Files are posted as a message's own attachment, and the composer puts none in the rich text: it permits
only mentions and link embeds. The server still keeps any attachment whose signed id resolves, a blob
included, and Action Text's blob partial links to a representation URL that makes the preview on the
first request, without the limits the POST has, and on every request while it fails.
The app's own partial shows an image's preview only if it was already made, and otherwise the file's
name and size, as it does for a file that isn't an image. The cached presentation's version goes up,
since Action Text renders the partial by name and the template digest doesn't see it.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Bj8KnxpTf9sj2Ysa8aLAVa
A video's preview and a picture's thumbnail are made inside the request that posts the message, and
nothing bounded how long either could take.
- The video preview filter also selects any frame from 5 seconds on. Rails' filter takes the second
frame it selects, which a video with a single keyframe and no scene change only gives at its end, so
ffmpeg decoded all of it.
- TimeLimitedVideoPreviewer gives ffmpeg 10 seconds of wall-clock time, kills it past that, and reports
a failed preview, so the message is posted without one.
- Pictures and videos above 250 megapixels, or whose size couldn't be read, get no preview: decoding
costs in proportion to the pixels, however small the file.
- The view shows a preview only if it was made when the message was posted. Its URL used to make it on
view, so a preview that failed or was skipped would be attempted again on every view. The cached
presentation's version goes up, so cached messages pick this up.
- A video's poster is made, when the message is posted, at the size the view shows it. The full-size WebP
made until now wasn't shown anywhere, and encoding it costs in proportion to the frame's pixels.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Bj8KnxpTf9sj2Ysa8aLAVa
The room caches each message's rendered presentation, and its key can't
see the link preview partial, which ActionText renders by name rather than
through a render call the digestor can follow. Without a new version, a
message already in the cache would keep its old preview.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0186eyzivcTn6wqjEE4Wnxdt
* Bump thruster 0.1.15 → 0.1.23
* Scrub disallowed attributes on allowed tags in message rendering
SanitizeTags removes disallowed tags from message presentation, but
attributes on the tags it allows passed through untouched. Extend the
content-filter chain with a SanitizeAttributes filter that runs Rails'
safe-list sanitizer over the remaining markup, stripping event-handler
attributes and unsafe URI schemes as defense-in-depth alongside the
existing Content-Security-Policy.
Running it after SanitizeTags with the same allowed-tags list makes the
sanitizer's tag pass a no-op, preserving SanitizeTags' remove-not-unwrap
semantics while scrubbing attributes. The attribute allowlist is the
standard ActionText set (which keeps attachments intact) plus class,
which presentation styling relies on.
GPT on behalf of DHH
Marcello Costagliola
Rosa Gutierrez
Jeremy Daer
Kevin McConnell