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Helpers for interacting with the Snap system within a Snap

Project description

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A Python library to interact with snap configuration and properties from inside a snap.

It exposes a top-level snaphelpers.Snap object which provides access to:

  • snap details:

    >>> snap = snaphelpers.Snap()
    >>> snap.name
    'testapp'
    >>> snap.instance_name
    'testapp'
    >>> snap.version
    '0+git.fdf80cd'
    >>> snap.revision
    'x1'
    
  • paths:

    >>> snap.paths.common
    PosixPath('/var/snap/testapp/common')
    >>> snap.paths.data
    PosixPath('/var/snap/testapp/x1')
    >>> snap.paths.snap
    PosixPath('/snap/testapp/x1')
    >>> snap.paths.user_common
    PosixPath('/home/ack/snap/testapp/common')
    >>> snap.paths.user_data
    PosixPath('/home/ack/snap/testapp/x1')
    
  • snap-related environment variables:

    >>> pprint.pprint(dict(snap.environ))
    {'ARCH': 'amd64',
     'COMMON': '/var/snap/testapp/common',
     'CONTEXT': 'ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890',
     'COOKIE': 'ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890',
     'DATA': '/var/snap/testapp/x1',
     'INSTANCE_KEY': '',
     'INSTANCE_NAME': 'testapp',
     'LIBRARY_PATH': '/var/lib/snapd/lib/gl:/var/lib/snapd/lib/gl32:/var/lib/snapd/void',
     'NAME': 'testapp',
     'REEXEC': '',
     'REVISION': 'x1',
     'SNAP': '/snap/testapp/x1',
     'USER_COMMON': '/home/ack/snap/testapp/common',
     'USER_DATA': '/home/ack/snap/testapp/x1',
     'VERSION': '0+git.fdf80cd'}
    >>> snap.environ.ARCH
    'amd64'
    
  • configuration options:

    >>> snap.config.set({'foo.bar': 'baz', 'asdf': 3})  # this needs to be run as root
    >>> options = snap.config.get_options('foo', 'asdf')
    >>> options['foo']
    {'bar': 'baz'}
    >>> options['foo.bar']
    'baz'
    >>> options['asdf']
    3
    >>> options.as_dict()
    {'asdf': 3, 'foo': {'bar': 'baz'}}
    
  • setting snap health status, along with message and optional status code:

    >>> snap.health.okay()
    >>> snap.health.waiting('foo must happen first', code='wait-foo')
    

    Health status (when different from okay) is visible from the snap CLI:

    $ snap info snap-helpers
    name:    snap-helpers
    summary: Test snap for snap-helpers
    health:
      status:  waiting
      message: foo must happen first
      code:    wait-foo
      checked: today at 16:23 CEST
    

Hook helpers

The library provides helpers to reduce boilerplate when setting up hooks for the snap.

Hooks can be defined by simply registering functions to be called as hooks via entry_points in the application setup.py:

setup(
    # ...
    entry_points={
        'snaphelpers.hooks': [
            'configure = testapp:configure_hook',
            'install = testapp:install_hook'
        ]
    }
)

Hook functions are called with a Snap object as argument:

def install_hook(snap: snaphelpers.Snap):
    # ...


def configure_hook(snap: snaphelpers.Snap):
    # ...

snap-helpers will take care of the hooks plumbing (i.e. creating hook files in $SNAP/snap/hooks).

Testing with the snap

The snap-helpers snap provides a way to easily test code using the library in a real snap environment with strict confinement.

It provides the python and ipython commands:

$ snap-helpers.python -c 'from pprint import pprint; import snaphelpers; pprint(dict(snaphelpers.SnapEnviron()))'
{'ARCH': 'amd64',
 'COMMON': '/var/snap/snap-helpers/common',
 'CONTEXT': 'ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890',
 'COOKIE': 'ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890',
 'DATA': '/var/snap/snap-helpers/x1',
 'INSTANCE_KEY': '',
 'INSTANCE_NAME': 'snap-helpers',
 'LIBRARY_PATH': '/var/lib/snapd/lib/gl:/var/lib/snapd/lib/gl32:/var/lib/snapd/void',
 'NAME': 'snap-helpers',
 'REEXEC': '',
 'REVISION': 'x1',
 'SNAP': '/snap/snap-helpers/x1',
 'USER_COMMON': '/home/ack/snap/snap-helpers/common',
 'USER_DATA': '/home/ack/snap/snap-helpers/x1',
 'VERSION': '0+git.26e1e9d'}

The snap can be built and installed as follows:

$ snapcraft
$ sudo snap install --dangerous snap-helpers_*.snap

Installation

snap-helpers can be installed from PyPI.

Run:

$ pip install snap-helpers

Documentation

Full documentation is available on ReadTheDocs.

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