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.google.cloud.storage.*;
  import com.google.protobuf.InvalidProtocolBufferException;
  import feast.proto.core.RegistryProto;
  import java.util.Optional;
  
  public class GSRegistryFile implements RegistryFile {
    private Blob blob;
  
    public GSRegistryFile(Storage storage, String url) {
      blob = storage.get(BlobId.fromGsUtilUri(url));
      if (blob == null) {
        throw new RuntimeException(String.format("Registry file %s was not found", url));
      }
    }
  
    public RegistryProto.Registry getContent() {
      try {
        return RegistryProto.Registry.parseFrom(blob.getContent());
      } catch (InvalidProtocolBufferException e) {
        throw new RuntimeException(
            String.format(
                "Couldn't read remote registry: %s. Error: %s",
                blob.getBlobId().toGsUtilUri(), e.getMessage()));
      }
    }
  
    public Optional<RegistryProto.Registry> getContentIfModified() {
      try {
        this.blob = blob.reload(Blob.BlobSourceOption.generationNotMatch());
      } catch (StorageException e) {
        if (e.getCode() == 304) {
          // Content not modified
          return Optional.empty();
        } else {
          throw new RuntimeException(
              String.format(
                  "Couldn't read remote registry: %s. Error: %s",
                  blob.getBlobId().toGsUtilUri(), e.getMessage()));
        }
      }
  
      return Optional.of(this.getContent());
    }
  }
  