Creation of redirect fail breaks use of jupyter notebook list

[ChrisHowlin]

Description

The introduction of a redirect file in 270c0f9 breaks usage of jupyter notebook list, as the logic for determining running notebook servers relies on iterating over all files in runtime-dir with prefix "nbserver-" and trying to load as JSON.

See:

notebook/notebook/notebookapp.py

Line 1842 in 51dae23

if file_name.startswith('nbserver-'):

Reproduction

1. jupyter notebook
2. jupyter notebook list

Error:

  File "<env>/python3.6/site-packages/notebook/notebookapp.py", line 1836, in list_running_servers
    info = json.load(f)
  File "<env>/lib/python3.6/json/__init__.py", line 299, in load
    parse_constant=parse_constant, object_pairs_hook=object_pairs_hook, **kw)
  File "<env>/lib/python3.6/json/__init__.py", line 354, in loads
    return _default_decoder.decode(s)
  File "<env>/lib/python3.6/json/decoder.py", line 339, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
  File "<env>/lib/python3.6/json/decoder.py", line 357, in raw_decode
    raise JSONDecodeError("Expecting value", s, err.value) from None
json.decoder.JSONDecodeError: Expecting value: line 2 column 1 (char 1)

Change

The use of the redirect file (format nbserver-%s-open.html) breaks this assumption and causes a JSON parsing error (trying to parse an HTML file as JSON).

How to fix

Two possibilities for resolving:

1. Use different prefix for redirect file
2. Update notebook list behaviour to filter for files matching format nbserver-\d+.json

[ChrisHowlin]

Tagging @takluyver as original committer of 270c0f9

[ChrisHowlin]

Introduced in 5.7.3

[takluyver]

Gah, sorry. I didn't think to check that, and our test suite wasn't sufficient to pick it up. #4284 should fix it, and add the missing test. Can you give that a try and check that there aren't any other problems affecting your use cases? Hopefully I can do a 5.7.4 soon.

[ChrisHowlin]

No worries, I was able to revert to 5.7.2 which works fine. I'll test against the fix now and confirm it works OK.

[ChrisHowlin]

Looks good to me. I've checked out the fix and jupyter notebook list works as expected.

[takluyver]

Thanks! I'm going to bed soon, so 5.7.4 will probably be tomorrow.