Basic error event communication

packages/firebase_database/android/src/main/java/io/flutter/plugins/firebase/database/FirebaseDatabasePlugin.java

@@ -179,7 +179,12 @@ private void sendEvent(String eventType, DataSnapshot snapshot, String previousC
     }
 
     @Override
-    public void onCancelled(DatabaseError error) {}
+    public void onCancelled(DatabaseError error) {
+      Map<String, Object> arguments = new HashMap<>();
+      arguments.put("handle", handle);
+      arguments.put("error", asMap(error));
+      channel.invokeMethod("Error", arguments);
+    }
 
     @Override
     public void onChildAdded(DataSnapshot snapshot, String previousChildName) {
@@ -371,11 +376,7 @@ public void onComplete(
                   Map<String, Object> completionMap = new HashMap<>();
                   completionMap.put("transactionKey", arguments.get("transactionKey"));
                   if (databaseError != null) {
-                    Map<String, Object> errorMap = new HashMap<>();
-                    errorMap.put("code", databaseError.getCode());
-                    errorMap.put("message", databaseError.getMessage());
-                    errorMap.put("details", databaseError.getDetails());
-                    completionMap.put("error", errorMap);
+                    completionMap.put("error", asMap(databaseError));
                   }
                   completionMap.put("committed", committed);
                   if (dataSnapshot != null) {
@@ -445,4 +446,12 @@ public void onComplete(
         }
     }
   }
+
+  private static Map<String, Object> asMap(DatabaseError error) {
+    Map<String, Object> map = new HashMap<>();
+    map.put("code", error.getCode());
+    map.put("message", error.getMessage());
+    map.put("details", error.getDetails());
+    return map;
+  }
 }

packages/firebase_database/example/lib/main.dart

@@ -40,6 +40,7 @@ class _MyHomePageState extends State<MyHomePage> {
 
   String _kTestKey = 'Hello';
   String _kTestValue = 'world!';
+  DatabaseError _error;
 
   @override
   void initState() {
@@ -49,12 +50,19 @@ class _MyHomePageState extends State<MyHomePage> {
     _counterRef.keepSynced(true);
     _counterSubscription = _counterRef.onValue.listen((Event event) {
       setState(() {
+        _error = null;
         _counter = event.snapshot.value ?? 0;
       });
+    }, onError: (DatabaseError error) {
+      setState(() {
+        _error = error;
+      });
     });
     _messagesSubscription =
         _messagesRef.limitToLast(10).onChildAdded.listen((Event event) {
       print('Child added: ${event.snapshot.value}');
+    }, onError: (DatabaseError error) {
+      print('Error: ${error.code} ${error.message}');
     });
   }
 
@@ -96,11 +104,14 @@ class _MyHomePageState extends State<MyHomePage> {
         children: <Widget>[
           new Flexible(
             child: new Center(
-              // ignore: prefer_const_constructors
-              child: new Text(
-                'Button tapped $_counter time${ _counter == 1 ? '' : 's' }.\n\n'
-                    'This includes all devices, ever.',
-              ),
+              child: _error == null
+                  ? new Text(
+                      'Button tapped $_counter time${ _counter == 1 ? '' : 's' }.\n\n'
+                          'This includes all devices, ever.',
+                    )
+                  : new Text(
+                      'Error retrieving button tap count:\n${_error.message}',
+                    ),
             ),
           ),
           new ListTile(

packages/firebase_database/ios/Classes/FirebaseDatabasePlugin.m

@@ -11,6 +11,7 @@ @interface FLTFirebaseDatabasePlugin ()
 
 @interface NSError (FlutterError)
 @property(readonly, nonatomic) FlutterError *flutterError;
+@property(readonly, nonatomic) NSDictionary *dictionary;
 @end
 
 @implementation NSError (FlutterError)
@@ -19,6 +20,14 @@ - (FlutterError *)flutterError {
                              message:self.domain
                              details:self.localizedDescription];
 }
+
+- (NSDictionary *)dictionary {
+  return @{
+    @"code" : @(self.code),
+    @"message" : self.domain ?: [NSNull null],
+    @"details" : self.localizedDescription ?: [NSNull null],
+  };
+}
 @end
 
