Regression from 04d5a556. Keying the resize cache on identity meant the
disc response no longer carried a content hash, and the full-size branch
set no ETag either — so WriteImageHeaders fell back to the empty hash
and emitted `ETag: ""` for every full-size disc image. Since ifNoneMatch
compares the unquoted value, a client echoing that back matched, and got
a 304 even after the image was replaced.
The full-size branch now carries the same identity validator the sized
branch uses, so it moves when the folder's images change.
WriteImageHeaders is hardened against the class as well: an empty
validator is no validator, so it is neither emitted nor matched.
Reported by Codex on #5847.
- A negative size (Subsonic size / Jellyfin maxwidth accept signed ints) reached
resizeStaticImage, where the square path builds image.NewNRGBA(Rect(0,0,size,size))
— a giant rectangle that panics/OOMs. Clamp size<0 to 0 (full-size) at the Service
entry. Positive sizes were already clamped to the original.
- imghttp used a plain func Test with a table; convert to a Ginkgo DescribeTable with
the suite entry point in imghttp_suite_test.go (AGENTS.md test-framework requirement).
The ETag was the pixel hash of the original image, so a CoverArtQuality or
EnableWebPEncoding change altered the resized bytes without changing the ETag —
revalidating clients got a spurious 304 and kept the old encoding. Resized responses
now carry a representation ETag (hash + size + square + encode settings) used for the
ETag header and If-None-Match, while the immutable decision stays on the pixel hash
(URLs remain pixel-identity per the spec, so hash-suffixed clients keep zero-request
caching). Full-size originals fall back to the pixel hash as before.
