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1"""Weak ETag + Cache-Control on public GET responses (API 1.1).23Pure ASGI middleware so it can sit *inside* GZip (the hash is computed on the uncompressed JSON body — gzip output embeds a4timestamp and would never be stable). `If-None-Match` matching the body hash → `304 Not Modified` with an empty body.5Admin, docs and non-200 responses are left untouched."""6from __future__ import annotations78import hashlib9from typing import Any1011from starlette.types import ASGIApp, Message, Receive, Scope, Send1213PUBLIC_PREFIX = "/api/v1/"14SKIP_PREFIXES = ("/api/v1/admin", "/api/v1/docs", "/api/v1/openapi.json", "/api/v1/api-keys")15CACHE_CONTROL = "public, max-age=60, stale-while-revalidate=300"16MAX_BUFFER = 8 * 1024 * 1024 # bodies above this are passed through unhashed171819def weak_etag(body: bytes) -> str:20 return 'W/"' + hashlib.sha1(body).hexdigest() + '"'212223def _etags_match(header: str | None, etag: str) -> bool:24 if not header:25 return False26 if header.strip() == "*":27 return True28 wanted = {t.strip() for t in header.split(",")}29 strong = etag.removeprefix("W/")30 return etag in wanted or strong in wanted or any((t.removeprefix("W/")) == strong for t in wanted)313233class ETagMiddleware:34 def __init__(self, app: ASGIApp) -> None:35 self.app = app3637 async def __call__(self, scope: Scope, receive: Receive, send: Send) -> None:38 if scope["type"] != "http" or scope.get("method") != "GET":39 await self.app(scope, receive, send)40 return41 path: str = scope.get("path", "")42 if not path.startswith(PUBLIC_PREFIX) or path.startswith(SKIP_PREFIXES):43 await self.app(scope, receive, send)44 return45 headers = {k.decode("latin-1").lower(): v.decode("latin-1") for k, v in scope.get("headers", [])}46 inm = headers.get("if-none-match")4748 start: Message | None = None49 chunks: list[bytes] = []50 passthrough = False51 size = 05253 async def send_wrapper(message: Message) -> None:54 nonlocal start, passthrough, size55 if passthrough:56 await send(message)57 return58 if message["type"] == "http.response.start":59 start = message60 if message.get("status") != 200:61 passthrough = True62 await send(message)63 return64 if message["type"] == "http.response.body":65 body = message.get("body", b"")66 size += len(body)67 if size > MAX_BUFFER:68 passthrough = True69 assert start is not None70 await send(start)71 for c in chunks:72 await send({"type": "http.response.body", "body": c, "more_body": True})73 await send(message)74 return75 chunks.append(body)76 if message.get("more_body"):77 return78 assert start is not None79 full = b"".join(chunks)80 etag = weak_etag(full)81 raw_headers: list[tuple[bytes, bytes]] = [(k, v) for k, v in start.get("headers", []) if k.lower() not in (b"etag", b"cache-control")]82 raw_headers.append((b"etag", etag.encode("latin-1")))83 raw_headers.append((b"cache-control", CACHE_CONTROL.encode("latin-1")))84 if _etags_match(inm, etag):85 keep = {b"etag", b"cache-control", b"vary", b"x-content-type-options", b"referrer-policy", b"access-control-allow-origin"}86 hdrs = [(k, v) for k, v in raw_headers if k.lower() in keep]87 await send({"type": "http.response.start", "status": 304, "headers": hdrs})88 await send({"type": "http.response.body", "body": b"", "more_body": False})89 return90 await send({"type": "http.response.start", "status": 200, "headers": raw_headers})91 await send({"type": "http.response.body", "body": full, "more_body": False})92 return93 await send(message)9495 await self.app(scope, receive, send_wrapper)969798def etag_of(value: Any) -> str:99 """Helper for tests and callers holding an already-rendered body."""100 return weak_etag(value if isinstance(value, bytes) else str(value).encode())101102103__all__ = ["CACHE_CONTROL", "ETagMiddleware", "etag_of", "weak_etag"]104