 FIRDatabaseReference *getReference(NSDictionary *arguments) {
@@ -252,15 +261,14 @@ - (void)handleMethodCall:(FlutterMethodCall *)call result:(FlutterResult)result
           // Invoke transaction completion on the Dart side.
           result(@{
             @"transactionKey" : call.arguments[@"transactionKey"],
-            @"error" : error.flutterError ?: [NSNull null],
+            @"error" : error.dictionary ?: [NSNull null],
             @"committed" : [NSNumber numberWithBool:committed],
             @"snapshot" : @{@"key" : snapshot.key ?: [NSNull null], @"value" : snapshot.value}
           });
         }];
   } else if ([@"Query#observe" isEqualToString:call.method]) {
     FIRDataEventType eventType = parseEventType(call.arguments[@"eventType"]);
-    __block FIRDatabaseHandle handle = [getQuery(call.arguments)
-                      observeEventType:eventType
+    __block FIRDatabaseHandle handle = [getQuery(call.arguments) observeEventType:eventType
         andPreviousSiblingKeyWithBlock:^(FIRDataSnapshot *snapshot, NSString *previousSiblingKey) {
           [self.channel invokeMethod:@"Event"
                            arguments:@{
@@ -271,6 +279,13 @@ - (void)handleMethodCall:(FlutterMethodCall *)call result:(FlutterResult)result
                              },
                              @"previousSiblingKey" : previousSiblingKey ?: [NSNull null],
                            }];
+        }
+        withCancelBlock:^(NSError *error) {
+          [self.channel invokeMethod:@"Error"
+                           arguments:@{
+                             @"handle" : [NSNumber numberWithUnsignedInteger:handle],
+                             @"error" : error.dictionary,
+                           }];
         }];
     result([NSNumber numberWithUnsignedInteger:handle]);
   } else if ([@"Query#removeObserver" isEqualToString:call.method]) {

packages/firebase_database/lib/src/firebase_database.dart

@@ -20,19 +20,26 @@ class FirebaseDatabase {
 
   FirebaseDatabase._() {
     _channel.setMethodCallHandler((MethodCall call) async {
-      if (call.method == 'Event') {
-        final Event event = new Event._(call.arguments);
-        _observers[call.arguments['handle']].add(event);
-      } else if (call.method == 'DoTransaction') {
-        final MutableData mutableData =
-            new MutableData.private(call.arguments['snapshot']);
-        final MutableData updated =
-            await _transactions[call.arguments['transactionKey']](mutableData);
-        return <String, dynamic>{'value': updated.value};
-      } else {
-        throw new MissingPluginException(
-          '${call.method} method not implemented on the Dart side.',
-        );
+      switch (call.method) {
+        case 'Event':
+          final Event event = new Event._(call.arguments);
+          _observers[call.arguments['handle']].add(event);
+          return null;
+        case 'Error':
+          final DatabaseError error =
+              new DatabaseError._(call.arguments['error']);
+          _observers[call.arguments['handle']].addError(error);
+          return null;
+        case 'DoTransaction':
+          final MutableData mutableData =
+              new MutableData.private(call.arguments['snapshot']);
+          final MutableData updated = await _transactions[
+              call.arguments['transactionKey']](mutableData);
+          return <String, dynamic>{'value': updated.value};
+        default:
+          throw new MissingPluginException(
+            '${call.method} method not implemented on the Dart side.',
+          );
       }
     });
   }

packages/firebase_database/lib/ui/firebase_list.dart

@@ -6,13 +6,15 @@ import 'dart:collection';
 
 import 'package:meta/meta.dart';
 
-import '../firebase_database.dart' show DataSnapshot, Event, Query;
+import '../firebase_database.dart'
+    show DatabaseError, DataSnapshot, Event, Query;
 import 'utils/stream_subscriber_mixin.dart';
 
 typedef void ChildCallback(int index, DataSnapshot snapshot);
 typedef void ChildMovedCallback(
     int fromIndex, int toIndex, DataSnapshot snapshot);
 typedef void ValueCallback(DataSnapshot snapshot);
+typedef void ErrorCallback(DatabaseError error);
 
 /// Sorts the results of `query` on the client side using `DataSnapshot.key`.
 class FirebaseList extends ListBase<DataSnapshot>
@@ -24,13 +26,14 @@ class FirebaseList extends ListBase<DataSnapshot>
     this.onChildChanged,
     this.onChildMoved,
     this.onValue,
+    this.onError,
   }) {
     assert(query != null);
-    listen(query.onChildAdded, _onChildAdded);
-    listen(query.onChildRemoved, _onChildRemoved);
-    listen(query.onChildChanged, _onChildChanged);
-    listen(query.onChildMoved, _onChildMoved);
-    listen(query.onValue, _onValue);
+    listen(query.onChildAdded, _onChildAdded, onError: _onError);
+    listen(query.onChildRemoved, _onChildRemoved, onError: _onError);
+    listen(query.onChildChanged, _onChildChanged, onError: _onError);
+    listen(query.onChildMoved, _onChildMoved, onError: _onError);
+    listen(query.onValue, _onValue, onError: _onError);
   }
 
   /// Database query used to populate the list
@@ -51,6 +54,9 @@ class FirebaseList extends ListBase<DataSnapshot>
   /// Called when the data of the list has finished loading
   final ValueCallback onValue;
 
+  /// Called when an error is reported (e.g. permission denied)
+  final ErrorCallback onError;
+
   // ListBase implementation
   final List<DataSnapshot> _snapshots = <DataSnapshot>[];
 
