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- # Copyright 2014-2016 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.
- # You may obtain a copy of the License at
- #
- # http://www.apache.org/licenses/LICENSE-2.0
- #
- # Unless required by applicable law or agreed to in writing, software
- # distributed under the License is distributed on an "AS IS" BASIS,
- # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- # See the License for the specific language governing permissions and
- # limitations under the License.
- from collections import OrderedDict
- from typing import Hashable, Optional, Tuple
- from synapse.api.errors import LimitExceededError
- from synapse.storage.databases.main import DataStore
- from synapse.types import Requester
- from synapse.util import Clock
- class Ratelimiter:
- """
- Ratelimit actions marked by arbitrary keys.
- Args:
- clock: A homeserver clock, for retrieving the current time
- rate_hz: The long term number of actions that can be performed in a second.
- burst_count: How many actions that can be performed before being limited.
- """
- def __init__(
- self, store: DataStore, clock: Clock, rate_hz: float, burst_count: int
- ):
- self.clock = clock
- self.rate_hz = rate_hz
- self.burst_count = burst_count
- self.store = store
- # A ordered dictionary keeping track of actions, when they were last
- # performed and how often. Each entry is a mapping from a key of arbitrary type
- # to a tuple representing:
- # * How many times an action has occurred since a point in time
- # * The point in time
- # * The rate_hz of this particular entry. This can vary per request
- self.actions: OrderedDict[Hashable, Tuple[float, float, float]] = OrderedDict()
- async def can_do_action(
- self,
- requester: Optional[Requester],
- key: Optional[Hashable] = None,
- rate_hz: Optional[float] = None,
- burst_count: Optional[int] = None,
- update: bool = True,
- n_actions: int = 1,
- _time_now_s: Optional[float] = None,
- ) -> Tuple[bool, float]:
- """Can the entity (e.g. user or IP address) perform the action?
- Checks if the user has ratelimiting disabled in the database by looking
- for null/zero values in the `ratelimit_override` table. (Non-zero
- values aren't honoured, as they're specific to the event sending
- ratelimiter, rather than all ratelimiters)
- Args:
- requester: The requester that is doing the action, if any. Used to check
- if the user has ratelimits disabled in the database.
- key: An arbitrary key used to classify an action. Defaults to the
- requester's user ID.
- 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
- n_actions: The number of times the user wants to do this action. If the user
- cannot do all of the actions, the user's action count is not incremented
- at all.
- _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
- """
- if key is None:
- if not requester:
- raise ValueError("Must supply at least one of `requester` or `key`")
- key = requester.user.to_string()
- if requester:
- # 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
- # Check if ratelimiting has been disabled for the user.
- #
- # Note that we don't use the returned rate/burst count, as the table
- # is specifically for the event sending ratelimiter. Instead, we
- # only use it to (somewhat cheekily) infer whether the user should
- # be subject to any rate limiting or not.
- override = await self.store.get_ratelimit_for_user(
- requester.authenticated_entity
- )
- if override and not override.messages_per_second:
- return True, -1.0
- # Override default values if set
- time_now_s = _time_now_s if _time_now_s is not None else self.clock.time()
- rate_hz = rate_hz if rate_hz is not None else self.rate_hz
- burst_count = burst_count if burst_count is not None else self.burst_count
- # Remove any expired entries
- self._prune_message_counts(time_now_s)
- # Check if there is an existing count entry for this key
- action_count, time_start, _ = self.actions.get(key, (0.0, time_now_s, 0.0))
- # Check whether performing another action is allowed
- time_delta = time_now_s - time_start
- performed_count = action_count - time_delta * rate_hz
- if performed_count < 0:
- performed_count = 0
- time_start = time_now_s
- # This check would be easier read as performed_count + n_actions > burst_count,
- # but performed_count might be a very precise float (with lots of numbers
- # following the point) in which case Python might round it up when adding it to
- # n_actions. Writing it this way ensures it doesn't happen.
- if performed_count > burst_count - n_actions:
- # Deny, we have exceeded our burst count
- allowed = False
- else:
- # We haven't reached our limit yet
- allowed = True
- action_count = performed_count + n_actions
- if update:
- self.actions[key] = (action_count, time_start, rate_hz)
- if rate_hz > 0:
- # Find out when the count of existing actions expires
- time_allowed = time_start + (action_count - burst_count + 1) / rate_hz
- # Don't give back a time in the past
- if time_allowed < time_now_s:
- time_allowed = time_now_s
- else:
- # XXX: Why is this -1? This seems to only be used in
- # self.ratelimit. I guess so that clients get a time in the past and don't
- # feel afraid to try again immediately
- time_allowed = -1
- return allowed, time_allowed
- def _prune_message_counts(self, time_now_s: float):
- """Remove message count entries that have not exceeded their defined
- rate_hz limit
- Args:
- time_now_s: The current time
- """
- # We create a copy of the key list here as the dictionary is modified during
- # the loop
- for key in list(self.actions.keys()):
- action_count, time_start, rate_hz = self.actions[key]
- # Rate limit = "seconds since we started limiting this action" * rate_hz
- # If this limit has not been exceeded, wipe our record of this action
- time_delta = time_now_s - time_start
- if action_count - time_delta * rate_hz > 0:
- continue
- else:
- del self.actions[key]
- async def ratelimit(
- self,
- requester: Optional[Requester],
- key: Optional[Hashable] = None,
- rate_hz: Optional[float] = None,
- burst_count: Optional[int] = None,
- update: bool = True,
- n_actions: int = 1,
- _time_now_s: Optional[float] = None,
- ):
- """Checks if an action can be performed. If not, raises a LimitExceededError
- Checks if the user has ratelimiting disabled in the database by looking
- for null/zero values in the `ratelimit_override` table. (Non-zero
- values aren't honoured, as they're specific to the event sending
- ratelimiter, rather than all ratelimiters)
- Args:
- requester: The requester that is doing the action, if any. Used to check for
- if the user has ratelimits disabled.
- key: An arbitrary key used to classify an action. Defaults to the
- requester's user ID.
- 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
- n_actions: The number of times the user wants to do this action. If the user
- cannot do all of the actions, the user's action count is not incremented
- at all.
- _time_now_s: The current time. Optional, defaults to the current time according
- to self.clock. Only used by tests.
- Raises:
- LimitExceededError: If an action could not be performed, along with the time in
- milliseconds until the action can be performed again
- """
- time_now_s = _time_now_s if _time_now_s is not None else self.clock.time()
- allowed, time_allowed = await self.can_do_action(
- requester,
- key,
- rate_hz=rate_hz,
- burst_count=burst_count,
- update=update,
- n_actions=n_actions,
- _time_now_s=time_now_s,
- )
- if not allowed:
- raise LimitExceededError(
- retry_after_ms=int(1000 * (time_allowed - time_now_s))
- )
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