Implement MSC4380: Invite blocking (#19203)

MSC4380 aims to be a simplified implementation of MSC4155; the hope is
that we can get it specced and rolled out rapidly, so that we can
resolve the fact that `matrix.org` has enabled MSC4155.

The implementation leans heavily on what's already there for MSC4155.

It has its own `experimental_features` flag. If both MSC4155 and MSC4380
are enabled, and a user has both configurations set, then we prioritise
the MSC4380 one.

Contributed wearing my 🎩 Spec Core Team hat.

Author: richvdh

changelog.d/19203.feature

@@ -0,0 +1 @@
+Add experimentatal implememntation of [MSC4380](https://github.com/matrix-org/matrix-spec-proposals/pull/4380) (invite blocking).

synapse/api/constants.py

@@ -307,6 +307,10 @@ class AccountDataTypes:
     MSC4155_INVITE_PERMISSION_CONFIG: Final = (
         "org.matrix.msc4155.invite_permission_config"
     )
+    # MSC4380: Invite blocking
+    MSC4380_INVITE_PERMISSION_CONFIG: Final = (
+        "org.matrix.msc4380.invite_permission_config"
+    )
     # Synapse-specific behaviour. See "Client-Server API Extensions" documentation
     # in Admin API for more information.
     SYNAPSE_ADMIN_CLIENT_CONFIG: Final = "io.element.synapse.admin_client_config"

synapse/api/errors.py

@@ -137,7 +137,7 @@ class Codes(str, Enum):
     PROFILE_TOO_LARGE = "M_PROFILE_TOO_LARGE"
     KEY_TOO_LARGE = "M_KEY_TOO_LARGE"
 
-    # Part of MSC4155
+    # Part of MSC4155/MSC4380
     INVITE_BLOCKED = "ORG.MATRIX.MSC4155.M_INVITE_BLOCKED"
 
     # Part of MSC4190

synapse/config/experimental.py

@@ -596,3 +596,6 @@ def read_config(
         # MSC4306: Thread Subscriptions
         # (and MSC4308: Thread Subscriptions extension to Sliding Sync)
         self.msc4306_enabled: bool = experimental.get("msc4306_enabled", False)
+
+        # MSC4380: Invite blocking
+        self.msc4380_enabled: bool = experimental.get("msc4380_enabled", False)

synapse/rest/client/versions.py

@@ -182,6 +182,8 @@ async def on_GET(self, request: SynapseRequest) -> tuple[int, JsonDict]:
                     "org.matrix.msc4306": self.config.experimental.msc4306_enabled,
                     # MSC4169: Backwards-compatible redaction sending using `/send`
                     "com.beeper.msc4169": self.config.experimental.msc4169_enabled,
+                    # MSC4380: Invite blocking
+                    "org.matrix.msc4380": self.config.experimental.msc4380_enabled,
                 },
             },
         )

synapse/storage/databases/main/account_data.py

@@ -40,7 +40,12 @@
 )
 from synapse.storage.databases.main.cache import CacheInvalidationWorkerStore
 from synapse.storage.databases.main.push_rule import PushRulesWorkerStore
-from synapse.storage.invite_rule import InviteRulesConfig
+from synapse.storage.invite_rule import (
+    AllowAllInviteRulesConfig,
+    InviteRulesConfig,
+    MSC4155InviteRulesConfig,
+    MSC4380InviteRulesConfig,
+)
 from synapse.storage.util.id_generators import MultiWriterIdGenerator
 from synapse.types import JsonDict, JsonMapping
 from synapse.util.caches.descriptors import cached
@@ -104,6 +109,7 @@ def __init__(
         )
 
         self._msc4155_enabled = hs.config.experimental.msc4155_enabled
+        self._msc4380_enabled = hs.config.experimental.msc4380_enabled
 
     def get_max_account_data_stream_id(self) -> int:
         """Get the current max stream ID for account data stream
@@ -562,20 +568,28 @@ async def ignored_users(self, user_id: str) -> frozenset[str]:
 
     async def get_invite_config_for_user(self, user_id: str) -> InviteRulesConfig:
         """
-        Get the invite configuration for the current user.
+        Get the invite configuration for the given user.
 
