254 lines
8.5 KiB
Python
254 lines
8.5 KiB
Python
from __future__ import annotations
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import bisect
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import threading
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import time
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from collections import Counter, defaultdict
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from math import floor
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import limits.typing
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from limits.storage.base import (
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MovingWindowSupport,
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SlidingWindowCounterSupport,
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Storage,
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TimestampedSlidingWindow,
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)
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class Entry:
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def __init__(self, expiry: float) -> None:
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self.atime = time.time()
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self.expiry = self.atime + expiry
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class MemoryStorage(
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Storage, MovingWindowSupport, SlidingWindowCounterSupport, TimestampedSlidingWindow
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):
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"""
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rate limit storage using :class:`collections.Counter`
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as an in memory storage for fixed and sliding window strategies,
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and a simple list to implement moving window strategy.
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"""
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STORAGE_SCHEME = ["memory"]
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def __init__(self, uri: str | None = None, wrap_exceptions: bool = False, **_: str):
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self.storage: limits.typing.Counter[str] = Counter()
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self.locks: defaultdict[str, threading.RLock] = defaultdict(threading.RLock)
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self.expirations: dict[str, float] = {}
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self.events: dict[str, list[Entry]] = {}
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self.timer: threading.Timer = threading.Timer(0.01, self.__expire_events)
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self.timer.start()
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super().__init__(uri, wrap_exceptions=wrap_exceptions, **_)
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def __getstate__(self) -> dict[str, limits.typing.Any]: # type: ignore[explicit-any]
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state = self.__dict__.copy()
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del state["timer"]
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del state["locks"]
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return state
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def __setstate__(self, state: dict[str, limits.typing.Any]) -> None: # type: ignore[explicit-any]
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self.__dict__.update(state)
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self.locks = defaultdict(threading.RLock)
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self.timer = threading.Timer(0.01, self.__expire_events)
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self.timer.start()
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def __expire_events(self) -> None:
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for key in list(self.events.keys()):
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with self.locks[key]:
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if events := self.events.get(key, []):
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oldest = bisect.bisect_left(
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events, -time.time(), key=lambda event: -event.expiry
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)
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self.events[key] = self.events[key][:oldest]
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if not self.events.get(key, None):
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self.locks.pop(key, None)
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for key in list(self.expirations.keys()):
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if self.expirations[key] <= time.time():
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self.storage.pop(key, None)
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self.expirations.pop(key, None)
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self.locks.pop(key, None)
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def __schedule_expiry(self) -> None:
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if not self.timer.is_alive():
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self.timer = threading.Timer(0.01, self.__expire_events)
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self.timer.start()
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@property
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def base_exceptions(
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self,
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) -> type[Exception] | tuple[type[Exception], ...]: # pragma: no cover
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return ValueError
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def incr(self, key: str, expiry: float, amount: int = 1) -> int:
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"""
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increments the counter for a given rate limit key
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:param key: the key to increment
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:param expiry: amount in seconds for the key to expire in
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:param amount: the number to increment by
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"""
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self.get(key)
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self.__schedule_expiry()
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with self.locks[key]:
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self.storage[key] += amount
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if self.storage[key] == amount:
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self.expirations[key] = time.time() + expiry
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return self.storage.get(key, 0)
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def decr(self, key: str, amount: int = 1) -> int:
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"""
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decrements the counter for a given rate limit key
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:param key: the key to decrement
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:param amount: the number to decrement by
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"""
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self.get(key)
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self.__schedule_expiry()
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with self.locks[key]:
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self.storage[key] = max(self.storage[key] - amount, 0)
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return self.storage.get(key, 0)
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def get(self, key: str) -> int:
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"""
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:param key: the key to get the counter value for
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"""
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if self.expirations.get(key, 0) <= time.time():
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self.storage.pop(key, None)
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self.expirations.pop(key, None)
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self.locks.pop(key, None)
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return self.storage.get(key, 0)
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def clear(self, key: str) -> None:
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"""
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:param key: the key to clear rate limits for
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"""
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self.storage.pop(key, None)
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self.expirations.pop(key, None)
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self.events.pop(key, None)
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self.locks.pop(key, None)
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def acquire_entry(self, key: str, limit: int, expiry: int, amount: int = 1) -> bool:
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"""
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:param key: rate limit key to acquire an entry in
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:param limit: amount of entries allowed
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:param expiry: expiry of the entry
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:param amount: the number of entries to acquire
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"""
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if amount > limit:
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return False
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self.__schedule_expiry()
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with self.locks[key]:
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self.events.setdefault(key, [])
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timestamp = time.time()
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try:
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entry = self.events[key][limit - amount]
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except IndexError:
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entry = None
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if entry and entry.atime >= timestamp - expiry:
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return False
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else:
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self.events[key][:0] = [Entry(expiry)] * amount
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return True
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def get_expiry(self, key: str) -> float:
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"""
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:param key: the key to get the expiry for
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"""
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return self.expirations.get(key, time.time())
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def get_moving_window(self, key: str, limit: int, expiry: int) -> tuple[float, int]:
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"""
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returns the starting point and the number of entries in the moving
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window
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:param key: rate limit key
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:param expiry: expiry of entry
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:return: (start of window, number of acquired entries)
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"""
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timestamp = time.time()
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if events := self.events.get(key, []):
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oldest = bisect.bisect_left(
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events, -(timestamp - expiry), key=lambda entry: -entry.atime
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)
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return events[oldest - 1].atime, oldest
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return timestamp, 0
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def acquire_sliding_window_entry(
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self,
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key: str,
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limit: int,
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expiry: int,
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amount: int = 1,
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) -> bool:
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if amount > limit:
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return False
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now = time.time()
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previous_key, current_key = self.sliding_window_keys(key, expiry, now)
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(
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previous_count,
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previous_ttl,
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current_count,
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_,
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) = self._get_sliding_window_info(previous_key, current_key, expiry, now)
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weighted_count = previous_count * previous_ttl / expiry + current_count
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if floor(weighted_count) + amount > limit:
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return False
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else:
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# Hit, increase the current counter.
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# If the counter doesn't exist yet, set twice the theorical expiry.
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current_count = self.incr(current_key, 2 * expiry, amount=amount)
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weighted_count = previous_count * previous_ttl / expiry + current_count
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if floor(weighted_count) > limit:
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# Another hit won the race condition: revert the incrementation and refuse this hit
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# Limitation: during high concurrency at the end of the window,
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# the counter is shifted and cannot be decremented, so less requests than expected are allowed.
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self.decr(current_key, amount)
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return False
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return True
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def _get_sliding_window_info(
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self,
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previous_key: str,
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current_key: str,
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expiry: int,
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now: float,
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) -> tuple[int, float, int, float]:
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previous_count = self.get(previous_key)
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current_count = self.get(current_key)
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if previous_count == 0:
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previous_ttl = float(0)
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else:
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previous_ttl = (1 - (((now - expiry) / expiry) % 1)) * expiry
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current_ttl = (1 - ((now / expiry) % 1)) * expiry + expiry
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return previous_count, previous_ttl, current_count, current_ttl
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def get_sliding_window(
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self, key: str, expiry: int
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) -> tuple[int, float, int, float]:
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now = time.time()
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previous_key, current_key = self.sliding_window_keys(key, expiry, now)
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return self._get_sliding_window_info(previous_key, current_key, expiry, now)
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def check(self) -> bool:
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"""
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check if storage is healthy
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"""
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return True
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def reset(self) -> int | None:
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num_items = max(len(self.storage), len(self.events))
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self.storage.clear()
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self.expirations.clear()
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self.events.clear()
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self.locks.clear()
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return num_items
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