Snapcraft has a lot of official plugins included by default (with more being added all the time). However, sometimes one wants to write and use one’s own instead, whether that’s because:
- The official Snapcraft plugins don’t do quite the right thing (in which case one should log a bug)
- The build system being used isn’t supported by Snapcraft (in which case one should consider submitting one’s plugin upstream once complete)
- One wants to use custom Debian repositories for
stage-packages
Regardless of the reason, the purpose of this document is to provide a simple tutorial for doing it, from scratch.
This feature has been deprecated. Local plugins do not work with Snapcraft 7, although earlier versions of Snapcraft can still be used.
Step 1: Create new project
Get into an empty directory that we’ll use for this project:
$ mkdir -p ~/src/snaps/local-plugins
$ cd ~/src/snaps/local-plugins
Now create a new snapcraft.yaml:
$ snapcraft init
Created snap/snapcraft.yaml.
Edit the file to your liking or run `snapcraft` to get started
Step 2: Create new plugin
Snapcraft plugins are written in Python, so we need to create a new Python module to hold our new plugin. These are placed in the snap/plugins/ directory. Let’s call our plugin “my-plugin”, although the module we create must use an underscore instead of the hyphen:
$ cd ~/src/snaps/local-plugins
$ mkdir snap/plugins
$ touch snap/plugins/my_plugin.py
Step 3: Write plugin
Each plugin must adhere to the Plugin API. We won’t discuss it in depth here, but here’s our example:
import snapcraft
class MyPlugin(snapcraft.BasePlugin):
@classmethod
def schema(cls):
schema = super().schema()
# Add a new property called "my-property"
schema['properties']['my-property'] = {
'type': 'string',
}
# The "my-option" property is now required
schema['required'].append('my-property')
return schema
def pull(self):
super().pull()
print('Pull done. Here is "my-property": {}'.format(
self.options.my_property))
def build(self):
super().build()
print('Build done.')
Step 4: Use plugin in snapcraft.yaml
Now we can use our local plugin just like any other Snapcraft plugin:
name: my-snap-name # you probably want to 'snapcraft register <name>'
version: '0.1' # just for humans, typically '1.2+git' or '1.3.2'
summary: Single-line elevator pitch for your amazing snap # 79 char long summary
description: |
This is my-snap's description. You have a paragraph or two to tell the
most important story about your snap. Keep it under 100 words though,
we live in tweetspace and your description wants to look good in the snap
store.
grade: devel # must be 'stable' to release into candidate/stable channels
confinement: devmode # use 'strict' once you have the right plugs and slots
parts:
my-part:
plugin: my-plugin
my-property: test value
Step 5: Build snap
Now we can build our snap just like normal:
$ snapcraft
Searching for local plugin for my-plugin
Preparing to pull my-part
Pulling my-part
Look ma, I pulled! Here is "my-property": test value
Preparing to build my-part
Building my-part
Look ma, I built!
Staging my-part
Priming my-part
Snapping 'my-snap-name' |
Snapped my-snap-name_0.1_amd64.snap
Conclusion
Now you should understand the basics of writing a local plugin that you can keep alongside your snapcraft.yaml. You should try deleting the my-property specification in the snapcraft.yaml, and you’ll see that you’ll get an error, because we specified that it was required in the plugin.