         Args:
-            user_id:
+            user_id: The user whose invite configuration should be returned.
         """
+        if self._msc4380_enabled:
+            data = await self.get_global_account_data_by_type_for_user(
+                user_id, AccountDataTypes.MSC4380_INVITE_PERMISSION_CONFIG
+            )
+            # If the user has an MSC4380-style config setting, prioritise that
+            # above an MSC4155 one
+            if data is not None:
+                return MSC4380InviteRulesConfig.from_account_data(data)
+
+        if self._msc4155_enabled:
+            data = await self.get_global_account_data_by_type_for_user(
+                user_id, AccountDataTypes.MSC4155_INVITE_PERMISSION_CONFIG
+            )
+            if data is not None:
+                return MSC4155InviteRulesConfig(data)
 
-        if not self._msc4155_enabled:
-            # This equates to allowing all invites, as if the setting was off.
-            return InviteRulesConfig(None)
-
-        data = await self.get_global_account_data_by_type_for_user(
-            user_id, AccountDataTypes.MSC4155_INVITE_PERMISSION_CONFIG
-        )
-        return InviteRulesConfig(data)
+        return AllowAllInviteRulesConfig()
 
     async def get_admin_client_config_for_user(self, user_id: str) -> AdminClientConfig:
         """

synapse/storage/invite_rule.py

@@ -1,7 +1,9 @@
 import logging
+from abc import abstractmethod
 from enum import Enum
 from typing import Pattern
 
+import attr
 from matrix_common.regex import glob_to_regex
 
 from synapse.types import JsonMapping, UserID
@@ -18,9 +20,29 @@ class InviteRule(Enum):
 
 
 class InviteRulesConfig:
-    """Class to determine if a given user permits an invite from another user, and the action to take."""
+    """An object encapsulating a given user's choices about whether to accept invites."""
 
-    def __init__(self, account_data: JsonMapping | None):
+    @abstractmethod
+    def get_invite_rule(self, inviter_user_id: str) -> InviteRule:
+        """Get the invite rule that matches this user. Will return InviteRule.ALLOW if no rules match
+
+        Args:
+            inviter_user_id: The user ID of the inviting user.
+        """
+
+
+@attr.s(slots=True)
+class AllowAllInviteRulesConfig(InviteRulesConfig):
+    """An `InviteRulesConfig` implementation which will accept all invites."""
+
+    def get_invite_rule(self, inviter_user_id: str) -> InviteRule:
+        return InviteRule.ALLOW
+
+
+class MSC4155InviteRulesConfig(InviteRulesConfig):
+    """An object encapsulating [MSC4155](https://github.com/matrix-org/matrix-spec-proposals/pull/4155) invite rules."""
+
+    def __init__(self, account_data: JsonMapping):
         self.allowed_users: list[Pattern[str]] = []
         self.ignored_users: list[Pattern[str]] = []
         self.blocked_users: list[Pattern[str]] = []
@@ -110,3 +132,21 @@ def get_invite_rule(self, user_id: str) -> InviteRule:
                     return rule
 
         return InviteRule.ALLOW
+
+
+@attr.s(slots=True, auto_attribs=True)
+class MSC4380InviteRulesConfig(InviteRulesConfig):
+    default_invite_rule: InviteRule
+    """The invite rule to apply to all invites."""
+
+    @classmethod
+    def from_account_data(cls, data: JsonMapping) -> "MSC4380InviteRulesConfig":
+        default = data.get("default_action")
+
+        default_invite_rule = (
+            InviteRule.BLOCK if default == "block" else InviteRule.ALLOW
+        )
+        return cls(default_invite_rule=default_invite_rule)
+
+    def get_invite_rule(self, inviter_user_id: str) -> InviteRule:
+        return self.default_invite_rule

tests/handlers/test_room_member.py

@@ -458,7 +458,9 @@ def test_deduplicate_joins(self) -> None:
         self.assertEqual(initial_count, new_count)
 
