refactor(realtime)!: replace listener callbacks with streams

MIGRATION.md

@@ -110,6 +110,149 @@ flushed once the join succeeds, so only channels that were never subscribed thro
 
 `httpSend()` requires a Realtime server running v2.97.0 or newer.
 
+### Realtime listener callbacks are now streams
+
+Every recurring-event listener in `realtime_client` is now a Dart `Stream` instead of a callback,
+following the shape `RealtimeClient.onHeartbeat` already had. Streams compose (`map`, `where`,
+`firstWhere`, `timeout`), support multiple listeners, and removing a listener is a
+`StreamSubscription.cancel()`, which the callback API had no public equivalent for.
+
+On `RealtimeClient`, the connection listeners are broadcast stream getters instead of
+callback-registration methods:
+
+```dart
+// Before
+client.onOpen(() => print('open'));
+client.onClose((event) => print('closed: $event'));
+client.onError((error) => print('error: $error'));
+client.onMessage((message) => print('message: $message'));
+
+// After
+client.onOpen.listen((_) => print('open'));
+client.onClose.listen((event) => print('closed: $event'));
+client.onError.listen((error) => print('error: $error'));
+client.onMessage.listen((message) => print('message: $message'));
+```
+
+On `RealtimeChannel`, `onPostgresChanges` and `onBroadcast` no longer take a `callback` parameter
+and return a typed stream instead of the channel, so they can no longer be chained. Repeated calls
+with the same arguments return the same stream. For `postgres_changes` the stream still has to be
+created before `subscribe()`, because the requested changes are part of the join payload, but it
+can be listened to at any point:
+
+```dart
+// Before
+supabase
+    .channel('room')
+    .onPostgresChanges(
+      event: PostgresChangeEvent.insert,
+      schema: 'public',
+      table: 'messages',
+      callback: (payload) => print(payload),
+    )
+    .onBroadcast(
+      event: 'cursor-pos',
+      callback: (payload) => print(payload),
+    )
+    .subscribe();
+
+// After
+final channel = supabase.channel('room');
+channel
+    .onPostgresChanges(
+      event: PostgresChangeEvent.insert,
+      schema: 'public',
+      table: 'messages',
+    )
+    .listen(print);
+channel.onBroadcast(event: 'cursor-pos').listen(print);
+channel.subscribe();
+```
+
+The presence and system listeners are stream getters, and `onSystemEvents` emits a typed
+`RealtimeSystemPayload` instead of a raw payload:
+
+```dart
+// Before
+channel.onPresenceSync((payload) { /* ... */ });
+channel.onPresenceJoin((payload) { /* ... */ });
+channel.onPresenceLeave((payload) { /* ... */ });
+channel.onSystemEvents((payload) {
+  final system = RealtimeSystemPayload.fromJson(
+    Map<String, dynamic>.from(payload as Map),
+  );
+});
+
+// After
+channel.onPresenceSync.listen((payload) { /* ... */ });
+channel.onPresenceJoin.listen((payload) { /* ... */ });
+channel.onPresenceLeave.listen((payload) { /* ... */ });
+channel.onSystemEvents.listen((system) { /* ... */ });
+```
+
+`subscribe()` no longer takes a status callback. Status changes are emitted on the new
+`RealtimeChannel.onStatusChange` stream as `RealtimeSubscribeStatusChange` values, which carry the
+`RealtimeSubscribeStatus` and, for `channelError`, the error that caused it. The optional timeout
+moved up to be the first positional parameter:
+
+```dart
+// Before
+channel.subscribe((status, [error]) {
+  if (status == RealtimeSubscribeStatus.subscribed) {
+    // ...
+  } else if (status == RealtimeSubscribeStatus.channelError) {
+    print('error: $error');
+  }
+}, const Duration(seconds: 10));
+
+// After
+channel.onStatusChange.listen((change) {
+  if (change.status == RealtimeSubscribeStatus.subscribed) {
+    // ...
+  } else if (change.status == RealtimeSubscribeStatus.channelError) {
+    print('error: ${change.error}');
+  }
+});
+channel.subscribe(const Duration(seconds: 10));
+```
+
+All channel streams complete when the channel closes, so `await for` loops and `onDone` handlers
+end on their own once the channel is gone.
+
+### `Binding` and `BindingCallback` are internal
+
+`Binding` and `BindingCallback` were the raw registration primitives underneath the channel
+listeners, exported by accident: their only consumers, `RealtimeChannel.onEvents` and
+`RealtimeChannel.off`, have always been internal. They are no longer exported. Use the typed
+channel streams (`onPostgresChanges`, `onBroadcast`, `onPresenceSync`, `onPresenceJoin`,
+`onPresenceLeave`, `onSystemEvents`) instead.
+
+### `RealtimePresence` is internal
+
+`RealtimePresence` and its helper types (`PresenceOptions`, `PresenceEvents`, `PresenceChooser`,
+`PresenceOnJoinCallback`, `PresenceOnLeaveCallback`) are now `@internal`, along with the
+`RealtimeChannel.presence` field. They were presence bookkeeping that leaked into the public API,
+and registering a callback through `channel.presence.onJoin(...)` silently disabled the channel's
+own presence events, because the channel's forwarders occupied the same single callback slot.
+
+Everything the class offered is available on the channel:
+
+```dart
+// Before
+channel.presence.onJoin((key, current, joined) { /* ... */ });
+channel.presence.onLeave((key, current, left) { /* ... */ });
+channel.presence.onSync(() { /* ... */ });
+final state = channel.presence.state;
+
+// After
+channel.onPresenceJoin.listen((payload) { /* ... */ });
+channel.onPresenceLeave.listen((payload) { /* ... */ });
+channel.onPresenceSync.listen((payload) { /* ... */ });
+final state = channel.presenceState();
+```
+
+The `Presence` payload class is unchanged and stays public.
+
 ### Plural enum names singularized
 
