Implement knock feature

changelog.d/6739.feature

@@ -0,0 +1 @@
+Implement "room knocking" as per [MSC2403](https://github.com/matrix-org/matrix-doc/pull/2403). Contributed by Sorunome and anoa.

docs/sample_config.yaml

@@ -1452,7 +1452,9 @@ metrics_flags:
 
 ## API Configuration ##
 
-# A list of event types that will be included in the room_invite_state
+# A list of event types from a room that will be given to users when they
+# are invited to a room. This allows clients to display information about the
+# room that they've been invited to, without actually being in the room yet.
 #
 #room_invite_state_types:
 #  - "m.room.join_rules"

synapse/api/constants.py

@@ -39,7 +39,7 @@ class Membership:
 
     INVITE = "invite"
     JOIN = "join"
-    KNOCK = "knock"
+    KNOCK = "xyz.amorgan.knock"
     LEAVE = "leave"
     BAN = "ban"
     LIST = (INVITE, JOIN, KNOCK, LEAVE, BAN)
@@ -55,7 +55,7 @@ class PresenceState:
 
 class JoinRules:
     PUBLIC = "public"
-    KNOCK = "knock"
+    KNOCK = "xyz.amorgan.knock"
     INVITE = "invite"
     PRIVATE = "private"
 

synapse/api/room_versions.py

@@ -57,7 +57,7 @@ class RoomVersion:
     state_res = attr.ib(type=int)  # one of the StateResolutionVersions
     enforce_key_validity = attr.ib(type=bool)
 
-    # bool: before MSC2261/MSC2432, m.room.aliases had special auth rules and redaction rules
+    # Before MSC2432, m.room.aliases had special auth rules and redaction rules
     special_case_aliases_auth = attr.ib(type=bool)
     # Strictly enforce canonicaljson, do not allow:
     # * Integers outside the range of [-2 ^ 53 + 1, 2 ^ 53 - 1]
@@ -69,6 +69,9 @@ class RoomVersion:
     limit_notifications_power_levels = attr.ib(type=bool)
     # MSC2174/MSC2176: Apply updated redaction rules algorithm.
     msc2176_redaction_rules = attr.ib(type=bool)
+    # MSC2403: Allows join_rules to be set to 'knock', changes auth rules to allow sending
+    # m.room.membership event with membership 'knock'.
+    allow_knocking = attr.ib(type=bool)
 
 
 class RoomVersions:
@@ -82,6 +85,7 @@ class RoomVersions:
         strict_canonicaljson=False,
         limit_notifications_power_levels=False,
         msc2176_redaction_rules=False,
+        allow_knocking=False,
     )
     V2 = RoomVersion(
         "2",
@@ -93,6 +97,7 @@ class RoomVersions:
         strict_canonicaljson=False,
         limit_notifications_power_levels=False,
         msc2176_redaction_rules=False,
+        allow_knocking=False,
     )
     V3 = RoomVersion(
         "3",
@@ -104,6 +109,7 @@ class RoomVersions:
         strict_canonicaljson=False,
         limit_notifications_power_levels=False,
         msc2176_redaction_rules=False,
+        allow_knocking=False,
     )
     V4 = RoomVersion(
         "4",
@@ -115,6 +121,7 @@ class RoomVersions:
         strict_canonicaljson=False,
         limit_notifications_power_levels=False,
         msc2176_redaction_rules=False,
+        allow_knocking=False,
     )
     V5 = RoomVersion(
         "5",
@@ -126,6 +133,7 @@ class RoomVersions:
         strict_canonicaljson=False,
         limit_notifications_power_levels=False,
         msc2176_redaction_rules=False,
+        allow_knocking=False,
     )
     V6 = RoomVersion(
         "6",
@@ -137,6 +145,7 @@ class RoomVersions:
         strict_canonicaljson=True,
         limit_notifications_power_levels=True,
         msc2176_redaction_rules=False,
+        allow_knocking=False,
     )
     MSC2176 = RoomVersion(
         "org.matrix.msc2176",
@@ -148,6 +157,19 @@ class RoomVersions:
         strict_canonicaljson=True,
         limit_notifications_power_levels=True,
         msc2176_redaction_rules=True,
+        allow_knocking=False,
+    )
+    MSC2403_DEV = RoomVersion(
+        "xyz.amorgan.knock",
+        RoomDisposition.UNSTABLE,
+        EventFormatVersions.V3,
+        StateResolutionVersions.V2,
+        enforce_key_validity=True,
+        special_case_aliases_auth=False,
+        strict_canonicaljson=True,
+        limit_notifications_power_levels=True,
+        msc2176_redaction_rules=False,
+        allow_knocking=True,
     )
 
