[Remote Config] add connectRemoteConfigEmulator to Remote Config

.changeset/proud-swans-tie.md

@@ -0,0 +1,5 @@
+---
+"@firebase/remote-config": minor
+---
+
+[Remote Config] add `connectRemoteConfigEmulator` to allow the SDK to connect to the Remote Config emulator (#6486)

common/api-review/remote-config.api.md

@@ -9,6 +9,9 @@ import { FirebaseApp } from '@firebase/app';
 // @public
 export function activate(remoteConfig: RemoteConfig): Promise<boolean>;
 
+// @public
+export function connectRemoteConfigEmulator(remoteConfig: RemoteConfig, url: string): void;
+
 // @public
 export function ensureInitialized(remoteConfig: RemoteConfig): Promise<void>;
 

packages/remote-config-compat/src/remoteConfig.ts

@@ -35,7 +35,8 @@ import {
   getNumber,
   getString,
   getValue,
-  isSupported
+  isSupported,
+  connectRemoteConfigEmulator
 } from '@firebase/remote-config';
 
 export { isSupported };
@@ -73,6 +74,10 @@ export class RemoteConfigCompatImpl
     return activate(this._delegate);
   }
 
+  useEmulator(url: string): void {
+    connectRemoteConfigEmulator(this._delegate, url);
+  }
+
   ensureInitialized(): Promise<void> {
     return ensureInitialized(this._delegate);
   }

packages/remote-config/src/api.ts

@@ -23,7 +23,7 @@ import {
 } from './public_types';
 import { RemoteConfigAbortSignal } from './client/remote_config_fetch_client';
 import { RC_COMPONENT_NAME } from './constants';
-import { ErrorCode, hasErrorCode } from './errors';
+import { ErrorCode, ERROR_FACTORY, hasErrorCode } from './errors';
 import { RemoteConfig as RemoteConfigImpl } from './remote_config';
 import { Value as ValueImpl } from './value';
 import { LogLevel as FirebaseLogLevel } from '@firebase/logger';
@@ -73,6 +73,36 @@ export async function activate(remoteConfig: RemoteConfig): Promise<boolean> {
   return true;
 }
 
+/**
+ * Configures the Remote Config SDK to talk to a local emulator
+ * instead of product.
+ *
+ * Must be called before performing any fetches against production
+ * Remote Config.
+ *
+ * @param remoteConfig - The {@link RemoteConfig} instance.
+ * @param url - The url of the local emulator
+ *
+ * @public
+ */
+export function connectRemoteConfigEmulator(
+  remoteConfig: RemoteConfig,
+  url: string
+): void {
+  const rc = getModularInstance(remoteConfig) as RemoteConfigImpl;
+
+  // To avoid the footgun of fetching from prod first,
+  // then the emulator, only allow emulator setup
+  // if no fetches have been made.
+  if (rc._storageCache.getLastFetchStatus() !== undefined) {
+    throw ERROR_FACTORY.create(ErrorCode.ALREADY_FETCHED);
+  }
+
+  window.FIREBASE_REMOTE_CONFIG_URL_BASE = url;
+
+  rc._logger.debug('Connected to the Remote Config emulator.');
+}
+
 /**
  * Ensures the last activated config are available to the getters.
  * @param remoteConfig - The {@link RemoteConfig} instance.

packages/remote-config/src/errors.ts

@@ -31,7 +31,8 @@ export const enum ErrorCode {
   FETCH_THROTTLE = 'fetch-throttle',
   FETCH_PARSE = 'fetch-client-parse',
   FETCH_STATUS = 'fetch-status',
-  INDEXED_DB_UNAVAILABLE = 'indexed-db-unavailable'
+  INDEXED_DB_UNAVAILABLE = 'indexed-db-unavailable',
+  ALREADY_FETCHED = 'already-fetched'
 }
 
 const ERROR_DESCRIPTION_MAP: { readonly [key in ErrorCode]: string } = {
@@ -67,7 +68,9 @@ const ERROR_DESCRIPTION_MAP: { readonly [key in ErrorCode]: string } = {
   [ErrorCode.FETCH_STATUS]:
     'Fetch server returned an HTTP error status. HTTP status: {$httpStatus}.',
   [ErrorCode.INDEXED_DB_UNAVAILABLE]:
-    'Indexed DB is not supported by current browser'
+    'Indexed DB is not supported by current browser',
+  [ErrorCode.ALREADY_FETCHED]:
+    'Cannot connect to emulator after a fetch has been made.'
 };
 
 // Note this is effectively a type system binding a code to params. This approach overlaps with the

packages/remote-config/test/remote_config.test.ts

@@ -518,4 +518,28 @@ describe('RemoteConfig', () => {
       );
     });
   });
+
+  describe('connectRemoteConfigEmulator', () => {
+    it('changes the remote config API URL', () => {
+      const emulatorUrl = 'http://localhost:9200';
+
+      // init storage as if it had never fetched
+      storageCache.getLastFetchStatus = sinon.stub().returns(undefined);
+
+      api.connectRemoteConfigEmulator(rc, emulatorUrl);
+      expect(window.FIREBASE_REMOTE_CONFIG_URL_BASE === emulatorUrl).to.be.true;
+    });
+
+    it('can not be called if a fetch has already happened', () => {
+      const emulatorUrl = 'http://localhost:9200';
+
+      // init storage as if it had already fetched
+      storageCache.getLastFetchStatus = sinon.stub().returns('success');
+
+      const expectedError = ERROR_FACTORY.create(ErrorCode.ALREADY_FETCHED);
+      expect(() => api.connectRemoteConfigEmulator(rc, emulatorUrl)).to.throw(
+        expectedError.message
+      );
+    });
+  });
 });