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Fancy Mumble

Link previews

When a user pastes a URL in chat, the server can fetch the page, pull out the Open Graph tags, and send a preview card back. Other Fancy Mumble clients render the card inline.

Rendering on the server has two advantages:

  • Every client sees the same preview, even if they cannot reach the target site.
  • The target site only sees one fetch per shared link, not one per client.
Chat message with a link-preview card showing title, snippet, and image

How it works

Section titled “How it works”

When a Fancy Mumble client posts a chat message that contains a URL, it sends a FancyLinkPreviewRequest to the server. The server:

  1. Validates the URL is safe to fetch (rejects private IP ranges to avoid Server-Side Request Forgery).
  2. Rate-limits the request per session.
  3. Fetches the page.
  4. Parses the HTML for Open Graph tags (og:title, og:image, og:description, plus twitter: fallbacks).
  5. Returns a FancyLinkPreviewResponse containing the metadata and the preview image encoded inline as base64 bytes.

The receiving Fancy clients render the card. Preview images travel inside the protobuf message, not through the file server.

Privacy

Section titled “Privacy”

Link previewing means the server fetches URLs that users paste. Consider:

  • The server’s IP is logged by the target site.
  • A user who can post in chat can trigger arbitrary outbound fetches.

The server refuses to fetch RFC 1918 (private) IP ranges by default, which mitigates the most obvious abuse.

Configuration

Section titled “Configuration”

There are no documented server MUMBLE_CONFIG_* keys or plugin.* keys for link previews in the example config. The behavior is controlled in-code. If you need to disable it for your deployment, contact the maintainers or build a server image without the LinkPreviewPlugin compiled in.

Pitfalls

Section titled “Pitfalls”
  • No previews ever: confirm the server can reach the public internet. Try docker exec mumble-server curl -sI https://example.com.
  • A specific site never previews: it might return JavaScript- rendered Open Graph that the server cannot parse, or it might block the server’s user-agent.

Next step

Section titled “Next step”

Continue with Reactions & polls.