content: /*
   * Copyright (c) 2019 abc123lzf <abc123lzf@126.com>
   *
   * Permission is hereby granted, free of charge, to any person obtaining a copy
   * of this software and associated documentation files (the "Software"), to deal
   * in the Software without restriction, including without limitation the rights
   * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
   * copies of the Software, and to permit persons to whom the Software is
   * furnished to do so, subject to the following conditions:
   *
   * The above copyright notice and this permission notice shall be included in all
   * copies or substantial portions of the Software.
   *
   * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
   * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
   * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
   * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
   * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
   * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
   * SOFTWARE.
   */
  package com.lzf.flyingsocks.misc;
  
  import io.netty.buffer.ByteBuf;
  import io.netty.channel.ChannelHandler;
  import io.netty.channel.ChannelHandlerContext;
  import io.netty.channel.ChannelInboundHandlerAdapter;
  import io.netty.util.ReferenceCountUtil;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import java.util.Objects;
  
  /**
   * 用于检测消息头是否合法，辨别出非flyingsocks端并强制关闭连接
   *
   * @author lzf abc123lzf@126.com
   * @since 2021/1/26 4:09
   */
  @ChannelHandler.Sharable
  public final class MessageHeaderCheckHandler extends ChannelInboundHandlerAdapter {
  
      private static final Logger log = LoggerFactory.getLogger(MessageHeaderCheckHandler.class);
  
      private final byte[] header;
  
      private final int headerLength;
  
      public MessageHeaderCheckHandler(byte[] header) {
          this.header = Objects.requireNonNull(header);
          this.headerLength = header.length;
      }
  
      @Override
      public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
          if (msg instanceof ByteBuf) {
              ByteBuf buf = (ByteBuf) msg;
  
              if (buf.readableBytes() < headerLength) {
                  ReferenceCountUtil.release(msg);
                  ctx.close();
                  return;
              }
  
              int index = buf.readerIndex();
              boolean pass = true;
              for (int i = 0; i < headerLength; i++) {
                  if (buf.getByte(index + i) != header[i]) {
                      pass = false;
                  }
              }
  
              if (!pass) {
                  log.warn("Message header check failure");
                  ReferenceCountUtil.release(msg);
                  ctx.close();
                  return;
              }
          }
  
          ctx.fireChannelRead(msg);
      }
  
  
      @Override
      public boolean isSharable() {
          return true;
      }
  }
  