Use environment variables for Firebase emulator, if available.

packages/dart_firebase_admin/lib/src/app/firebase_admin.dart

@@ -24,8 +24,17 @@ class FirebaseAdminApp {
   /// Use the Firebase Emulator Suite to run the app locally.
   void useEmulator() {
     _isUsingEmulator = true;
-    authApiHost = Uri.http('127.0.0.1:9099', 'identitytoolkit.googleapis.com/');
-    firestoreApiHost = Uri.http('127.0.0.1:8080', '/');
+    final env =
+        Zone.current[envSymbol] as Map<String, String>? ?? Platform.environment;
+
+    authApiHost = Uri.http(
+      env['FIREBASE_AUTH_EMULATOR_HOST'] ?? '127.0.0.1:9099',
+      'identitytoolkit.googleapis.com/',
+    );
+    firestoreApiHost = Uri.http(
+      env['FIRESTORE_EMULATOR_HOST'] ?? '127.0.0.1:8080',
+      '/',
+    );
   }
 
   @internal

packages/dart_firebase_admin/lib/src/google_cloud_firestore/document_reader.dart

@@ -122,7 +122,8 @@ class _DocumentReader<T> {
           // Only retry if we made progress.
           resultCount > 0 &&
           // Don't retry permanent errors.
-          StatusCode.batchGetRetryCodes.contains(firestoreError.errorCode.statusCode);
+          StatusCode.batchGetRetryCodes
+              .contains(firestoreError.errorCode.statusCode);
       if (shoulRetry) {
         return _fetchDocuments();
       } else {

packages/dart_firebase_admin/lib/src/google_cloud_firestore/transaction.dart

@@ -35,7 +35,8 @@ class Transaction {
   ) {
     _firestore = firestore;
 
-    _maxAttempts = transactionOptions?.maxAttempts ?? defaultMaxTransactionsAttempts;
+    _maxAttempts =
+        transactionOptions?.maxAttempts ?? defaultMaxTransactionsAttempts;
 
     switch (transactionOptions) {
       case ReadOnlyTransactionOptions():
@@ -50,9 +51,11 @@ class Transaction {
   static const int defaultMaxTransactionsAttempts = 5;
 
   //Error message for transactional reads that were executed after performing writes.
-  static const String readAfterWriteErrorMsg = 'Firestore transactions require all reads to be executed before all writes.';
+  static const String readAfterWriteErrorMsg =
+      'Firestore transactions require all reads to be executed before all writes.';
 
-  static const String readOnlyWriteErrorMsg = 'Firestore read-only transactions cannot execute writes.';
+  static const String readOnlyWriteErrorMsg =
+      'Firestore read-only transactions cannot execute writes.';
 
   late final Firestore _firestore;
 
@@ -91,7 +94,8 @@ class Transaction {
     if (_writeBatch != null && _writeBatch._operations.isNotEmpty) {
       throw Exception(readAfterWriteErrorMsg);
     }
-    return _withLazyStartedTransaction<DocumentReference<T>, DocumentSnapshot<T>>(
+    return _withLazyStartedTransaction<DocumentReference<T>,
+        DocumentSnapshot<T>>(
       docRef,
       fieldMask: null,
       resultFn: _getSingleFn,
@@ -115,7 +119,8 @@ class Transaction {
     if (_writeBatch != null && _writeBatch._operations.isNotEmpty) {
       throw Exception(readAfterWriteErrorMsg);
     }
-    return _withLazyStartedTransaction<List<DocumentReference<T>>, List<DocumentSnapshot<T>>>(
+    return _withLazyStartedTransaction<List<DocumentReference<T>>,
+        List<DocumentSnapshot<T>>>(
       documentsRefs,
       fieldMask: fieldMasks,
       resultFn: _getBatchFn<T>,
@@ -162,15 +167,18 @@ class Transaction {
   ///
   /// A [Precondition] restricting this update.
   ///
-  void update(DocumentReference<dynamic> documentRef, Map<Object?, Object?> data, {Precondition? precondition}) {
+  void update(
+      DocumentReference<dynamic> documentRef, Map<Object?, Object?> data,
+      {Precondition? precondition}) {
     if (_writeBatch == null) {
       throw Exception(readOnlyWriteErrorMsg);
     }
 
