Function maybeUpdate

packages/service-worker/worker/src/assets.ts:472–498

* Possibly update a resource, if it's expired and needs to be updated. A no-op otherwise.

(
    updateFrom: UpdateSource,
    req: Request,
    cache: Cache,
  )

   * Possibly update a resource, if it's expired and needs to be updated. A no-op otherwise.
   */
  protected async maybeUpdate(
    updateFrom: UpdateSource,
    req: Request,
    cache: Cache,
  ): Promise<boolean> {
    const url = this.adapter.normalizeUrl(req.url);
    // Check if this resource is hashed and already exists in the cache of a prior version.
    if (this.hashes.has(url)) {
      const hash = this.hashes.get(url)!;

      // Check the caches of prior versions, using the hash to ensure the correct version of
      // the resource is loaded.
      const res = await updateFrom.lookupResourceWithHash(url, hash);

      // If a previously cached version was available, copy it over to this cache.
      if (res !== null) {
        // Copy to this cache.
        await cache.put(req, res);

        // No need to do anything further with this resource, it's now cached properly.
        return true;
      }
    }

    // No up-to-date version of this resource could be found.
    return false;
  }

  /**
   * Create a new `Request` based on the specified URL and `RequestInit` options, preserving only