Java tutorial
/* * Copyright 2019 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 org.traccar.helper.BufferUtil; public class ItsFrameDecoder extends BaseFrameDecoder { private static final int MINIMUM_LENGTH = 20; private ByteBuf readFrame(ByteBuf buf, int delimiterIndex, int skip) { int headerIndex = buf.indexOf(buf.readerIndex() + 1, buf.writerIndex(), (byte) '$'); if (headerIndex > 0 && headerIndex < delimiterIndex) { return buf.readRetainedSlice(headerIndex - buf.readerIndex()); } else { ByteBuf frame = buf.readRetainedSlice(delimiterIndex - buf.readerIndex()); buf.skipBytes(skip); return frame; } } @Override protected Object decode(ChannelHandlerContext ctx, Channel channel, ByteBuf buf) throws Exception { while (buf.isReadable() && buf.getByte(buf.readerIndex()) != '$') { buf.skipBytes(1); } int delimiterIndex = BufferUtil.indexOf("\r\n", buf); if (delimiterIndex > MINIMUM_LENGTH) { return readFrame(buf, delimiterIndex, 2); } else { delimiterIndex = buf.indexOf(buf.readerIndex(), buf.writerIndex(), (byte) '*'); if (delimiterIndex > MINIMUM_LENGTH) { if (buf.writerIndex() > delimiterIndex + 1 && buf.getByte(delimiterIndex + 1) == '*') { delimiterIndex += 1; } if (buf.getByte(delimiterIndex - 2) == ',') { return readFrame(buf, delimiterIndex - 1, 2); // skip binary checksum } else { return readFrame(buf, delimiterIndex, 1); } } } return null; } }