add FIREBASE_DATABASE_EMULATOR_HOST_VAR

src/database/database.ts

@@ -5,6 +5,14 @@ import {Database} from '@firebase/database';
 
 import * as validator from '../utils/validator';
 
+/**
+ * This variable is redefined in the firebase-js-sdk. Before modifying this
+ * definition, please consult the definition in firebase-js-sdk and ensure that
+ * they are consistent.
+ *
+ * https://github.com/firebase/firebase-js-sdk
+ */
+export const FIREBASE_DATABASE_EMULATOR_HOST_VAR = 'FIREBASE_DATABASE_EMULATOR_HOST';
 
 /**
  * Internals of a Database instance.
@@ -79,6 +87,10 @@ export class DatabaseService implements FirebaseServiceInterface {
     } else if (typeof this.appInternal.options.databaseURL !== 'undefined') {
       return this.appInternal.options.databaseURL;
     }
+    const dbEmulatorUrl = process.env[FIREBASE_DATABASE_EMULATOR_HOST_VAR];
+    if (dbEmulatorUrl) {
+      return 'http://' + dbEmulatorUrl;
+    }
     throw new FirebaseDatabaseError({
       code: 'invalid-argument',
       message: 'Can\'t determine Firebase Database URL.',

test/unit/firebase-app.spec.ts

@@ -41,6 +41,7 @@ import {Database} from '@firebase/database';
 import {InstanceId} from '../../src/instance-id/instance-id';
 import {ProjectManagement} from '../../src/project-management/project-management';
 import { FirebaseAppError, AppErrorCodes } from '../../src/utils/error';
+import { FIREBASE_DATABASE_EMULATOR_HOST_VAR } from '../../src/database/database';
 
 chai.should();
 chai.use(sinonChai);
@@ -434,12 +435,29 @@ describe('FirebaseApp', () => {
     });
 
     it('should throw when databaseURL is not set', () => {
+      delete process.env[FIREBASE_DATABASE_EMULATOR_HOST_VAR];
       const app = firebaseNamespace.initializeApp(mocks.appOptionsNoDatabaseUrl, mocks.appName);
       expect(() => {
         app.database();
       }).to.throw('Can\'t determine Firebase Database URL.');
     });
 
+    it('should use FIREBASE_DATABASE_EMULATOR_HOST when databaseURL not set', () => {
+      const url = 'localhost.com:9000?ns=test';
+      process.env[FIREBASE_DATABASE_EMULATOR_HOST_VAR] = url;
+      const app = firebaseNamespace.initializeApp(mocks.appOptionsNoDatabaseUrl, mocks.appName);
+      const db: Database = app.database();
+      expect(db.ref().toString()).to.equal('http://localhost.com:9000/');
+    });
+
+    it('should prefer databaseURL when FIREBASE_DATABASE_EMULATOR_HOST set', () => {
+      const url = 'localhost.com:9000?ns=test';
+      process.env[FIREBASE_DATABASE_EMULATOR_HOST_VAR] = url;
+      const app = firebaseNamespace.initializeApp(mocks.appOptions, mocks.appName);
+      const db: Database = app.database();
+      expect(db.ref().toString()).to.equal('https://databasename.firebaseio.com/');
+    });
+
     it('should return a cached version of Database on subsequent calls', () => {
       const app = firebaseNamespace.initializeApp(mocks.appOptions, mocks.appName);
       const db1: Database = app.database();

test/unit/firebase.spec.ts

@@ -29,6 +29,8 @@ import * as mocks from '../resources/mocks';
 import * as firebaseAdmin from '../../src/index';
 import {ApplicationDefaultCredential, CertCredential, RefreshTokenCredential} from '../../src/auth/credential';
 
+import {FIREBASE_DATABASE_EMULATOR_HOST_VAR} from '../../src/database/database';
+
 chai.should();
 chai.use(chaiAsPromised);
 
@@ -168,6 +170,7 @@ describe('Firebase', () => {
     });
 
     it('should throw given no databaseURL key when initializing the app', () => {
+      delete process.env[FIREBASE_DATABASE_EMULATOR_HOST_VAR];
       firebaseAdmin.initializeApp(mocks.appOptionsNoDatabaseUrl);
 
       expect(() => {