mgmt: factor out filtering by mgmt-permission:... events

Split actual filtering done by mgmt-permission: events into calling an
event and applying returned filters. This way filtering done in
mgmt.Events handler could reuse the same function.

qubes/mgmt.py

@@ -81,6 +81,14 @@ def api(name, *, no_payload=False):
 
     return decorator
 
+
+def apply_filters(iterable, filters):
+    '''Apply filters returned by mgmt-permission:... event'''
+    for selector in filters:
+        iterable = filter(selector, iterable)
+    return iterable
+
+
 class AbstractQubesMgmt(object):
     '''Common code for Qubes Management Protocol handling
 
@@ -167,9 +175,8 @@ class AbstractQubesMgmt(object):
 
     def fire_event_for_filter(self, iterable, **kwargs):
         '''Fire an event on the source qube to filter for permission'''
-        for selector in self.fire_event_for_permission(**kwargs):
-            iterable = filter(selector, iterable)
-        return iterable
+        return apply_filters(iterable,
+            self.fire_event_for_permission(**kwargs))
 
 
 class QubesMgmt(AbstractQubesMgmt):
@@ -588,9 +595,9 @@ class QubesMgmt(AbstractQubesMgmt):
                 return
             if event.startswith('mgmt-permission:'):
                 return
-            for selector in event_filters:
-                if not selector((subject, event, kwargs)):
-                    return
+            if not list(apply_filters([(subject, event, kwargs)],
+                    event_filters)):
+                return
             self.send_event(subject, event, **kwargs)
 
         if self.dest.name == 'dom0':