CodeSampleX

Sample

express-rate-limit 8.6.2: rateLimit

Verified sample for npm express-rate-limit 8.6.2: rateLimit. The contract ran on node 22 · linux debian/x64 · docker and passed.

sha256:5d525f15afa50d51f1bb4985f699db1b2f61a3908a1ac73e3bf190478af8ebda

This network offers one thing: a sample that builds. It ran the sample in a sandbox and kept the signed receipt. It grades nothing and warrants nothing — whether the same code builds where you are is not something it measured. How many distinct signing keys filed a passing contract receipt. One is the author alone; more than one means somebody else built it too. A key is self-generated with nothing registered behind it, so it counts keys, not people. MIT-0

Execution evidence

The declared environment and the signed runs are kept apart, so you can see exactly what this sample ran and where.

Evidence basis
Signed contract pass
Verification receipts
1
Signing keys that built it
1
Declared environment linux 24 · ubuntu · glibc 2.39 x64 npm

Verification-run environments

Environment Contract Stages Run
node 22 · linux debian/x64 · docker ed25519:c1973797be207ac4 PASS compile:SKIPPED · contract:PASS · load:PASS · resolve:PASS
CONTAINER_RUN · node-typescript@1node:22@sha256:8a34c4ab3ea2…		 2026-09-14

Case

HOW
Goal
verify express-rate-limit.rateLimit in pkg:npm/express-rate-limit@8.6.2
Packages
Symbols
  • express-rate-limit.rateLimit
Created
2026-09-14T22:34:30Z

Contract

  1. rateLimit middleware allows requests within configured limit and attaches rate limit status metadata to request
  2. rateLimit sends HTTP 429 status code with configured message and sets standard Retry-After headers when request limit is exceeded
  3. rateLimit sets standard RateLimit draft-7 and legacy X-RateLimit headers indicating limit, remaining count, and reset time
  4. rateLimit partitions client rate limits using custom keyGenerator function with ipKeyGenerator fallback
  5. rateLimit invokes custom handler when client exceeds rate limit threshold
  6. rateLimit conditionally bypasses rate limiting when skip predicate returns true
  7. rateLimit resetKey resets accumulated hit count for a targeted client key
  8. MemoryStore tracks hit counts and supports increment, decrement, get, and resetKey operations

Files

  • PROMPT.md
  • csx.json
  • package-lock.json
  • package.json
  • spec.json
  • test/contract.mjs

Download the source artifact (tar.gz)

Source

PROMPT.md
Clean-room public code sample — generation instructions

Write a brand-new, minimal, self-contained code sample in this clean-room directory.
Do not copy, paraphrase, or reference any existing project source. Work only from this spec.

A csx.json manifest scaffold already exists. Do not recreate it from memory. Preserve its case.goal, packages and symbols; fill its empty case.contract with exact assertions and correct its environment, commands and verifierAdapter for the files you generate.

Goal: verify express-rate-limit.rateLimit in pkg:npm/express-rate-limit@8.6.2
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:npm/express-rate-limit@8.6.2
Demonstrate these symbols/APIs:
  - express-rate-limit.rateLimit

Rules:
  - One focused purpose; the smallest project that proves the goal.
  - Include a contract test (test/contract.*) that runs OFFLINE and exits 0 exactly when the goal behavior works.
  - Pin every dependency with a lockfile so resolution is reproducible.
  - No secrets, credentials, or tokens. No real URLs (only example.com or localhost). No absolute paths.
  - No personal names, emails, company names, or project identifiers of any kind.
  - No binaries and no generated output (node_modules, dist, target, venv, .git, .env).
  - Keep it under 200 files and 256KB packed.
csx.json
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package-lock.json
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package.json
{
  "name": "sample-express-rate-limit",
  "version": "1.0.0",
  "type": "module",
  "private": true,
  "license": "MIT-0",
  "dependencies": {
    "express-rate-limit": "8.6.2"
  }
}
spec.json
{
  "schemaVersion": 1,
  "goal": "verify express-rate-limit.rateLimit in pkg:npm/express-rate-limit@8.6.2",
  "kind": "HOW",
  "packages": [
    "pkg:npm/express-rate-limit@8.6.2"
  ],
  "symbols": [
    "express-rate-limit.rateLimit"
  ]
}
test/contract.mjs
import assert from 'node:assert/strict';
import { rateLimit, MemoryStore, ipKeyGenerator } from 'express-rate-limit';

function createMockReqRes(options = {}) {
  const ip = options.ip || '127.0.0.1';
  const headers = options.headers || {};
  const resHeaders = {};
  let body = null;

