fix(realtime_client): No exception is thrown when connection is closed. (supabase#620)

* fix: realtime throwing error when connection is closed

* fix: adjust test case to align with js client

Author: dshukertjr

packages/realtime_client/lib/src/realtime_channel.dart

@@ -328,7 +328,7 @@ class RealtimeChannel {
   /// Registers a callback that will be executed when the channel encounteres an error.
   void onError(void Function(String?) callback) {
     onEvents(ChannelEvents.error.eventName(), ChannelFilter(),
-        (reason, [ref]) => callback(reason.toString()));
+        (reason, [ref]) => callback(reason?.toString()));
   }
 
   RealtimeChannel on(

packages/realtime_client/lib/src/realtime_client.dart

@@ -26,6 +26,26 @@ typedef RealtimeDecode = void Function(
   void Function(dynamic result) callback,
 );
 
+/// Event details for when the connection closed.
+class RealtimeCloseEvent {
+  /// Web socket protocol status codes for when a connection is closed.
+  ///
+  /// The full list can be found at the following:
+  ///
+  /// https://datatracker.ietf.org/doc/html/rfc6455#section-7.4
+  final int code;
+
+  /// Connection closed reason sent from the server
+  ///
+  /// https://datatracker.ietf.org/doc/html/rfc6455#section-7.1.6
+  final String? reason;
+
+  const RealtimeCloseEvent({
+    required this.code,
+    required this.reason,
+  });
+}
+
 class RealtimeClient {
   String? accessToken;
   List<RealtimeChannel> channels = [];
@@ -387,13 +407,17 @@ class RealtimeClient {
 
   /// communication has been closed
   void _onConnClose() {
-    final event = conn?.closeReason ?? '';
+    final statusCode = conn?.closeCode;
+    RealtimeCloseEvent? event;
+    if (statusCode != null) {
+      event = RealtimeCloseEvent(code: statusCode, reason: conn?.closeReason);
+    }
     log('transport', 'close', event);
 
     /// SocketStates.disconnected: by user with socket.disconnect()
     /// SocketStates.closed: NOT by user, should try to reconnect
     if (connState == SocketStates.closed) {
-      _triggerChanError(event);
+      _triggerChanError();
       reconnectTimer.scheduleTimeout();
     }
     if (heartbeatTimer != null) heartbeatTimer!.cancel();

packages/realtime_client/test/mock_test.dart

@@ -289,9 +289,9 @@ void main() {
     });
 
     test("correct CHANNEL_ERROR data on heartbeat timeout", () async {
-      final subscribeCallback = expectAsync2((event, [data]) {
+      final subscribeCallback = expectAsync2((event, [error]) {
         if (event == "CHANNEL_ERROR") {
-          expect(data, "heartbeat timeout");
+          expect(error, isNull);
         } else {
           expect(event, "CLOSED");
         }