code: /*
   * SPDX-License-Identifier: Apache-2.0
   * Copyright 2018-2021 The Feast Authors
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *     https://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  package feast.serving.registry;
  
  import com.amazonaws.AmazonServiceException;
  import com.amazonaws.services.s3.AmazonS3;
  import com.amazonaws.services.s3.model.GetObjectRequest;
  import com.amazonaws.services.s3.model.S3Object;
  import com.amazonaws.services.s3.model.S3ObjectInputStream;
  import feast.proto.core.RegistryProto;
  import java.io.IOException;
  import java.util.Optional;
  
  public class S3RegistryFile implements RegistryFile {
    private final AmazonS3 s3Client;
    private S3Object s3Object;
  
    public S3RegistryFile(AmazonS3 s3Client, String url) {
      this.s3Client = s3Client;
  
      String[] split = url.replace("s3://", "").split("/");
      String objectPath = String.join("/", java.util.Arrays.copyOfRange(split, 1, split.length));
      this.s3Object = this.s3Client.getObject(split[0], objectPath);
    }
  
    @Override
    public RegistryProto.Registry getContent() {
      S3ObjectInputStream is = this.s3Object.getObjectContent();
  
      try {
        return RegistryProto.Registry.parseFrom(is);
      } catch (IOException e) {
        throw new RuntimeException(
            String.format(
                "Couldn't read remote registry file: %s. Error: %s",
                String.format("s3://%s/%s", this.s3Object.getBucketName(), this.s3Object.getKey()),
                e.getMessage()));
      } finally {
        try {
          is.close();
        } catch (IOException e) {
          e.printStackTrace();
        }
      }
    }
  
    @Override
    public Optional<RegistryProto.Registry> getContentIfModified() {
      GetObjectRequest request =
          new GetObjectRequest(this.s3Object.getBucketName(), this.s3Object.getKey())
              .withNonmatchingETagConstraint(this.s3Object.getObjectMetadata().getETag());
  
      S3Object updatedS3Object;
      try {
        updatedS3Object = this.s3Client.getObject(request);
      } catch (AmazonServiceException e) {
        e.printStackTrace();
        return Optional.empty();
      }
  
      if (updatedS3Object == null) {
        return Optional.empty();
      }
  
      this.s3Object = updatedS3Object;
      return Optional.of(this.getContent());
    }
  }
  