[Bug 1864204] Re: nondeterministic failure when no keyring backends are available

[Dan Streetman]

** Also affects: python-launchpadlib (Ubuntu)
   Importance: Undecided
       Status: New

** Changed in: python-launchpadlib (Ubuntu Eoan)
   Importance: Undecided => Medium

** Changed in: python-launchpadlib (Ubuntu Focal)
   Importance: Undecided => Medium

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Title:
  nondeterministic failure when no keyring backends are available

Status in Python Keyring:
  New
Status in python-keyring package in Ubuntu:
  New
Status in python-launchpadlib package in Ubuntu:
  New
Status in python-keyring source package in Eoan:
  New
Status in python-launchpadlib source package in Eoan:
  New
Status in python-keyring source package in Focal:
  New
Status in python-launchpadlib source package in Focal:
  New

Bug description:
  [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 affects Eoan and later, including upstream.

  This does not affect Bionic or earlier, as they do not have the commit
  that introduces the bug.

  this was introduced upstream by commit
  0114733e91f249246c8fec9e659cd7ba2388ea0d which was first included in
  version 16.1.0.

  [other info]

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

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