Address PR feedback

- add code and test to handle configuration of an empty array
- move docstrings around and update class level documentation

synapse/rulecheck/domain_rule_checker.py

@@ -19,25 +19,25 @@ from synapse.config._base import ConfigError
 
 logger = logging.getLogger(__name__)
 
-"""
-DomainRuleChecker
-
-Takes a config in the format:
-
-spam_checker:
-    module: "rulecheck.DomainRuleChecker"
-    config:
-      domain_mapping:
-        "inviter_domain": [ "invitee_domain_permitted", "other_invitee_domain_permitted" ]
-        "other_inviter_domain": [ "invitee_domain_permitted" ]
-      default: False
-    }
-
-Don't forget to consider if you can invite users from your own domain.
-"""
-
 
 class DomainRuleChecker(object):
+    """
+    A re-implementation of the SpamChecker that prevents users in one domain from
+    inviting users in other domains to rooms, based on a configuration.
+
+    Takes a config in the format:
+
+    spam_checker:
+        module: "rulecheck.DomainRuleChecker"
+        config:
+          domain_mapping:
+            "inviter_domain": [ "invitee_domain_permitted", "other_domain_permitted" ]
+            "other_inviter_domain": [ "invitee_domain_permitted" ]
+          default: False
+        }
+
+    Don't forget to consider if you can invite users from your own domain.
+    """
 
     def __init__(self, config):
         self.domain_mapping = config["domain_mapping"] or {}
@@ -50,11 +50,10 @@ class DomainRuleChecker(object):
         inviter_domain = self._get_domain_from_id(inviter_userid)
         invitee_domain = self._get_domain_from_id(invitee_userid)
 
-        valid_targets = self.domain_mapping.get(inviter_domain)
-        if not valid_targets:
+        if inviter_domain not in self.domain_mapping:
             return self.default
 
-        return invitee_domain in valid_targets
+        return invitee_domain in self.domain_mapping.get(inviter_domain)
 
     def user_may_create_room(self, userid):
         return True

tests/rulecheck/test_domainrulecheck.py

@@ -43,7 +43,8 @@ class DomainRuleCheckerTestCase(unittest.TestCase):
             "default": True,
             "domain_mapping": {
                 "source_one": ["target_one", "target_two"],
-                "source_two": ["target_two"]
+                "source_two": ["target_two"],
+                "source_four": []
             }
         }
         check = DomainRuleChecker(config)
@@ -53,6 +54,8 @@ class DomainRuleCheckerTestCase(unittest.TestCase):
                                                "test:target_three", "room"))
         self.assertFalse(check.user_may_invite("test:source_two",
                                                "test:target_one", "room"))
+        self.assertFalse(check.user_may_invite("test:source_four",
+                                               "test:target_one", "room"))
 
     def test_default_allow(self):
         config = {