patchingfailed reported on v3.44 stable: a gallery named `Ägypten` with
photo `Ägypten_individual_0050.jpg` downloads as `gypten_...` —
the leading umlaut is dropped entirely. Their hypothesis was a
Content-Disposition encoding issue, but the actual root cause sits
one layer earlier: at UPLOAD time when `generatePhotoFilename` calls
`sanitizeFilename`.
`sanitizeFilename` did:
String(str).trim()
.replace(/\s+/g, '_')
.replace(/[^a-zA-Z0-9_\-\.]/g, '') // ← drops `Ä` outright
.replace(/[_\-]{2,}/g, '_')
.replace(/^[_\-]+|[_\-]+$/g, ''); // ← would strip a leading _ too
For `Ägypten`: alphanumeric-strip → `gypten` (Ä gone, no underscore
left behind because the regex used '' as the replacement, not '_'). The
result is stored in `photos.filename` and that's what downloads serve.
By that point `buildContentDisposition` is doing the right thing
(emits both `filename="..."` ASCII fallback AND RFC 5987
`filename*=UTF-8''…` — Chrome correctly picks the UTF-8 form), but the
string it's encoding has already lost the umlaut at the DB layer.
Cure: NFD-normalize + strip combining marks BEFORE the alphanumeric
strip. Same pipeline `utils/slug.js` (#525) already uses for URL
slugs:
sanitized = sanitized
.normalize('NFD')
.replace(/[̀-ͯ]/g, '');
Now `Ägypten` → NFD-decomposed `A` + combining diaeresis → strip
combining mark → `Agypten` survives the alphanumeric pass. Filename
and URL slug stay in sync (the URL was already `Agypten`, per
patchingfailed's report — the filename now matches).
Test surface: new `filenameSanitizer.test.js` pins:
- the headline #607 contract for German / Portuguese / French / Spanish
accented inputs (with a counter-example using the pre-fix pipeline so
a future edit can't quietly regress it)
- ASCII-input parity — pre-#607 byte-identical output for every
pre-existing ASCII case
- `generatePhotoFilename` composed round-trip
- `sanitizeForContentDisposition` + `buildContentDisposition` RFC 6266
dual-form output (since the helper sits next to this function and is
the next thing to break if a refactor goes sideways)
- `sanitizeForZipEntry` path-traversal blocking
31 cases total, all pass.
Bundled into PR #609 since it's a small targeted fix and that PR is
already an admin-UI polish branch with low review weight.
Paul Nothaft
620163f2db