content: /*
   * The Alluxio Open Foundation licenses this work under the Apache License, version 2.0
   * (the "License"). You may not use this work except in compliance with the License, which is
   * available at www.apache.org/licenses/LICENSE-2.0
   *
   * This software is distributed on an "AS IS" basis, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
   * either express or implied, as more fully set forth in the License.
   *
   * See the NOTICE file distributed with this work for information regarding copyright ownership.
   */
  
  package alluxio.underfs;
  
  import java.io.IOException;
  import java.util.Optional;
  
  /**
   * Interface for returning the content hash. Instances of {@link java.io.OutputStream} returned by
   * {@link UnderFileSystem#create} may implement this interface if the UFS returns the hash of the
   * content written when the stream is closed. The content hash will then be used as part of
   * the metadata fingerprint when the file is completed on the Alluxio master.
   */
  public interface ContentHashable {
    /**
     * @return the content hash of the file written to the UFS if available
     * after the stream has been closed
     */
    Optional<String> getContentHash() throws IOException;
  }
  