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.hdfs;
  
  import alluxio.underfs.ContentHashable;
  import alluxio.util.UnderFileSystemUtils;
  
  import org.apache.hadoop.fs.FSDataOutputStream;
  import org.apache.hadoop.fs.FileStatus;
  import org.apache.hadoop.fs.FileSystem;
  import org.apache.hadoop.fs.Path;
  
  import java.io.IOException;
  import java.io.OutputStream;
  import java.util.Optional;
  import javax.annotation.concurrent.NotThreadSafe;
  
  /**
   * Output stream implementation for {@link HdfsUnderFileSystem}. This class is just a wrapper on top
   * of an underlying {@link FSDataOutputStream}, except all calls to {@link #flush()} will be
   * converted to {@link FSDataOutputStream#sync()}. This is currently safe because all invocations of
   * flush intend the functionality to be sync.
   */
  @NotThreadSafe
  public class HdfsUnderFileOutputStream extends OutputStream implements ContentHashable {
    /** Underlying output stream. */
    private final FSDataOutputStream mOut;
    private final FileSystem mFs;
    private final String mPath;
  
    /**
     * Basic constructor.
     *
     * @param fs the hdfs file system object
     * @param path the path being written
     * @param out underlying stream to wrap
     */
    public HdfsUnderFileOutputStream(FileSystem fs, String path, FSDataOutputStream out) {
      mFs = fs;
      mPath = path;
      mOut = out;
    }
  
    @Override
    public void close() throws IOException {
      mOut.close();
    }
  
    @Override
    public void flush() throws IOException {
      // TODO(calvin): This functionality should be restricted to select output streams.
      // Note that, hsync() flushes out the data in client's user buffer all the way to the disk
      // device which may result in much slower performance than sync().
      mOut.hsync();
    }
  
    @Override
    public void write(int b) throws IOException {
      mOut.write(b);
    }
  
    @Override
    public void write(byte[] b) throws IOException {
      mOut.write(b);
    }
  
    @Override
    public void write(byte[] b, int off, int len) throws IOException {
      mOut.write(b, off, len);
    }
  
    @Override
    public Optional<String> getContentHash() throws IOException {
      FileStatus fs = mFs.getFileStatus(new Path(mPath));
      // get the content hash immediately after the file has completed writing
      // which will be used for generating the fingerprint of the file in Alluxio
      // ideally this value would be received as a result from the close call
      // so that we would be sure to have the hash relating to the file uploaded
      // (but such an API is not available for HDFS)
      return Optional.of(UnderFileSystemUtils.approximateContentHash(
          fs.getLen(), fs.getModificationTime()));
    }
  }
  