Presence and Permissions

See who is online, what they are editing, and whether they may change it — without leaking document content.

Collaboration tools combine real-time transport with authorization. A user without edit permission must not apply operations even if they bypass the UI.

In practice

Figma stores file permissions in Postgres; presence in Redis. Notion blocks embed share settings per page tree. All validate ops server-side against ACL snapshot.

typescript — Presence heartbeat

// Redis presence with TTL heartbeat
async function heartbeat(docId: string, userId: string, cursor: Cursor) {
  await redis.setex(`presence:${docId}:${userId}`, 30, JSON.stringify(cursor));
  await redis.publish(`doc:${docId}`, JSON.stringify({ type: "cursor", userId, cursor }));
}

Key Takeaways

Presence heartbeats in Redis with TTL; disconnect clears avatar.
Document ACLs: owner, editor, commenter, viewer enforced on every op.
Cursors and selections are ephemeral broadcast, not durable history.
Share links map tokens to roles with expiration.
Audit log records permission changes, not every keystroke.
Google Docs 'anonymous animals' are presence UX on top of WebSocket fan-out.

presenceACLRedispermissionsWebSocket

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