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.arrow.flight.grpc;
  
  import io.netty.buffer.ByteBuf;
  import java.io.IOException;
  import java.io.OutputStream;
  import java.lang.reflect.Constructor;
  import java.lang.reflect.Field;
  import java.lang.reflect.InvocationTargetException;
  import java.lang.reflect.Method;
  import java.util.List;
  
  /**
   * Allow a user to add a ByteBuf based InputStream directly into GRPC WritableBuffer to avoid an
   * extra copy. This could be solved in GRPC by adding a ByteBufListable interface on InputStream and
   * letting BufferChainOutputStream take advantage of it.
   */
  public class AddWritableBuffer {
  
    private static final Constructor<?> bufConstruct;
    private static final Field bufferList;
    private static final Field current;
    private static final Method listAdd;
    private static final Class<?> bufChainOut;
  
    static {
      Constructor<?> tmpConstruct = null;
      Field tmpBufferList = null;
      Field tmpCurrent = null;
      Class<?> tmpBufChainOut = null;
      Method tmpListAdd = null;
  
      try {
        Class<?> nwb = Class.forName("io.grpc.netty.NettyWritableBuffer");
  
        Constructor<?> tmpConstruct2 = nwb.getDeclaredConstructor(ByteBuf.class);
        tmpConstruct2.setAccessible(true);
  
        Class<?> tmpBufChainOut2 =
            Class.forName("io.grpc.internal.MessageFramer$BufferChainOutputStream");
  
        Field tmpBufferList2 = tmpBufChainOut2.getDeclaredField("bufferList");
        tmpBufferList2.setAccessible(true);
  
        Field tmpCurrent2 = tmpBufChainOut2.getDeclaredField("current");
        tmpCurrent2.setAccessible(true);
  
        Method tmpListAdd2 = List.class.getDeclaredMethod("add", Object.class);
  
        // output fields last.
        tmpConstruct = tmpConstruct2;
        tmpBufferList = tmpBufferList2;
        tmpCurrent = tmpCurrent2;
        tmpListAdd = tmpListAdd2;
        tmpBufChainOut = tmpBufChainOut2;
  
      } catch (Exception ex) {
        new RuntimeException("Failed to initialize AddWritableBuffer, falling back to slow path", ex)
            .printStackTrace();
      }
  
      bufConstruct = tmpConstruct;
      bufferList = tmpBufferList;
      current = tmpCurrent;
      listAdd = tmpListAdd;
      bufChainOut = tmpBufChainOut;
    }
  
    /**
     * Add the provided ByteBuf to the gRPC BufferChainOutputStream if possible, else copy the buffer
     * to the stream.
     *
     * @param buf The buffer to add.
     * @param stream The Candidate OutputStream to add to.
     * @param tryZeroCopy If true, try to zero-copy append the buffer to the stream. This may not
     *     succeed.
     * @return True if buffer was zero-copy added to the stream. False if the buffer was copied.
     * @throws IOException if the fast path is not enabled and there was an error copying the buffer
     *     to the stream.
     */
    public static boolean add(ByteBuf buf, OutputStream stream, boolean tryZeroCopy)
        throws IOException {
      if (!tryZeroCopy || !tryAddBuffer(buf, stream)) {
        buf.getBytes(0, stream, buf.readableBytes());
        return false;
      }
      return true;
    }
  
    private static boolean tryAddBuffer(ByteBuf buf, OutputStream stream) throws IOException {
  
      if (bufChainOut == null) {
        return false;
      }
  
      if (!stream.getClass().equals(bufChainOut)) {
        return false;
      }
  
      try {
        if (current.get(stream) != null) {
          return false;
        }
  
        buf.retain();
        Object obj = bufConstruct.newInstance(buf);
        Object list = bufferList.get(stream);
        listAdd.invoke(list, obj);
        current.set(stream, obj);
        return true;
      } catch (IllegalAccessException
          | IllegalArgumentException
          | InvocationTargetException
          | InstantiationException e) {
        e.printStackTrace();
        return false;
      }
    }
  }
  