adds a path mode to /v1/ffmpeg:
{ input: "as_…" } → stored as a new asset, 201
{ inputPath: "/…", outputPath: "/…" } → written where you said, 200 { path, bytes }
THIS REVISES THE INVARIANT IN docs/SECURITY.md, deliberately, and that document now
says so at the top rather than being quietly contradicted by the code.
it used to read "the caller never supplies a path, for input or output". that was
right for an upload service and av-club is not one: both of its real consumers —
a right-click on ~/Movies/thing.mkv, and a commander watching an upload folder —
already have the file, and obeying the rule meant copying gigabytes in and back out
to convert something that never moved. a rule that expensive gets worked around,
and the workaround is where the hole would have been.
so it is narrower now and says what it was always for. argv never a shell,
-protocol_whitelist file, filters allowlisted, work bounded — all unchanged. what
is gone is only the claim that a path never appears, replaced by one small module
every path goes through:
absolute (a relative path resolves against a cwd the caller cannot see)
realpath FIRST, then check — checking the path as written and opening the
resolved one is the classic way this fails
inside as `root` or `root + sep`, never a bare startsWith, which accepts
/home/user-backup for a root of /home/user
for an output the PARENT is resolved, and must already exist
errors never say which of "outside" or "missing" it was, or this becomes an
oracle for what exists elsewhere on the disk
VERIFIED against the running service, not reasoned about: `..` traversal, an
absolute path outside the root, a write outside the root, a relative path, a
symlink pointing into /etc, and a write THROUGH a symlinked directory — all
refused, nothing written outside the root.
the output is moved into place at the END. ffmpeg encodes into a temp dir, so a job
killed by the timeout or a restart leaves the caller's directory as it was. pointing
ffmpeg at the destination would leave a truncated file where a good one might have
been — and a task that then deleted its source would have destroyed something.
rename first, copy on EXDEV, which is the normal case rather than the error one
since tmp is often tmpfs.
docs/API.md said this endpoint was "designed, not yet built" while it was routed and
working. that is fixed too: it was read as a gap and nearly rebuilt.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Exposes sharp and ffprobe with their own vocabulary — operations are named what
sharp names them, ffprobe fields come back spelled the way ffprobe spells them —
so the tools' own documentation applies and there is no house dialect to learn.
Safety comes from one architectural invariant rather than from filtering: the
caller never supplies a path, a URL or a protocol. Input is an id we issued, output
is a name we chose. That removes the entire class of attack that makes "just pass
the flags through" a remote shell, which is precisely what makes it safe to open up
everything else. docs/SECURITY.md has the reasoning and the specific attacks.
The vocabulary is a data table, so the validator and docs/SHARP.md are generated
from one source and cannot drift. Two things are deliberately absent from it:
withMetadata, because that is how a client's GPS coordinates get published, and
limitInputPixels, because a caller who could raise it could turn a 1 KB PNG into a
40 GB allocation.
Verified against a running server, not asserted: traversal ids rejected, unknown
operations and typo'd parameters rejected by name, out-of-range values rejected
with the bound, a GPS-tagged photo coming out clean end to end, video probe, Range
requests, and a rejected upload leaving nothing on disk.
Found while building: config threw at import if AV_CLUB_TOKEN was unset, so
generating documentation required a production secret. The token is read at boot in
server.ts now — still a refusal to start, no longer a module-scope landmine.
ffmpeg is designed in docs/API.md and not built yet.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
pastilhasandClaude Opus 5