  const req = {
    ip,
    headers: { ...headers },
    socket: { remoteAddress: ip },
    app: { get: () => false },
    ...options.reqExtra,
  };

  const res = {
    statusCode: 200,
    headersSent: false,
    setHeader(name, val) {
      resHeaders[name.toLowerCase()] = String(val);
    },
    getHeader(name) {
      return resHeaders[name.toLowerCase()];
    },
    hasHeader(name) {
      return name.toLowerCase() in resHeaders;
    },
    status(code) {
      this.statusCode = code;
      return this;
    },
    send(data) {
      body = data;
      this.headersSent = true;
      return this;
    },
    json(data) {
      body = JSON.stringify(data);
      this.headersSent = true;
      return this;
    },
    end(data) {
      if (data) body = data;
      this.headersSent = true;
      return this;
    },
  };

  return { req, res, getBody: () => body, getHeaders: () => resHeaders };
}

async function runContract() {
  // 1. rateLimit middleware allows requests within configured limit and attaches rate limit status metadata to request
  {
    const limiter = rateLimit({
      windowMs: 60 * 1000,
      limit: 3,
      standardHeaders: 'draft-7',
      legacyHeaders: true,
    });

    let nextCalled = 0;
    const m1 = createMockReqRes({ ip: '10.0.1.1' });
    await limiter(m1.req, m1.res, () => {
      nextCalled++;
    });

    assert.equal(nextCalled, 1, 'next() should be called within rate limit');
    assert.ok(m1.req.rateLimit, 'req.rateLimit should be attached');
    assert.equal(m1.req.rateLimit.limit, 3, 'req.rateLimit.limit should match configuration');
    assert.equal(m1.req.rateLimit.used, 1, 'req.rateLimit.used should be 1');
    assert.equal(m1.req.rateLimit.remaining, 2, 'req.rateLimit.remaining should be 2');
    assert.equal(m1.req.rateLimit.key, '10.0.1.1', 'req.rateLimit.key should match client IP');
  }

  // 2. rateLimit sends HTTP 429 status code with configured message and sets standard Retry-After headers when request limit is exceeded
  {
    const message = 'Too many requests from this IP, please try again after a minute.';
    const limiter = rateLimit({
      windowMs: 60 * 1000,
      limit: 2,
      message,
    });

    let nextCalls = 0;
    const next = () => {
      nextCalls++;
    };

    const m1 = createMockReqRes({ ip: '10.0.1.2' });
    await limiter(m1.req, m1.res, next);
    const m2 = createMockReqRes({ ip: '10.0.1.2' });
    await limiter(m2.req, m2.res, next);
    assert.equal(nextCalls, 2, 'First 2 requests should be permitted');

    const m3 = createMockReqRes({ ip: '10.0.1.2' });
    await limiter(m3.req, m3.res, next);
    assert.equal(nextCalls, 2, 'Third request exceeding limit should not call next()');
    assert.equal(m3.res.statusCode, 429, 'Exceeded request should return HTTP 429');
    assert.equal(m3.getBody(), message, 'Response body should contain configured message');
    assert.ok(m3.getHeaders()['retry-after'], 'Retry-After header should be set');
  }

  // 3. rateLimit sets standard RateLimit draft-7 and legacy X-RateLimit headers indicating limit, remaining count, and reset time
  {
    const limiter = rateLimit({
      windowMs: 60 * 1000,
      limit: 5,
      standardHeaders: 'draft-7',
      legacyHeaders: true,
    });

    const m = createMockReqRes({ ip: '10.0.1.3' });
    await limiter(m.req, m.res, () => {});

    const headers = m.getHeaders();
    assert.equal(headers['x-ratelimit-limit'], '5', 'X-RateLimit-Limit should be set');
    assert.equal(headers['x-ratelimit-remaining'], '4', 'X-RateLimit-Remaining should decrement');
    assert.ok(headers['x-ratelimit-reset'], 'X-RateLimit-Reset should be set');
    assert.equal(headers['ratelimit-policy'], '5;w=60', 'RateLimit-Policy should indicate quota and window');
    assert.ok(headers['ratelimit'].includes('limit=5'), 'RateLimit header should include limit');
    assert.ok(headers['ratelimit'].includes('remaining=4'), 'RateLimit header should include remaining count');
  }

