FileThumbnailController::preview() writes at most one FilePreviewed row
per viewer per file per five minutes, because a browser turns one video
into a long tail of Range requests against the same URL. Its docblock
names the anonymous route as the place the same act happens without an
account -- and that route logs unconditionally.
Measured: five requests for the same public file, five
PublicFilePreviewed rows, against one for the signed-in twin. One visitor
watching one clip buries the public half of the activity log, which is
also the half an operator reads to see what the outside world is doing.
The window is now a shared PreviewLog, next to PreviewKind, which the two
preview routes already share for the same reason. Keying is unchanged for
a signed-in viewer; an anonymous one has no account to key on, so the
request IP stands in -- the same substitute the API's rate limiter makes
for an unauthenticated caller. It is a cache key with a five-minute life
and never reaches the log, which keeps its own decision about recording an
IP (ActivityLogger::shouldRecordIp, Setting::DownloadIpLogging).
Three tests: the replay is one row, two visitors are two rows, and the
window is per file. Without the fix the first goes red.
v1 could preview four kinds of file in a modal — images, video, audio and
PDF. v2 previewed only images, and not by decision: preview shipped as part
of the image *thumbnail* work (1c68aa1), so "previewable" quietly became a
synonym for "GD can decode it". FileThumbnailController::preview() gated on
ThumbnailGenerator::SUPPORTED_MIME_TYPES, the frontend mirrored the same
four types, and the dialog was a hardcoded <img>.
Rather than widen that list — it drives pathFor(), extensionFor(),
generate() and FileDiskCleanup, and a video reaching getimagesize() is a
500 — this separates the two questions. PreviewKind now answers "may these
bytes be served inline, and what element renders them?", while
ThumbnailGenerator keeps answering the narrower "can this app decode it
itself?", which is what renditions, the cache and the watermark hook
actually depend on. Image delegates to it so the two cannot drift.
The allowlist stays a security boundary: mime_type is sniffed from the
bytes, so text/html and image/svg+xml remain excluded, and PreviewKind is
deliberately narrower than "formats a browser might cope with" — no
quicktime, avi or matroska, because an embedded player for those shows a
black rectangle. Those still download exactly as before.
docs/security-audit-2026-08-05.md finding 1 recorded that adding
application/pdf "should be a conscious decision". This is that decision,
and three things were measured rather than assumed:
- An <iframe sandbox> cannot be used. Chrome refuses to run its PDF viewer
in a sandboxed frame at all (ERR_BLOCKED_BY_CLIENT, with or without
allow-same-origin) — the attribute removes the feature, it does not
harden it.
- nginx's `Content-Security-Policy: sandbox; default-src 'none'` on
/protected-files/ does work (a <video> frame lands in an opaque origin),
but Chrome exempts its PDF viewer from it, so it is not what protects
the PDF case.
- What does is the allowlist plus the browser's own PDF sandbox, where PDF
JavaScript has no DOM and no cookies.
Range requests were verified end to end: 206 with a correct Content-Range,
a byte-perfect file reassembled from three ranges, and a real browser
seeking to 10s of a 20s clip. nginx drops the upstream Content-Length on
the X-Accel path, so there is no collision.
Two settings, both defaulting on so no installation loses what it has:
clients_can_preview_files and public_listing_preview_enabled. Staff are
never gated. The anonymous side needed a route of its own — there was no
public preview endpoint — with its own throttle bucket, since a bare
throttle: shares one counter across that whole block.
A preview now logs at most one FilePreviewed per viewer per file per five
minutes: a <video> turns one deliberate act into a long tail of Range
requests, and a row each would bury the log.
Also fixes a layout bug the tests could never catch. A portal file row was
flex justify-between with three children — name, comment trigger, download
— so the middle one settled wherever the name happened to end and the
comment icon sat at a different place on every row. The name block now
takes the slack and every action lives in one trailing group, with the
comment trigger in a fixed-width slot so the icons form a column. And
because half the previewable files have no thumbnail to click — a PDF, an
mp3 and an mp4 all render as a generic icon — every row gains an explicit
PreviewAction beside DownloadAction, matching whatever style that theme
gives its download control.
denkfabrik-li