Add a new room version for MSC3787's knock+restricted join rule (#12623)

6 files changed, 68 insertions, 7 deletions

diff --git a/changelog.d/12623.feature b/changelog.d/12623.feature
new file mode 100644
index 0000000000..cdee19fafa
--- /dev/null
+++ b/changelog.d/12623.feature
@@ -0,0 +1 @@
+Add support for [MSC3787: Allowing knocks to restricted rooms](https://github.com/matrix-org/matrix-spec-proposals/pull/3787).
\ No newline at end of file
diff --git a/synapse/api/constants.py b/synapse/api/constants.py
index 0ccd4c9558..330de21f6b 100644
--- a/synapse/api/constants.py
+++ b/synapse/api/constants.py
@@ -65,6 +65,8 @@ class JoinRules:
     PRIVATE: Final = "private"
     # As defined for MSC3083.
     RESTRICTED: Final = "restricted"
+    # As defined for MSC3787.
+    KNOCK_RESTRICTED: Final = "knock_restricted"
 
 
 class RestrictedJoinRuleTypes:
diff --git a/synapse/api/room_versions.py b/synapse/api/room_versions.py
index a747a40814..3f85d61b46 100644
--- a/synapse/api/room_versions.py
+++ b/synapse/api/room_versions.py
@@ -81,6 +81,9 @@ class RoomVersion:
     msc2716_historical: bool
     # MSC2716: Adds support for redacting "insertion", "chunk", and "marker" events
     msc2716_redactions: bool
+    # MSC3787: Adds support for a `knock_restricted` join rule, mixing concepts of
+    # knocks and restricted join rules into the same join condition.
+    msc3787_knock_restricted_join_rule: bool
 
 
 class RoomVersions:
@@ -99,6 +102,7 @@ class RoomVersions:
         msc2403_knocking=False,
         msc2716_historical=False,
         msc2716_redactions=False,
+        msc3787_knock_restricted_join_rule=False,
     )
     V2 = RoomVersion(
         "2",
@@ -115,6 +119,7 @@ class RoomVersions:
         msc2403_knocking=False,
         msc2716_historical=False,
         msc2716_redactions=False,
+        msc3787_knock_restricted_join_rule=False,
     )
     V3 = RoomVersion(
         "3",
@@ -131,6 +136,7 @@ class RoomVersions:
         msc2403_knocking=False,
         msc2716_historical=False,
         msc2716_redactions=False,
+        msc3787_knock_restricted_join_rule=False,
     )
     V4 = RoomVersion(
         "4",
@@ -147,6 +153,7 @@ class RoomVersions:
         msc2403_knocking=False,
         msc2716_historical=False,
         msc2716_redactions=False,
+        msc3787_knock_restricted_join_rule=False,
     )
     V5 = RoomVersion(
         "5",
@@ -163,6 +170,7 @@ class RoomVersions:
         msc2403_knocking=False,
         msc2716_historical=False,
         msc2716_redactions=False,
+        msc3787_knock_restricted_join_rule=False,
     )
     V6 = RoomVersion(
         "6",
@@ -179,6 +187,7 @@ class RoomVersions:
         msc2403_knocking=False,
         msc2716_historical=False,
         msc2716_redactions=False,
+        msc3787_knock_restricted_join_rule=False,
     )
     MSC2176 = RoomVersion(
         "org.matrix.msc2176",
@@ -195,6 +204,7 @@ class RoomVersions:
         msc2403_knocking=False,
         msc2716_historical=False,
         msc2716_redactions=False,
+        msc3787_knock_restricted_join_rule=False,
     )
     V7 = RoomVersion(
         "7",
@@ -211,6 +221,7 @@ class RoomVersions:
         msc2403_knocking=True,
         msc2716_historical=False,
         msc2716_redactions=False,
+        msc3787_knock_restricted_join_rule=False,
     )
     V8 = RoomVersion(
         "8",
@@ -227,6 +238,7 @@ class RoomVersions:
         msc2403_knocking=True,
         msc2716_historical=False,
         msc2716_redactions=False,
+        msc3787_knock_restricted_join_rule=False,
     )
     V9 = RoomVersion(
         "9",
@@ -243,6 +255,7 @@ class RoomVersions:
         msc2403_knocking=True,
         msc2716_historical=False,
         msc2716_redactions=False,
+        msc3787_knock_restricted_join_rule=False,
     )
     MSC2716v3 = RoomVersion(
         "org.matrix.msc2716v3",
@@ -259,6 +272,24 @@ class RoomVersions:
         msc2403_knocking=True,
         msc2716_historical=True,
         msc2716_redactions=True,
+        msc3787_knock_restricted_join_rule=False,
+    )
+    MSC3787 = RoomVersion(
+        "org.matrix.msc3787",
+        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,
+        msc3083_join_rules=True,
+        msc3375_redaction_rules=True,
+        msc2403_knocking=True,
+        msc2716_historical=False,
+        msc2716_redactions=False,
+        msc3787_knock_restricted_join_rule=True,
     )
 
