@Override
    public void onCompletion(Long result, Exception exception) {
      this.exception = exception;
      channel.close();
    }
Creates a callback to close {@code channel} on {@link #onCompletion(Long, Exception)}.
@param channel the {@link ByteBufferAsyncWritableChannel} that needs to be closed.
ambry-commons/src/main/java/com/github/ambry/commons/ReadableStreamChannelInputStream.java