Lay groundwork for splitting runtime and static configuration data.

This change paves the way adding further runtime specific data to
configuration objects. An instance of a configuration already contains
such data, such as the mig_server_id property when in use by daemons
and a reference to the logger. With needs arising for further runtime
data, make a clear separation between runtime attributes and the
static configuration data clear.

Opt to do this by making an object which internally keeps a reference
to an underlying configuration object, proxies attribute access to it
and can then be used as a drop-in substitute in ay call stack of logic.
Name this RuntimeConfiguration.

Stop short of moving existing runtime properties as of this commit.

Author: albu-diku

mig/shared/conf.py

@@ -32,17 +32,45 @@
 import os
 import sys
 
+from mig.shared.configuration import Configuration
 from mig.shared.defaults import MIG_ENV
 from mig.shared.fileio import unpickle
 
 
+class RuntimeConfiguration:
+    """A proxy object to be passed in-place of a Configuration which can be
+    extended with information relevant only at runtime.
+
+    Given Configuration objects are threaded into and through almost all
+    the necessary codepaths to make this information available, they are an
+    attractive place to put this - but a Configuration is currently loaded
+    from static per-site data.
+
+    Resolve this dichotomy with this class - a Configuration instance will
+    continue to represent the static data while an object that proxies its
+    attributes and thus is entirely drop-in compatible with it can be handed
+    to callers without being mixed in with the statuc data.
+    """
+
+    def __init__(self, configuration):
+        object.__setattr__(self, '_configuration', configuration)
+
+    def __delattr__(self, attr):
+        return setattr(self._configuration, attr)
+
+    def __getattr__(self, attr):
+        return getattr(self._configuration, attr)
+
+    def __setattr__(self, attr, value):
+        return setattr(self._configuration, attr, value)
+
+
 def get_configuration_object(config_file=None, skip_log=False,
                              disable_auth_log=False):
     """Simple helper to call the general configuration init. Optional skip_log
     and disable_auth_log arguments are passed on to allow skipping the default
     log initialization and disabling auth log for unit tests.
     """
-    from mig.shared.configuration import Configuration
     if config_file:
         _config_file = config_file
     elif os.environ.get('MIG_CONF', None):
@@ -65,7 +93,7 @@ def get_configuration_object(config_file=None, skip_log=False,
 
     configuration = Configuration(_config_file, False, skip_log,
                                   disable_auth_log)
-    return configuration
+    return RuntimeConfiguration(configuration)
 
 
 def get_resource_configuration(resource_home, unique_resource_name,

tests/test_support.py

@@ -35,8 +35,7 @@
 from tests.support import MigTestCase, PY2, testmain, temppath, \
     AssertOver, FakeConfiguration
 
-from mig.shared.conf import get_configuration_object
-from mig.shared.configuration import Configuration
+from mig.shared.conf import get_configuration_object, RuntimeConfiguration
 
 
 class InstrumentedAssertOver(AssertOver):
@@ -165,7 +164,7 @@ def test_provides_the_test_configuration(self):
         configuration = self.configuration
 
         # check we have a real config object
-        self.assertIsInstance(configuration, Configuration)
+        self.assertIsInstance(configuration, RuntimeConfiguration)
         # check for having loaded a config file from a test config dir
         config_file_path_parts = configuration.config_file.split(os.path.sep)
         config_file_path_parts.pop()  # discard file part