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 H02FrameDecoder extends BaseFrameDecoder { private static final int MESSAGE_SHORT = 32; private static final int MESSAGE_LONG = 45; private int messageLength; public H02FrameDecoder(int messageLength) { this.messageLength = messageLength; } @Override protected Object decode(ChannelHandlerContext ctx, Channel channel, ByteBuf buf) throws Exception { char marker = (char) buf.getByte(buf.readerIndex()); while (marker != '*' && marker != '$' && marker != 'X' && buf.readableBytes() > 0) { buf.skipBytes(1); if (buf.readableBytes() > 0) { marker = (char) buf.getByte(buf.readerIndex()); } } switch (marker) { case '*': // Return text message int index = buf.indexOf(buf.readerIndex(), buf.writerIndex(), (byte) '#'); if (index != -1) { ByteBuf result = buf.readRetainedSlice(index + 1 - buf.readerIndex()); while (buf.isReadable() && (buf.getByte(buf.readerIndex()) == '\r' || buf.getByte(buf.readerIndex()) == '\n')) { buf.readByte(); // skip new line } return result; } break; case '$': if (messageLength == 0) { if (buf.readableBytes() == MESSAGE_LONG) { messageLength = MESSAGE_LONG; } else { messageLength = MESSAGE_SHORT; } } if (buf.readableBytes() >= messageLength) { return buf.readRetainedSlice(messageLength); } break; case 'X': if (buf.readableBytes() >= MESSAGE_SHORT) { return buf.readRetainedSlice(MESSAGE_SHORT); } break; default: return null; } return null; } }