 

synapse/appservice/api.py

@@ -18,7 +18,7 @@
 
 from prometheus_client import Counter
 
-from synapse.api.constants import EventTypes, ThirdPartyEntityKind
+from synapse.api.constants import EventTypes, Membership, ThirdPartyEntityKind
 from synapse.api.errors import CodeMessageException
 from synapse.events import EventBase
 from synapse.events.utils import serialize_event
@@ -248,9 +248,14 @@ def _serialize(self, service, events):
                 e,
                 time_now,
                 as_client_event=True,
-                is_invite=(
+                # If this is an invite or a knock membership event, and we're interested
+                # in this user, then include any stripped state alongside the event.
+                include_stripped_room_state=(
                     e.type == EventTypes.Member
-                    and e.membership == "invite"
+                    and (
+                        e.membership == Membership.INVITE
+                        or e.membership == Membership.KNOCK
+                    )
                     and service.is_interested_in_user(e.state_key)
                 ),
             )

synapse/config/api.py

@@ -1,4 +1,5 @@
 # Copyright 2015, 2016 OpenMarket Ltd
+# Copyright 2020 The Matrix.org Foundation C.I.C.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -16,27 +17,31 @@
 
 from ._base import Config
 
+# The default types of room state to send to users to are invited to or knock on a room.
+DEFAULT_ROOM_STATE_TYPES = [
+    EventTypes.JoinRules,
+    EventTypes.CanonicalAlias,
+    EventTypes.RoomAvatar,
+    EventTypes.RoomEncryption,
+    EventTypes.Name,
+]
+
 
 class ApiConfig(Config):
     section = "api"
 
     def read_config(self, config, **kwargs):
         self.room_invite_state_types = config.get(
-            "room_invite_state_types",
-            [
-                EventTypes.JoinRules,
-                EventTypes.CanonicalAlias,
-                EventTypes.RoomAvatar,
-                EventTypes.RoomEncryption,
-                EventTypes.Name,
-            ],
+            "room_invite_state_types", DEFAULT_ROOM_STATE_TYPES
         )
 
     def generate_config_section(cls, **kwargs):
         return """\
         ## API Configuration ##
 
-        # A list of event types that will be included in the room_invite_state
+        # A list of event types from a room that will be given to users when they
+        # are invited to a room. This allows clients to display information about the
+        # room that they've been invited to, without actually being in the room yet.
         #
         #room_invite_state_types:
         #  - "{JoinRules}"

synapse/config/experimental.py

@@ -13,6 +13,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from synapse.api.room_versions import KNOWN_ROOM_VERSIONS, RoomVersions
 from synapse.config._base import Config
 from synapse.types import JsonDict
 
@@ -27,3 +28,11 @@ def read_config(self, config: JsonDict, **kwargs):
 
         # MSC2858 (multiple SSO identity providers)
         self.msc2858_enabled = experimental.get("msc2858_enabled", False)  # type: bool
+
+        # MSC2403 (room knocking)
+        self.msc2403_enabled = experimental.get("msc2403_enabled", False)  # type: bool
+        if self.msc2403_enabled:
+            # Enable the MSC2403 unstable room version
+            KNOWN_ROOM_VERSIONS.update(
+                {RoomVersions.MSC2403_DEV.identifier: RoomVersions.MSC2403_DEV}
+            )

synapse/event_auth.py

@@ -161,6 +161,7 @@ def check(
     if logger.isEnabledFor(logging.DEBUG):
         logger.debug("Auth events: %s", [a.event_id for a in auth_events.values()])
 
+    # 5. If type is m.room.membership
     if event.type == EventTypes.Member:
         _is_membership_change_allowed(event, auth_events)
         logger.debug("Allowing! %s", event)
@@ -247,6 +248,7 @@ def _is_membership_change_allowed(
 
     caller_in_room = caller and caller.membership == Membership.JOIN
     caller_invited = caller and caller.membership == Membership.INVITE
+    caller_knocked = caller and caller.membership == Membership.KNOCK
 
