Design a Collaborative Document Editor
System design for a collaborative editor like Google Docs: real-time sync (CRDTs vs OT), cursor presence, rich text (contentEditable vs ProseMirror/Tiptap), conflict resolution, offline, version history, comments, and permissions.
Designing a collaborative document editor tests real-time sync, rich text editing, conflict resolution, and complex state. Here's a structured approach.
Requirements Clarification
Functional Requirements
- Editing: Rich text (bold, italic, lists, headings); possibly images, tables.
- Collaboration: Multiple cursors; see others' edits in real time; no overwrites.
- Comments: Inline comments and suggestions; resolve, reply.
- History: Version history; restore previous version.
- Offline: Edit offline; sync when back online.
- Permissions: View-only, comment-only, edit; per-user or per-document.
Non-Functional Requirements
- Low latency for collaboration (<100ms typical).
- Conflict-free merging; eventual consistency.
- Accessibility: keyboard navigation, screen reader support for structure.
- Scale to documents with 100k+ characters and 10+ concurrent users.
High-Level Architecture
┌─────────────────────────────────────────────────────────────────────┐
│ DocumentEditorRoot │
├─────────────────────────────────────────────────────────────────────┤
│ EditorCore (ProseMirror / Tiptap / Slate) │
│ - Document model (OT/CRDT) │
│ - Local edits → transform → broadcast │
├─────────────────────────────────────────────────────────────────────┤
│ CollaborationLayer │
│ - WebSocket: receive remote ops, merge, apply │
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