main: Add action loading and running infrastructure.

[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 e69de29bb2d1d6434b8b29ae775ad8c2e48c5391..da07b6d495146a615e29ca4c8a22b807d8de39bb 100644 (file)
--- a/src/lib/backupninja/handlers/__init__.py
+++ b/src/lib/backupninja/handlers/__init__.py
@@ -0,0 +1,81 @@
+#
+#    Backupninja python reimplementation, based on original backupninja program
+#    by riseup.net.
+#    Copyright (C) 2010  Matthijs Kooijman <matthijs@stdin.nl>
+#
+#    This program is free software; you can redistribute it and/or modify
+#    it under the terms of the GNU General Public License as published by
+#    the Free Software Foundation; either version 2 of the License, or
+#    (at your option) any later version.
+#
+#    This program is distributed in the hope that it will be useful,
+#    but WITHOUT ANY WARRANTY; without even the implied warranty of
+#    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+#    GNU General Public License for more details.
+#
+#    You should have received a copy of the GNU General Public License along
+#    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 """
+
+import sys
+import logging as log
+
+class Handler(object):
+    def __init__(self, conf):
+        self.conf = conf
+
+    def run(self):
+        """
+        Run this handler for a single target. Override this method
+        in a subclass
+        """
+        pass
+
+    def finish(self):
+        """
+        Called when all targets have been processed. Can be overridden
+        in a subclass.
+        """
+        pass
+
+def create_handler(ty, conf):
+    """
+    Create a new (subclass of) Handler object for an action with the
+    given type. conf is the configuration to pass to the handler.
+
+    If the handler cannot be loaded, it is logged and None is returned
+    (but any exceptions raised by the handler code itself are not
+    handled).
+    """
+    modname = 'backupninja.handlers.%s' % ty
+    # Load the handler if it is not loaded yet
+    if not modname in sys.modules:
+        try:
+            __import__(modname, globals(), locals(), [])
+        except ImportError, e:
+            log.error('Cannot load action handler for "%s": %s'
+                     , ty, e)
+            return None
+    # Get the module from the module table
+    module = sys.modules[modname]
+
+    # Check that the module has a "handler" top level function, which
+    # should create a new Handler object.
+    if not hasattr(module, 'handler'):
+        log.error('Action handler for "%s" (in "%s) is not valid: it '
+                  'does not have a "handler" top level function.'
+                 , ty, module.__file__)
+        return None
+
+    # Call the "handler" function to create the actual handler
+    handler = module.handler(conf)
+   
+    # Check if the handler returned is really a subclass of Handler
+    if not isinstance(handler, Handler):
+        log.error('Action handler for "%s" (in "%s) is not valid: it '
+                  'does not return a subclass of backupninja.handlers.Handler.'
+                 , ty, module.__file__)
+        return None
+    return handler