@Override
  public BlobDescriptor writeTo(OutputStream outputStream) throws IOException {
    try (InputStream fileIn = new BufferedInputStream(Files.newInputStream(file))) {
      return Digests.computeDigest(fileIn, outputStream);
    }
  }
A {@link Blob} that holds a {@link Path}.
jib-core/src/main/java/com/google/cloud/tools/jib/blob/FileBlob.java