add connectRemoteConfigEmulator function

Author: jhuleatt

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/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
+) {
+  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