177 lines
7.0 KiB
Python
177 lines
7.0 KiB
Python
# Copyright 2014-2016 OpenMarket Ltd
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# Copyright 2020 The Matrix.org Foundation C.I.C.
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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from collections import OrderedDict
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from typing import Any, Optional, Tuple
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from synapse.api.errors import LimitExceededError
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from synapse.util import Clock
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class Ratelimiter(object):
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"""
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Ratelimit actions marked by arbitrary keys.
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Args:
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clock: A homeserver clock, for retrieving the current time
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rate_hz: The long term number of actions that can be performed in a second.
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burst_count: How many actions that can be performed before being limited.
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"""
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def __init__(self, clock: Clock, rate_hz: float, burst_count: int):
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self.clock = clock
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self.rate_hz = rate_hz
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self.burst_count = burst_count
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# A ordered dictionary keeping track of actions, when they were last
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# performed and how often. Each entry is a mapping from a key of arbitrary type
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# to a tuple representing:
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# * How many times an action has occurred since a point in time
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# * The point in time
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# * The rate_hz of this particular entry. This can vary per request
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self.actions = OrderedDict() # type: OrderedDict[Any, Tuple[float, int, float]]
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def can_do_action(
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self,
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key: Any,
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rate_hz: Optional[float] = None,
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burst_count: Optional[int] = None,
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update: bool = True,
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_time_now_s: Optional[int] = None,
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) -> Tuple[bool, float]:
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"""Can the entity (e.g. user or IP address) perform the action?
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Args:
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key: The key we should use when rate limiting. Can be a user ID
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(when sending events), an IP address, etc.
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rate_hz: The long term number of actions that can be performed in a second.
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Overrides the value set during instantiation if set.
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burst_count: How many actions that can be performed before being limited.
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Overrides the value set during instantiation if set.
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update: Whether to count this check as performing the action
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_time_now_s: The current time. Optional, defaults to the current time according
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to self.clock. Only used by tests.
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Returns:
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A tuple containing:
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* A bool indicating if they can perform the action now
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* The reactor timestamp for when the action can be performed next.
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-1 if rate_hz is less than or equal to zero
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"""
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# Override default values if set
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time_now_s = _time_now_s if _time_now_s is not None else self.clock.time()
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rate_hz = rate_hz if rate_hz is not None else self.rate_hz
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burst_count = burst_count if burst_count is not None else self.burst_count
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# Remove any expired entries
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self._prune_message_counts(time_now_s)
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# Check if there is an existing count entry for this key
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action_count, time_start, _ = self.actions.get(key, (0.0, time_now_s, 0.0))
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# Check whether performing another action is allowed
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time_delta = time_now_s - time_start
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performed_count = action_count - time_delta * rate_hz
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if performed_count < 0:
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# Allow, reset back to count 1
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allowed = True
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time_start = time_now_s
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action_count = 1.0
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elif performed_count > burst_count - 1.0:
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# Deny, we have exceeded our burst count
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allowed = False
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else:
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# We haven't reached our limit yet
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allowed = True
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action_count += 1.0
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if update:
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self.actions[key] = (action_count, time_start, rate_hz)
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if rate_hz > 0:
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# Find out when the count of existing actions expires
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time_allowed = time_start + (action_count - burst_count + 1) / rate_hz
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# Don't give back a time in the past
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if time_allowed < time_now_s:
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time_allowed = time_now_s
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else:
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# XXX: Why is this -1? This seems to only be used in
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# self.ratelimit. I guess so that clients get a time in the past and don't
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# feel afraid to try again immediately
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time_allowed = -1
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return allowed, time_allowed
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def _prune_message_counts(self, time_now_s: int):
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"""Remove message count entries that have not exceeded their defined
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rate_hz limit
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Args:
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time_now_s: The current time
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"""
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# We create a copy of the key list here as the dictionary is modified during
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# the loop
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for key in list(self.actions.keys()):
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action_count, time_start, rate_hz = self.actions[key]
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# Rate limit = "seconds since we started limiting this action" * rate_hz
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# If this limit has not been exceeded, wipe our record of this action
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time_delta = time_now_s - time_start
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if action_count - time_delta * rate_hz > 0:
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continue
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else:
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del self.actions[key]
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def ratelimit(
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self,
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key: Any,
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rate_hz: Optional[float] = None,
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burst_count: Optional[int] = None,
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update: bool = True,
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_time_now_s: Optional[int] = None,
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):
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"""Checks if an action can be performed. If not, raises a LimitExceededError
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Args:
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key: An arbitrary key used to classify an action
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rate_hz: The long term number of actions that can be performed in a second.
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Overrides the value set during instantiation if set.
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burst_count: How many actions that can be performed before being limited.
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Overrides the value set during instantiation if set.
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update: Whether to count this check as performing the action
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_time_now_s: The current time. Optional, defaults to the current time according
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to self.clock. Only used by tests.
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Raises:
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LimitExceededError: If an action could not be performed, along with the time in
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milliseconds until the action can be performed again
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"""
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time_now_s = _time_now_s if _time_now_s is not None else self.clock.time()
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allowed, time_allowed = self.can_do_action(
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key,
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rate_hz=rate_hz,
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burst_count=burst_count,
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update=update,
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_time_now_s=time_now_s,
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)
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if not allowed:
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raise LimitExceededError(
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retry_after_ms=int(1000 * (time_allowed - time_now_s))
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)
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