/*
    * 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.giraph.comm.netty.handler;
  
  import org.apache.giraph.comm.netty.NettyClient;
  import org.apache.giraph.comm.netty.SaslNettyClient;
  import org.apache.giraph.comm.requests.RequestType;
  import org.apache.giraph.comm.requests.SaslCompleteRequest;
  import org.apache.giraph.comm.requests.SaslTokenMessageRequest;
  import org.apache.giraph.comm.requests.WritableRequest;
  import org.apache.hadoop.conf.Configuration;
  import org.apache.hadoop.util.ReflectionUtils;
  import org.apache.log4j.Logger;
  import io.netty.buffer.ByteBuf;
  import io.netty.buffer.ByteBufInputStream;
  import io.netty.channel.ChannelHandlerContext;
  import io.netty.channel.ChannelInboundHandlerAdapter;
  import io.netty.handler.codec.FixedLengthFrameDecoder;
  import io.netty.util.ReferenceCountUtil;
  
  import java.io.IOException;
  
  /**
   * Client-side Netty pipeline component that allows authentication with a
   * server.
   */
  public class SaslClientHandler extends ChannelInboundHandlerAdapter {
    /** Class logger */
    private static final Logger LOG = Logger.getLogger(SaslClientHandler.class);
    /** Configuration */
    private final Configuration conf;
  
    /**
     * Constructor.
     *
     * @param conf Configuration
     */
    public SaslClientHandler(Configuration conf) {
      this.conf = conf;
    }
  
    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg)
      throws Exception {
      WritableRequest decodedMessage = decode(ctx, msg);
      // Generate SASL response to server using Channel-local SASL client.
      SaslNettyClient saslNettyClient = ctx.attr(NettyClient.SASL).get();
      if (saslNettyClient == null) {
        throw new Exception("handleUpstream: saslNettyClient was unexpectedly " +
            "null for channel: " + ctx.channel());
      }
      if (decodedMessage.getClass() == SaslCompleteRequest.class) {
        if (LOG.isDebugEnabled()) {
          LOG.debug("handleUpstream: Server has sent us the SaslComplete " +
              "message. Allowing normal work to proceed.");
        }
        synchronized (saslNettyClient.getAuthenticated()) {
          saslNettyClient.getAuthenticated().notify();
        }
        if (!saslNettyClient.isComplete()) {
          LOG.error("handleUpstream: Server returned a Sasl-complete message, " +
              "but as far as we can tell, we are not authenticated yet.");
          throw new Exception("handleUpstream: Server returned a " +
              "Sasl-complete message, but as far as " +
              "we can tell, we are not authenticated yet.");
        }
        // Remove SaslClientHandler and replace LengthFieldBasedFrameDecoder
        // from client pipeline.
        ctx.pipeline().remove(this);
        ctx.pipeline().replace("length-field-based-frame-decoder",
            "fixed-length-frame-decoder",
            new FixedLengthFrameDecoder(RequestServerHandler.RESPONSE_BYTES));
        return;
      }
      SaslTokenMessageRequest serverToken =
        (SaslTokenMessageRequest) decodedMessage;
      if (LOG.isDebugEnabled()) {
        LOG.debug("handleUpstream: Responding to server's token of length: " +
            serverToken.getSaslToken().length);
      }
      // Generate SASL response (but we only actually send the response if it's
      // non-null.
      byte[] responseToServer = saslNettyClient.saslResponse(serverToken);
     if (responseToServer == null) {
       // If we generate a null response, then authentication has completed (if
       // not, warn), and return without sending a response back to the server.
       if (LOG.isDebugEnabled()) {
         LOG.debug("handleUpstream: Response to server is null: " +
             "authentication should now be complete.");
       }
       if (!saslNettyClient.isComplete()) {
         LOG.warn("handleUpstream: Generated a null response, " +
             "but authentication is not complete.");
       }
       return;
     } else {
       if (LOG.isDebugEnabled()) {
         LOG.debug("handleUpstream: Response to server token has length:" +
             responseToServer.length);
       }
     }
     // Construct a message containing the SASL response and send it to the
     // server.
     SaslTokenMessageRequest saslResponse =
       new SaslTokenMessageRequest(responseToServer);
     ctx.channel().writeAndFlush(saslResponse);
   }
 
   /**
    * Decode the message read by handler
    *
    * @param ctx channel handler context
    * @param msg message to decode into a writable request
    * @return decoded writablerequest object
    * @throws Exception
    */
   protected WritableRequest decode(ChannelHandlerContext ctx, Object msg)
     throws Exception {
     if (!(msg instanceof ByteBuf)) {
       throw new IllegalStateException("decode: Got illegal message " + msg);
     }
     // Decode msg into an object whose class C implements WritableRequest:
     //  C will be either SaslTokenMessage or SaslComplete.
     //
     // 1. Convert message to a stream that can be decoded.
     ByteBuf buf = (ByteBuf) msg;
     ByteBufInputStream inputStream = new ByteBufInputStream(buf);
     // 2. Get first byte: message type:
     int enumValue = inputStream.readByte();
     RequestType type = RequestType.values()[enumValue];
     if (LOG.isDebugEnabled()) {
       LOG.debug("decode: Got a response of type " + type + " from server:" +
         ctx.channel().remoteAddress());
     }
     // 3. Create object of the type determined in step 2.
     Class<? extends WritableRequest> writableRequestClass =
       type.getRequestClass();
     WritableRequest serverResponse =
       ReflectionUtils.newInstance(writableRequestClass, conf);
     // 4. Deserialize the inputStream's contents into the newly-constructed
     // serverResponse object.
     try {
       serverResponse.readFields(inputStream);
     } catch (IOException e) {
       LOG.error("decode: Exception when trying to read server response: " + e);
     }
     ReferenceCountUtil.release(buf);
     // serverResponse can now be used in the next stage in pipeline.
     return serverResponse;
   }
 }