feat(xep): Implement XEP 0421 in Moxxmpp.

Signed-off-by: Ikjot Singh Dhody <ikjotsd@gmail.com>

packages/moxxmpp/lib/moxxmpp.dart

@@ -85,6 +85,7 @@ export 'package:moxxmpp/src/xeps/xep_0388/errors.dart';
 export 'package:moxxmpp/src/xeps/xep_0388/negotiators.dart';
 export 'package:moxxmpp/src/xeps/xep_0388/user_agent.dart';
 export 'package:moxxmpp/src/xeps/xep_0388/xep_0388.dart';
+export 'package:moxxmpp/src/xeps/xep_0421.dart';
 export 'package:moxxmpp/src/xeps/xep_0424.dart';
 export 'package:moxxmpp/src/xeps/xep_0444.dart';
 export 'package:moxxmpp/src/xeps/xep_0446.dart';

packages/moxxmpp/lib/src/managers/namespaces.dart

@@ -32,3 +32,4 @@ const messageReactionsManager = 'org.moxxmpp.messagereactionsmanager';
 const stickersManager = 'org.moxxmpp.stickersmanager';
 const entityCapabilitiesManager = 'org.moxxmpp.entitycapabilities';
 const messageProcessingHintManager = 'org.moxxmpp.messageprocessinghint';
+const occupantIdManager = 'org.moxxmpp.occupantidmanager';

packages/moxxmpp/lib/src/namespaces.dart

@@ -123,6 +123,9 @@ const sasl2Xmlns = 'urn:xmpp:sasl:2';
 // XEP-0420
 const sceXmlns = 'urn:xmpp:sce:1';
 
+// XEP-0421
+const occupantIdXmlns = 'urn:xmpp:occupant-id:0';
+
 // XEP-0422
 const fasteningXmlns = 'urn:xmpp:fasten:0';
 

packages/moxxmpp/lib/src/xeps/xep_0421.dart

@@ -0,0 +1,66 @@
+import 'dart:async';
+import 'package:moxxmpp/src/managers/base.dart';
+import 'package:moxxmpp/src/managers/data.dart';
+import 'package:moxxmpp/src/managers/handlers.dart';
+import 'package:moxxmpp/src/managers/namespaces.dart';
+import 'package:moxxmpp/src/namespaces.dart';
+import 'package:moxxmpp/src/stanza.dart';
+import 'package:moxxmpp/src/stringxml.dart';
+
+/// Representation of a <occupant-id /> element.
+class OccupantIdData implements StanzaHandlerExtension {
+  const OccupantIdData(
+    this.id,
+  );
+
+  /// The unique occupant id.
+  final String id;
+
+  XMLNode toXML() {
+    return XMLNode.xmlns(
+      tag: 'occupant-id',
+      xmlns: occupantIdXmlns,
+      attributes: {
+        'id': id,
+      },
+    );
+  }
+}
+
+class OccupantIdManager extends XmppManagerBase {
+  OccupantIdManager() : super(occupantIdManager);
+
+  @override
+  List<String> getDiscoFeatures() => [
+        occupantIdXmlns,
+      ];
+
+  @override
+  List<StanzaHandler> getIncomingStanzaHandlers() => [
+        StanzaHandler(
+          stanzaTag: 'message',
+          callback: _onMessage,
+          // Before the MessageManager
+          priority: -99,
+        ),
+      ];
+
+  @override
+  Future<bool> isSupported() async => true;
+
+  Future<StanzaHandlerData> _onMessage(
+    Stanza stanza,
+    StanzaHandlerData state,
+  ) async {
+    OccupantIdData? occupantId;
+    final occupantIdElement =
+        stanza.firstTag('occupant-id', xmlns: occupantIdXmlns);
+    // Process the occupant id
+    if (occupantIdElement != null) {
+      occupantId =
+          OccupantIdData(occupantIdElement.attributes['id']! as String);
+      state.extensions.set(occupantId);
+    }
+    return state;
+  }
+}