A URL that points straight at an image file (Content-Type: image/*) has
no HTML to scrape Open Graph tags from, so the fetch found nothing and
the message showed no preview at all -- reported against
https://imgs.xkcd.com/comics/creepy.png.
link_preview_service now recognizes an allowed image content-type (same
list storage.py uses for uploads) before falling through to the HTML/og:
path, and returns the URL itself as the preview (LinkPreview.is_image).
No need to download the body -- the already-SSRF-validated URL is the
image. The frontend renders that case as a real expandable image
(message-image + lightbox, same as an actual attachment) instead of the
small title+description card, which would have nothing to show anyway.
Verified end-to-end against the reported URL.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Slack/Discord-style link unfurling: the first http(s) URL in a message's
content gets a small preview card (title/description/image/site name)
fetched from the page's Open Graph tags.
Backend:
- Message.preview_url (extracted at create/edit time, cheap regex, no
I/O) points at a link_previews cache row keyed by URL -- the same URL
posted in different messages/rooms fetches once, and a failed fetch is
cached too so a dead URL isn't retried on every reference.
- The actual fetch runs in a background asyncio.create_task from
broadcast_new_message/broadcast_message_update, on its own DB session,
so a slow third-party site never delays message delivery. A separate
"link_preview" WS envelope carries the result once it resolves.
- SSRF protection reuses app/services/ssrf.py's validate_target_url
(renamed from UnsafeWebhookUrlError to UnsafeUrlError now that it's
shared with webhooks), but re-validates before every hop of a redirect
chain rather than once up front -- redirects are followed manually so
each intermediate URL is checked before it's ever connected to.
- Parsed with stdlib html.parser -- no new dependency.
Frontend: a LinkPreviewCard rendered under message content when present,
patched into state live via the new WS envelope and included in message
history for reloads.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
ksmithandClaude Sonnet 5
