server.conf is lazily loaded

pulp.server.config would load /etc/pulp/server.conf unconditionally at
import time. Converting this to lazily loading the config file allows
for the config object to be instantiated without immediately trying
to read the conf. This also allows changing the config files before
loading them, which makes pulp.server.config testable.

fixes #607

devel/pulp/devel/unit/server/base.py

@@ -49,14 +49,53 @@ def _load_test_config():
 
     config.config.set('database', 'name', 'pulp_unittest')
     config.config.set('server', 'storage_dir', '/tmp/pulp')
+    override_config_attrs()
+
+    start_logging()
+
+
+def override_config_attrs():
+    # Remove server.conf from the autoloaded config files
+    # does not get restored by restore_config_attrs; server.conf shouldn't ever be used in testing
+    block_load_conf()
+
+    if not hasattr(config, '_overridden_attrs'):
+        # only save these once so we don't end up saving _enforce_config as the "original" values
+        setattr(config, '_overridden_attrs', {
+            '__setattr__': config.__setattr__,
+            'load_configuration': config.load_configuration,
+            'config.set': config.config.set,
+        })
 
     # Prevent the tests from altering the config so that nobody accidentally makes global changes
-    config.config.set = _enforce_config
-    config.load_configuration = _enforce_config
     config.__setattr__ = _enforce_config
-    config.config.__setattr__ = _enforce_config
+    config.load_configuration = _enforce_config
+    config.config.set = _enforce_config
 
-    start_logging()
+
+def restore_config_attrs():
+    # Restore values overridden by _override_config_attrs
+    if not hasattr(config, '_overridden_attrs'):
+        return
+
+    for attr in '__setattr__', 'load_configuration':
+        setattr(config, attr, config._overridden_attrs[attr])
+    setattr(config.config, attr, config._overridden_attrs['config.set'])
+
+    del(config._overridden_attrs)
+
+
+def block_load_conf():
+    # Remove server.conf from the list of autoloaded config files
+    # This is needed when testing modules that create objects using conf data found in the
+    # server config, such as DB connections, celery, etc. This should be used as little as
+    # possible and as early as possible, before config file loads happen
+    conf = '/etc/pulp/server.conf'
+    try:
+        config.remove_config_file(conf)
+    except RuntimeError:
+        # server.conf already removed, move along...
+        pass
 
 
 class PulpWebservicesTests(unittest.TestCase):

devel/test/unit/server/test_base.py

@@ -61,7 +61,6 @@ def test_load_test_config(self, start_logging, stop_logging, config_set):
         self.assertTrue(config.config.set is base._enforce_config)
         self.assertTrue(config.load_configuration is base._enforce_config)
         self.assertTrue(config.__setattr__ is base._enforce_config)
-        self.assertTrue(config.config.__setattr__ is base._enforce_config)
 
 
 class StartDatabaseConnectionTestCase(unittest.TestCase):

nodes/test/nodes_tests/__init__.py

@@ -1,4 +1,7 @@
 from pulp.devel.unit.server import base as devel_base
+from pulp.devel.unit.server.base import block_load_conf
+
+block_load_conf()
 
 
 def setup():

server/pulp/server/config.py

@@ -3,7 +3,45 @@
 from ConfigParser import SafeConfigParser
 
 
-config = None  # ConfigParser.SafeConfigParser instance
+class LazyConfigParser(SafeConfigParser):
+    def __init__(self, *args, **kwargs):
+        self.reload()
+        SafeConfigParser.__init__(self, *args, **kwargs)
+
+        # The superclass _sections attr takes precedence over the property of
+        # the same name defined below. Deleting it exposes that property to hook
+        # the config loading mechanism into an attribute used by just about every
+        # ConfigParser method.
+        self._lazy_sections = self._sections
+        del self._sections
+
+    def reload(self):
+        self._loaded = False
+
+    @property
+    def _sections(self):
+        self._load_config()
+        return self._lazy_sections
+
+    def _load_config(self):
+        # calls to self.get/self.set access _sections, which triggers _load_config,
+        # so to avoid infinite recursion _loaded is set before calling those methods
+        if self._loaded:
+            return
+        self._loaded = True
+
+        # add the defaults first
+        self._sections.clear()
+        for section, settings in _default_values.items():
+            self.add_section(section)
+            for option, value in settings.items():
+                self.set(section, option, value)
+
+        # check and load config files
+        check_config_files()
+        self.read(_config_files)
+
+config = LazyConfigParser()
 
 # to guarantee that a section and/or setting exists, add a default value here
 _default_values = {
@@ -112,16 +150,10 @@ def load_configuration():
     """
     Check the configuration files and load the global 'config' object from them.
     """
-    global config
-    check_config_files()
-    config = SafeConfigParser()
-    # add the defaults first
-    for section, settings in _default_values.items():
-        config.add_section(section)
-        for option, value in settings.items():
-            config.set(section, option, value)
-    # read the config files
-    return config.read(_config_files)
+    # config is lazy, so this doesn't immediately trigger a load
+    # the actual load will occur the next time config is accessed
+    config.reload()
+    return config
 
 
 def add_config_file(file_path):
@@ -132,11 +164,10 @@ def add_config_file(file_path):
     @type file_path: str
     @param file_path: full path to the new file to add
     """
-    global _config_files
     if file_path in _config_files:
         raise RuntimeError('File, %s, already in configuration files' % file_path)
     _config_files.append(file_path)
-    load_configuration()
+    config.reload()
 
 
 def remove_config_file(file_path):
@@ -147,11 +178,7 @@ def remove_config_file(file_path):
     @type file_path: str
     @param file_path: full path to the file to remove
     """
-    global _config_files
     if file_path not in _config_files:
         raise RuntimeError('File, %s, not in configuration files' % file_path)
     _config_files.remove(file_path)
-    load_configuration()
-
-
-load_configuration()
+    config.reload()

server/test/unit/plugins/util/test_publish_step.py

@@ -23,7 +23,6 @@
 from pulp.server.db import model
 from pulp.server.managers import factory
 
-
 factory.initialize()