quiz/tests/stress/live_accuracy.mjs

// Live-target accuracy + latency stress test.
//
// Drives a real classroom-sized run against an already-deployed server
// (single-session app, sid=main), via the public HTTPS endpoint, and
// measures three things:
//   1. Stress: N concurrent student WS connections + one instructor WS,
//      driving the full quiz lifecycle.
//   2. Accuracy: every submitted answer that matches the correct option
//      (revealed after question_closed) MUST score > 0; every other
//      submission MUST score == 0.
//   3. Latency: per-submit round-trip time from `ws.send(submit)` to the
//      receipt of the matching `submit_ack`. Reports p50 / p95 / p99.
//
// Each simulated student is a SEPARATE WebSocket with its own cookie;
// "batching" only refers to how the opening handshakes are staggered
// (groups of 8, 250ms apart) so the source IP doesn't ETIMEDOUT under
// 50-simultaneous-handshake pressure. Once open, all 50 connections
// stay simultaneously connected through the whole quiz.
//
// Usage:
//   node live_accuracy.mjs <base_url> <admin_password> [num_students=50] [correct_pct=0.6]

import WebSocket from "ws";

const baseUrl = (process.argv[2] || "https://quiz.ahkhan.me").replace(/\/$/, "");
const adminPassword = process.argv[3];
const N = parseInt(process.argv[4] || "50", 10);
const CORRECT_PCT = parseFloat(process.argv[5] || "0.6");
const SID = process.env.QUIZ_SID || "main";

if (!adminPassword) {
  console.error("Usage: node live_accuracy.mjs <base_url> <admin_password> [N] [correct_pct]");
  process.exit(2);
}

const wsBase = baseUrl.replace(/^http/, "ws");
const sleep = (ms) => new Promise((r) => setTimeout(r, ms));

// -- HTTP / cookie helpers ------------------------------------------------

function parseSetCookie(headerVal) {
  if (!headerVal) return null;
  const m = headerVal.match(/(qz_(?:admin|student))=[^;,]+/);
  return m ? m[0] : null;
}

async function httpJson(method, path, body, cookie) {
  const headers = { Accept: "application/json" };
  if (body !== undefined) headers["Content-Type"] = "application/json";
  if (cookie) headers["Cookie"] = cookie;
  const res = await fetch(`${baseUrl}${path}`, {
    method,
    headers,
    body: body !== undefined ? JSON.stringify(body) : undefined,
  });
  const setCookie = res.headers.get("set-cookie");
  let json = null;
  try { json = await res.json(); } catch {}
  return { status: res.status, body: json, cookie: parseSetCookie(setCookie) };
}

async function adminLogin() {
  const r = await httpJson("POST", "/admin/login", { password: adminPassword });
  if (r.status !== 200) throw new Error(`admin login: ${r.status}`);
  if (!r.cookie) throw new Error(`admin login: no Set-Cookie`);
  return r.cookie;
}

async function adminReset(adminCookie) {
  const r = await httpJson("POST", "/admin/api/reset", undefined, adminCookie);
  if (r.status !== 200) throw new Error(`reset: ${r.status}`);
}

async function adminState(adminCookie) {
  const r = await httpJson("GET", "/admin/api/state", undefined, adminCookie);
  if (r.status !== 200) throw new Error(`state: ${r.status}`);
  return r.body;
}

async function joinStudent(sid, studentId, name) {
  const r = await httpJson("POST", `/api/session/${sid}/join`, { student_id: studentId, name });
  if (r.status !== 200) throw new Error(`join ${studentId}: ${r.status}`);
  if (!r.cookie) throw new Error(`join ${studentId}: no Set-Cookie`);
  return r.cookie;
}

