Method _getSourceAsync

modules/services/VectorTileService.js:191–228

* _getSourceAsync * Create a new cache to hold data for the given template * @param {string} template - A url template for fetching data (e.g. a z/x/y tileserver or .pmtiles) * @return Promise resolved to the source object once it is ready to use

(template)

   * @return  Promise resolved to the source object once it is ready to use
   */
  _getSourceAsync(template) {
    if (!template) return Promise.reject(new Error('No template'));

    let source = this._sources.get(template);

    if (!source) {  // create it
      const url = new URL(template);
      const hostname = url.hostname;
      const filename = url.pathname.split('/').at(-1);

      source = {
        id:           utilHashcode(template).toString(),
        displayName:  hostname,
        template:     template,
        inflight:     new Map(),   // Map(tileID -> AbortController)
        loaded:       new Map(),   // Map(tileID -> Tile)
        zoomCache:    new Map(),   // Map(zoom -> Object zoomCache)
        lastv:        null         // viewport version last time we fetched data
      };

      this._sources.set(template, source);

      // Special handling for PMTiles sources
      // Create a PMTiles instance and fetch the header so we know more about the source.
      if (filename && /\.pmtiles$/.test(filename)) {
        source.displayName = filename;
        source.pmtiles = new PMTiles(template);
        source.readyPromise = source.pmtiles.getHeader()
          .then(header => source.header = header)
          .then(() => Promise.resolve(source));

      } else {
        source.readyPromise = Promise.resolve(source);
      }
    }

    return source.readyPromise;
  }


  /**