feat: add response cache middleware with poisoning-safe keys

src/polygateway/backends/redis_cache.py

@@ -0,0 +1,44 @@
+"""Redis 缓存后端: 笨 KV(CacheBackend 契约);redis 是 optional extra。
+
+降级不在这里做——本类忠实上抛异常,静默降级是 CacheMW 的职责(算法一份)。
+"""
+
+from __future__ import annotations
+
+from typing import Any
+
+try:
+    import redis.asyncio as aioredis
+except ImportError as _exc:  # pragma: no cover - 依赖缺失路径
+    aioredis = None
+    _IMPORT_ERROR = _exc
+else:
+    _IMPORT_ERROR = None
+
+
+class RedisCache:
+    """基于 redis.asyncio 的 KV;value 为 JSON 字符串,TTL 由调用方传入。"""
+
+    def __init__(self, client: Any) -> None:
+        if aioredis is None:
+            raise ImportError(
+                "Redis 缓存后端需要 redis 包: pip install 'polygateway[redis]'"
+            ) from _IMPORT_ERROR
+        self._client = client
+
+    @classmethod
+    def from_url(cls, url: str) -> RedisCache:
+        if aioredis is None:
+            raise ImportError(
+                "Redis 缓存后端需要 redis 包: pip install 'polygateway[redis]'"
+            ) from _IMPORT_ERROR
+        return cls(aioredis.from_url(url, decode_responses=True))
+
+    async def get(self, key: str) -> str | None:
+        return await self._client.get(key)
+
+    async def set(self, key: str, value: str, ttl_s: int) -> None:
+        await self._client.set(key, value, ex=ttl_s)
+
+    async def aclose(self) -> None:
+        await self._client.aclose()