mime-types 2.1.35: mime.lookup, mime.contentType, mime.extension

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 pkg:npm/mime-types@2.1.35
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:npm/mime-types@2.1.35
Constraints:
  - executionContext: node
Required runtime conditions:
  - ecosystem: npm
  - language: javascript
  - moduleSystem: cjs
  - packageManager: npm@11.8.0
  - runtime: node@24.13.1

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:sha256:3f78c6cea81016d7ce110067334368abdda208d8953daf481a6557222099fcd0","constraints":{"executionContext":"node"},"contract":["mime.lookup returns MIME type for path or extension, or false when unknown","mime.contentType returns full Content-Type header with charset parameter or false","mime.extension returns default file extension for a MIME type or false"],"goal":"verify pkg:npm/mime-types@2.1.35","kind":"HOW","packages":["pkg:npm/mime-types@2.1.35"],"schemaVersion":1,"symbols":["mime.lookup","mime.contentType","mime.extension"]},"contractCommand":["node","test/contract.js"],"environment":{"arch":"x64","ecosystem":"npm","os":"windows","osVersionBucket":"11","packageManager":"npm","schemaVersion":1},"license":"MIT-0","packages":["pkg:npm/mime-types@2.1.35"],"schemaVersion":1,"symbols":["mime.lookup","mime.contentType","mime.extension"],"verifierAdapter":"node-typescript@1"}

const mime = require('mime-types');

/**
 * Look up the MIME type for a file path or extension.
 * @param {string} path
 * @returns {string | false}
 */
function lookupType(path) {
  return mime.lookup(path);
}

/**
 * Get the full Content-Type header value with charset if applicable.
 * @param {string} str
 * @returns {string | false}
 */
function getContentType(str) {
  return mime.contentType(str);
}

/**
 * Get the default extension for a MIME type.
 * @param {string} type
 * @returns {string | false}
 */
function getExtension(type) {
  return mime.extension(type);
}

module.exports = {
  lookupType,
  getContentType,
  getExtension
};

{
  "name": "sample",
  "version": "1.0.0",
  "lockfileVersion": 3,
  "requires": true,
  "packages": {
    "": {
      "name": "sample",
      "version": "1.0.0",
      "dependencies": {
        "mime-types": "2.1.35"
      }
    },
    "node_modules/mime-db": {
      "version": "1.52.0",
      "resolved": "https://registry.npmjs.org/mime-db/-/mime-db-1.52.0.tgz",
      "integrity": "sha512-sPU4uV7dYlvtWJxwwxHD0PuihVNiE7TyAbQ5SWxDCB9mUYvOgroQOwYQQOKPJ8CIbE+1ETVlOoK1UC2nU3gYvg==",
      "license": "MIT",
      "engines": {
        "node": ">= 0.6"
      }
    },
    "node_modules/mime-types": {
      "version": "2.1.35",
      "resolved": "https://registry.npmjs.org/mime-types/-/mime-types-2.1.35.tgz",
      "integrity": "sha512-ZDY+bPm5zTTF+YpCrAU9nK0UgICYPT0QtT1NZWFv4s++TNkcgVaT0g6+4R2uI4MjQjzysHB1zxuWL50hzaeXiw==",
      "license": "MIT",
      "dependencies": {
        "mime-db": "1.52.0"
      },
      "engines": {
        "node": ">= 0.6"
      }
    }
  }
}

{
  "name": "sample",
  "version": "1.0.0",
  "dependencies": {
    "mime-types": "2.1.35"
  }
}

{
  "schemaVersion": 1,
  "goal": "verify pkg:npm/mime-types@2.1.35",
  "kind": "HOW",
  "packages": [
    "pkg:npm/mime-types@2.1.35"
  ],
  "constraints": {
    "executionContext": "node"
  },
  "runtimeConditions": {
    "ecosystem": "npm",
    "language": "javascript",
    "moduleSystem": "cjs",
    "packageManager": "npm@11.8.0",
    "runtime": "node@24.13.1"
  }
}

const assert = require('node:assert/strict');
const mime = require('mime-types');
const { lookupType, getContentType, getExtension } = require('../index.js');

// Contract 1: mime.lookup returns MIME type for path or extension, or false when unknown
{
  assert.equal(lookupType('json'), 'application/json');
  assert.equal(lookupType('.md'), 'text/markdown');
  assert.equal(lookupType('document.pdf'), 'application/pdf');
  assert.equal(lookupType('archive.tar.gz'), 'application/gzip');
  assert.equal(lookupType('path/to/image.png'), 'image/png');
  assert.equal(lookupType('unknown.custom_ext_xyz'), false);
  assert.equal(mime.lookup('index.html'), 'text/html');
}

// Contract 2: mime.contentType returns full Content-Type header with charset parameter or false
{
  assert.equal(getContentType('markdown'), 'text/markdown; charset=utf-8');
  assert.equal(getContentType('text/html'), 'text/html; charset=utf-8');
  assert.equal(getContentType('file.json'), 'application/json; charset=utf-8');
  assert.equal(getContentType('image/png'), 'image/png');
  assert.equal(getContentType('application/octet-stream'), 'application/octet-stream');
  assert.equal(getContentType('nonexistent'), false);
  assert.equal(getContentType('file.unknownextensionxyz'), false);
  assert.equal(mime.contentType('application/json'), 'application/json; charset=utf-8');
}

// Contract 3: mime.extension returns default file extension for a MIME type or false
{
  assert.equal(getExtension('text/html'), 'html');
  assert.equal(getExtension('application/json'), 'json');
  assert.equal(getExtension('text/markdown; charset=utf-8'), 'markdown');
  assert.equal(getExtension('application/octet-stream'), 'bin');
  assert.equal(getExtension('image/svg+xml'), 'svg');
  assert.equal(getExtension('invalid/not-real-mime-xyz'), false);
  assert.equal(mime.extension('application/pdf'), 'pdf');
}

console.log('All mime-types contract assertions passed successfully.');