 
@@ -276,6 +307,7 @@ KNOWN_ROOM_VERSIONS: Dict[str, RoomVersion] = {
         RoomVersions.V8,
         RoomVersions.V9,
         RoomVersions.MSC2716v3,
+        RoomVersions.MSC3787,
     )
 }
 
diff --git a/synapse/event_auth.py b/synapse/event_auth.py
index 621a3efccc..4c0b587a76 100644
--- a/synapse/event_auth.py
+++ b/synapse/event_auth.py
@@ -414,7 +414,12 @@ def _is_membership_change_allowed(
             raise AuthError(403, "You are banned from this room")
         elif join_rule == JoinRules.PUBLIC:
             pass
-        elif room_version.msc3083_join_rules and join_rule == JoinRules.RESTRICTED:
+        elif (
+            room_version.msc3083_join_rules and join_rule == JoinRules.RESTRICTED
+        ) or (
+            room_version.msc3787_knock_restricted_join_rule
+            and join_rule == JoinRules.KNOCK_RESTRICTED
+        ):
             # This is the same as public, but the event must contain a reference
             # to the server who authorised the join. If the event does not contain
             # the proper content it is rejected.
@@ -440,8 +445,13 @@ def _is_membership_change_allowed(
                 if authorising_user_level < invite_level:
                     raise AuthError(403, "Join event authorised by invalid server.")
 
-        elif join_rule == JoinRules.INVITE or (
-            room_version.msc2403_knocking and join_rule == JoinRules.KNOCK
+        elif (
+            join_rule == JoinRules.INVITE
+            or (room_version.msc2403_knocking and join_rule == JoinRules.KNOCK)
+            or (
+                room_version.msc3787_knock_restricted_join_rule
+                and join_rule == JoinRules.KNOCK_RESTRICTED
+            )
         ):
             if not caller_in_room and not caller_invited:
                 raise AuthError(403, "You are not invited to this room.")
@@ -462,7 +472,10 @@ def _is_membership_change_allowed(
         if user_level < ban_level or user_level <= target_level:
             raise AuthError(403, "You don't have permission to ban")
     elif room_version.msc2403_knocking and Membership.KNOCK == membership:
-        if join_rule != JoinRules.KNOCK:
+        if join_rule != JoinRules.KNOCK and (
+            not room_version.msc3787_knock_restricted_join_rule
+            or join_rule != JoinRules.KNOCK_RESTRICTED
+        ):
             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")
diff --git a/synapse/handlers/event_auth.py b/synapse/handlers/event_auth.py
index d441ebb0ab..6bed464351 100644
--- a/synapse/handlers/event_auth.py
+++ b/synapse/handlers/event_auth.py
@@ -241,7 +241,15 @@ class EventAuthHandler:
 
         # If the join rule is not restricted, this doesn't apply.
         join_rules_event = await self._store.get_event(join_rules_event_id)
-        return join_rules_event.content.get("join_rule") == JoinRules.RESTRICTED
+        content_join_rule = join_rules_event.content.get("join_rule")
+        if content_join_rule == JoinRules.RESTRICTED:
+            return True
+
+        # also check for MSC3787 behaviour
+        if room_version.msc3787_knock_restricted_join_rule:
+            return content_join_rule == JoinRules.KNOCK_RESTRICTED
+
+        return False
 
     async def get_rooms_that_allow_join(
         self, state_ids: StateMap[str]
diff --git a/synapse/handlers/room_summary.py b/synapse/handlers/room_summary.py
index ff24ec8063..af83de3193 100644
--- a/synapse/handlers/room_summary.py
+++ b/synapse/handlers/room_summary.py
@@ -562,8 +562,13 @@ class RoomSummaryHandler:
         if join_rules_event_id:
             join_rules_event = await self._store.get_event(join_rules_event_id)
             join_rule = join_rules_event.content.get("join_rule")
-            if join_rule == JoinRules.PUBLIC or (
-                room_version.msc2403_knocking and join_rule == JoinRules.KNOCK
+            if (
+                join_rule == JoinRules.PUBLIC
+                or (room_version.msc2403_knocking and join_rule == JoinRules.KNOCK)
+                or (
+                    room_version.msc3787_knock_restricted_join_rule
+                    and join_rule == JoinRules.KNOCK_RESTRICTED
+                )
             ):
                 return True