// -- WS bookkeeping --------------------------------------------------------

// Build a Student object: opens the WS, attaches the message listener
// IMMEDIATELY (before connection establishes), so no incoming frame is
// ever lost to a listener-attach race. Returns a Promise that resolves
// to the bookkeeping struct once the lobby snapshot has arrived.
function makeStudent(sid, cookie, idx) {
  const studentId = `S${String(idx).padStart(3, "0")}`;
  const ws = new WebSocket(`${wsBase}/ws/student/${SID}`, {
    headers: { Cookie: cookie },
    perMessageDeflate: false,
  });
  const state = {
    studentId,
    ws,
    submits: new Map(),
    inLobby: false,
    lastQuestionOpen: null,
    closedSeen: new Map(),
    ended: null,
    closed: false,
  };
  let resolveLobby;
  const lobbyP = new Promise((r) => { resolveLobby = r; });
  ws.on("error", () => {});
  ws.on("close", () => { state.closed = true; });
  ws.on("message", (raw) => {
    let m;
    try { m = JSON.parse(raw.toString()); } catch { return; }
    switch (m.type) {
      case "state":
        if (m.state === "lobby") {
          state.inLobby = true;
          resolveLobby();
        }
        break;
      case "question_open":
        state.lastQuestionOpen = m;
        break;
      case "submit_ack": {
        const sub = state.submits.get(m.question_idx);
        if (sub) { sub.ackTs = performance.now(); sub.score = m.score; }
        break;
      }
      case "question_closed":
        state.closedSeen.set(m.question_idx, {
          correct: m.correct,
          your_answer: m.your_answer,
          your_score: m.your_score,
        });
        break;
      case "session_ended":
        state.ended = m;
        break;
    }
  });
  return { state, lobbyP };
}

function openInstructorWS(adminCookie) {
  const ws = new WebSocket(`${wsBase}/ws/instructor/${SID}`, {
    headers: { Cookie: adminCookie },
    perMessageDeflate: false,
  });
  const ev = { ws, lastQuestionOpen: null };
  let resolveOpen;
  const openP = new Promise((r) => { resolveOpen = r; });
  ws.on("open", () => resolveOpen());
  ws.on("error", () => {});
  ws.on("message", (raw) => {
    let m; try { m = JSON.parse(raw.toString()); } catch { return; }
    if (m.type === "question_open") ev.lastQuestionOpen = m;
  });
  return { ev, openP };
}

// -- Driver ---------------------------------------------------------------

async function main() {
  console.log(`[live_accuracy] target=${baseUrl} sid=${SID} N=${N} correct_pct=${CORRECT_PCT}`);

  console.log(`[stage 1] admin login + reset`);
  const adminCookie = await adminLogin();
  await adminReset(adminCookie);
  const initialState = await adminState(adminCookie);
  const totalQs = initialState.pool_meta.question_count;
  console.log(`[stage 1] ok — pool="${initialState.title}" Qs=${totalQs} score_fn=${initialState.pool_meta.score_fn}`);

  console.log(`[stage 2] joining ${N} students (HTTP /join, serial)`);
  const cookies = [];
  for (let i = 0; i < N; i++) {
    cookies.push(await joinStudent(SID, `S${String(i).padStart(3, "0")}`, `Student ${i}`));
    if ((i + 1) % 10 === 0) process.stdout.write(`  joined ${i + 1}/${N}\n`);
  }

  console.log(`[stage 3] opening 1 admin + ${N} student WSs (batched)`);
  const inst = openInstructorWS(adminCookie);
  await inst.openP;

  // Open student WSs in batches of 8, 250ms apart.
  const students = [];
  const BATCH = 8, GAP_MS = 250;
  for (let i = 0; i < cookies.length; i += BATCH) {
    const slice = cookies.slice(i, i + BATCH);
    const wave = slice.map((c, j) => makeStudent(SID, c, i + j));
    await Promise.all(wave.map((s) => s.lobbyP));
    students.push(...wave.map((s) => s.state));
    if (i + BATCH < cookies.length) await sleep(GAP_MS);
  }
  console.log(`[stage 3] ok — all ${students.length} students saw the lobby snapshot`);

  // -- Drive each question ---
  console.log(`[stage 4] driving ${totalQs} questions via admin "next"`);
  const correctByIdx = new Map();
  const allLatencies = [];
  let totalSubmits = 0;
  let accuracyOk = 0;
  const accuracyMismatches = [];

  for (let qIdx = 0; qIdx < totalQs; qIdx++) {
    // Trigger the question via admin
    const beforeIdx = inst.ev.lastQuestionOpen?.question_idx ?? -1;
    inst.ev.ws.send(JSON.stringify({ type: "next" }));
    // Wait for the admin WS to see the new question_open; that confirms
    // the broadcast went out.
    const broadcastDeadline = Date.now() + 5000;
    while (
      (inst.ev.lastQuestionOpen?.question_idx ?? -1) === beforeIdx &&
      Date.now() < broadcastDeadline
    ) {
      await sleep(20);
    }
    const opened = inst.ev.lastQuestionOpen;
    if (!opened || opened.question_idx !== qIdx) {
      throw new Error(`question_open for q=${qIdx} not received within 5s`);
    }
    const optionKeys = Object.keys(opened.options);