     # get info about the target
     key = (EventTypes.Member, target_user_id)
@@ -289,9 +291,12 @@ def _is_membership_change_allowed(
             raise AuthError(403, "%s is banned from the room" % (target_user_id,))
         return
 
-    if Membership.JOIN != membership:
+    # Require the user to be in the room for membership changes other than join/knock.
+    if Membership.JOIN != membership and Membership.KNOCK != membership:
+        # If the user has been invited or has knocked, they are allowed to change their
+        # membership event to leave
         if (
-            caller_invited
+            (caller_invited or caller_knocked)
             and Membership.LEAVE == membership
             and target_user_id == event.user_id
         ):
@@ -324,7 +329,7 @@ def _is_membership_change_allowed(
             raise AuthError(403, "You are banned from this room")
         elif join_rule == JoinRules.PUBLIC:
             pass
-        elif join_rule == JoinRules.INVITE:
+        elif join_rule in (JoinRules.INVITE, JoinRules.KNOCK):
             if not caller_in_room and not caller_invited:
                 raise AuthError(403, "You are not invited to this room.")
         else:
@@ -343,6 +348,17 @@ def _is_membership_change_allowed(
     elif Membership.BAN == membership:
         if user_level < ban_level or user_level <= target_level:
             raise AuthError(403, "You don't have permission to ban")
+    elif Membership.KNOCK == membership:
+        if join_rule != JoinRules.KNOCK:
+            raise AuthError(403, "You don't have permission to knock")
+        elif target_user_id != event.user_id:
+            raise AuthError(403, "You cannot knock for other users")
+        elif target_in_room:
+            raise AuthError(403, "You cannot knock on a room you are already in")
+        elif caller_invited:
+            raise AuthError(403, "You are already invited to this room")
+        elif target_banned:
+            raise AuthError(403, "You are banned from this room")
     else:
         raise AuthError(500, "Unknown membership %s" % membership)
 
@@ -703,7 +719,7 @@ def auth_types_for_event(event: EventBase) -> Set[Tuple[str, str]]:
 
     if event.type == EventTypes.Member:
         membership = event.content["membership"]
-        if membership in [Membership.JOIN, Membership.INVITE]:
+        if membership in [Membership.JOIN, Membership.INVITE, Membership.KNOCK]:
             auth_types.add((EventTypes.JoinRules, ""))
 
         auth_types.add((EventTypes.Member, event.state_key))

synapse/events/utils.py

@@ -240,6 +240,7 @@ def format_event_for_client_v1(d):
         "replaces_state",
         "prev_content",
         "invite_room_state",
+        "knock_room_state",
     )
     for key in copy_keys:
         if key in d["unsigned"]:
@@ -276,7 +277,7 @@ def serialize_event(
     event_format=format_event_for_client_v1,
     token_id=None,
     only_event_fields=None,
-    is_invite=False,
+    include_stripped_room_state=False,
 ):
     """Serialize event for clients
 
@@ -287,8 +288,10 @@ def serialize_event(
         event_format
         token_id
         only_event_fields
-        is_invite (bool): Whether this is an invite that is being sent to the
-            invitee
+        include_stripped_room_state (bool): Some events can have stripped room state
+            stored in the `unsigned` field. This is required for invite and knock
+            functionality. If this option is False, that state will be removed from the
+            event before it is returned. Otherwise, it will be kept.
 
     Returns:
         dict
@@ -320,11 +323,13 @@ def serialize_event(
             if txn_id is not None:
                 d["unsigned"]["transaction_id"] = txn_id
 
-    # If this is an invite for somebody else, then we don't care about the
-    # invite_room_state as that's meant solely for the invitee. Other clients
-    # will already have the state since they're in the room.
-    if not is_invite:
+    # invite_room_state and knock_room_state are a list of stripped room state events
+    # that are meant to provide metadata about a room to an invitee/knocker. They are
+    # intended to only be included in specific circumstances, such as down sync, and
+    # should not be included in any other case.
+    if not include_stripped_room_state:
         d["unsigned"].pop("invite_room_state", None)
+        d["unsigned"].pop("knock_room_state", None)
 
     if as_client_event:
         d = event_format(d)