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 io.netty.buffer.ByteBuf; import io.netty.channel.Channel; import io.netty.channel.ChannelHandlerContext; import org.traccar.BaseFrameDecoder; public class Gt06FrameDecoder extends BaseFrameDecoder { @Override protected Object decode(ChannelHandlerContext ctx, Channel channel, ByteBuf buf) throws Exception { if (buf.readableBytes() < 5) { return null; } int length = 2 + 2; // head and tail if (buf.getByte(buf.readerIndex()) == 0x78) { length += 1 + buf.getUnsignedByte(buf.readerIndex() + 2); } else { length += 2 + buf.getUnsignedShort(buf.readerIndex() + 2); } if (buf.readableBytes() >= length && buf.getUnsignedShort(buf.readerIndex() + length - 2) == 0x0d0a) { return buf.readRetainedSlice(length); } int endIndex = buf.readerIndex() - 1; do { endIndex = buf.indexOf(endIndex + 1, buf.writerIndex(), (byte) 0x0d); if (endIndex > 0 && buf.writerIndex() > endIndex + 1 && buf.getByte(endIndex + 1) == 0x0a) { return buf.readRetainedSlice(endIndex + 2 - buf.readerIndex()); } } while (endIndex > 0); return null; } }