signal-bot/DOCS-add-photo.md

Adding a photo from the chat: !add_photo

How a member of an album's group proposes a photo for it by sending one, how the operator approves it, and what keeps that path from leaking anything. The album itself — where it lives, what its manifests look like, how several albums coexist — is DOCS-photo-pack.md.

Send a photo captioned !dodaj alfa wakacje2019 in one of the album's groups. alfa resolves to that person's key; wakacje2019 matches nobody and travels as a proposed label. The photo is stripped and lands in the album's pending/, and the reply is czeka na zatwierdzenie: 1. It is not in the album yet: !alfa and !losowe wakacje2019 cannot find it until somebody approves it.

Approval: the management page, and nothing else

./web.sh shows a Waiting for approval section above the tagger whenever pending/ is not empty (web/src/views/pending.tsx). Each queued photo is a card with the album's people as checkboxes — the ones the sender named are pre-ticked — and one checkbox per proposed label. Approve moves the file into media/, writes tags.json, mints any ticked label in custom.json, records the sender in adds.json (with approved_at), and asks the bot for POST /_reload. From that moment !losowe wakacje2019 answers with it, with no restart. Reject deletes the file and its sidecar; nothing else to undo, because nothing else was written.

The queue is the only door in. The bot's own process never approves anything; it writes pending/<content-hash>.<ext> plus a .json sidecar (keys, labels, by, at, group) and reads the result back at the reload. The page can only approve a label the sender actually proposed (anything else is 400), and it can keep fewer — an unticked label is simply not minted. If the bot then refuses the reload (a stale alias, say) the page reports it and does not roll back: the photo is in the album with the tags the approver chose, and the bot's reason is about something else.

What holds:

• No typed label travels. Labels become keys in the registry's arg_resolver, at the dispatcher, before the line that logs the command name; a new word becomes a per-message token (new1, new2) and is claimed back by its own handler, so concurrent frames cannot swap labels. The reply is counts only — czeka na zatwierdzenie: 2 · 1 już było — and the proposed word exists in exactly one place, the sidecar inside the album's 0700. scripts/check_personal_data.sh reads those sidecars too, so a proposed name is on the forbidden list before it is ever approved.
• No cap. No cooldown, no size limit, no daily limit. !random takes the ordinary pack cooldown; !add_photo takes no decorator at all.
• At most six labels, the same ceiling !alfa beta … has.
• The attachment must be on the same message, never a quoted one: a reply carries the quoted message's media in quote.attachments, and taking it would let anyone re-file somebody else's photo.
• A duplicate changes nothing. The stored name is a content hash, so a photo already in the album is już było, one already waiting is już czeka — the same photo twice in one message counts as waiting too — and a mixed batch queues the new files and says how many were which.
• Approval is whole or not at all. Media, tags.json, custom.json and adds.json are written, the album is loaded again, and only a load that succeeds keeps them. A load that fails rolls all four back and leaves the photo in the queue with a 400 naming the reason.
• The second copy goes. signal-cli keeps its own copy of every inbound attachment outside the album's 0700. !add_photo deletes it once the file is queued, and also when the upload was refused.
• Stripping happens before the wait. The file in pending/ is already the stripped one; scripts/e2e.sh re-reads the queue with exiftool before approving anything, and the album after.

Stripping: exiftool, with a positive check

ffmpeg -map_metadata -1 -c copy was tried first and fails silently on photos: given a JPEG with a real APP1 Exif segment it returned a byte-identical file, GPS marker intact, and exited 0. -c copy passes the compressed frame through as an opaque packet and a JPEG's Exif lives inside it. Do not reintroduce ffmpeg for this.

