content: /*
   * Copyright 2022 paxos.cn.
   *
   * 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 cn.paxos.mysql.codec;
  
  import io.netty.buffer.ByteBuf;
  import io.netty.channel.ChannelHandlerContext;
  import io.netty.handler.codec.MessageToByteEncoder;
  
  public abstract class AbstractPacketEncoder<T extends MysqlPacket> extends MessageToByteEncoder<T> {
  
  	@Override
  	final protected void encode(ChannelHandlerContext ctx, T packet, ByteBuf buf) throws Exception {
  		final int writerIdx = buf.writerIndex();
  		buf.writeInt(0); // Advance the writer index so we can set the packet length after encoding
  		encodePacket(ctx, packet, buf);
  		final int len = buf.writerIndex() - writerIdx - 4;
  		buf.setMediumLE(writerIdx, len)
  				.setByte(writerIdx + 3, packet.getSequenceId());
  	}
  
  	protected abstract void encodePacket(ChannelHandlerContext ctx, T packet, ByteBuf buf) throws Exception;
  
  }
  