@@ -127,4 +133,8 @@ class FirebaseList extends ListBase<DataSnapshot>
   void _onValue(Event event) {
     onValue(event.snapshot);
   }
+
+  void _onError(DatabaseError error) {
+    onError?.call(error);
+  }
 }

packages/firebase_database/lib/ui/firebase_sorted_list.dart

@@ -6,8 +6,9 @@ import 'dart:collection';
 
 import 'package:meta/meta.dart';
 
-import '../firebase_database.dart' show DataSnapshot, Event, Query;
-import 'firebase_list.dart' show ChildCallback, ValueCallback;
+import '../firebase_database.dart'
+    show DatabaseError, DataSnapshot, Event, Query;
+import 'firebase_list.dart' show ChildCallback, ErrorCallback, ValueCallback;
 import 'utils/stream_subscriber_mixin.dart';
 
 /// Sorts the results of `query` on the client side using to the `comparator`.
@@ -26,13 +27,14 @@ class FirebaseSortedList extends ListBase<DataSnapshot>
     this.onChildRemoved,
     this.onChildChanged,
     this.onValue,
+    this.onError,
   }) {
     assert(query != null);
     assert(comparator != null);
-    listen(query.onChildAdded, _onChildAdded);
-    listen(query.onChildRemoved, _onChildRemoved);
-    listen(query.onChildChanged, _onChildChanged);
-    listen(query.onValue, _onValue);
+    listen(query.onChildAdded, _onChildAdded, onError: _onError);
+    listen(query.onChildRemoved, _onChildRemoved, onError: _onError);
+    listen(query.onChildChanged, _onChildChanged, onError: _onError);
+    listen(query.onValue, _onValue, onError: _onError);
   }
 
   /// Database query used to populate the list
@@ -53,6 +55,9 @@ class FirebaseSortedList extends ListBase<DataSnapshot>
   /// Called when the data of the list has finished loading
   final ValueCallback onValue;
 
+  /// Called when an error is reported (e.g. permission denied)
+  final ErrorCallback onError;
+
   // ListBase implementation
   final List<DataSnapshot> _snapshots = <DataSnapshot>[];
 
@@ -108,4 +113,8 @@ class FirebaseSortedList extends ListBase<DataSnapshot>
   void _onValue(Event event) {
     onValue(event.snapshot);
   }
+
+  void _onError(DatabaseError error) {
+    onError?.call(error);
+  }
 }

packages/firebase_database/lib/ui/utils/stream_subscriber_mixin.dart

@@ -10,9 +10,9 @@ abstract class StreamSubscriberMixin<T> {
   List<StreamSubscription<T>> _subscriptions = <StreamSubscription<T>>[];
 
   /// Listens to a stream and saves it to the list of subscriptions.
-  void listen(Stream<T> stream, void onData(T data)) {
+  void listen(Stream<T> stream, void onData(T data), {Function onError}) {
     if (stream != null) {
-      _subscriptions.add(stream.listen(onData));
+      _subscriptions.add(stream.listen(onData, onError: onError));
     }
   }
 

packages/firebase_database/test/firebase_database_test.dart

@@ -285,6 +285,48 @@ void main() {
           ],
         );
       });
+      test('observing error events', () async {
+        mockHandleId = 99;
+        const int errorCode = 12;
+        const String errorDetails = 'Some details';
+        final Query query = database.reference().child('some path');
+        Future<Null> simulateError(String errorMessage) async {
+          await BinaryMessages.handlePlatformMessage(
+            channel.name,
+            channel.codec.encodeMethodCall(
+              new MethodCall('Error', <String, dynamic>{
+                'handle': 99,
+                'error': <String, dynamic>{
+                  'code': errorCode,
+                  'message': errorMessage,
+                  'details': errorDetails,
+                },
+              }),
+            ),
+            (_) {},
+          );
+        }
+
+        final AsyncQueue<DatabaseError> errors =
+            new AsyncQueue<DatabaseError>();
+
+        // Subscribe and allow subscription to complete.
+        final StreamSubscription<Event> subscription =
+            query.onValue.listen((_) {}, onError: errors.add);
+        await new Future<Null>.delayed(const Duration(seconds: 0));
+
+        await simulateError('Bad foo');
+        await simulateError('Bad bar');
+        final DatabaseError error1 = await errors.remove();
+        final DatabaseError error2 = await errors.remove();
+        subscription.cancel();
+        expect(error1.code, errorCode);
+        expect(error1.message, 'Bad foo');
+        expect(error1.details, errorDetails);
+        expect(error2.code, errorCode);
+        expect(error2.message, 'Bad bar');
+        expect(error2.details, errorDetails);
+      });
       test('observing value events', () async {
         mockHandleId = 87;
         final String path = 'foo';