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; import java.nio.charset.StandardCharsets; public class Pt502FrameDecoder extends BaseFrameDecoder { private static final int BINARY_HEADER = 5; @Override protected Object decode(ChannelHandlerContext ctx, Channel channel, ByteBuf buf) throws Exception { if (buf.readableBytes() < 10) { return null; } if (buf.getUnsignedByte(buf.readerIndex()) == 0xbf && buf.toString(buf.readerIndex() + BINARY_HEADER, 4, StandardCharsets.US_ASCII).equals("$PHD")) { int length = buf.getUnsignedShortLE(buf.readerIndex() + 3); if (buf.readableBytes() >= length) { buf.skipBytes(BINARY_HEADER); ByteBuf result = buf.readRetainedSlice(length - BINARY_HEADER - 2); buf.skipBytes(2); // line break return result; } } else { if (buf.getUnsignedByte(buf.readerIndex()) == 0xbf) { buf.skipBytes(BINARY_HEADER); } int index = buf.indexOf(buf.readerIndex(), buf.writerIndex(), (byte) '\r'); if (index < 0) { index = buf.indexOf(buf.readerIndex(), buf.writerIndex(), (byte) '\n'); } if (index > 0) { ByteBuf result = buf.readRetainedSlice(index - buf.readerIndex()); while (buf.isReadable() && (buf.getByte(buf.readerIndex()) == '\r' || buf.getByte(buf.readerIndex()) == '\n')) { buf.skipBytes(1); } return result; } } return null; } }