feat: add response cache middleware with poisoning-safe keys

2026-07-20 07:10:42 -04:00
parent c3d5079d39
commit 6286086551
4 changed files with 434 additions and 0 deletions
@@ -0,0 +1,155 @@
+"""CacheMW: 响应缓存中间件;key 公式在此(算法一份),后端是笨 KV。
+
+ARCH §7.5: key = sha256(canonical_json({model, messages_digest, namespace,
+salt}));多模态 part 先摘要再 hash(防 Video-Tree 整段 base64 进 hash 的
+开销);namespace 必填防跨项目/租户毒化;只缓存阶梯通过的成功响应
+(StructuredMW 在内层,能返回即已通过)。读写失败静默降级(铁律)。
+"""
+
+from __future__ import annotations
+
+import asyncio
+import dataclasses
+import hashlib
+import json
+import uuid
+from typing import TYPE_CHECKING, Any
+
+from loguru import logger
+
+from polygateway.types import ChatRequest, LLMResponse
+
+if TYPE_CHECKING:
+    from polygateway.ports import CacheBackend, CallNext, StructuredOutputStrategy
+
+_KEY_PREFIX = "pgw:cache:"
+_RESPONSE_FIELDS = {f.name for f in dataclasses.fields(LLMResponse)}
+
+
+def digest_messages(messages: list[dict[str, Any]]) -> list[dict[str, Any]]:
+    """多模态 content part 先各自 sha256 摘要再参与序列化;文本原文参与。
+
+    与遥测落库共用同一函数(ARCH §7.8),保证缓存 key 与遥测口径一致。
+    """
+    digested = []
+    for msg in messages:
+        content = msg.get("content")
+        if isinstance(content, list):
+            parts = [_digest_part(part) for part in content]
+            digested.append({**msg, "content": parts})
+        else:
+            digested.append(msg)
+    return digested
+
+
+def _digest_part(part: Any) -> Any:
+    if isinstance(part, dict) and part.get("type") == "image_url":
+        url = str(part.get("image_url", {}).get("url", ""))
+        return {"type": "image_url", "sha256": hashlib.sha256(url.encode()).hexdigest()}
+    return part
+
+
+def build_cache_key(
+    model_fingerprint: str, messages: list[dict[str, Any]], namespace: str, salt: str | None
+) -> str:
+    """缓存 key 公式;salt 仅非 None 时参与(VT 旧键语义: 不传 salt 键形不变)。"""
+    key_obj: dict[str, Any] = {
+        "model": model_fingerprint,
+        "messages": digest_messages(messages),
+        "namespace": namespace,
+    }
+    if salt is not None:
+        key_obj["salt"] = salt
+    payload = json.dumps(key_obj, sort_keys=True, ensure_ascii=False)
+    return _KEY_PREFIX + hashlib.sha256(payload.encode("utf-8")).hexdigest()
+
+
+class CacheMW:
+    """洋葱第二层(遥测内、结构化外)。
+
+    model_fingerprint 由装配层从源列表计算(多源 scope = 排序去重的 model
+    名合集);源集合变化 → key 变化 → 一次性冷启动,换取跨源集合零毒化。
+    """
+
+    def __init__(
+        self,
+        *,
+        backend: CacheBackend,
+        model_fingerprint: str,
+        default_namespace: str,
+        ttl_s: int,
+        strategy: StructuredOutputStrategy | None = None,
+    ) -> None:
+        if not default_namespace.strip():
+            raise ValueError("缓存 namespace 不能为空(防跨项目/租户毒化)")
+        if ttl_s <= 0:
+            raise ValueError("缓存 TTL 必须 > 0(禁止永不过期)")
+        self._backend = backend
+        self._fingerprint = model_fingerprint
+        self._namespace = default_namespace
+        self._ttl_s = ttl_s
+        self._strategy = strategy
+
+    async def __call__(self, request: ChatRequest, call_next: CallNext) -> LLMResponse:
+        namespace = request.cache_namespace or self._namespace
+        key = build_cache_key(self._fingerprint, request.messages, namespace, request.cache_salt)
+        cached = await self._safe_get(key)
+        if cached is not None:
+            hit = self._rehydrate(cached, request)
+            if hit is not None:
+                return hit
+        response = await call_next(request)
+        await self._safe_set(key, self._serialize(response))
+        return response
+
+    # —— 命中路径 ——
+
+    def _rehydrate(self, raw: str, request: ChatRequest) -> LLMResponse | None:
+        """反序列化 + 按本次调用的 structured 档零网络重建;失败按未命中。"""
+        try:
+            data = json.loads(raw)
+            fields = {k: v for k, v in data.items() if k in _RESPONSE_FIELDS}
+            structured_data = self._rebuild_structured(fields.get("content", ""), request)
+            fields.update(
+                cache_hit=True, latency_ms=0, ttft_ms=None, max_inter_token_ms=None,
+                call_id=str(uuid.uuid4()), structured_data=structured_data,
+            )
+            return LLMResponse(**fields)
+        except Exception as exc:
+            logger.warning("缓存命中重建失败,按未命中回源: {}", exc)
+            return None
+
+    def _rebuild_structured(self, content: str, request: ChatRequest) -> Any | None:
+        """对缓存 content 重跑阶梯②③(schema 变更后旧缓存自动重校验,设计 §2.1)。"""
+        if request.structured is None:
+            return None
+        if self._strategy is None:
+            raise ValueError("structured 调用需要装配 strategy 才能命中重建")
+        parsed = self._strategy.parse(content)
+        if request.structured == "json":
+            return parsed
+        return request.structured.model_validate(parsed)
+
+    # —— 写路径与降级 ——
+
+    def _serialize(self, response: LLMResponse) -> str:
+        data = dataclasses.asdict(response)
+        data.pop("structured_data", None)  # pydantic 实例不可 JSON 往返(设计 §2.1)
+        return json.dumps(data, ensure_ascii=False)
+
+    async def _safe_get(self, key: str) -> str | None:
+        try:
+            return await self._backend.get(key)
+        except asyncio.CancelledError:
+            raise
+        except Exception as exc:
+            logger.warning("缓存读取失败,降级为未命中: {}", exc)
+            return None
+
+    async def _safe_set(self, key: str, value: str) -> None:
+        try:
+            await self._backend.set(key, value, self._ttl_s)
+        except asyncio.CancelledError:
+            raise
+        except Exception as exc:
+            logger.warning("缓存写入失败,跳过缓存: {}", exc)