSlice(length); } } return null; } }