Validate group ids when parsing

May as well do it whenever we parse a Group ID. We check the sigil and basic
structure here so it makes sense to check the grammar in the same place.

synapse/groups/groups_server.py

@@ -15,7 +15,6 @@
 
 import logging
 
-from synapse import types
 from synapse.api.errors import SynapseError
 from synapse.types import GroupID, RoomID, UserID, get_domain_from_id
 from twisted.internet import defer
@@ -696,9 +695,11 @@ class GroupsServerHandler(object):
     def create_group(self, group_id, user_id, content):
         group = yield self.check_group_is_ours(group_id)
 
-        _validate_group_id(group_id)
-
         logger.info("Attempting to create group with ID: %r", group_id)
+
+        # parsing the id into a GroupID validates it.
+        group_id_obj = GroupID.from_string(group_id)
+
         if group:
             raise SynapseError(400, "Group already exists")
 
@@ -708,7 +709,7 @@ class GroupsServerHandler(object):
                 raise SynapseError(
                     403, "Only server admin can create group on this server",
                 )
-            localpart = GroupID.from_string(group_id).localpart
+            localpart = group_id_obj.localpart
             if not localpart.startswith(self.hs.config.group_creation_prefix):
                 raise SynapseError(
                     400,
@@ -784,15 +785,3 @@ def _parse_visibility_from_contents(content):
         is_public = True
 
     return is_public
-
-
-def _validate_group_id(group_id):
-    """Validates the group ID is valid for creation on this home server
-    """
-    localpart = GroupID.from_string(group_id).localpart
-
-    if types.contains_invalid_mxid_characters(localpart):
-        raise SynapseError(
-            400,
-            "Group ID can only contain characters a-z, 0-9, or '=_-./'",
-        )

synapse/types.py

@@ -161,6 +161,23 @@ class GroupID(DomainSpecificString):
     """Structure representing a group ID."""
     SIGIL = "+"
 
+    @classmethod
+    def from_string(cls, s):
+        group_id = super(GroupID, cls).from_string(s)
+        if not group_id.localpart:
+            raise SynapseError(
+                400,
+                "Group ID cannot be empty",
+            )
+
+        if contains_invalid_mxid_characters(group_id.localpart):
+            raise SynapseError(
+                400,
+                "Group ID can only contain characters a-z, 0-9, or '=_-./'",
+            )
+
+        return group_id
+
 
 mxid_localpart_allowed_characters = set("_-./=" + string.ascii_lowercase + string.digits)
 

tests/test_types.py

@@ -17,7 +17,7 @@ from tests import unittest
 
 from synapse.api.errors import SynapseError
 from synapse.server import HomeServer
-from synapse.types import UserID, RoomAlias
+from synapse.types import UserID, RoomAlias, GroupID
 
 mock_homeserver = HomeServer(hostname="my.domain")
 
@@ -60,3 +60,25 @@ class RoomAliasTestCase(unittest.TestCase):
         room = RoomAlias("channel", "my.domain")
 
         self.assertEquals(room.to_string(), "#channel:my.domain")
+
+
+class GroupIDTestCase(unittest.TestCase):
+    def test_parse(self):
+        group_id = GroupID.from_string("+group/=_-.123:my.domain")
+        self.assertEqual("group/=_-.123", group_id.localpart)
+        self.assertEqual("my.domain", group_id.domain)
+
+    def test_validate(self):
+        bad_ids = [
+            "$badsigil:domain",
+            "+:empty",
+        ] + [
+            "+group" + c + ":domain" for c in "A%?æ£"
+        ]
+        for id_string in bad_ids:
+            try:
+                GroupID.from_string(id_string)
+                self.fail("Parsing '%s' should raise exception" % id_string)
+            except SynapseError as exc:
+                self.assertEqual(400, exc.code)
+                self.assertEqual("M_UNKNOWN", exc.errcode)