  // 4. rateLimit partitions client rate limits using custom keyGenerator function with ipKeyGenerator fallback
  {
    const limiter = rateLimit({
      windowMs: 60 * 1000,
      limit: 1,
      keyGenerator: (req) => req.headers['x-api-client-id'] || ipKeyGenerator(req.ip),
    });

    let allowed = 0;
    const next = () => {
      allowed++;
    };

    const clientA1 = createMockReqRes({ ip: '10.0.1.4', headers: { 'x-api-client-id': 'client-alpha' } });
    await limiter(clientA1.req, clientA1.res, next);
    assert.equal(allowed, 1);

    const clientB1 = createMockReqRes({ ip: '10.0.1.4', headers: { 'x-api-client-id': 'client-beta' } });
    await limiter(clientB1.req, clientB1.res, next);
    assert.equal(allowed, 2);

    const clientA2 = createMockReqRes({ ip: '10.0.1.99', headers: { 'x-api-client-id': 'client-alpha' } });
    await limiter(clientA2.req, clientA2.res, next);
    assert.equal(allowed, 2);
    assert.equal(clientA2.res.statusCode, 429);
  }

  // 5. rateLimit invokes custom handler when client exceeds rate limit threshold
  {
    let handlerInvoked = false;
    let receivedLimit = 0;

    const limiter = rateLimit({
      windowMs: 60 * 1000,
      limit: 1,
      handler: (req, res, next, options) => {
        handlerInvoked = true;
        receivedLimit = options.limit;
        res.status(429).json({ error: 'quota_exceeded', maxRequests: options.limit });
      },
    });

    const m1 = createMockReqRes({ ip: '10.0.1.5' });
    await limiter(m1.req, m1.res, () => {});

    const m2 = createMockReqRes({ ip: '10.0.1.5' });
    await limiter(m2.req, m2.res, () => {});

    assert.equal(handlerInvoked, true, 'Custom handler should be called');
    assert.equal(receivedLimit, 1, 'Custom handler should receive limiter options');
    assert.equal(m2.res.statusCode, 429, 'Status should be set by custom handler');
    assert.equal(m2.getBody(), JSON.stringify({ error: 'quota_exceeded', maxRequests: 1 }));
  }

  // 6. rateLimit conditionally bypasses rate limiting when skip predicate returns true
  {
    const limiter = rateLimit({
      windowMs: 60 * 1000,
      limit: 1,
      skip: (req) => req.headers['x-internal-admin'] === 'true',
    });

    let passCount = 0;
    const next = () => {
      passCount++;
    };

    for (let i = 0; i < 5; i++) {
      const reqRes = createMockReqRes({ ip: '10.0.1.6', headers: { 'x-internal-admin': 'true' } });
      await limiter(reqRes.req, reqRes.res, next);
    }

    assert.equal(passCount, 5, 'All requests matching skip criteria should pass through');
  }

  // 7. rateLimit resetKey resets accumulated hit count for a targeted client key
  {
    const limiter = rateLimit({
      windowMs: 60 * 1000,
      limit: 1,
    });

    let count = 0;
    const next = () => {
      count++;
    };

    const targetIp = '10.0.1.7';
    const m1 = createMockReqRes({ ip: targetIp });
    await limiter(m1.req, m1.res, next);
    assert.equal(count, 1);

    const m2 = createMockReqRes({ ip: targetIp });
    await limiter(m2.req, m2.res, next);
    assert.equal(count, 1);
    assert.equal(m2.res.statusCode, 429);

    await limiter.resetKey(targetIp);

    const m3 = createMockReqRes({ ip: targetIp });
    await limiter(m3.req, m3.res, next);
    assert.equal(count, 2, 'Request after resetKey should be accepted');
  }

  // 8. MemoryStore tracks hit counts and supports increment, decrement, get, and resetKey operations
  {
    const store = new MemoryStore();
    store.init({ windowMs: 60 * 1000 });

    const key = 'test-client-store';
    const hit1 = await store.increment(key);
    assert.equal(hit1.totalHits, 1, 'First increment should record 1 hit');

    const hit2 = await store.increment(key);
    assert.equal(hit2.totalHits, 2, 'Second increment should record 2 hits');

    await store.decrement(key);
    const afterDec = await store.get(key);
    assert.equal(afterDec.totalHits, 1, 'get() after decrement should return 1 hit');

    await store.resetKey(key);
    const afterReset = await store.get(key);
    assert.equal(afterReset, undefined, 'get() after resetKey should return undefined');
  }

  console.log('All express-rate-limit@8.6.2 contract assertions passed.');
}

runContract().catch((err) => {
  console.error('Contract test failed:', err);
  process.exit(1);
});

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