Comment 0 for bug 1864204

[impact]

when no backends are available for python-keyring, it will sometimes silently ignore all requests to set or get credentials, and sometimes it will raise RuntimeError for all requests.

[test case]

when there are no backends, there are 2 built-in backends that will be the only ones available, the 'chainer' backend and the 'fail' backend. The 'fail' backend always has priority 0, while the 'chainer' backend has priority 10 if it contains any actual backends, and priority 0 if it is empty. So in the situtation where there are no actual backends, both 'chainer' and 'fail' will have priority 0. Since the 'backends' class stores its backend implementation instances in a python set(), which is unordered, it is non-deterministic which of those backends are used at any given time.

Since the behavior is non-deterministic, simply trying this multiple times may result in each behavior. Rebooting or logout/login can help 'switch' the behavior.

>>> import keyring
>>> [keyring.backend.get_all_keyring()]

the above python code will show the current list of backends, and since they both have the same priority (in this situation) the first in the list will be used. If the list looks like:

[[<keyring.backends.chainer.ChainerBackend object at 0x7f1f7018f3d0>, <keyring.backends.fail.Keyring object at 0x7f1f6fff0820>]]

with 'ChainerBackend' first, all keyring functions will return silently with None, e.g.:

>>> keyring.set_password('test', 'test', 'test')
>>> keyring.get_password('test', 'test')
>>>

with 'fail.Keyring' first, all keyring functions will raise RuntimeError:

>>> import keyring
>>> [keyring.backend.get_all_keyring()]
[[<keyring.backends.fail.Keyring object at 0x7f3b6ade73d0>, <keyring.backends.chainer.ChainerBackend object at 0x7f3b6ac48820>]]
>>> keyring.set_password('test', 'test', 'test')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3/dist-packages/keyring/core.py", line 63, in set_password
    _keyring_backend.set_password(service_name, username, password)
  File "/usr/lib/python3/dist-packages/keyring/backends/fail.py", line 24, in get_password
    raise RuntimeError(msg)
RuntimeError: No recommended backend was available. Install a recommended 3rd party backend package; or, install the keyrings.alt package if you want to use the non-recommended backends. See https://pypi.org/project/keyring for details.
>>> keyring.get_password('test', 'test')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3/dist-packages/keyring/core.py", line 57, in get_password
    return _keyring_backend.get_password(service_name, username)
  File "/usr/lib/python3/dist-packages/keyring/backends/fail.py", line 24, in get_password
    raise RuntimeError(msg)
RuntimeError: No recommended backend was available. Install a recommended 3rd party backend package; or, install the keyrings.alt package if you want to use the non-recommended backends. See https://pypi.org/project/keyring for details.

[regression potential]

TBD as this is still an upstream bug

[scope]

this still affects upstream, as well as all Debian and Ubuntu releases

[other info]

this affects any application that uses the python-launchpadlib library, as that internally uses keyrings.