Method onResponseStart

lib/handler/cache-handler.js:186–431

* @param {import('../../types/dispatcher.d.ts').default.DispatchController} controller * @param {number} statusCode * @param {import('../../types/header.d.ts').IncomingHttpHeaders} resHeaders * @param {string} statusMessage

(
    controller,
    statusCode,
    resHeaders,
    statusMessage
  )

   * @param {string} statusMessage
   */
  onResponseStart (
    controller,
    statusCode,
    resHeaders,
    statusMessage
  ) {
    const downstreamOnHeaders = () =>
      this.#handler.onResponseStart?.(
        controller,
        statusCode,
        resHeaders,
        statusMessage
      )
    const handler = this

    if (
      !arrayIncludes(util.safeHTTPMethods, this.#cacheKey.method) &&
      statusCode >= 200 &&
      statusCode <= 399
    ) {
      // Successful response to an unsafe method, delete it from cache
      //  https://www.rfc-editor.org/rfc/rfc9111.html#name-invalidating-stored-response
      invalidateUnsafeRequest(this.#store, this.#cacheKey, resHeaders)
      return downstreamOnHeaders()
    }

    const cacheControlHeader = resHeaders['cache-control']
    const heuristicallyCacheable = resHeaders['last-modified'] && arrayIncludes(HEURISTICALLY_CACHEABLE_STATUS_CODES, statusCode)
    if (
      !cacheControlHeader &&
      !resHeaders['expires'] &&
      !heuristicallyCacheable &&
      !this.#cacheByDefault
    ) {
      if (statusCode === 304 && resHeaders.vary && isInvalidOrWildcardVaryHeader(resHeaders.vary)) {
        deleteCachedValue(this.#store, this.#cacheKey)
      }

      // Don't have anything to tell us this response is cachable and we're not
      //  caching by default
      return downstreamOnHeaders()
    }

    const cacheControlDirectives = cacheControlHeader ? parseCacheControlHeader(cacheControlHeader) : {}
    if (!canCacheResponse(this.#cacheType, statusCode, resHeaders, cacheControlDirectives, this.#cacheKey.headers)) {
      if (statusCode === 304 && (cacheControlHeader || revalidationResponseDisallowsCachedReuse(this.#cacheType, resHeaders, cacheControlDirectives))) {
        deleteCachedValue(this.#store, this.#cacheKey)
      }

      return downstreamOnHeaders()
    }

    const now = Date.now()
    const resAge = Object.hasOwn(resHeaders, 'age') ? getAge(resHeaders.age) : undefined
    if (resAge !== undefined && resAge >= MAX_RESPONSE_AGE) {
      // Response considered stale
      deleteCachedValueIfNotModified(statusCode, this.#store, this.#cacheKey)
      return downstreamOnHeaders()