Possibility to get direct rxdart stream to avoid memory leaks

CHANGELOG.md

@@ -1,3 +1,6 @@
+## 2.3.15
+* provide option to listen on source location stream which doesn't cause memory leaks
+
 ## 2.3.14
 * upgrade dependencies  
 * fix for query results duplicate after 1250km as described in [this issue](https://github.com/beerstorm-net/GeoFlutterFire2/issues/13)  

README.md

@@ -70,6 +70,12 @@ Calling `geoFirePoint.data` returns an object that contains a [geohash string](h
 ![](https://firebasestorage.googleapis.com/v0/b/geo-test-c92e4.appspot.com/o/point1.png?alt=media&token=0c833700-3dbd-476a-99a9-41c1143dbe97)
 
 ## Query Geo data
+> **Warning**
+> Querying locations creates 9 separated stream listeners on firestore. One for central geo hash and 8 surrounding it.
+> `within` function creates a convenient broadcast stream, if you need more than one subscriber for the locations. But it also causes
+> memory leak, because underlying stream listeners are not cancelled when you cancel StreamSubscription from `within` method.
+> 
+> It's much safer to use withinAsSingleStreamSubscription which you can cancel, and it will also cancel 9 underlying streams as well.
 
 To query a collection of documents with 50kms from a point
 
@@ -220,4 +226,4 @@ radius.add(25);
 
 ### Acknowledgements  
 **NB! `GeoFlutterFire2` is a revisited and updated version of [GeoFlutterFire](https://github.com/DarshanGowda0/GeoFlutterFire)**  
-The work originates from [GeoFlutterFire](https://github.com/DarshanGowda0/GeoFlutterFire) by Darshan Narayanaswamy 
+The work originates from [GeoFlutterFire](https://github.com/DarshanGowda0/GeoFlutterFire) by Darshan Narayanaswamy 

lib/src/collection.dart

@@ -77,9 +77,12 @@ class GeoFireCollectionRef {
     }
   }
 
-  /// query firestore documents based on geographic [radius] from geoFirePoint [center]
-  /// [field] specifies the name of the key in the document
-  Stream<List<DocumentSnapshot>> within({
+  /// Create combined stream listeners for each geo hash around (including) central point.
+  /// It creates 9 listeners and the hood.
+  ///
+  /// Returns [StreamController.stream] instance from rxdart, which is combined stream,
+  /// for all 9 listeners.
+  Stream<List<DocumentSnapshot>> _buildQueryStream({
     required GeoFirePoint center,
     required double radius,
     required String field,
@@ -140,7 +143,54 @@ class GeoFireCollectionRef {
       });
       return filteredList.map((element) => element.documentSnapshot).toList();
     });
-    return filtered.asBroadcastStream();
+    return filtered;
+  }
+
+  /// Query firestore documents based on geographic [radius] from geoFirePoint [center]
+  /// [field] specifies the name of the key in the document
+  /// returns merged stream as broadcast stream.
+  ///
+  /// Returns original stream from the underlying rxdart implementation, which
+  /// could be safely cancelled without memory leaks. It's single stream subscription,
+  /// so only single listener could be created at a time.
+  ///
+  /// This works the best if you have central point of listening for locations,
+  /// not per widget.
+  Stream<List<DocumentSnapshot>> withinAsSingleStreamSubscription({
+    required GeoFirePoint center,
+    required double radius,
+    required String field,
+    bool strictMode = false,
+  }) {
+    return _buildQueryStream(
+      center: center,
+      radius: radius,
+      field: field,
+      strictMode: strictMode,
+    );
+  }
+
+  /// Query firestore documents based on geographic [radius] from geoFirePoint [center]
+  /// [field] specifies the name of the key in the document
+  /// returns merged stream as broadcast stream.
+  ///
+  /// !WARNING! This causes memory leaks because under the hood rxdart StreamController
+  /// never causes it's subscriptions to be cancelled. So, even you cancel stream
+  /// subscription created from this method, under the hood listeners are still working.
+  ///
+  /// More at: https://github.com/dart-lang/sdk/issues/26686#issuecomment-225346901
+  Stream<List<DocumentSnapshot>> within({
+    required GeoFirePoint center,
+    required double radius,
+    required String field,
+    bool strictMode = false,
+  }) {
+    return _buildQueryStream(
+      center: center,
+      radius: radius,
+      field: field,
+      strictMode: strictMode,
+    ).asBroadcastStream();
   }
 
   Stream<List<DistanceDocSnapshot>> mergeObservable(