content: /*
   * 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.util;
  
  import java.util.LinkedList;
  
  import com.google.common.base.Preconditions;
  import io.netty.buffer.ByteBuf;
  import io.netty.buffer.CompositeByteBuf;
  import io.netty.buffer.Unpooled;
  import io.netty.channel.ChannelHandlerContext;
  import io.netty.channel.ChannelInboundHandlerAdapter;
  
  /**
   * A customized frame decoder that allows intercepting raw data.
   * <p>
   * This behaves like Netty's frame decoder (with harcoded parameters that match this library's
   * needs), except it allows an interceptor to be installed to read data directly before it's
   * framed.
   * <p>
   * Unlike Netty's frame decoder, each frame is dispatched to child handlers as soon as it's
   * decoded, instead of building as many frames as the current buffer allows and dispatching
   * all of them. This allows a child handler to install an interceptor if needed.
   * <p>
   * If an interceptor is installed, framing stops, and data is instead fed directly to the
   * interceptor. When the interceptor indicates that it doesn't need to read any more data,
   * framing resumes. Interceptors should not hold references to the data buffers provided
   * to their handle() method.
   */
  public class TransportFrameDecoder extends ChannelInboundHandlerAdapter {
  
    public static final String HANDLER_NAME = "frameDecoder";
    private static final int LENGTH_SIZE = 8;
    private static final int MAX_FRAME_SIZE = Integer.MAX_VALUE;
    private static final int UNKNOWN_FRAME_SIZE = -1;
  
    private final LinkedList<ByteBuf> buffers = new LinkedList<>();
    private final ByteBuf frameLenBuf = Unpooled.buffer(LENGTH_SIZE, LENGTH_SIZE);
  
    private long totalSize = 0;
    private long nextFrameSize = UNKNOWN_FRAME_SIZE;
    private volatile Interceptor interceptor;
  
    @Override
    public void channelRead(ChannelHandlerContext ctx, Object data) throws Exception {
      ByteBuf in = (ByteBuf) data;
      buffers.add(in);
      totalSize += in.readableBytes();
  
      while (!buffers.isEmpty()) {
        // First, feed the interceptor, and if it's still, active, try again.
        if (interceptor != null) {
          ByteBuf first = buffers.getFirst();
          int available = first.readableBytes();
          if (feedInterceptor(first)) {
            assert !first.isReadable() : "Interceptor still active but buffer has data.";
          }
  
          int read = available - first.readableBytes();
          if (read == available) {
            buffers.removeFirst().release();
          }
          totalSize -= read;
        } else {
          // Interceptor is not active, so try to decode one frame.
          ByteBuf frame = decodeNext();
          if (frame == null) {
            break;
          }
          ctx.fireChannelRead(frame);
        }
      }
    }
  
    private long decodeFrameSize() {
      if (nextFrameSize != UNKNOWN_FRAME_SIZE || totalSize < LENGTH_SIZE) {
        return nextFrameSize;
      }
  
      // We know there's enough data. If the first buffer contains all the data, great. Otherwise,
      // hold the bytes for the frame length in a composite buffer until we have enough data to read
      // the frame size. Normally, it should be rare to need more than one buffer to read the frame
      // size.
      ByteBuf first = buffers.getFirst();
      if (first.readableBytes() >= LENGTH_SIZE) {
        nextFrameSize = first.readLong() - LENGTH_SIZE;
        totalSize -= LENGTH_SIZE;
        if (!first.isReadable()) {
          buffers.removeFirst().release();
        }
        return nextFrameSize;
      }
  
      while (frameLenBuf.readableBytes() < LENGTH_SIZE) {
        ByteBuf next = buffers.getFirst();
        int toRead = Math.min(next.readableBytes(), LENGTH_SIZE - frameLenBuf.readableBytes());
        frameLenBuf.writeBytes(next, toRead);
        if (!next.isReadable()) {
          buffers.removeFirst().release();
        }
      }
  
      nextFrameSize = frameLenBuf.readLong() - LENGTH_SIZE;
      totalSize -= LENGTH_SIZE;
      frameLenBuf.clear();
      return nextFrameSize;
    }
  
    private ByteBuf decodeNext() throws Exception {
      long frameSize = decodeFrameSize();
      if (frameSize == UNKNOWN_FRAME_SIZE || totalSize < frameSize) {
        return null;
      }
  
      // Reset size for next frame.
      nextFrameSize = UNKNOWN_FRAME_SIZE;
  
      Preconditions.checkArgument(frameSize < MAX_FRAME_SIZE, "Too large frame: %s", frameSize);
      Preconditions.checkArgument(frameSize > 0, "Frame length should be positive: %s", frameSize);
  
      // If the first buffer holds the entire frame, return it.
      int remaining = (int) frameSize;
      if (buffers.getFirst().readableBytes() >= remaining) {
        return nextBufferForFrame(remaining);
      }
  
      // Otherwise, create a composite buffer.
      CompositeByteBuf frame = buffers.getFirst().alloc().compositeBuffer(Integer.MAX_VALUE);
      while (remaining > 0) {
        ByteBuf next = nextBufferForFrame(remaining);
        remaining -= next.readableBytes();
        frame.addComponent(next).writerIndex(frame.writerIndex() + next.readableBytes());
      }
      assert remaining == 0;
      return frame;
    }
  
    /**
     * Takes the first buffer in the internal list, and either adjust it to fit in the frame
     * (by taking a slice out of it) or remove it from the internal list.
     */
    private ByteBuf nextBufferForFrame(int bytesToRead) {
      ByteBuf buf = buffers.getFirst();
      ByteBuf frame;
  
      if (buf.readableBytes() > bytesToRead) {
        frame = buf.retain().readSlice(bytesToRead);
        totalSize -= bytesToRead;
      } else {
        frame = buf;
        buffers.removeFirst();
        totalSize -= frame.readableBytes();
      }
  
      return frame;
    }
  
    @Override
    public void channelInactive(ChannelHandlerContext ctx) throws Exception {
      for (ByteBuf b : buffers) {
        b.release();
      }
      if (interceptor != null) {
        interceptor.channelInactive();
      }
      frameLenBuf.release();
      super.channelInactive(ctx);
    }
  
    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
      if (interceptor != null) {
        interceptor.exceptionCaught(cause);
      }
      super.exceptionCaught(ctx, cause);
    }
  
    public void setInterceptor(Interceptor interceptor) {
      Preconditions.checkState(this.interceptor == null, "Already have an interceptor.");
      this.interceptor = interceptor;
    }
  
    /**
     * @return Whether the interceptor is still active after processing the data.
     */
    private boolean feedInterceptor(ByteBuf buf) throws Exception {
      if (interceptor != null && !interceptor.handle(buf)) {
        interceptor = null;
      }
      return interceptor != null;
    }
  
    public interface Interceptor {
  
      /**
       * Handles data received from the remote end.
       *
       * @param data Buffer containing data.
       * @return "true" if the interceptor expects more data, "false" to uninstall the interceptor.
       */
      boolean handle(ByteBuf data) throws Exception;
  
      /** Called if an exception is thrown in the channel pipeline. */
      void exceptionCaught(Throwable cause) throws Exception;
  
      /** Called if the channel is closed and the interceptor is still installed. */
      void channelInactive() throws Exception;
  
    }
  
  }
  