Fix refFromURL

Author: samtstern

packages/database/src/api/Database.ts

@@ -102,6 +102,7 @@ export class Database implements FirebaseService {
    * @param port the emulator port (ex: 8080)
    */
   useEmulator(host: string, port: number): void {
+    this.checkDeleted_('useEmulator');
     if (this.instanceStarted_) {
       fatal(
         'Cannot call useEmulator() after instance has already been initialized.'
@@ -156,14 +157,15 @@ export class Database implements FirebaseService {
     validateUrl(apiName, 1, parsedURL);
 
     const repoInfo = parsedURL.repoInfo;
-    if (repoInfo.host !== this.repo_.repoInfo_.host) {
+    const expectedHost = this.repo_.originalHost;
+    if (repoInfo.host !== expectedHost) {
       fatal(
         apiName +
           ': Host name does not match the current database: ' +
           '(found ' +
           repoInfo.host +
           ' but expected ' +
-          (this.repo_.repoInfo_ as RepoInfo).host +
+          expectedHost +
           ')'
       );
     }
@@ -175,7 +177,7 @@ export class Database implements FirebaseService {
    * @param {string} apiName
    */
   private checkDeleted_(apiName: string) {
-    if (this.repo_ === null) {
+    if (this.repoInternal_ === null) {
       fatal('Cannot call ' + apiName + ' on a deleted database.');
     }
   }

packages/database/src/core/Repo.ts

@@ -57,6 +57,9 @@ export class Repo {
   /** Key for uniquely identifying this repo, used in RepoManager */
   readonly key: string;
 
+  /** Record of the original host, which does not change even if useEmulator mutates the repo */
+  readonly originalHost: string;
+
   dataUpdateCount = 0;
   private infoSyncTree_: SyncTree;
   private serverSyncTree_: SyncTree;
@@ -90,6 +93,7 @@ export class Repo {
   ) {
     // This key is intentionally not updated if RepoInfo is later changed or replaced
     this.key = this.repoInfo_.toURLString();
+    this.originalHost = this.repoInfo_.host;
   }
 
   start(): void {

packages/database/test/database.test.ts

@@ -278,4 +278,12 @@ describe('Database Tests', () => {
       db.useEmulator('localhost', 1234);
     }).to.throw(/Cannot call useEmulator/);
   });
+
+  it('refFromURL returns an emulated ref with useEmulator', () => {
+    const db = (firebase as any).database();
+    db.useEmulator('localhost', 1234);
+
+    const ref = db.refFromURL(DATABASE_ADDRESS + '/path/to/data');
+    expect(ref.toString()).to.equal(`http://localhost:1234/path/to/data`);
+  });
 });