baseimage-tutorial-framework/tfw/fsm/yaml_fsm.py

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from subprocess import Popen, run
from functools import partial, singledispatch
from contextlib import suppress
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import yaml
import jinja2
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from transitions import State
from .fsm_base import FSMBase
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class YamlFSM(FSMBase):
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"""
This is a state machine capable of building itself from a YAML config file.
"""
def __init__(self, config_file, jinja2_variables=None):
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"""
:param config_file: path of the YAML file
:param jinja2_variables: dict containing jinja2 variables
or str with filename of YAML file to
parse and use as dict.
jinja2 support is disabled if this is None
"""
self.config = ConfigParser(config_file, jinja2_variables).config
self.setup_states()
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super().__init__() # FSMBase.__init__() requires states
self.setup_transitions()
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def setup_states(self):
self.for_config_states_and_transitions_do(self.wrap_callbacks_with_subprocess_call)
self.states = [State(**state) for state in self.config['states']]
def setup_transitions(self):
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self.for_config_states_and_transitions_do(self.subscribe_and_remove_predicates)
for transition in self.config['transitions']:
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self.add_transition(**transition)
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def for_config_states_and_transitions_do(self, what):
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for array in ('states', 'transitions'):
for json_obj in self.config[array]:
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what(json_obj)
@staticmethod
def wrap_callbacks_with_subprocess_call(json_obj):
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topatch = ('on_enter', 'on_exit', 'prepare', 'before', 'after')
for key in json_obj:
if key in topatch:
json_obj[key] = partial(run_command_async, json_obj[key])
def subscribe_and_remove_predicates(self, json_obj):
if 'predicates' in json_obj:
for predicate in json_obj['predicates']:
self.subscribe_predicate(
json_obj['trigger'],
partial(
command_statuscode_is_zero,
predicate
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)
)
with suppress(KeyError):
json_obj.pop('predicates')
def run_command_async(command, _):
Popen(command, shell=True)
def command_statuscode_is_zero(command):
return run(command, shell=True).returncode == 0
class ConfigParser:
def __init__(self, config_file, jinja2_variables):
self.read_variables = singledispatch(self._read_variables)
self.read_variables.register(dict, self._read_variables_dict)
self.read_variables.register(str, self._read_variables_str)
self.config = self.parse_config(config_file, jinja2_variables)
def parse_config(self, config_file, jinja2_variables):
config_string = self.read_file(config_file)
if jinja2_variables is not None:
variables = self.read_variables(jinja2_variables)
template = jinja2.Environment(loader=jinja2.BaseLoader).from_string(config_string)
config_string = template.render(**variables)
return yaml.safe_load(config_string)
@staticmethod
def read_file(filename):
with open(filename, 'r') as ifile:
return ifile.read()
@staticmethod
def _read_variables(variables):
raise TypeError(f'Invalid variables type {type(variables)}')
@staticmethod
def _read_variables_str(variables):
with open(variables, 'r') as ifile:
return yaml.safe_load(ifile)
@staticmethod
def _read_variables_dict(variables):
return variables