Function stripNecessaryHeaders

deps/undici/src/lib/handler/cache-handler.js:534–576

* Strips headers required to be removed in cached responses * @param {import('../../types/header.d.ts').IncomingHttpHeaders} resHeaders * @param {import('../../types/cache-interceptor.d.ts').default.CacheControlDirectives} cacheControlDirectives * @returns {Record }

(resHeaders, cacheControlDirectives)

 * @returns {Record<string, string | string []>}
 */
function stripNecessaryHeaders (resHeaders, cacheControlDirectives) {
  const headersToRemove = [
    'connection',
    'proxy-authenticate',
    'proxy-authentication-info',
    'proxy-authorization',
    'proxy-connection',
    'te',
    'transfer-encoding',
    'upgrade',
    // We'll add age back when serving it
    'age'
  ]

  if (resHeaders['connection']) {
    if (Array.isArray(resHeaders['connection'])) {
      // connection: a
      // connection: b
      headersToRemove.push(...resHeaders['connection'].map(header => header.trim()))
    } else {
      // connection: a, b
      headersToRemove.push(...resHeaders['connection'].split(',').map(header => header.trim()))
    }
  }

  if (Array.isArray(cacheControlDirectives['no-cache'])) {
    headersToRemove.push(...cacheControlDirectives['no-cache'])
  }

  if (Array.isArray(cacheControlDirectives['private'])) {
    headersToRemove.push(...cacheControlDirectives['private'])
  }

  let strippedHeaders
  for (const headerName of headersToRemove) {
    if (resHeaders[headerName]) {
      strippedHeaders ??= { ...resHeaders }
      delete strippedHeaders[headerName]
    }
  }

  return strippedHeaders ?? resHeaders
}

/**
 * @param {Date} date