97 lines
3.9 KiB
Python
97 lines
3.9 KiB
Python
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"""限流计数后端：Redis 固定窗口计数，**Redis 不可用时一律放行**。
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取舍（为什么是固定窗口，而不是 ZSET 滑动窗口或令牌桶）：
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- 固定窗口用一条 `INCR` + `TTL` 就能原子地完成"计数 + 取重试等待时间"，不需要 Lua
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或事务，故障面最小；滑动窗口要 `ZREMRANGEBYSCORE`/`ZADD`/`ZCARD`/`EXPIRE` 四条命令
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才能近似原子，令牌桶还要在服务端保存补充速率的状态。本平台的限流目的是**保护**
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底座不被单个客户端打爆，不是做精确计费，窗口边界最多放过一个窗口的量可以接受。
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- 计数键带 TTL，Redis 自己回收，不需要额外的清理任务，也不会留下永久脏键。
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降级语义（用户要求，也是 `MemoryCacheAdapter` 的同一原则）：限流是保护措施，不能因为
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Redis 故障把正常请求全部拒掉。因此后端**只返回 `None` 表示"无法判定"**，由调用方放行；
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这里绝不抛异常、绝不返回"计数超限"。
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Redis 客户端是**懒建**的：进程启动时 Redis 不可用不应该让应用起不来，第一次真正需要
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限流判定时才建连（与 `bootstrap.py` 的记忆缓存适配器一致）。
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"""
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import logging
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from typing import Any, Protocol
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from app.core.config import get_settings
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logger = logging.getLogger(__name__)
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class CounterBackend(Protocol):
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"""限流计数后端。
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`increment` 返回 `(窗口内计数, 剩余秒数)`；返回 `None` 表示后端不可用，
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调用方必须**放行**（fail-open）。
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"""
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async def increment(self, key: str, window_seconds: int) -> tuple[int, int] | None: ...
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class RedisCounterBackend:
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def __init__(
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self,
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redis_url: str,
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*,
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connect_timeout_seconds: float,
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client_factory: Any | None = None,
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) -> None:
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self._redis_url = redis_url
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self._connect_timeout_seconds = connect_timeout_seconds
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# 注入点仅用于测试：默认走 `redis.asyncio.Redis.from_url`。
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self._client_factory = client_factory
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self._client: Any | None = None
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async def _client_or_none(self) -> Any | None:
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if self._client is not None:
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return self._client
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try:
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if self._client_factory is not None:
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client = self._client_factory()
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else:
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from redis.asyncio import Redis
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client = Redis.from_url(
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self._redis_url,
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socket_connect_timeout=self._connect_timeout_seconds,
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socket_timeout=self._connect_timeout_seconds,
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decode_responses=True,
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)
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self._client = client
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except Exception:
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logger.warning("限流后端不可用：Redis 客户端构造失败，本次降级放行", exc_info=True)
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return None
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return self._client
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async def increment(self, key: str, window_seconds: int) -> tuple[int, int] | None:
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client = await self._client_or_none()
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if client is None:
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return None
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try:
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async with client.pipeline(transaction=False) as pipe:
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pipe.incr(key)
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pipe.ttl(key)
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count, ttl = await pipe.execute()
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remaining = int(ttl)
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if remaining < 0:
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# 键首次创建（或历史上丢过 TTL）：补一次过期为窗口长度。
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await client.expire(key, window_seconds)
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remaining = window_seconds
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return int(count), max(1, remaining)
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except Exception:
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logger.warning("限流后端不可用：Redis 计数失败，本次降级放行", exc_info=True)
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return None
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def default_counter_backend() -> CounterBackend:
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settings = get_settings()
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return RedisCounterBackend(
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settings.redis_url, connect_timeout_seconds=settings.redis_connect_timeout_seconds
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)
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