 
-class TestInviteFiltering(FederatingHomeserverTestCase):
+class TestMSC4155InviteFiltering(FederatingHomeserverTestCase):
+    """Tests for MSC4155-style invite filtering."""
+
     servlets = [
         synapse.rest.admin.register_servlets,
         synapse.rest.client.login.register_servlets,
@@ -618,3 +620,145 @@ def test_msc4155_block_invite_remote_server(self) -> None:
         ).value
         self.assertEqual(f.code, 403)
         self.assertEqual(f.errcode, "ORG.MATRIX.MSC4155.M_INVITE_BLOCKED")
+
+
+class TestMSC4380InviteBlocking(FederatingHomeserverTestCase):
+    """Tests for MSC4380-style invite filtering."""
+
+    servlets = [
+        synapse.rest.admin.register_servlets,
+        synapse.rest.client.login.register_servlets,
+        synapse.rest.client.room.register_servlets,
+    ]
+
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
+        self.handler = hs.get_room_member_handler()
+        self.fed_handler = hs.get_federation_handler()
+        self.store = hs.get_datastores().main
+
+        # Create two users.
+        self.alice = self.register_user("alice", "pass")
+        self.alice_token = self.login("alice", "pass")
+        self.bob = self.register_user("bob", "pass")
+        self.bob_token = self.login("bob", "pass")
+
+    @override_config({"experimental_features": {"msc4380_enabled": True}})
+    def test_misc4380_block_invite_local(self) -> None:
+        """Test that MSC4380 will block a user from being invited to a room"""
+        room_id = self.helper.create_room_as(self.alice, tok=self.alice_token)
+
+        self.get_success(
+            self.store.add_account_data_for_user(
+                self.bob,
+                AccountDataTypes.MSC4380_INVITE_PERMISSION_CONFIG,
+                {
+                    "default_action": "block",
+                },
+            )
+        )
+
+        f = self.get_failure(
+            self.handler.update_membership(
+                requester=create_requester(self.alice),
+                target=UserID.from_string(self.bob),
+                room_id=room_id,
+                action=Membership.INVITE,
+            ),
+            SynapseError,
+        ).value
+        self.assertEqual(f.code, 403)
+        self.assertEqual(f.errcode, "ORG.MATRIX.MSC4155.M_INVITE_BLOCKED")
+
+    @override_config({"experimental_features": {"msc4380_enabled": True}})
+    def test_misc4380_non_string_setting(self) -> None:
+        """Test that `default_action` being set to something non-stringy is the same as "accept"."""
+        room_id = self.helper.create_room_as(self.alice, tok=self.alice_token)
+
+        self.get_success(
+            self.store.add_account_data_for_user(
+                self.bob,
+                AccountDataTypes.MSC4380_INVITE_PERMISSION_CONFIG,
+                {
+                    "default_action": 1,
+                },
+            )
+        )
+
+        self.get_success(
+            self.handler.update_membership(
+                requester=create_requester(self.alice),
+                target=UserID.from_string(self.bob),
+                room_id=room_id,
+                action=Membership.INVITE,
+            )
+        )
+
+    @override_config({"experimental_features": {"msc4380_enabled": False}})
+    def test_msc4380_disabled_allow_invite_local(self) -> None:
+        """Test that, when MSC4380 is not enabled, invites are accepted as normal"""
+        room_id = self.helper.create_room_as(self.alice, tok=self.alice_token)
+
+        self.get_success(
+            self.store.add_account_data_for_user(
+                self.bob,
+                AccountDataTypes.MSC4380_INVITE_PERMISSION_CONFIG,
+                {
+                    "default_action": "block",
+                },
+            )
+        )
+
+        self.get_success(
+            self.handler.update_membership(
+                requester=create_requester(self.alice),
+                target=UserID.from_string(self.bob),
+                room_id=room_id,
+                action=Membership.INVITE,
+            ),
+        )
+
+    @override_config({"experimental_features": {"msc4380_enabled": True}})
+    def test_msc4380_block_invite_remote(self) -> None:
+        """Test that MSC4380 will block a user from being invited to a room by a remote user."""
+        # A remote user who sends the invite
+        remote_server = "otherserver"
+        remote_user = "@otheruser:" + remote_server
+
+        self.get_success(
+            self.store.add_account_data_for_user(
+                self.bob,
+                AccountDataTypes.MSC4380_INVITE_PERMISSION_CONFIG,
+                {"default_action": "block"},
+            )
+        )
+
+        room_id = self.helper.create_room_as(
+            room_creator=self.alice, tok=self.alice_token
+        )
+        room_version = self.get_success(self.store.get_room_version(room_id))
+
+        invite_event = event_from_pdu_json(
+            {
+                "type": EventTypes.Member,
+                "content": {"membership": "invite"},
+                "room_id": room_id,
+                "sender": remote_user,
+                "state_key": self.bob,
+                "depth": 32,
+                "prev_events": [],
+                "auth_events": [],
+                "origin_server_ts": self.clock.time_msec(),
+            },
+            room_version,
+        )
+
+        f = self.get_failure(
+            self.fed_handler.on_invite_request(
+                remote_server,
+                invite_event,
+                invite_event.room_version,
+            ),
+            SynapseError,
+        ).value
+        self.assertEqual(f.code, 403)
+        self.assertEqual(f.errcode, "ORG.MATRIX.MSC4155.M_INVITE_BLOCKED")