 A Dart enum type names one value rather than the set, so its name should be singular. Five enums

examples/realtime_room/lib/room_channel.dart

@@ -15,7 +15,7 @@ import 'models.dart';
 ///   roster.
 ///
 /// The channel is created but not connected in the constructor; call
-/// [subscribe] to join and [dispose] to leave and release the streams.
+/// [subscribe] to join and [dispose] to leave, which also closes the streams.
 class RoomChannel {
   RoomChannel({
     required SupabaseClient client,
@@ -32,7 +32,36 @@ class RoomChannel {
          // inserted right after joining can be missed, because replication is
          // set up asynchronously after the join is confirmed.
          opts: const RealtimeChannelConfig(self: true, replicationReady: true),
-       );
+       ) {
+    // Postgres Changes: new rows in the `messages` table.
+    onMessageInserted = _channel
+        .onPostgresChanges(
+          event: PostgresChangeEvent.insert,
+          schema: 'public',
+          table: 'messages',
+        )
+        .map((payload) => Message.fromJson(payload.newRecord));
+
+    // Postgres Changes: deleted rows. The delete payload carries the removed
+    // row under `oldRecord`.
+    onMessageDeleted = _channel
+        .onPostgresChanges(
+          event: PostgresChangeEvent.delete,
+          schema: 'public',
+          table: 'messages',
+        )
+        .map((payload) => payload.oldRecord['id'] as String);
+
+    // Broadcast: transient "typing" pings. Our own pings are filtered out.
+    onTyping = _channel
+        .onBroadcast(event: _typingEvent)
+        .map((payload) => payload['username'] as String)
+        .where((name) => name != username);
+
+    // Presence: fires whenever the roster changes. Read the full state back
+    // and map it to the connected users.
+    onlineUsers = _channel.onPresenceSync.map((_) => _currentUsers());
+  }
 
   final SupabaseClient _client;
   final RealtimeChannel _channel;
@@ -44,93 +73,62 @@ class RoomChannel {
   /// messages, typing pings and presence.
   final String roomName;
 
-  final _messageInserted = StreamController<Message>.broadcast();
-  final _messageDeleted = StreamController<String>.broadcast();
-  final _typing = StreamController<String>.broadcast();
-  final _onlineUsers = StreamController<List<OnlineUser>>.broadcast();
-
   /// A message someone added to the room (from a Postgres Changes insert
   /// event).
-  Stream<Message> get onMessageInserted => _messageInserted.stream;
+  late final Stream<Message> onMessageInserted;
 
   /// The id of a message someone removed (from a Postgres Changes delete
   /// event).
-  Stream<String> get onMessageDeleted => _messageDeleted.stream;
+  late final Stream<String> onMessageDeleted;
 
   /// The username of another client that is currently typing (from a broadcast
-  /// event). Our own typing pings are filtered out.
-  Stream<String> get onTyping => _typing.stream;
+  /// event).
+  late final Stream<String> onTyping;
 
