http-cache-semantics 4.2.0: evaluate HTTP request and response cache freshness and revalidation headers

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: evaluate HTTP request and response cache freshness and revalidation headers
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:npm/http-cache-semantics@4.2.0
Demonstrate these symbols/APIs:
  - CachePolicy

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.

{"case":{"caseId":"case:sha256:8501183094d71489e86ef91f0e6500534a9579ee4b4e486a3f97d9d9a7c7fbaa","contract":["CachePolicy.storable evaluates whether an HTTP response can be stored in cache according to Cache-Control headers","CachePolicy.stale evaluates whether a cached HTTP response has expired based on max-age","CachePolicy.satisfiesWithoutRevalidation determines if a cached response can satisfy a new incoming HTTP request","CachePolicy.revalidationHeaders generates conditional request headers including if-none-match for 304 revalidation","CachePolicy.revalidatedPolicy returns updated policy instance merging cached headers with 304 revalidation response headers"],"goal":"evaluate HTTP request and response cache freshness and revalidation headers","kind":"HOW","packages":["pkg:npm/http-cache-semantics@4.2.0"],"schemaVersion":1,"symbols":["CachePolicy"]},"contractCommand":["node","test/contract.mjs"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"npm","executionContext":"node","libc":"glibc","libcVersion":"2.39","moduleSystem":"esm","os":"linux","osVersionBucket":"24","packageManager":"npm","packageManagerVersion":"10.9.8","runtime":"node","runtimeVersion":"22.23.2","schemaVersion":1},"license":"MIT-0","packages":["pkg:npm/http-cache-semantics@4.2.0"],"schemaVersion":1,"subject":"pkg:npm/http-cache-semantics@4.2.0","symbols":["CachePolicy"],"verifierAdapter":"node-typescript@1"}

{
  "name": "sample-http-cache-semantics",
  "version": "1.0.0",
  "lockfileVersion": 3,
  "requires": true,
  "packages": {
    "": {
      "name": "sample-http-cache-semantics",
      "version": "1.0.0",
      "license": "MIT-0",
      "dependencies": {
        "http-cache-semantics": "4.2.0"
      }
    },
    "node_modules/http-cache-semantics": {
      "version": "4.2.0",
      "resolved": "https://registry.npmjs.org/http-cache-semantics/-/http-cache-semantics-4.2.0.tgz",
      "integrity": "sha512-dTxcvPXqPvXBQpq5dUr6mEMJX4oIEFv6bwom3FDwKRDsuIjjJGANqhBuoAn9c1RQJIdAKav33ED65E2ys+87QQ==",
      "license": "BSD-2-Clause"
    }
  }
}

{
  "name": "sample-http-cache-semantics",
  "version": "1.0.0",
  "private": true,
  "description": "evaluate HTTP request and response cache freshness and revalidation headers",
  "type": "module",
  "main": "index.mjs",
  "scripts": {
    "test": "node test/contract.mjs"
  },
  "dependencies": {
    "http-cache-semantics": "4.2.0"
  },
  "license": "MIT-0"
}

{
  "schemaVersion": 1,
  "goal": "evaluate HTTP request and response cache freshness and revalidation headers",
  "kind": "HOW",
  "packages": [
    "pkg:npm/http-cache-semantics@4.2.0"
  ],
  "symbols": [
    "CachePolicy"
  ]
}

import CachePolicy from 'http-cache-semantics';

export { CachePolicy };

/**
 * Creates a new CachePolicy instance.
 * @param {object} request - Request representation { url, method, headers }
 * @param {object} response - Response representation { status, headers }
 * @param {object} [options] - CachePolicy options
 * @returns {CachePolicy}
 */
export function createCachePolicy(request, response, options) {
  return new CachePolicy(request, response, options);
}

/**
 * Evaluates whether an HTTP request/response pair is storable in cache.
 * @param {object} request - Request representation
 * @param {object} response - Response representation
 * @param {object} [options] - CachePolicy options
 * @returns {boolean}
 */
export function isResponseStorable(request, response, options) {
  const policy = new CachePolicy(request, response, options);
  return policy.storable();
}

/**
 * Checks if a cached policy is still fresh (not stale).
 * @param {CachePolicy} policy
 * @returns {boolean}
 */
export function isCacheFresh(policy) {
  return !policy.stale();
}

/**
 * Checks if a cached response satisfies a new incoming request without contacting origin.
 * @param {CachePolicy} policy
 * @param {object} request
 * @returns {boolean}
 */
export function canSatisfyRequest(policy, request) {
  return policy.satisfiesWithoutRevalidation(request);
}

/**
 * Generates conditional request headers for cache revalidation.
 * @param {CachePolicy} policy
 * @param {object} request
 * @returns {Record<string, string>}
 */
export function getRevalidationHeaders(policy, request) {
  return policy.revalidationHeaders(request);
}

