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;
  
  import alluxio.retry.RetryPolicy;
  
  import org.apache.http.HttpStatus;
  import org.jets3t.service.ServiceException;
  import org.jets3t.service.impl.rest.httpclient.GoogleStorageService;
  import org.jets3t.service.model.GSObject;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import java.io.BufferedInputStream;
  import java.io.IOException;
  import java.io.InputStream;
  import javax.annotation.concurrent.NotThreadSafe;
  
  /**
   * A stream for reading a file from GCS. The main purpose is to provide a faster skip method, as
   * the underlying implementation will read and discard bytes until the number to skip has been
   * reached. This input stream returns 0 when calling read with an empty buffer.
   */
  @NotThreadSafe
  public final class GCSInputStream extends InputStream {
    private static final Logger LOG = LoggerFactory.getLogger(GCSInputStream.class);
  
    /** Bucket name of the Alluxio GCS bucket. */
    private final String mBucketName;
  
    /** Key of the file in GCS to read. */
    private final String mKey;
  
    /** The JetS3t client for GCS operations. */
    private final GoogleStorageService mClient;
  
    /** The underlying input stream. */
    private BufferedInputStream mInputStream;
  
    /** Position of the stream. */
    private long mPos;
  
    /**
     * Policy determining the retry behavior in case the key does not exist. The key may not exist
     * because of eventual consistency.
     */
    private final RetryPolicy mRetryPolicy;
  
    /**
     * Creates a new instance of {@link GCSInputStream}.
     *
     * @param bucketName the name of the bucket
     * @param key the key of the file
     * @param client the client for GCS
     * @param retryPolicy retry policy in case the key does not exist
     */
    GCSInputStream(String bucketName, String key, GoogleStorageService client,
        RetryPolicy retryPolicy) {
      this(bucketName, key, client, 0L, retryPolicy);
    }
  
    /**
     * Creates a new instance of {@link GCSInputStream}, at a specific position.
     *
     * @param bucketName the name of the bucket
     * @param key the key of the file
     * @param client the client for GCS
     * @param pos the position to start
     * @param retryPolicy retry policy in case the key does not exist
     */
    GCSInputStream(String bucketName, String key, GoogleStorageService client,
        long pos, RetryPolicy retryPolicy) {
      mBucketName = bucketName;
      mKey = key;
      mClient = client;
      mPos = pos;
      mRetryPolicy = retryPolicy;
    }
  
    @Override
    public void close() throws IOException {
      closeStream();
    }
  
    @Override
    public int read() throws IOException {
      if (mInputStream == null) {
        openStream();
      }
      int value = mInputStream.read();
      if (value != -1) {
        mPos++;
      }
      return value;
    }
  
    @Override
    public int read(byte[] b) throws IOException {
      return read(b, 0, b.length);
    }
  
    @Override
    public int read(byte[] b, int off, int len) throws IOException {
      if (len == 0) {
        return 0;
      }
      if (mInputStream == null) {
        openStream();
      }
      int ret = mInputStream.read(b, off, len);
      if (ret != -1) {
        mPos += ret;
      }
      return ret;
    }
  
    /**
     * This method leverages the ability to open a stream from GCS from a given offset. When the
     * underlying stream has fewer bytes buffered than the skip request, the stream is closed, and
     * a new stream is opened starting at the requested offset.
     *
     * @param n number of bytes to skip
     * @return the number of bytes skipped
     */
    @Override
    public long skip(long n) throws IOException {
      if (n <= 0) {
        return 0;
      }
      if (mInputStream.available() >= n) {
        return mInputStream.skip(n);
      }
      closeStream();
      mPos += n;
      openStream();
      return n;
    }
  
    /**
     * Opens a new stream at mPos if the wrapped stream mInputStream is null.
     */
    private void openStream() throws IOException {
      ServiceException lastException = null;
      String errorMessage = String.format("Failed to open key: %s bucket: %s", mKey, mBucketName);
      while (mRetryPolicy.attempt()) {
        try {
          GSObject object;
          if (mPos > 0) {
            object = mClient.getObject(mBucketName, mKey, null, null, null, null, mPos, null);
          } else {
            object = mClient.getObject(mBucketName, mKey);
          }
          mInputStream = new BufferedInputStream(object.getDataInputStream());
          return;
        } catch (ServiceException e) {
          errorMessage = String
              .format("Failed to open key: %s bucket: %s attempts: %d error: %s", mKey, mBucketName,
                  mRetryPolicy.getAttemptCount(), e.getMessage());
          if (e.getResponseCode() != HttpStatus.SC_NOT_FOUND) {
            throw new IOException(errorMessage, e);
          }
          // Key does not exist
          lastException = e;
        }
      }
      // Failed after retrying key does not exist
      throw new IOException(errorMessage, lastException);
    }
  
    /**
     * Closes the current stream.
     */
    private void closeStream() throws IOException {
      if (mInputStream == null) {
        return;
      }
      mInputStream.close();
      mInputStream = null;
    }
  }
  