/*
 * 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.spark.network.server;

import java.net.SocketAddress;

import io.netty.channel.Channel;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelFutureListener;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;

import org.apache.spark.internal.LogKeys;
import org.apache.spark.internal.SparkLogger;
import org.apache.spark.internal.SparkLoggerFactory;
import org.apache.spark.internal.MDC;
import org.apache.spark.network.buffer.ManagedBuffer;
import org.apache.spark.network.client.TransportClient;
import org.apache.spark.network.protocol.ChunkFetchFailure;
import org.apache.spark.network.protocol.ChunkFetchRequest;
import org.apache.spark.network.protocol.ChunkFetchSuccess;
import org.apache.spark.network.protocol.Encodable;
import org.apache.spark.network.util.JavaUtils;

import static org.apache.spark.network.util.NettyUtils.*;

/**
 * A dedicated ChannelHandler for processing ChunkFetchRequest messages. When sending response
 * of ChunkFetchRequest messages to the clients, the thread performing the I/O on the underlying
 * channel could potentially be blocked due to disk contentions. If several hundreds of clients
 * send ChunkFetchRequest to the server at the same time, it could potentially occupying all
 * threads from TransportServer's default EventLoopGroup for waiting for disk reads before it
 * can send the block data back to the client as part of the ChunkFetchSuccess messages. As a
 * result, it would leave no threads left to process other RPC messages, which takes much less
 * time to process, and could lead to client timing out on either performing SASL authentication,
 * registering executors, or waiting for response for an OpenBlocks messages.
 */
public class ChunkFetchRequestHandler extends SimpleChannelInboundHandler<ChunkFetchRequest> {
  private static final SparkLogger logger =
    SparkLoggerFactory.getLogger(ChunkFetchRequestHandler.class);

  private final TransportClient client;
  private final StreamManager streamManager;
  /** The max number of chunks being transferred and not finished yet. */
  private final long maxChunksBeingTransferred;
  private final boolean syncModeEnabled;

  public ChunkFetchRequestHandler(
      TransportClient client,
      StreamManager streamManager,
      Long maxChunksBeingTransferred,
      boolean syncModeEnabled) {
    this.client = client;
    this.streamManager = streamManager;
    this.maxChunksBeingTransferred = maxChunksBeingTransferred;
    this.syncModeEnabled = syncModeEnabled;
  }

  @Override
  public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
    logger.warn("Exception in connection from {}", cause,
      MDC.of(LogKeys.HOST_PORT, getRemoteAddress(ctx.channel())));
    ctx.close();
  }

  @Override
  protected void channelRead0(
      ChannelHandlerContext ctx,
      final ChunkFetchRequest msg) throws Exception {
    Channel channel = ctx.channel();
    processFetchRequest(channel, msg);
  }

  public void processFetchRequest(
      final Channel channel, final ChunkFetchRequest msg) throws Exception {
    if (logger.isTraceEnabled()) {
      logger.trace("Received req from {} to fetch block {}", getRemoteAddress(channel),
        msg.streamChunkId);
    }
    if (maxChunksBeingTransferred < Long.MAX_VALUE) {
      long chunksBeingTransferred = streamManager.chunksBeingTransferred();
      if (chunksBeingTransferred >= maxChunksBeingTransferred) {
        logger.warn("The number of chunks being transferred {} is above {}, close the connection.",
          MDC.of(LogKeys.NUM_CHUNKS, chunksBeingTransferred),
          MDC.of(LogKeys.MAX_NUM_CHUNKS, maxChunksBeingTransferred));
        channel.close();
        return;
      }
    }
    ManagedBuffer buf;
    try {
      streamManager.checkAuthorization(client, msg.streamChunkId.streamId());
      buf = streamManager.getChunk(msg.streamChunkId.streamId(), msg.streamChunkId.chunkIndex());
      if (buf == null) {
        throw new IllegalStateException("Chunk was not found");
      }
    } catch (Exception e) {
      logger.error("Error opening block {} for request from {}", e,
        MDC.of(LogKeys.STREAM_CHUNK_ID, msg.streamChunkId),
        MDC.of(LogKeys.HOST_PORT, getRemoteAddress(channel)));
      respond(channel, new ChunkFetchFailure(msg.streamChunkId,
        JavaUtils.stackTraceToString(e)));
      return;
    }

    streamManager.chunkBeingSent(msg.streamChunkId.streamId());
    respond(channel, new ChunkFetchSuccess(msg.streamChunkId, buf)).addListener(
      (ChannelFutureListener) future -> streamManager.chunkSent(msg.streamChunkId.streamId()));
  }

  /**
   * The invocation to channel.writeAndFlush is async, and the actual I/O on the
   * channel will be handled by the EventLoop the channel is registered to. So even
   * though we are processing the ChunkFetchRequest in a separate thread pool, the actual I/O,
   * which is the potentially blocking call that could deplete server handler threads, is still
   * being processed by TransportServer's default EventLoopGroup.
   *
   * When syncModeEnabled is true, Spark will throttle the max number of threads that channel I/O
   * for sending response to ChunkFetchRequest, the thread calling channel.writeAndFlush will wait
   * for the completion of sending response back to client by invoking await(). This will throttle
   * the rate at which threads from ChunkFetchRequest dedicated EventLoopGroup submit channel I/O
   * requests to TransportServer's default EventLoopGroup, thus making sure that we can reserve
   * some threads in TransportServer's default EventLoopGroup for handling other RPC messages.
   */
  private ChannelFuture respond(
      final Channel channel,
      final Encodable result) throws InterruptedException {
    final SocketAddress remoteAddress = channel.remoteAddress();
    ChannelFuture channelFuture;
    if (syncModeEnabled) {
      channelFuture = channel.writeAndFlush(result).await();
    } else {
      channelFuture = channel.writeAndFlush(result);
    }
    return channelFuture.addListener((ChannelFutureListener) future -> {
      if (future.isSuccess()) {
        logger.trace("Sent result {} to client {}", result, remoteAddress);
      } else {
        logger.error("Error sending result {} to {}; closing connection",
          future.cause(),
          MDC.of(LogKeys.RESULT, result),
          MDC.of(LogKeys.HOST_PORT, remoteAddress));
        channel.close();
      }
    });
  }
}
