{
    "schemaVersion": "Version of current schema", 
    "checkpointId": "Checkpoint ID", 
    "createdTimeMs": "Created time in epoch milliseconds", 
    "jobName": "Job name", 
    "jobInstance": "Instance ID of the job", 
    "taskName": "Name of the task", 
    "storeName": "Store name", 
    "dirIndex": {
        "filesPresent": [
            {
                "fileName": "Name of the file uploaded to Ambry", 
                "blobs": [
                    {
                        "blobID": "Blob ID", 
                        "offset": "File chunk offset [optional]"
                    }
                ], 
                "mtime": "Last updated time in epoch milliseconds", 
                "ctime": "Created time in epoch milliseconds",
                "sizeInBytes": "Size of the file", 
                "crc": "crc32 checksum of the file", 
                "attribs": "permission attributes of the file"
            }
        ],
        "filesRemoved": [
            {
                "fileName": "Name of the file to delete from Ambry", 
                "blobs": [
                    {
                        "blobID": "Blob ID", 
                        "offset": "File chunk offset [optional]"
                    }
                ]
            }
        ],
        "subDirectoriesPresent": [
            {
                "dirIndex": {
                     ……
                 }
            }
        ],
        "subDirectoriesRemoved": [
            {
                "dirIndex": {
                     ……
                 }
            }
        ]
    }, 
  "prevSnapshotIndexBlobId": “Blob ID of previous snapshot index”
}

/**
 * Provides interface for common blob store operations: GET, PUT and DELETE
 */
@InterfaceStability.Unstable
public interface BlobStoreManager {
  /**
   * Initialize underlying blob store client, if necessary.
   *
   */
  void init();

  /**
   * Non-blocking PUT call to remote blob store with supplied metadata
   * @param inputStream InputStream to read the file
   * @param metadata user supplied {@link Metadata} of the request
   * @return a future containing the blob ID of the uploaded blob if the upload is successful.
   */
  CompletionStage<String> put(InputStream inputStream, Metadata metadata);

  /**
   * Non-blocking GET call to remote blob store
   * @param id Blob ID of the blob to get
   * @param outputStream OutputStream to write the downloaded blob
   * @param metadata User supplied {@link Metadata} of the request
   * @return A future that completes when all the chunks are downloaded and written successfully to the OutputStream
   * @throws org.apache.samza.storage.blobstore.exceptions.DeletedException returned future should complete
   *         exceptionally with DeletedException on failure with the blob already deleted error.
   */
  CompletionStage<Void> get(String id, OutputStream outputStream, Metadata metadata);

  /**
   * Non-blocking call to mark a blob for deletion in the remote blob store
   * @param id Blob ID of the blob to delete
   * @param metadata User supplied {@link Metadata} of the request
   * @return A future that completes when the blob is successfully deleted from the blob store.
   * @throws org.apache.samza.storage.blobstore.exceptions.DeletedException returned future should complete
   *         exceptionally with DeletedException on failure with the blob already deleted error. This exception is
   *         caught and ignored by the caller of the delete method during initial cleanup and SnapshotIndex read.
   */
  CompletionStage<Void> delete(String id, Metadata metadata);

  /**
   * Non-blocking call to remove the Time-To-Live (TTL) for a blob and make it permanent.
   * @param blobId Blob ID of blob to remove TTL for.
   * @param metadata User supplied {@link Metadata} of the request
   * @return a future that completes when the TTL for the blob is removed.
   * @throws org.apache.samza.storage.blobstore.exceptions.DeletedException returned future should complete
   *         exceptionally with DeletedException on failure with the blob already deleted error.
   */
  CompletionStage<Void> removeTTL(String blobId, Metadata metadata);

  /**
   * Cleanly close resources like blob store client
   */
  void close();
}