Revert "Remove soon-to-be-deprecated usage of AsdfFile.open"

[jdavies-st]

Reverts #2814

[jdavies-st]

So while #2814 passed our regression tests, it turns out that if you try to read a file that is read-only:

In [2]: a = asdf.open('/grp/crds/cache/references/jwst/jwst_nircam_specwcs_0010.asdf')                                                                          
---------------------------------------------------------------------------
PermissionError                           Traceback (most recent call last)
<ipython-input-2-753b8171a465> in <module>
----> 1 a = asdf.open('/grp/crds/cache/references/jwst/jwst_nircam_specwcs_0010.asdf')

~/miniconda3/envs/jwst_dev/lib/python3.7/site-packages/asdf/asdf.py in open_asdf(fd, uri, mode, validate_checksums, extensions, do_not_fill_defaults, ignore_version_mismatch, ignore_unrecognized_tag, _force_raw_types, copy_arrays, lazy_load, custom_schema, strict_extension_check, ignore_missing_extensions, _compat)
   1357         _force_raw_types=_force_raw_types,
   1358         strict_extension_check=strict_extension_check,
-> 1359         ignore_missing_extensions=ignore_missing_extensions)
   1360 
   1361 

~/miniconda3/envs/jwst_dev/lib/python3.7/site-packages/asdf/asdf.py in _open_impl(cls, self, fd, uri, mode, validate_checksums, do_not_fill_defaults, _get_yaml_content, _force_raw_types, strict_extension_check, ignore_missing_extensions)
    711                 _force_raw_types=_force_raw_types,
    712                 strict_extension_check=strict_extension_check,
--> 713                 ignore_missing_extensions=ignore_missing_extensions)
    714 
    715     @classmethod

~/miniconda3/envs/jwst_dev/lib/python3.7/site-packages/asdf/asdf.py in _open_asdf(cls, self, fd, uri, mode, validate_checksums, do_not_fill_defaults, _get_yaml_content, _force_raw_types, strict_extension_check, ignore_missing_extensions)
    608         self._mode = mode
    609 
--> 610         fd = generic_io.get_file(fd, mode=self._mode, uri=uri)
    611         self._fd = fd
    612         # The filename is currently only used for tracing warning information

~/miniconda3/envs/jwst_dev/lib/python3.7/site-packages/asdf/generic_io.py in get_file(init, mode, uri, close)
   1188                 fd = atomicfile.atomic_open(realpath, realmode)
   1189             else:
-> 1190                 fd = open(realpath, realmode)
   1191             fd = fd.__enter__()
   1192             return RealFile(fd, mode, close=True, uri=uri)

PermissionError: [Errno 13] Permission denied: '/grp/crds/cache/references/jwst/jwst_nircam_specwcs_0010.asdf'

You get an error. You have to specify when opening that it is to be read in read-only mode now:

In [3]: a = asdf.open('/grp/crds/cache/references/jwst/jwst_nircam_specwcs_0010.asdf', mode='r')                                                                

[jdavies-st]

What I expect this means is that we have to expose the mode='r' or mode='rw' ASDF API in datamodels. We should probably revert this PR for now, and discuss the best way forward next week.

[jdavies-st]

Of course the other option is to ask asdf to not default to mode='rw', but I don't know what is involved there. Anyway, let's get this reverted and sort it out next week.