feat: WebSocket real-time + rAF render gate + guest board + screen picker
Classroom performance: - WebSocket server (ws-server.js) for low-latency cursor & stroke preview Replaces HTTP POST per event → eliminates per-message auth overhead Session member cache (30s TTL) avoids SQLite query per WS message Fallback to HTTP POST when WS not connected - Cursor throttle reduced 100ms → 33ms (~30fps) - Stroke preview throttle reduced 50ms → 20ms - whiteboard.js: render() is now rAF-gated (_doRender/_rafPending) Multiple render() calls within one frame collapse into one repaint document.hidden check — zero CPU when tab is in background visibilitychange listener restores canvas on tab focus Guest board: - guestClassroom.js route: public token-based read-only access - guest-board.html: name entry + read-only whiteboard + SSE - SSE: addGuestClient/removeGuestClient/emitToGuests Screen share picker: - Discord-style modal with tab switching (screen/window/tab) - Live video preview before confirming share - useExistingScreenStream() in ClassroomRTC Fullscreen exit overlay: - #cr-fs-exit-overlay button inside cr-board-wrap - Visible only via CSS :fullscreen selector (touchpad users) File sharing from library: - Teacher picks file from library, sends as styled card in chat - crDownloadLibraryFile() fetches with Bearer auth Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
This commit is contained in:
Maxim Dolgolyov
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/**
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* WebSocket server for low-latency real-time classroom events.
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*
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* Handles two message types from clients:
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* { type:'cursor', sessionId, x, y, pageNum }
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* { type:'preview', sessionId, liveId, tool, data, pageNum, cancel }
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*
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* Auth: JWT token in ?token= query param on upgrade request.
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* Forwards events via SSE to session participants (no DB write).
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*
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* This replaces the HTTP POST /cursor and /stroke-preview endpoints
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* for connected clients, reducing per-event latency from ~50-120ms to ~2-5ms.
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*/
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const { WebSocketServer } = require('ws');
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const jwt = require('jsonwebtoken');
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const db = require('./db/db');
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const { emit, emitToGuests } = require('./sse');
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/* ── Session member cache (avoids DB query per WS message) ────────────── */
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const _cache = new Map(); // sessionId → { teacherId, classId, userIds, ts }
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const CACHE_TTL = 30_000;
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function _getMembers(sessionId) {
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const c = _cache.get(sessionId);
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if (c && Date.now() - c.ts < CACHE_TTL) return c;
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const session = db.prepare(
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"SELECT class_id, teacher_id FROM classroom_sessions WHERE id=? AND status='active'"
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).get(sessionId);
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if (!session) { _cache.delete(sessionId); return null; }
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let userIds;
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if (session.class_id) {
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const members = db.prepare('SELECT user_id FROM class_members WHERE class_id=?').all(session.class_id);
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userIds = [session.teacher_id, ...members.map(m => m.user_id)];
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} else {
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const invites = db.prepare('SELECT user_id FROM classroom_invites WHERE session_id=?').all(sessionId);
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userIds = [session.teacher_id, ...invites.map(i => i.user_id)];
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}
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const entry = { teacherId: session.teacher_id, classId: session.class_id, userIds, ts: Date.now() };
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_cache.set(sessionId, entry);
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return entry;
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}
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function _invalidateSession(sessionId) {
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_cache.delete(sessionId);
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}
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/* Forward serialized SSE payload to all session members */
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function _broadcast(sessionId, data, includeGuests) {
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const members = _getMembers(sessionId);
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if (!members) return;
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for (const uid of members.userIds) emit(uid, data);
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if (includeGuests) emitToGuests(sessionId, data);
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}
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/* Check draw permissions (teacher always can; students need explicit grant) */
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const _drawCache = new Map(); // `${sessionId}:${userId}` → { allowed, ts }
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const DRAW_TTL = 10_000;
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function _canDraw(sessionId, userId, members) {
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if (!members) return false;
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if (members.teacherId === userId) return true;
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const key = `${sessionId}:${userId}`;
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const c = _drawCache.get(key);
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if (c && Date.now() - c.ts < DRAW_TTL) return c.allowed;
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const allowed = !!db.prepare(
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'SELECT 1 FROM classroom_draw_permissions WHERE session_id=? AND user_id=?'
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).get(sessionId, userId);
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_drawCache.set(key, { allowed, ts: Date.now() });
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return allowed;
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}
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/* ── WebSocket server ──────────────────────────────────────────────────── */
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function attach(httpServer) {
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const wss = new WebSocketServer({ server: httpServer, path: '/ws' });
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wss.on('connection', (ws, req) => {
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/* ── Auth ── */
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let user = null;
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try {
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const url = new URL(req.url, 'http://localhost');
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const token = url.searchParams.get('token') || '';
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user = jwt.verify(token, process.env.JWT_SECRET, { algorithms: ['HS256'] });
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} catch {
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ws.close(4001, 'Unauthorized');
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return;
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}
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ws.userId = user.id;
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ws.userName = user.name || user.email || '';
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ws.isAlive = true;
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ws.on('pong', () => { ws.isAlive = true; });
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ws.on('message', raw => {
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let msg;
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try { msg = JSON.parse(raw); } catch { return; }
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const { type, sessionId } = msg;
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if (!sessionId || typeof sessionId !== 'number') return;
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/* ── cursor broadcast ── */
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if (type === 'cursor') {
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const members = _getMembers(sessionId);
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if (!members || !members.userIds.includes(ws.userId)) return;
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_broadcast(sessionId, {
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type: 'classroom_cursor',
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sessionId,
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x: msg.x,
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y: msg.y,
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pageNum: msg.pageNum || 1,
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userId: ws.userId,
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userName: ws.userName,
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}, true);
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/* ── stroke preview broadcast ── */
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} else if (type === 'preview') {
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const members = _getMembers(sessionId);
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if (!members) return;
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if (!_canDraw(sessionId, ws.userId, members)) return;
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const liveId = msg.liveId;
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if (!liveId && !msg.cancel) return;
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_broadcast(sessionId, {
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type: 'classroom_stroke_preview',
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sessionId,
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pageNum: msg.pageNum || 1,
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liveId,
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tool: msg.tool,
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data: msg.data,
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cancel: msg.cancel || false,
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userId: ws.userId,
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userName: ws.userName,
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}, true);
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}
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});
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ws.on('error', () => {});
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ws.on('close', () => {});
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});
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/* ── Ping/pong keepalive ── */
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const pingTimer = setInterval(() => {
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for (const ws of wss.clients) {
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if (!ws.isAlive) { ws.terminate(); continue; }
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ws.isAlive = false;
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try { ws.ping(); } catch {}
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}
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}, 30_000);
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wss.on('close', () => clearInterval(pingTimer));
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return wss;
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}
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module.exports = { attach, invalidateSession: _invalidateSession };
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