Send GeoJSON data from worker to main if loaded from a URL

src/source/geojson_source.test.ts

@@ -495,6 +495,20 @@ describe('GeoJSONSource.update', () => {
         expect(transformSpy).toHaveBeenCalledTimes(1);
         expect(transformSpy.mock.calls[0][0]).toBe('https://example.com/data.geojson');
     });
+
+    test('updates _data.geojson when worker returns data from URL load', async () => {
+        const source = new GeoJSONSource('id', {data: 'https://example.com/data.geojson'} as GeoJSONSourceOptions, wrapDispatcher({
+            sendAsync() { return Promise.resolve({data: hawkHill}); }
+        }), undefined);
+        source.map = {_requestManager: {transformRequest: (url) => ({url})}} as any;
+
+        const promise = waitForEvent(source, 'data', (e: MapSourceDataEvent) => e.sourceDataType === 'metadata');
+        source.load();
+        await promise;
+
+        expect((source as any)._data.geojson).toStrictEqual(hawkHill);
+    });
+
     test('fires event when metadata loads', async () =>  {
         const mockDispatcher = wrapDispatcher({
             sendAsync(_message: ActorMessage<MessageType>) {

src/source/geojson_source.ts

@@ -424,7 +424,8 @@ export class GeoJSONSource extends Evented implements Source {
                 return;
             }
 
-            if (diff) this._applyDiff(diff);
+            if (result.data) this._data.geojson = result.data;
+            else if (diff) this._applyDiff(diff);
 
             let resourceTiming: PerformanceResourceTiming[] = null;
             if (result.resourceTiming && result.resourceTiming[this.id]) {

src/source/geojson_worker_source.test.ts

@@ -157,6 +157,7 @@ describe('resourceTiming', () => {
 
         const result = await source.loadData({source: 'testSource', data: geoJson} as LoadGeoJSONParameters);
         expect(result.resourceTiming).toBeUndefined();
+        expect(result.data).toBeUndefined();
     });
 
 });
@@ -296,7 +297,8 @@ describe('loadData', () => {
         const load1Promise = worker.loadData({source: 'source1', request: {url: ''}} as LoadGeoJSONParameters);
         server.respond();
 
-        await load1Promise;
+        const result = await load1Promise;
+        expect(result.data).toStrictEqual(updateableGeoJson);
         await expect(worker.loadData({source: 'source1', dataDiff: {removeAll: true}} as LoadGeoJSONParameters)).resolves.toBeDefined();
     });
 
@@ -320,14 +322,16 @@ describe('loadData', () => {
         const worker = new GeoJSONWorkerSource(actor, layerIndex, []);
 
         await worker.loadData({source: 'source1', data: updateableGeoJson} as LoadGeoJSONParameters);
-        await expect(worker.loadData({source: 'source1', dataDiff: {
+        const result = await worker.loadData({source: 'source1', dataDiff: {
             add: [{
                 type: 'Feature',
                 id: 'update_point',
                 geometry: {type: 'Point', coordinates: [0, 0]},
                 properties: {}
             }]
-        }} as LoadGeoJSONParameters)).resolves.toBeDefined();
+        }} as LoadGeoJSONParameters);
+        expect(result).toBeDefined();
+        expect(result.data).toBeUndefined();
     });
 
     test('loadData should reject as first call with no data', async () => {

src/source/geojson_worker_source.ts

@@ -130,6 +130,12 @@ export class GeoJSONWorkerSource extends VectorTileWorkerSource {
 
             const result: GeoJSONWorkerSourceLoadDataResult = {};
 
+            // Sending a large GeoJSON payload from the worker thread to the main thread
+            // is SLOW so we only do it if absolutely nescessary.
+            // The main thread already has a copy of this data UNLESS it was loaded
+            // from a URL.
+            if (params.request) result.data = data;
+
             this._finishPerformance(perf, params, result);
             return result;
         } catch (err) {

src/util/actor_messages.ts

@@ -29,6 +29,7 @@ export type GetClusterLeavesParams = ClusterIDAndSource & { limit: number; offse
 export type GeoJSONWorkerSourceLoadDataResult = {
     resourceTiming?: {[_: string]: Array<PerformanceResourceTiming>};
     abandoned?: boolean;
+    data?: GeoJSON.GeoJSON;
 };
 
 /**