   /// The current room roster (recomputed on every presence sync event).
-  Stream<List<OnlineUser>> get onlineUsers => _onlineUsers.stream;
+  late final Stream<List<OnlineUser>> onlineUsers;
 
   static const _typingEvent = 'typing';
 
-  /// Registers the realtime listeners and joins the channel. Completes once the
-  /// server confirms both the subscription and that Postgres Changes
-  /// replication is live, so a message sent right afterwards is guaranteed to
-  /// stream back.
+  /// Joins the channel. Completes once the server confirms both the
+  /// subscription and that Postgres Changes replication is live, so a message
+  /// sent right afterwards is guaranteed to stream back.
   Future<void> subscribe() {
     final ready = Completer<void>();
 
-    _channel
-        // Postgres Changes: new rows in the `messages` table.
-        .onPostgresChanges(
-          event: PostgresChangeEvent.insert,
-          schema: 'public',
-          table: 'messages',
-          callback: (payload) =>
-              _messageInserted.add(Message.fromJson(payload.newRecord)),
-        )
-        // Postgres Changes: deleted rows. The delete payload carries the
-        // removed row under `oldRecord`.
-        .onPostgresChanges(
-          event: PostgresChangeEvent.delete,
-          schema: 'public',
-          table: 'messages',
-          callback: (payload) =>
-              _messageDeleted.add(payload.oldRecord['id'] as String),
-        )
-        // Broadcast: a transient "typing" ping from another client.
-        .onBroadcast(
-          event: _typingEvent,
-          callback: (payload) {
-            final name = payload['username'] as String;
-            if (name != username) _typing.add(name);
-          },
-        )
-        // Presence: fires whenever the roster changes. Read the full state back
-        // and map it to the connected users.
-        .onPresenceSync((_) => _onlineUsers.add(_currentUsers()))
-        // The replication-ready signal requested with `replicationReady: true`.
-        // It arrives after the join, once Postgres Changes is actually
-        // streaming, so this is what completes [subscribe].
-        .onSystemEvents((payload) {
-          final system = RealtimeSystemPayload.fromJson(
-            Map<String, dynamic>.from(payload as Map),
-          );
-          if (system.extension != 'system' || ready.isCompleted) return;
-          if (system.status == 'ok') {
-            ready.complete();
-          } else {
-            ready.completeError(Exception(system.message));
-          }
-        })
-        .subscribe((status, error) {
-          if (status == RealtimeSubscribeStatus.subscribed) {
-            // Announce ourselves to the room now that we're connected. The
-            // payload is arbitrary JSON the other clients read back as
-            // presence.
-            unawaited(
-              _channel.track({
-                'username': username,
-                'online_at': DateTime.now().toIso8601String(),
-              }),
-            );
-          } else if (error != null && !ready.isCompleted) {
-            ready.completeError(error);
-          }
-        });
+    // The replication-ready signal requested with `replicationReady: true`.
+    // It arrives after the join, once Postgres Changes is actually streaming,
+    // so this is what completes [subscribe].
+    _channel.onSystemEvents.listen((system) {
+      if (system.extension != 'system' || ready.isCompleted) return;
+      if (system.status == 'ok') {
+        ready.complete();
+      } else {
+        ready.completeError(Exception(system.message));
+      }
+    });
+
+    _channel.onStatusChange.listen((change) {
+      if (change.status == RealtimeSubscribeStatus.subscribed) {
+        // Announce ourselves to the room now that we're connected. The
+        // payload is arbitrary JSON the other clients read back as presence.
+        unawaited(
+          _channel.track({
+            'username': username,
+            'online_at': DateTime.now().toIso8601String(),
+          }),
+        );
+      } else if (change.error != null && !ready.isCompleted) {
+        ready.completeError(change.error!);
+      } else if (change.status == RealtimeSubscribeStatus.closed &&
+          !ready.isCompleted) {
+        ready.completeError(
+          StateError('channel closed before the subscription completed'),
+        );
+      }
+    });
+
+    _channel.subscribe();
 
     return ready.future;
   }
@@ -152,12 +150,9 @@ class RoomChannel {
         .toList();
   }
 
-  /// Leaves the room (which also untracks our presence) and closes the streams.
+  /// Leaves the room (which also untracks our presence). Closing the channel
+  /// also closes all of its streams.
   Future<void> dispose() async {
     await _client.removeChannel(_channel);
-    await _messageInserted.close();
-    await _messageDeleted.close();
-    await _typing.close();
-    await _onlineUsers.close();
   }
 }