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.gcs.v2;
  
  import alluxio.underfs.ContentHashable;
  
  import com.google.cloud.WriteChannel;
  import com.google.cloud.storage.Blob;
  import com.google.cloud.storage.BlobId;
  import com.google.cloud.storage.BlobInfo;
  import com.google.cloud.storage.Storage;
  import com.google.cloud.storage.StorageException;
  import com.google.common.base.Preconditions;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import java.io.IOException;
  import java.io.OutputStream;
  import java.nio.ByteBuffer;
  import java.nio.channels.ClosedChannelException;
  import java.security.MessageDigest;
  import java.security.NoSuchAlgorithmException;
  import java.util.Optional;
  import java.util.concurrent.atomic.AtomicBoolean;
  import javax.annotation.concurrent.NotThreadSafe;
  
  /**
   * A stream for writing a file into GCS using Google cloud API (GCS output stream version 2).
   * The data is streaming writing to GCS without waiting for the complete file
   * to arrive in Alluxio worker.
   */
  @NotThreadSafe
  public final class GCSV2OutputStream extends OutputStream implements ContentHashable {
    private static final Logger LOG = LoggerFactory.getLogger(GCSV2OutputStream.class);
  
    /** Bucket name of the Alluxio GCS bucket. */
    private final String mBucketName;
  
    /** Key of the file when it is uploaded to GCS. */
    private final String mKey;
  
    /** The Google cloud storage client. */
    private final Storage mClient;
  
    /** The pre-allocated buffer for single byte write operation. */
    private final ByteBuffer mSingleByteBuffer;
  
    /** The blob information of the key. */
    private final BlobInfo mBlobInfo;
  
    /** The write channel of Google storage object. */
    private WriteChannel mWriteChannel;
  
    /** The MD5 hash of the file. */
    private MessageDigest mHash;
  
    /** Flag to indicate this stream has been closed, to ensure close is only done once. */
    private AtomicBoolean mClosed = new AtomicBoolean(false);
  
    private String mContentHash;
  
    /**
     * Constructs a new stream for writing a file.
     *
     * @param bucketName the name of the bucket
     * @param key the key of the file
     * @param client the Google cloud storage client
     */
    public GCSV2OutputStream(String bucketName, String key, Storage client) {
      Preconditions.checkArgument(bucketName != null && !bucketName.isEmpty(), "Bucket name must "
          + "not be null or empty.");
      mBucketName = bucketName;
      mKey = key;
      mClient = client;
      mSingleByteBuffer = ByteBuffer.allocate(1);
      mBlobInfo = BlobInfo.newBuilder(BlobId.of(mBucketName, mKey)).build();
      try {
        mHash = MessageDigest.getInstance("MD5");
      } catch (NoSuchAlgorithmException e) {
        LOG.warn("Algorithm not available for MD5 hash.", e);
        mHash = null;
      }
    }
  
    @Override
    public void write(int b) throws IOException {
      if (mHash != null) {
        mHash.update((byte) b);
      }
      if (mWriteChannel == null) {
        createWriteChannel();
      }
      mSingleByteBuffer.clear();
      mSingleByteBuffer.putInt(b);
  
      try {
        mWriteChannel.write(mSingleByteBuffer);
      } catch (StorageException e) {
        throw new IOException(String
            .format("Failed to write to a channel of %s in %s", mKey, mBucketName), e);
      }
    }
  
    @Override
    public void write(byte[] b) throws IOException {
      write(b, 0, b.length);
    }
  
    @Override
    public void write(byte[] b, int off, int len) throws IOException {
      if (mHash != null) {
        mHash.update(b, off, len);
      }
      if (mWriteChannel == null) {
        createWriteChannel();
      }
      ByteBuffer buffer = ByteBuffer.wrap(b, off, len);
      try {
        mWriteChannel.write(buffer);
      } catch (StorageException e) {
        throw new IOException(String
            .format("Failed to write to a channel of %s in %s", mKey, mBucketName), e);
      }
    }
  
    @Override
    public void flush() throws IOException {
      // Google storage write channel does not support flush operation
    }
  
    @Override
    public void close() throws IOException {
      if (mClosed.getAndSet(true)) {
        return;
      }
      try {
        if (mWriteChannel != null) {
          mWriteChannel.close();
        } else {
          Blob blob = mClient.create(mBlobInfo);
          if (blob == null) {
            throw new IOException(String
                .format("Failed to create empty object %s in %s", mKey, mBucketName));
          }
          mContentHash = blob.getMd5();
        }
      } catch (ClosedChannelException e) {
        LOG.error("Channel already closed, possible duplicate close call.", e);
      } catch (IOException e) {
        LOG.error("Failed to upload {} to {}", mKey, mBucketName, e);
        throw e;
      }
    }
  
    private void createWriteChannel() throws IOException {
      try {
        mWriteChannel = mClient.writer(mBlobInfo);
      } catch (StorageException e) {
        throw new IOException(String
            .format("Failed to create write channel of %s in %s", mKey, mBucketName), e);
      }
    }
  
    @Override
    public Optional<String> getContentHash() {
      if (mContentHash != null) {
        return Optional.of(mContentHash);
      }
      return Optional.empty();
    }
  }
  