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   /*
    * Copyright 2012 The Netty Project
    *
    * The Netty Project licenses this file to you 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:
    *
    *   https://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 io.netty.handler.codec.socks;
  
  import io.netty.buffer.ByteBuf;
  import io.netty.channel.ChannelHandlerContext;
  import io.netty.handler.codec.ReplayingDecoder;
  import io.netty.handler.codec.socks.SocksInitRequestDecoder.State;
  import io.netty.util.internal.UnstableApi;
  
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.List;
  
  /**
   * Decodes {@link ByteBuf}s into {@link SocksInitRequest}.
   * Before returning SocksRequest decoder removes itself from pipeline.
   */
  public class SocksInitRequestDecoder extends ReplayingDecoder<State> {
  
      public SocksInitRequestDecoder() {
          super(State.CHECK_PROTOCOL_VERSION);
      }
  
      @Override
      protected void decode(ChannelHandlerContext ctx, ByteBuf byteBuf, List<Object> out) throws Exception {
          switch (state()) {
              case CHECK_PROTOCOL_VERSION: {
                  if (byteBuf.readByte() != SocksProtocolVersion.SOCKS5.byteValue()) {
                      out.add(SocksCommonUtils.UNKNOWN_SOCKS_REQUEST);
                      break;
                  }
                  checkpoint(State.READ_AUTH_SCHEMES);
              }
              case READ_AUTH_SCHEMES: {
                  final byte authSchemeNum = byteBuf.readByte();
                  final List<SocksAuthScheme> authSchemes;
                  if (authSchemeNum > 0) {
                      authSchemes = new ArrayList<SocksAuthScheme>(authSchemeNum);
                      for (int i = 0; i < authSchemeNum; i++) {
                          authSchemes.add(SocksAuthScheme.valueOf(byteBuf.readByte()));
                      }
                  } else {
                      authSchemes = Collections.emptyList();
                  }
                  out.add(new SocksInitRequest(authSchemes));
                  break;
              }
              default: {
                  throw new Error();
              }
          }
          ctx.pipeline().remove(this);
      }
  
      @UnstableApi
      public enum State {
          CHECK_PROTOCOL_VERSION,
          READ_AUTH_SCHEMES
      }
  }