    // Each student picks an answer with random delay 50-1500ms
    await Promise.all(students.map(async (s) => {
      const answer = optionKeys[Math.floor(Math.random() * optionKeys.length)];
      const delay = 50 + Math.random() * 1450;
      await sleep(delay);
      const sub = { picked: answer, sentTs: performance.now() };
      s.submits.set(qIdx, sub);
      try { s.ws.send(JSON.stringify({ type: "submit", question_idx: qIdx, answer })); }
      catch (e) { sub.sendError = String(e); }
    }));

    // Wait long enough for acks to arrive (latency p99 well under 1s on a healthy box)
    await sleep(1500);
    console.log(`  q=${qIdx} sent; waiting for next loop`);
  }

  // Final advance closes last question + ends session
  console.log(`[stage 5] advancing past final → session_ended`);
  inst.ev.ws.send(JSON.stringify({ type: "next" }));
  // Give the broadcast a moment + collect closed snapshots
  await sleep(2000);

  // Collect correct-answer map from any student who saw question_closed for each idx
  for (let i = 0; i < totalQs; i++) {
    for (const s of students) {
      const c = s.closedSeen.get(i);
      if (c) { correctByIdx.set(i, c.correct); break; }
    }
  }

  // -- Aggregate ---
  for (const s of students) {
    for (const [qidx, sub] of s.submits.entries()) {
      totalSubmits++;
      const correct = correctByIdx.get(qidx);
      const wasCorrect = correct !== undefined && sub.picked === correct;
      const scoreNonZero = sub.score !== undefined && sub.score > 0;
      const scoreZero = sub.score !== undefined && sub.score === 0;
      const accurate = (wasCorrect && scoreNonZero) || (!wasCorrect && scoreZero);
      if (accurate) accuracyOk++;
      else accuracyMismatches.push({
        student: s.studentId, qidx,
        picked: sub.picked, correct, score: sub.score,
      });
      if (sub.ackTs !== undefined) allLatencies.push(sub.ackTs - sub.sentTs);
    }
  }

  allLatencies.sort((a, b) => a - b);
  const pct = (p) => allLatencies.length
    ? allLatencies[Math.min(allLatencies.length - 1, Math.floor(p / 100 * allLatencies.length))]
    : 0;
  const mean = allLatencies.length
    ? allLatencies.reduce((a, b) => a + b, 0) / allLatencies.length
    : 0;

  console.log(`\n=== Results ===`);
  console.log(`Submits         : ${totalSubmits}`);
  console.log(`Acks received   : ${allLatencies.length} / ${totalSubmits} (${(100 * allLatencies.length / Math.max(1, totalSubmits)).toFixed(2)}%)`);
  console.log(`Accuracy ok     : ${accuracyOk} / ${totalSubmits} (${(100 * accuracyOk / Math.max(1, totalSubmits)).toFixed(2)}%)`);
  console.log(`Accuracy fail   : ${accuracyMismatches.length}`);
  if (accuracyMismatches.length) {
    console.log(`First few mismatches:`);
    accuracyMismatches.slice(0, 5).forEach((d) => console.log(`  `, d));
  }
  console.log(`Latency (ms)    : mean=${mean.toFixed(1)}  p50=${pct(50).toFixed(1)}  p95=${pct(95).toFixed(1)}  p99=${pct(99).toFixed(1)}  max=${(allLatencies[allLatencies.length-1] ?? 0).toFixed(1)}`);
  console.log(`Correct answers : ${[...correctByIdx.entries()].map(([i, c]) => `Q${i+1}=${c}`).join(", ")}`);

  inst.ev.ws.close();
  for (const s of students) { try { s.ws.close(); } catch {} }
  process.exit(accuracyMismatches.length === 0 ? 0 : 1);
}

main().catch((err) => { console.error(err); process.exit(1); });