anonymousland-synapse/synapse/api/ratelimiting.py

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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.
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from collections import OrderedDict
from typing import Hashable, Optional, Tuple
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from synapse.api.errors import LimitExceededError
from synapse.storage.databases.main import DataStore
from synapse.types import Requester
from synapse.util import Clock
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class Ratelimiter:
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"""
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.
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"""
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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
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self.actions: OrderedDict[Hashable, Tuple[float, float, float]] = OrderedDict()
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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,
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_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)
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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.
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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
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"""
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
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time_delta = time_now_s - time_start
performed_count = action_count - time_delta * rate_hz
if performed_count < 0:
performed_count = 0
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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
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allowed = False
else:
# We haven't reached our limit yet
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allowed = True
action_count = performed_count + n_actions
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if update:
self.actions[key] = (action_count, time_start, rate_hz)
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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
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if time_allowed < time_now_s:
time_allowed = time_now_s
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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
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time_allowed = -1
return allowed, time_allowed
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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
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time_delta = time_now_s - time_start
if action_count - time_delta * rate_hz > 0:
continue
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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,
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_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))
)