/**
    * Licensed to the Apache Software Foundation (ASF) under one
    * or more contributor license agreements.  See the NOTICE file
    * distributed with this work for additional information
    * regarding copyright ownership.  The ASF 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
    *
   *     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.apache.hadoop.hbase.security;
  
  import io.netty.buffer.ByteBuf;
  import io.netty.channel.ChannelHandlerContext;
  import io.netty.handler.codec.ByteToMessageDecoder;
  
  import java.io.IOException;
  import java.util.List;
  
  import org.apache.hadoop.hbase.HConstants;
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.ipc.RemoteException;
  
  /**
   * Decode the sasl challenge sent by RpcServer.
   */
  @InterfaceAudience.Private
  public class SaslChallengeDecoder extends ByteToMessageDecoder {
  
    private static final int MAX_CHALLENGE_SIZE = 1024 * 1024; // 1M
  
    private ByteBuf tryDecodeChallenge(ByteBuf in, int offset, int readableBytes) throws IOException {
      if (readableBytes < 4) {
        return null;
      }
      int len = in.getInt(offset);
      if (len <= 0) {
        // fall back to simple
        in.readerIndex(offset + 4);
        return in.retainedSlice(offset, 4);
      }
      if (len > MAX_CHALLENGE_SIZE) {
        throw new IOException(
            "Sasl challenge too large(" + len + "), max allowed is " + MAX_CHALLENGE_SIZE);
      }
      int totalLen = 4 + len;
      if (readableBytes < totalLen) {
        return null;
      }
      in.readerIndex(offset + totalLen);
      return in.retainedSlice(offset, totalLen);
    }
  
    // will throw a RemoteException out if data is enough, so do not need to return anything.
    private void tryDecodeError(ByteBuf in, int offset, int readableBytes) throws IOException {
      if (readableBytes < 4) {
        return;
      }
      int classLen = in.getInt(offset);
      if (classLen <= 0) {
        throw new IOException("Invalid exception class name length " + classLen);
      }
      if (classLen > MAX_CHALLENGE_SIZE) {
        throw new IOException("Exception class name length too large(" + classLen +
            "), max allowed is " + MAX_CHALLENGE_SIZE);
      }
      if (readableBytes < 4 + classLen + 4) {
        return;
      }
      int msgLen = in.getInt(offset + 4 + classLen);
      if (msgLen <= 0) {
        throw new IOException("Invalid exception message length " + msgLen);
      }
      if (msgLen > MAX_CHALLENGE_SIZE) {
        throw new IOException("Exception message length too large(" + msgLen + "), max allowed is " +
            MAX_CHALLENGE_SIZE);
      }
      int totalLen = classLen + msgLen + 8;
      if (readableBytes < totalLen) {
        return;
      }
      String className = in.toString(offset + 4, classLen, HConstants.UTF8_CHARSET);
      String msg = in.toString(offset + classLen + 8, msgLen, HConstants.UTF8_CHARSET);
      in.readerIndex(offset + totalLen);
      throw new RemoteException(className, msg);
    }
  
    @Override
    protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
      int readableBytes = in.readableBytes();
      if (readableBytes < 4) {
        return;
     }
     int offset = in.readerIndex();
     int status = in.getInt(offset);
     if (status == SaslStatus.SUCCESS.state) {
       ByteBuf challenge = tryDecodeChallenge(in, offset + 4, readableBytes - 4);
       if (challenge != null) {
         out.add(challenge);
       }
     } else {
       tryDecodeError(in, offset + 4, readableBytes - 4);
     }
   }
 }