The thumbnail ETag was "thumb-{file_id}-{size}-{format}", sent with
Cache-Control: public, max-age=31536000, immutable. Replacing a file's
content preserves its id — file_upload_service rebuilds the entity with
parts.id and a new hash, then fires on_file_updated, which deletes and
regenerates the thumbnails — so the server produced a new thumbnail while
still advertising the old ETag. Because `immutable` tells a conforming
browser not to revalidate at all inside the freshness window, clients kept
rendering the previous image for up to a year, unfixably.
Keyed on the content hash the directive becomes honest: a thumbnail is a
pure function of (source bytes, size, format), so that triple identifies
the response. New content yields a new ETag.
The same change fixes the opposite direction. A copy, or any dedup twin,
had a different id and therefore a different ETag, so clients refetched
bytes they already held even though both are served from the same derived
blob. Now identical content agrees on an ETag and revalidates to 304
across files, users and copies.
Both thumbnail endpoints were affected: the REST handler and the
NextCloud preview handler.
Cost is one PK lookup ahead of the 304 decision, where the id-keyed
version needed none — paid for by no longer serving stale images. It is
partly recovered: both handlers already resolved the same hash further
down for the render path, and that second lookup is now gone, so the
cache-miss path is unchanged and only the 304 path pays. The resolved
hash is also handed to get_cached_thumbnail instead of None, saving the
service its own lookup.
No new disclosure: content_hash is already on FileDto and returned by
GET /api/files/{id}.
Tests: thumbnail_etag_content_keyed.hurl covers invalidation — overwrite
in place via WebDAV PUT, assert the ETag changed, assert a client holding
the stale one gets 200 rather than 304. derived_blob_copy.hurl gains the
sharing direction: a copy answers with the SAME ETag and revalidates to
304, which is the one externally observable consequence of content-keying
and was not previously testable.
Edouard Vanbelle
a3a93b90ec