@trailstash/ultra/lib/queryProviders/duckdb.js

A web based tool for making MapLibre GL maps with data from sources such as Overpass, GeoJSON, GPX, KML, TCX, etc

import { geoJsonLayers as layers } from "./common.js";

export const version = "1.32.0";

// global connection singleton
let connInstance = null;

async function initDB() {
  // Return the connection directly if already initialized
  if (connInstance) return connInstance;

  const duckdb = await import(
    `https://cdn.jsdelivr.net/npm/@duckdb/duckdb-wasm@${version}/+esm`
  );

  const JSDELIVR_BUNDLES = duckdb.getJsDelivrBundles();
  const bundle = await duckdb.selectBundle(JSDELIVR_BUNDLES);

  const worker_url = URL.createObjectURL(
    new Blob([`importScripts("${bundle.mainWorker}");`], {
      type: "text/javascript",
    }),
  );

  const worker = new Worker(worker_url);
  const logger = new duckdb.ConsoleLogger();
  const db = new duckdb.AsyncDuckDB(logger, worker);

  await db.instantiate(bundle.mainModule, bundle.pthreadWorker);
  URL.revokeObjectURL(worker_url);

  // Open DB to override query & filesystem defaults
  await db.open({
    // in-memory db, same as default
    path: ":memory:",

    // Query options to use standard JS types
    query: {
      castBigIntToDouble: true,
      castTimestampToDate: true,
      castDecimalToDouble: true,
    },

    // Filesytem options to force Range requests
    filesystem: {
      allowFullHTTPReads: false,
      reliableHeadRequests: true,
      forceFullHTTPReads: false,
    },
  });

  // Establish the connection and store it globally
  connInstance = await db.connect();

  await connInstance.query(`INSTALL spatial; LOAD spatial;`);

  return connInstance;
}

const duckdb = {
  source: async function (query, controller, { geomCol = "geometry" }) {
    const conn = await initDB();

    const jsonQuery = `
      WITH _data AS (${query})
      SELECT json_object(
        'type', 'FeatureCollection',
        'features', COALESCE(json_group_array(
          json_object(
            'type', 'Feature',
            'geometry', ST_AsGeoJSON(${geomCol})::JSON,
            'properties', to_json(struct_pack(*COLUMNS(* EXCLUDE (${geomCol}))))
          )
        ), '[]'::JSON)
      )::VARCHAR AS geojson_string
      FROM _data;
    `;

    const arrowResult = await conn.query(jsonQuery);
    const rows = arrowResult.toArray();

    const data = JSON.parse(
      rows[0].toJSON ? rows[0].toJSON().geojson_string : rows[0].geojson_string,
    );

    return { type: "geojson", data };
  },
  layers,
};

export default duckdb;