So the gate is a positive check on the output, never an exit code:

exiftool -all= -time:all= -o <dst> <src>   # never --overwrite_original
exiftool -G0 -s -all <dst>                 # then read it back

-time:all= is not redundant with -all=. media_tags.ZEROED_DATE_TAGS allows the QuickTime date tags "by value" on the grounds that -all= zeroes rather than deletes them. Measured 2026-08-31: it does not. -all= alone left QuickTime:CreateDate at its real value, and the consequence was that every mp4 was refused — the code documented behaviour it did not get. -time:all= is what actually zeroes them.

and every surviving tag must be structural. Measured against exiftool 13.55, the plan's original "the surviving set must be empty" would have rejected every format except JPEG — a valid PNG always reports its IHDR under PNG, a GIF its screen descriptor under GIF, an MP4 some fifty QuickTime tags that are the container. So the allowlist is per tag name (signal_bot/media_tags.py), which keeps the property that matters: an atom nobody anticipated arrives as a name that is not on the list, and the upload is refused.

Allowlist, not blocklist, for the reason a naive gate misses: an MP4 geotag is a QuickTime udta/©xyz atom reported under QuickTime, not GPS.

Tracks: ffmpeg, for what no tag allowlist can see

A tag allowlist is structurally blind to one class, and it is the worst one. IMG_6924.mp4 in the live album carries two mebx timed-metadata tracks, and after a complete -all= -time:all= pass its bytes still contain:

com.apple.quicktime.detected-face
com.apple.quicktime.detected-face.bounds
com.apple.quicktime.detected-face.face-id
com.apple.quicktime.detected-face.roll-angle / .yaw-angle

Per-frame face bounding boxes and a face identity number. exiftool is not broken for missing them: mebx samples live in mdat as opaque payload, not as tags, so there is no tag to refuse. The only answer is to drop the track, which signal_bot/media_tracks.py does before exiftool runs:

ffmpeg -v error -i <src> -map 0:v -map "0:a?" -c copy \
       -map_metadata -1 -map_chapters -1 -y <dst>
ffprobe -v error -show_entries stream=codec_type -of csv=p=0 <dst>

and every surviving stream must be video or audio.

This is not the ffmpeg mistake above. That one was ffmpeg replacing exiftool for tag removal, where it silently failed on JPEG. Here ffmpeg removes tracks, exiftool still does every tag removal afterwards, and the gate is a positive read-back of which streams survived rather than an exit code. -c copy is safe for this job precisely because nothing is being claimed about the frames — the claim is about which tracks exist, and ffprobe answers that directly. Do not collapse the two jobs back together.

QuickTime:MetaFormat is deliberately absent from the allowlist: a file still reporting one has a metadata track the re-mux should have removed, and refusing it is the correct outcome.

Both entry points obey this. ./web.sh --import used to be a verbatim shutil.copy2; since 2026-08-31 it runs the same stripper, so the guarantee on this page covers the whole album and not just the chat path.

The list includes the codec's own configuration — CompressorName, VendorID, and the HEVC parameter set (HEVCConfigurationVersion, GeneralProfileIDC, BitDepthLuma, …). That was forced by measurement, not chosen for convenience: with them off the list exiftool 13.55 could produce no acceptable video and no acceptable HEIC, because CompressorName lives in the avc1 sample description and exiftool reports it as not writable at all (Sorry, QuickTime:CompressorName doesn't exist or isn't writable), and a real HEIC reports sixteen HEVC config tags. Since HEIC is the iPhone default, the choice was codec parameters or no phone photos. They describe how the picture is encoded, never where it was taken or who took it; every location and identity tag is still refused, and scripts/e2e.sh proves a QuickTime GPS atom does not survive on a file the album actually stored.

Formats are decided by magic bytes, never by the filename: jpg, png, gif, webp, mp4, mov, m4v, heic, heif, avif, webm and svg. Every one of them must also be in pack.MEDIA_TYPES, or a file that uploaded cleanly is refused by the next load and takes startup down.

⚠️ .webm and .svg are stored unstripped

exiftool 13.55 can write neither (exiftool -listwf lists no WEBM and no SVG; a strip attempt returns Can't write SVG files). Its SVG reader does not surface <metadata> content either, so there is no detection to fall back on.

kuhy's decision of 2026-08-31 is to keep both on the allowlist and store them as they arrive, metadata included. The consequence, stated plainly: an .svg carrying <metadata> or an embedded <image xlink:href="data:image/jpeg;base64,…"> keeps whatever is in it, and every later !alfa re-sends that file verbatim. Every other format on the list is stripped and verified.