Tar file breaks dataset viewer

[donkirkby]

A container generated a tar file of png files, and then the server displayed an error page when we went to view the dataset.

Traceback:

File "/opt/venv_kive/lib/python3.6/site-packages/django/core/handlers/exception.py" in inner
  34.             response = get_response(request)

File "/opt/venv_kive/lib/python3.6/site-packages/django/core/handlers/base.py" in _get_response
  115.                 response = self.process_exception_by_middleware(e, request)

File "/opt/venv_kive/lib/python3.6/site-packages/django/core/handlers/base.py" in _get_response
  113.                 response = wrapped_callback(request, *callback_args, **callback_kwargs)

File "/opt/venv_kive/lib/python3.6/site-packages/django/contrib/auth/decorators.py" in _wrapped_view
  21.                 return view_func(request, *args, **kwargs)

File "/usr/local/share/Kive/kive/librarian/views.py" in dataset_view
  144.                 sample_content = data_handle.read(1000)

File "/usr/lib64/python3.6/encodings/ascii.py" in decode
  26.         return codecs.ascii_decode(input, self.errors)[0]

Exception Type: UnicodeDecodeError at /dataset_view/1820806
Exception Value: 'ascii' codec can't decode byte 0x89 in position 1536: ordinal not in range(128)

I think we use a utility that tries to identify binary files, maybe it doesn't work with tar files. We should be able to catch the exception and then treat the file as binary.

[donkirkby]

I'm seeing the same error with PDF files. Workaround: download them through the API.