Add offline clip caching

backend/app/http_cache.py

@@ -0,0 +1,79 @@
+from __future__ import annotations
+
+import hashlib
+import json
+from collections.abc import Mapping, Sequence
+from datetime import datetime
+from typing import Any
+
+from fastapi import Request, Response
+from fastapi.encoders import jsonable_encoder
+
+
+def _strip_keys(value: Any, excluded_keys: set[str]) -> Any:
+    if isinstance(value, Mapping):
+        return {
+            key: _strip_keys(item, excluded_keys)
+            for key, item in value.items()
+            if key not in excluded_keys
+        }
+    if isinstance(value, Sequence) and not isinstance(value, (str, bytes, bytearray)):
+        return [_strip_keys(item, excluded_keys) for item in value]
+    return value
+
+
+def build_etag(payload: Any, *, exclude_keys: set[str] | None = None) -> str:
+    encoded = jsonable_encoder(payload)
+    if exclude_keys:
+        encoded = _strip_keys(encoded, exclude_keys)
+    serialized = json.dumps(encoded, sort_keys=True, separators=(",", ":"), ensure_ascii=False)
+    digest = hashlib.sha1(serialized.encode("utf-8")).hexdigest()
+    return f'"{digest}"'
+
+
+def is_matching_etag(request: Request, etag: str) -> bool:
+    header = request.headers.get("if-none-match")
+    if not header:
+        return False
+
+    for candidate in header.split(","):
+        if candidate.strip() in {etag, "*"}:
+            return True
+    return False
+
+
+def apply_cache_headers(
+    response: Response,
+    *,
+    cache_control: str,
+    etag: str | None = None,
+    last_modified: datetime | None = None,
+) -> None:
+    response.headers["Cache-Control"] = cache_control
+    response.headers["Vary"] = "Cookie, Authorization"
+    if etag is not None:
+        response.headers["ETag"] = etag
+    if last_modified is not None:
+        response.headers["Last-Modified"] = last_modified.strftime("%a, %d %b %Y %H:%M:%S GMT")
+
+
+def set_no_store(response: Response) -> None:
+    apply_cache_headers(response, cache_control="no-store")
+
+
+def set_private_revalidate(response: Response, *, etag: str | None = None, last_modified: datetime | None = None) -> None:
+    apply_cache_headers(
+        response,
+        cache_control="private, max-age=0, must-revalidate",
+        etag=etag,
+        last_modified=last_modified,
+    )
+
+
+def set_public_immutable(response: Response, *, etag: str | None = None, last_modified: datetime | None = None) -> None:
+    apply_cache_headers(
+        response,
+        cache_control="public, max-age=31536000, immutable",
+        etag=etag,
+        last_modified=last_modified,
+    )