Extract the config provider into its own sub-module

util/config/provider/baseprovider.py

@@ -0,0 +1,77 @@
+import yaml
+import logging
+
+logger = logging.getLogger(__name__)
+
+class CannotWriteConfigException(Exception):
+  """ Exception raised when the config cannot be written. """
+  pass
+
+def import_yaml(config_obj, config_file):
+  with open(config_file) as f:
+    c = yaml.safe_load(f)
+    if not c:
+      logger.debug('Empty YAML config file')
+      return
+
+    if isinstance(c, str):
+      raise Exception('Invalid YAML config file: ' + str(c))
+
+    for key in c.iterkeys():
+      if key.isupper():
+        config_obj[key] = c[key]
+
+  return config_obj
+
+
+def export_yaml(config_obj, config_file):
+  try:
+    with open(config_file, 'w') as f:
+      f.write(yaml.safe_dump(config_obj, encoding='utf-8', allow_unicode=True))
+  except IOError as ioe:
+    raise CannotWriteConfigException(str(ioe))
+
+
+class BaseProvider(object):
+  """ A configuration provider helps to load, save, and handle config override in the application.
+  """
+
+  def update_app_config(self, app_config):
+    """ Updates the given application config object with the loaded override config. """
+    raise NotImplementedError
+
+  def get_yaml(self):
+    """ Returns the contents of the YAML config override file, or None if none. """
+    raise NotImplementedError
+
+  def save_yaml(self, config_object):
+    """ Updates the contents of the YAML config override file to those given. """
+    raise NotImplementedError
+
+  def yaml_exists(self):
+    """ Returns true if a YAML config override file exists in the config volume. """
+    raise NotImplementedError
+
+  def volume_exists(self):
+    """ Returns whether the config override volume exists. """
+    raise NotImplementedError
+
+  def volume_file_exists(self, filename):
+    """ Returns whether the file with the given name exists under the config override volume. """
+    raise NotImplementedError
+
+  def get_volume_file(self, filename, mode='r'):
+    """ Returns a Python file referring to the given name under the config override volumne. """
+    raise NotImplementedError
+
+  def save_volume_file(self, filename, flask_file):
+    """ Saves the given flask file to the config override volume, with the given
+        filename.
+    """
+    raise NotImplementedError
+
+  def requires_restart(self, app_config):
+    """ If true, the configuration loaded into memory for the app does not match that on disk,
+        indicating that this container requires a restart.
+    """
+    raise NotImplementedError