static boolean isLayerFile(Path file) {
    return file.getFileName().toString().length() == DescriptorDigest.HASH_LENGTH;
  }
Returns whether or not {@code file} is a layer contents file.

@param file the file to check
@return {@code true} if {@code file} is a layer contents file; {@code false} otherwise
jib-core/src/main/java/com/google/cloud/tools/jib/cache/CacheStorageFiles.java