How to avoid StopIteration Error?

[meteoDaniel]

Dear all,
in the last time i often receive the following Error:

  File "/app/src/modules/decoder/grib_decoder.py", line 18, in __init__
    self._data = xarray_store.open_dataset(str(file_name))
  File "/usr/local/lib/python3.6/site-packages/cfgrib/xarray_store.py", line 47, in open_dataset
    store = cfgrib_.CfGribDataStore(path, **real_backend_kwargs)
  File "/usr/local/lib/python3.6/site-packages/cfgrib/cfgrib_.py", line 78, in __init__
    self.ds = cfgrib.open_file(filename, mode='r', **backend_kwargs)
  File "/usr/local/lib/python3.6/site-packages/cfgrib/dataset.py", line 452, in open_file
    return Dataset.from_path(path, **kwargs)
  File "/usr/local/lib/python3.6/site-packages/cfgrib/dataset.py", line 447, in from_path
    return cls(*build_dataset_components(stream, **flavour_kwargs))
  File "/usr/local/lib/python3.6/site-packages/cfgrib/dataset.py", line 395, in build_dataset_components
    index = stream.index(ALL_KEYS).subindex(filter_by_keys)
  File "/usr/local/lib/python3.6/site-packages/cfgrib/messages.py", line 211, in index
    return FileIndex.from_filestream(filestream=self, index_keys=index_keys)
  File "/usr/local/lib/python3.6/site-packages/cfgrib/messages.py", line 228, in from_filestream
    schema = make_message_schema(filestream.first(), index_keys)
  File "/usr/local/lib/python3.6/site-packages/cfgrib/messages.py", line 208, in first
    return next(iter(self))
StopIteration

Why cfgrib raise StopIteration Error? Whats wrong?

[alexamici]

@meteoDaniel I think you attempted to open a file with no valid GRIB message in it and I agree that the error is totally confusing. I'm considering it a bug and fixing it in master. Thanks for reporting!