handlers: Add fail_on_exception handler.

[matthijs/projects/backupninja.git] / src / lib / backupninja / handlers / __init__.py

diff --git a/src/lib/backupninja/handlers/__init__.py b/src/lib/backupninja/handlers/__init__.py
index ccb5c8c142ec1b8b9fd0dca30df8d71ed7d8b311..29dc75631823ed79d5ecda18b99698d6dcacb782 100644 (file)
--- a/src/lib/backupninja/handlers/__init__.py
+++ b/src/lib/backupninja/handlers/__init__.py
@@ -17,23 +17,48 @@
 #    with this program; if not, write to the Free Software Foundation, Inc.,
 #    51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 
-""" Handler superclass with common functionality """
+""" Action superclass with common functionality """
 
-import sys
+import sys, ConfigParser
 import logging as log
 
 from backupninja import config
 
-class Handler(object):
+def fail_on_exception(f):
+    """
+    This is a decorator meant for methods on the Action class. It
+    catches any exceptions thrown, sets the failed attribute to True and
+    rethrows the exception.
+    """
+    def inner(self, *args, **kwargs):
+        try:
+            f(self, *args, **kwargs)
+        except:
+            self.failed = True
+            raise
+    return inner
+
+class Action(object):
+    """
+    Subclasses of Action represent handlers for various action types.
+    This class is called Action instead of Handler, since even though the
+    classes could be referred to as handlers, the instances of this
+    class are really actions (i.e., it represents a specific action,
+    which is a combination of a action type and a specific action
+    configuration).
+    """
     def __init__(self):
         # Subclasses should overwrite this with their default config
         # See backupninja.config.load_config for the structure of this
         # value.
         self.default_config = {}
+        # Assume we'll run succesfully. If anything fails in the
+        # meanwhile, set this to True.
+        self.failed = False
 
     def run(self, **kwargs):
         """
-        Run this handler for a single target. Override this method
+        Run this action for a single target. Override this method
         in a subclass
         """
         pass
@@ -51,14 +76,40 @@ class Handler(object):
         """
         self.conf = config.load_config(filename, self.default_config)
 
-        
+    def get_config_optional(self, section, option):
+        """
+        Returns the value of the given option. If the option was not set
+        (and no default was set in self.default_config), return None.
+
+        This is a convenience wrapper for ConfigParser.get(), since that
+        throws an exception on unset options.
+        """
+        try:
+            return self.conf.get(section, option)
+        except ConfigParser.NoOptionError:
+            return None
+
+    def get_config_mandatory(self, section, option):
+        """
+        Returns the value of the given option. If the option was not set
+        (and no default was set in self.default_config), raises a
+        backupninja.config.ConfigError.
+
+        This is a convenience wrapper for ConfigParser.get(), since that
+        has a very generic exception message on unknown options.
+        """
+        try:
+            return self.conf.get(section, option)
+        except ConfigParser.NoOptionError:
+            raise config.ConfigError("Option '%s' in section '%s' is mandatory, please configure it" % (option, section))
 
-def create_handler(ty):
+def create_action(ty):
     """
-    Create a new (subclass of) Handler object for an action with the
+    Create a new (subclass of) Action object for an action with the
     given type.
 
-    If the handler cannot be loaded, an exception is thrown.
+    If the handler class for this type cannot be loaded, an exception is
+    thrown.
     """
     modname = 'backupninja.handlers.%s' % ty
     # Load the handler if it is not loaded yet
@@ -75,18 +126,18 @@ def create_handler(ty):
     module = sys.modules[modname]
 
     # Check that the module has a "handler" top level function, which
-    # should create a new Handler object.
+    # should create a new Action object.
     if not hasattr(module, 'handler'):
         raise ImportError('%s is not valid: it '
                           'does not have a "handler" top level function.' 
                           % (module.__file__))
 
-    # Call the "handler" function to create the actual handler
-    handler = module.handler()
+    # Call the "handler" function to create the actual action
+    action = module.handler()
    
-    # Check if the handler returned is really a subclass of Handler
-    if not isinstance(handler, Handler):
+    # Check if the handler returned is really a subclass of Action
+    if not isinstance(action, Action):
         raise TypeError('%s is not valid, %s.handler did not return a '
                         'subclass of backupninja.handlers.Handler.'
                         % (module.__file__, modname))
-    return handler
+    return action