Creating New Actions

Glazier’s Actions are the core of the system’s configuration language. Glazier ships with some existing actions, but for more custom functionality, you can also create your own.

Actions are defined under glazier/lib/actions.

BaseAction

All actions extend from the BaseAction class, which provides some core underlying functionality common to all actions. BaseAction is defined in base.py.

All actions receive two parameters, as defined by BaseAction: args and build_info.

• args is the data received from the configuration file. It can be any data type supported by YAML.

  • An example of the Get action with its args, as written in a config:

    Get:
        - ['windows10.wim', 'c:\base.wim', '4b5b6bf0e59dadb4663ad9b4110bf0794ba24c344291f30d47467d177feb4776']
    

• build_info is the internal state of the installer. This is automatically passed by the config handler while the configs are being parsed.

Action Definition

Under glazier/lib/actions there are several libraries. You can extend one of the existing libraries or create a new one. The layout is strictly organizational.

In this example, we’ll create the action FancyAction to be used in our imaging configs.

Import BaseAction and create a new Python class decended from it. The name of the class will be the name of the command we use in new configs.

from glazier.lib.actions.base import ActionError
from glazier.lib.actions.base import BaseAction

class FancyAction(BaseAction):
  """Do awesome things."""

  def Run(self):
    my_arg = self._args[0]
    try:
      DoFancyStuff(my_arg)
    except NotFancyEnough:
      raise ActionError("Problem running FancyAction with %s" % my_arg)

The class must declare at least one function, called Run. Run is called whenever Autobuild intends to execute the action. You can add any additional supporting functions you like to the class, as long as Run exists as the entrypoint. In this case, we pass the args to the DoFancyStuff function (not shown), for some additional processing.

Note that your class will have access to the config arguments via the self._args variable. This will be automatically populated, and you can reference it anywhere within the class that you need.

ActionError should be thrown any time your class encounters an error and cannot complete cleanly. This signals Autobuild that the action has failed, and it should abort the installation until things are fixed.

Once your action class has been defined, open glazier/lib/actions/__init__.py. Add a new line declaring the name of your class to export it to the config handler.

FancyAction = fancy.FancyAction

That’s it! You can now use FancyAction in your Glazier configs.

Validation

BaseAction classes include a second reserved function, Validate. Defining this function in your classes is optional, but recommended.

When Validate is called on an action, the self._args variable is interrogated for correctness. For example, the action Get expects to receive a list with a fixed number of parameters. If Get is passed something other than a list, we know a mistake has been made and the config is broken.

An example validator for Get:

def Validate(self):
  self._TypeValidator(self._args, list)
  for arg in self._args:
    self._ListOfStringsValidator(arg, 2, 3)

The Validate function should raise ValidationError if it finds a problem with self._args.

Config Testing

We can use the Validate function to implement presubmit or continuous build testing of our configs.

In this example, we’ll assume we have a Python script which will load each config file using the yaml module.

Once we have the config YAML, testing validity of the entire config is as simple as looping through each element, verifying that a corresponding Action exists, and calling its Validate function.

from glazier.lib import actions

...
# config = loaded config file content
...

for c in config:
  if c in dir(actions):
    act_obj = getattr(actions, str(c))
    a = act_obj(args=config[c], build_info=None)
    try:
      a.Validate()
    except actions.ValidationError as e:
      self.fail(e)  # broken config