Do not apply ratelimiting on joins to appservices (#8139)

Add new method ratelimiter.can_requester_do_action and ensure that appservices are exempt from being ratelimited.

Co-authored-by: Patrick Cloke <clokep@users.noreply.github.com>
Co-authored-by: Erik Johnston <erik@matrix.org>

2 files changed, 45 insertions, 6 deletions

diff --git a/synapse/api/ratelimiting.py b/synapse/api/ratelimiting.py
index ec6b3a69a2..e62ae50ac2 100644
--- a/synapse/api/ratelimiting.py
+++ b/synapse/api/ratelimiting.py
@@ -17,6 +17,7 @@ from collections import OrderedDict
 from typing import Any, Optional, Tuple
 
 from synapse.api.errors import LimitExceededError
+from synapse.types import Requester
 from synapse.util import Clock
 
 
@@ -43,6 +44,42 @@ class Ratelimiter(object):
         #   * The rate_hz of this particular entry. This can vary per request
         self.actions = OrderedDict()  # type: OrderedDict[Any, Tuple[float, int, float]]
 
+    def can_requester_do_action(
+        self,
+        requester: Requester,
+        rate_hz: Optional[float] = None,
+        burst_count: Optional[int] = None,
+        update: bool = True,
+        _time_now_s: Optional[int] = None,
+    ) -> Tuple[bool, float]:
+        """Can the requester perform the action?
+
+        Args:
+            requester: The requester to key off when rate limiting. The user property
+                will be used.
+            rate_hz: The long term number of actions that can be performed in a second.
+                Overrides the value set during instantiation if set.
+            burst_count: How many actions that can be performed before being limited.
+                Overrides the value set during instantiation if set.
+            update: Whether to count this check as performing the action
+            _time_now_s: The current time. Optional, defaults to the current time according
+                to self.clock. Only used by tests.
+
+        Returns:
+            A tuple containing:
+                * A bool indicating if they can perform the action now
+                * The reactor timestamp for when the action can be performed next.
+                  -1 if rate_hz is less than or equal to zero
+        """
+        # Disable rate limiting of users belonging to any AS that is configured
+        # not to be rate limited in its registration file (rate_limited: true|false).
+        if requester.app_service and not requester.app_service.is_rate_limited():
+            return True, -1.0
+
+        return self.can_do_action(
+            requester.user.to_string(), rate_hz, burst_count, update, _time_now_s
+        )
+
     def can_do_action(
         self,
         key: Any,
diff --git a/synapse/handlers/room_member.py b/synapse/handlers/room_member.py
index 3a6ee6378d..a03cb02792 100644
--- a/synapse/handlers/room_member.py
+++ b/synapse/handlers/room_member.py
@@ -491,9 +491,10 @@ class RoomMemberHandler(object):
 
             if is_host_in_room:
                 time_now_s = self.clock.time()
-                allowed, time_allowed = self._join_rate_limiter_local.can_do_action(
-                    requester.user.to_string(),
-                )
+                (
+                    allowed,
+                    time_allowed,
+                ) = self._join_rate_limiter_local.can_requester_do_action(requester,)
 
                 if not allowed:
                     raise LimitExceededError(
@@ -502,9 +503,10 @@ class RoomMemberHandler(object):
 
             else:
                 time_now_s = self.clock.time()
-                allowed, time_allowed = self._join_rate_limiter_remote.can_do_action(
-                    requester.user.to_string(),
-                )
+                (
+                    allowed,
+                    time_allowed,
+                ) = self._join_rate_limiter_remote.can_requester_do_action(requester,)
 
                 if not allowed:
                     raise LimitExceededError(