/**
 * Revalidates a cached policy with a 304 or new response.
 * @param {CachePolicy} policy
 * @param {object} revalidationRequest
 * @param {object} revalidationResponse
 * @returns {{ policy: CachePolicy, modified: boolean, matches: boolean }}
 */
export function applyRevalidation(policy, revalidationRequest, revalidationResponse) {
  return policy.revalidatedPolicy(revalidationRequest, revalidationResponse);
}

import assert from 'node:assert';
import CachePolicy from 'http-cache-semantics';
import {
  createCachePolicy,
  isResponseStorable,
  isCacheFresh,
  canSatisfyRequest,
  getRevalidationHeaders,
  applyRevalidation,
} from '../src/index.mjs';

function runContractTests() {
  const req = {
    url: 'https://example.com/api/items',
    method: 'GET',
    headers: {
      accept: 'application/json',
    },
  };

  const resFresh = {
    status: 200,
    headers: {
      'cache-control': 'public, max-age=3600',
      etag: '"v1-etag"',
      'last-modified': 'Wed, 21 Oct 2025 07:28:00 GMT',
      'content-type': 'application/json',
    },
  };

  // 1. Contract: CachePolicy.storable evaluates whether an HTTP response can be stored in cache
  const policyFresh = createCachePolicy(req, resFresh);
  assert.strictEqual(policyFresh.storable(), true, 'Cacheable response must be storable');
  assert.strictEqual(isResponseStorable(req, resFresh), true, 'Helper isResponseStorable must return true');

  const resUnstorable = {
    status: 200,
    headers: {
      'cache-control': 'no-store',
    },
  };
  const policyUnstorable = createCachePolicy(req, resUnstorable);
  assert.strictEqual(policyUnstorable.storable(), false, 'no-store response must not be storable');
  assert.strictEqual(isResponseStorable(req, resUnstorable), false, 'Helper isResponseStorable must return false for no-store');

  // 2. Contract: CachePolicy.stale evaluates whether a cached HTTP response has expired
  assert.strictEqual(policyFresh.stale(), false, 'Fresh response must not be stale');
  assert.strictEqual(isCacheFresh(policyFresh), true, 'Helper isCacheFresh must return true');
  assert.strictEqual(policyFresh.timeToLive() > 0, true, 'timeToLive must be positive for fresh cache');

  const resStale = {
    status: 200,
    headers: {
      'cache-control': 'public, max-age=0',
      etag: '"v1-etag"',
    },
  };
  const policyStale = createCachePolicy(req, resStale);
  assert.strictEqual(policyStale.stale(), true, 'max-age=0 response must be stale immediately');
  assert.strictEqual(isCacheFresh(policyStale), false, 'Helper isCacheFresh must return false for stale response');

  // 3. Contract: CachePolicy.satisfiesWithoutRevalidation determines if cached response satisfies a new request
  assert.strictEqual(policyFresh.satisfiesWithoutRevalidation(req), true, 'Fresh cached response must satisfy matching GET request');
  assert.strictEqual(canSatisfyRequest(policyFresh, req), true, 'Helper canSatisfyRequest must return true');

  const reqDifferentMethod = {
    url: 'https://example.com/api/items',
    method: 'POST',
    headers: {
      accept: 'application/json',
    },
  };
  assert.strictEqual(policyFresh.satisfiesWithoutRevalidation(reqDifferentMethod), false, 'Cached GET response must not satisfy POST request');
  assert.strictEqual(policyStale.satisfiesWithoutRevalidation(req), false, 'Stale cached response must not satisfy request without revalidation');

  // 4. Contract: CachePolicy.revalidationHeaders generates conditional request headers for 304 revalidation
  const revalHeaders = policyStale.revalidationHeaders(req);
  assert.strictEqual(revalHeaders['if-none-match'], '"v1-etag"', 'revalidationHeaders must include if-none-match matching etag');
  const helperRevalHeaders = getRevalidationHeaders(policyStale, req);
  assert.strictEqual(helperRevalHeaders['if-none-match'], '"v1-etag"', 'Helper getRevalidationHeaders must include etag');

  // 5. Contract: CachePolicy.revalidatedPolicy returns updated policy merging cached headers with 304 response headers
  const revalReq = {
    url: 'https://example.com/api/items',
    method: 'GET',
    headers: revalHeaders,
  };
  const reval304Res = {
    status: 304,
    headers: {
      'cache-control': 'public, max-age=7200',
      etag: '"v1-etag"',
    },
  };

  const revalidationResult = applyRevalidation(policyStale, revalReq, reval304Res);
  assert.strictEqual(revalidationResult.matches, true, 'Revalidated 304 response must match policy');
  assert.strictEqual(revalidationResult.modified, false, '304 Not Modified must indicate unmodified content');
  assert.strictEqual(revalidationResult.policy.storable(), true, 'Revalidated policy must be storable');
  assert.strictEqual(revalidationResult.policy.stale(), false, 'Revalidated policy with fresh max-age must not be stale');

  // 6. Contract: Serialization and deserialization via toObject and fromObject
  const serialized = policyFresh.toObject();
  assert.strictEqual(typeof serialized, 'object', 'toObject must return an object');
  const restoredPolicy = CachePolicy.fromObject(serialized);
  assert.strictEqual(restoredPolicy.storable(), true, 'Restored policy must maintain storable state');
  assert.strictEqual(restoredPolicy.stale(), false, 'Restored policy must maintain freshness state');

  console.log('Contract tests passed successfully.');
}

runContractTests();