Class FetchSource

js/src/index.ts:339–477

 * This also works around browser and storage-specific edge cases.
 */
export class FetchSource implements Source {
  url: string;

  /**
   * A [Headers](https://developer.mozilla.org/en-US/docs/Web/API/Headers) object, specfying custom [Headers](https://developer.mozilla.org/en-US/docs/Web/API/Headers) set for all requests to the remote archive.
   *
   * This should be used instead of maplibre's [transformRequest](https://maplibre.org/maplibre-gl-js/docs/API/classes/Map/#example) for PMTiles archives.
   */
  customHeaders: Headers;
  credentials: "same-origin" | "include" | undefined;
  /** @hidden */
  mustReload: boolean;
  /** @hidden */
  chromeWindowsNoCache: boolean;

  constructor(
    url: string,
    customHeaders: Headers = new Headers(),
    credentials: "same-origin" | "include" | undefined = undefined
  ) {
    this.url = url;
    this.customHeaders = customHeaders;
    this.credentials = credentials;
    this.mustReload = false;
    let userAgent = "";
    if ("navigator" in globalThis) {
      //biome-ignore lint: cf workers
      userAgent = (globalThis as any).navigator?.userAgent ?? "";
    }
    const isWindows = userAgent.indexOf("Windows") > -1;
    const isChromiumBased = /Chrome|Chromium|Edg|OPR|Brave/.test(userAgent);
    this.chromeWindowsNoCache = false;
    if (isWindows && isChromiumBased) {
      this.chromeWindowsNoCache = true;
    }
  }

  getKey() {
    return this.url;
  }

  /**
   * Mutate the custom [Headers](https://developer.mozilla.org/en-US/docs/Web/API/Headers) set for all requests to the remote archive.
   */
  setHeaders(customHeaders: Headers) {
    this.customHeaders = customHeaders;
  }

  async getBytes(
    offset: number,
    length: number,
    passedSignal?: AbortSignal,
    etag?: string
  ): Promise<RangeResponse> {
    let controller: AbortController | undefined;
    let signal: AbortSignal | undefined;
    if (passedSignal) {
      signal = passedSignal;