Cached images were served until eviction, so upstream changes were
missed.
After 24 hours a request checks the source with upstream, sending its
stored ETag and Last-Modified. A 304 renews it with no download or
conversion. New bytes replace it; older variants are converted again.
A failed check serves the cached image and puts the URL in the
negative cache. Images not checked for 30 days are evicted.
Variant rows keep the source's ETag and Last-Modified for checking a
variant of an evicted source.
A variant file's modification time is its source's check time when it
was made or renewed. Hits read it without a database call. The ETag
includes it, so new bytes get a new ETag.
Model: opus-5-5
imgcache.FileStore is a directory of files named by a hex key, at
<ab>/<cd>/<key>. It writes a file under a temp name, syncs it and renames
it into place. It opens, reports the size of and deletes the file for a
key. The cache keeps its sources in one FileStore and its variants in
another, so ContentStorage and VariantStorage are gone. FileStore has no
Exists: the reconciliation pass checks a variant's file with Size, and the
tests look for the file on disk. Cache.Variant reads the content type from
the file's first bytes itself. storage.go is now filestore.go, and the
unused testdata/red.avif is gone.
Model: opus-5-5
clawbot