Support custom tiles source

src/index.js

@@ -26,6 +26,8 @@ import WorkerPool from './util/worker_pool';
 import {prewarm, clearPrewarmedResources} from './util/global_worker_pool';
 import {clearTileCache} from './util/tile_request_cache';
 import {PerformanceUtils} from './util/performance';
+import type {RequestParameters, ResponseCallback} from './util/ajax';
+import type {Cancelable} from './types/cancelable';
 
 const exported = {
     version,
@@ -170,7 +172,32 @@ const exported = {
         clearTileCache(callback);
     },
 
-    workerUrl: ''
+    workerUrl: '',
+
+    /**
+     * Sets a custom load tile function that will be called when the using a source that starts with a custom url.
+     * The example below will be triggered for custom:// urls.
+     * The function to be used will recieve the request parameters and should call the callback with the resulting request,
+     * For example a pbf vector tile non compressed represented as ArrayBuffer:
+     * ```
+     * addCustomTilesFunction('custom', (params, callback) => {
+     *      const myArrayBufferOfTheTile = getTheTileByUsingTheRequest(params);
+     *      callback(null, myArrayBufferOfTheTile, null, null);
+     *      return { cancel: () => { } };
+     * });
+     * // the following is an example of a way to return an error when trying to load a tile
+     * addCustomTilesFunction('custom', (params, callback) => {
+     *      callback(new Error(someErrorMessage));
+     *      return { cancel: () => { } };
+     * });
+     * ```
+     */
+    addCustomTilesFunction(customUrl: string, loadFn: (requestParameters: RequestParameters, callback: ResponseCallback<any>) => Cancelable) {
+        config.LOAD_TILES_FUNCTION_MAP[customUrl] = loadFn;
+    },
+    removeCustomTilesFunction(customUrl: string) {
+        delete config.LOAD_TILES_FUNCTION_MAP[customUrl];
+    }
 };
 
 //This gets automatically stripped out in production builds.

src/util/ajax.js

@@ -242,6 +242,15 @@ export const makeRequest = function(requestParameters: RequestParameters, callba
     //   some versions (see https://bugs.webkit.org/show_bug.cgi?id=174980#c2)
     // - Requests for resources with the file:// URI scheme don't work with the Fetch API either. In
     //   this case we unconditionally use XHR on the current thread since referrers don't matter.
+    let key = Object.keys(config.LOAD_TILES_FUNCTION_MAP || {}).find(k => requestParameters.url.startsWith(k));
+    if (key) {
+        if (isWorker() && self.worker && self.worker.actor) {
+            return self.worker.actor.send('getResource', requestParameters, callback);
+        }
+        if (!isWorker()) {
+            return config.LOAD_TILES_FUNCTION_MAP[key](requestParameters, callback);
+        }
+    }
     if (!isFileURL(requestParameters.url)) {
         if (window.fetch && window.Request && window.AbortController && window.Request.prototype.hasOwnProperty('signal')) {
             return makeFetchRequest(requestParameters, callback);

src/util/config.js

@@ -6,7 +6,8 @@ type Config = {|
   FEEDBACK_URL: string,
   REQUIRE_ACCESS_TOKEN: boolean,
   ACCESS_TOKEN: ?string,
-  MAX_PARALLEL_IMAGE_REQUESTS: number
+  MAX_PARALLEL_IMAGE_REQUESTS: number,
+  LOAD_TILES_FUNCTION_MAP: object,
 |};
 
 const config: Config = {
@@ -24,7 +25,8 @@ const config: Config = {
     FEEDBACK_URL: 'https://apps.mapbox.com/feedback',
     REQUIRE_ACCESS_TOKEN: true,
     ACCESS_TOKEN: null,
-    MAX_PARALLEL_IMAGE_REQUESTS: 16
+    MAX_PARALLEL_IMAGE_REQUESTS: 16,
+    LOAD_TILES_FUNCTION_MAP: {}
 };
 
 export default config;