Function parseVaryHeader

deps/undici/src/lib/util/cache.js:286–304

* @param {string | string[]} varyHeader Vary header from the server * @param {Record } headers Request headers * @returns {Record }

(varyHeader, headers)

 * @returns {Record<string, string | string[]>}
 */
function parseVaryHeader (varyHeader, headers) {
  if (typeof varyHeader === 'string' && varyHeader.includes('*')) {
    return headers
  }

  const output = /** @type {Record<string, string | string[] | null>} */ ({})

  const varyingHeaders = typeof varyHeader === 'string'
    ? varyHeader.split(',')
    : varyHeader

  for (const header of varyingHeaders) {
    const trimmedHeader = header.trim().toLowerCase()

    output[trimmedHeader] = headers[trimmedHeader] ?? null
  }

  return output
}

/**
 * Note: this deviates from the spec a little. Empty etags ("", W/"") are valid,