Fix emulated database URL parse issue (#838)

Author: samtstern

package.json

@@ -31,6 +31,7 @@
     "build:pack": "rm -rf lib && npm install && tsc -p tsconfig.release.json && npm pack",
     "build:release": "npm install --production && npm install --no-save typescript firebase-admin && tsc -p tsconfig.release.json",
     "build": "tsc -p tsconfig.release.json",
+    "build:watch": "npm run build -- -w",
     "format": "prettier --check '**/*.{json,md,ts,yml,yaml}'",
     "format:fix": "prettier --write '**/*.{json,md,ts,yml,yaml}'",
     "lint": "tslint --config tslint.json --project tsconfig.json ",

spec/providers/database.spec.ts

@@ -472,6 +472,17 @@ describe('Database Functions', () => {
         );
       }).to.throw(Error);
     });
+
+    it('should use the emulator host when present', () => {
+      process.env.FIREBASE_DATABASE_EMULATOR_HOST = 'localhost:1234';
+      const [instance, path] = database.extractInstanceAndPath(
+        'projects/_/instances/foo/refs/bar',
+        'firebaseio-staging.com'
+      );
+      expect(instance).to.equal('http://localhost:1234/?ns=foo');
+      expect(path).to.equal('/bar');
+      delete process.env.FIREBASE_DATABASE_EMULATOR_HOST;
+    });
   });
 
   describe('DataSnapshot', () => {

src/providers/database.ts

@@ -334,8 +334,15 @@ export function extractInstanceAndPath(
       `Expect project to be '_' in a Firebase Realtime Database event`
     );
   }
-  const dbInstance = 'https://' + dbInstanceName + '.' + domain;
-  return [dbInstance, path];
+
+  const emuHost = process.env.FIREBASE_DATABASE_EMULATOR_HOST;
+  if (emuHost) {
+    const dbInstance = `http://${emuHost}/?ns=${dbInstanceName}`;
+    return [dbInstance, path];
+  } else {
+    const dbInstance = 'https://' + dbInstanceName + '.' + domain;
+    return [dbInstance, path];
+  }
 }
 
 /**