     _writeBatch.update(
       documentRef,
       {
-        for (final entry in data.entries) FieldPath.from(entry.key): entry.value,
+        for (final entry in data.entries)
+          FieldPath.from(entry.key): entry.value,
       },
       precondition: precondition,
     );
@@ -180,7 +188,8 @@ class Transaction {
   ///
   /// A delete for a non-existing document is treated as a success (unless
   /// [precondition] is specified, in which case it throws a [FirebaseFirestoreAdminException] with [FirestoreClientErrorCode.notFound]).
-  void delete(DocumentReference<Map<String, dynamic>> documentRef, {Precondition? precondition}) {
+  void delete(DocumentReference<Map<String, dynamic>> documentRef,
+      {Precondition? precondition}) {
     if (_writeBatch == null) {
       throw Exception(readOnlyWriteErrorMsg);
     }
@@ -233,7 +242,8 @@ class Transaction {
     // If there are any locks held, then rollback will eventually release them.
     // Rollback can be done concurrently thereby reducing latency caused by
     // otherwise blocking.
-    final rollBackRequest = firestore1.RollbackRequest(transaction: transactionId);
+    final rollBackRequest =
+        firestore1.RollbackRequest(transaction: transactionId);
     return _firestore._client.v1((client) {
       return client.projects.databases.documents
           .rollback(
@@ -264,25 +274,31 @@ class Transaction {
       // response because we are not starting a new transaction
       return _transactionIdPromise!
           .then(
-            (transactionId) => resultFn(docRef, transactionId: transactionId, fieldMask: fieldMask),
+            (transactionId) => resultFn(docRef,
+                transactionId: transactionId, fieldMask: fieldMask),
           )
           .then((r) => r.result);
     } else {
       if (_readOnlyReadTime != null) {
         // We do not start a transaction for read-only transactions
         // do not set _prevTransactionId
-        return resultFn(docRef, readTime: _readOnlyReadTime, fieldMask: fieldMask).then((r) => r.result);
+        return resultFn(docRef,
+                readTime: _readOnlyReadTime, fieldMask: fieldMask)
+            .then((r) => r.result);
       } else {
         // This is the first read of the transaction so we create the appropriate
         // options for lazily starting the transaction inside this first read op
         final opts = firestore1.TransactionOptions();
         if (_writeBatch != null) {
-          opts.readWrite = _prevTransactionId == null ? firestore1.ReadWrite() : firestore1.ReadWrite(retryTransaction: _prevTransactionId);
+          opts.readWrite = _prevTransactionId == null
+              ? firestore1.ReadWrite()
+              : firestore1.ReadWrite(retryTransaction: _prevTransactionId);
         } else {
           opts.readOnly = firestore1.ReadOnly();
         }
 
-        final resultPromise = resultFn(docRef, transactionOptions: opts, fieldMask: fieldMask);
+        final resultPromise =
+            resultFn(docRef, transactionOptions: opts, fieldMask: fieldMask);
 
         // Ensure the _transactionIdPromise is set synchronously so that
         // subsequent operations will not race to start another transaction
@@ -324,7 +340,8 @@ class Transaction {
       transactionOptions: transactionOptions,
     );
     final result = await reader._get();
-    return _TransactionResult(transaction: result.transaction, result: result.result.single);
+    return _TransactionResult(
+        transaction: result.transaction, result: result.result.single);
   }
 
   Future<_TransactionResult<List<DocumentSnapshot<T>>>> _getBatchFn<T>(
@@ -344,7 +361,8 @@ class Transaction {
     );
 
     final result = await reader._get();
-    return _TransactionResult(transaction: result.transaction, result: result.result);
+    return _TransactionResult(
+        transaction: result.transaction, result: result.result);
   }
 
   Future<T> _runTransaction<T>(

packages/dart_firebase_admin/lib/src/google_cloud_firestore/write_batch.dart

@@ -11,7 +11,8 @@ class WriteResult {
 
   @override
   bool operator ==(Object other) {
-    return identical(this, other) || other is WriteResult && writeTime == other.writeTime;
+    return identical(this, other) ||
+        other is WriteResult && writeTime == other.writeTime;
   }
 
   @override
@@ -91,7 +92,8 @@ class WriteBatch {
     final response = await _commit(transactionId: transactionId);
 
     return [
-      for (final writeResult in response.writeResults ?? <firestore1.WriteResult>[])
+      for (final writeResult
+          in response.writeResults ?? <firestore1.WriteResult>[])
         WriteResult._(
           Timestamp._fromString(
             writeResult.updateTime ?? response.commitTime!,
@@ -161,11 +163,13 @@ class WriteBatch {
 
     _verifyNotCommited();
 
-    final transform = _DocumentTransform.fromObject(documentReference, firestoreData);
+    final transform =
+        _DocumentTransform.fromObject(documentReference, firestoreData);
     transform.validate();
 
     firestore1.Write op() {
-      final document = DocumentSnapshot._fromObject(documentReference, firestoreData);
+      final document =
+          DocumentSnapshot._fromObject(documentReference, firestoreData);
 
       final write = document._toWriteProto();
       if (transform.transforms.isNotEmpty) {

packages/dart_firebase_admin/test/firebase_admin_app_test.dart

@@ -1,3 +1,5 @@
+import 'dart:async';
+
 import 'package:dart_firebase_admin/src/app.dart';
 import 'package:test/test.dart';
 
@@ -34,5 +36,40 @@ void main() {
         Uri.http('127.0.0.1:8080', '/'),
       );
     });
+
+    test(
+        'useEmulator() uses environment variables to set apiHost to the emulator',
+        () async {
+      const firebaseAuthEmulatorHost = '127.0.0.1:9000';
+      const firestoreEmulatorHost = '127.0.0.1:8000';
+      final testEnv = <String, String>{
+        'FIREBASE_AUTH_EMULATOR_HOST': firebaseAuthEmulatorHost,
+        'FIRESTORE_EMULATOR_HOST': firestoreEmulatorHost,
+      };
+
+      await runZoned(
+        zoneValues: {envSymbol: testEnv},
+        () async {
+          final app = FirebaseAdminApp.initializeApp(
+            'dart-firebase-admin',
+            Credential.fromApplicationDefaultCredentials(),
+          );
+
+          app.useEmulator();
+
+          expect(
+            app.authApiHost,
+            Uri.http(
+              firebaseAuthEmulatorHost,
+              'identitytoolkit.googleapis.com/',
+            ),
+          );
+          expect(
+            app.firestoreApiHost,
+            Uri.http(firestoreEmulatorHost, '/'),
+          );
+        },
+      );
+    });
   });
 }