feat(core): Check if we can do subscription pre-approval

packages/moxxmpp/lib/moxxmpp.dart

@@ -18,7 +18,6 @@ export 'package:moxxmpp/src/managers/namespaces.dart';
 export 'package:moxxmpp/src/managers/priorities.dart';
 export 'package:moxxmpp/src/message.dart';
 export 'package:moxxmpp/src/namespaces.dart';
-export 'package:moxxmpp/src/negotiators/manager.dart';
 export 'package:moxxmpp/src/negotiators/namespaces.dart';
 export 'package:moxxmpp/src/negotiators/negotiator.dart';
 export 'package:moxxmpp/src/ping.dart';

packages/moxxmpp/lib/src/namespaces.dart

@@ -9,6 +9,7 @@ const fullStanzaXmlns = 'urn:ietf:params:xml:ns:xmpp-stanzas';
 // RFC 6121
 const rosterXmlns = 'jabber:iq:roster';
 const rosterVersioningXmlns = 'urn:xmpp:features:rosterver';
+const subscriptionPreApprovalXmlns = 'urn:xmpp:features:pre-approval';
 
 // XEP-0004
 const dataFormsXmlns = 'jabber:x:data';

packages/moxxmpp/lib/src/negotiators/manager.dart

@@ -1 +0,0 @@
-

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

@@ -11,3 +11,4 @@ const sasl2Negotiator = 'org.moxxmpp.sasl.sasl2';
 const bind2Negotiator = 'org.moxxmpp.bind2';
 const saslFASTNegotiator = 'org.moxxmpp.sasl.fast';
 const carbonsNegotiator = 'org.moxxmpp.bind2.carbons';
+const presenceNegotiator = 'org.moxxmpp.core.presence';

packages/moxxmpp/lib/src/presence.dart

@@ -6,14 +6,44 @@ 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/negotiators/namespaces.dart';
+import 'package:moxxmpp/src/negotiators/negotiator.dart';
 import 'package:moxxmpp/src/stanza.dart';
 import 'package:moxxmpp/src/stringxml.dart';
+import 'package:moxxmpp/src/types/result.dart';
 
 /// A function that will be called when presence, outside of subscription request
 /// management, will be sent. Useful for managers that want to add [XMLNode]s to said
 /// presence.
 typedef PresencePreSendCallback = Future<List<XMLNode>> Function();
 
+/// A pseudo-negotiator that does not really negotiate anything. Instead, its purpose
+/// is to look for a stream feature indicating that we can pre-approve subscription
+/// requests, shown by [PresenceNegotiator.preApprovalSupported].
+class PresenceNegotiator extends XmppFeatureNegotiatorBase {
+  PresenceNegotiator()
+      : super(11, false, subscriptionPreApprovalXmlns, presenceNegotiator);
+
+  /// Flag indicating whether presence subscription pre-approval is supported
+  bool _supported = false;
+  bool get preApprovalSupported => _supported;
+
+  @override
+  Future<Result<NegotiatorState, NegotiatorError>> negotiate(
+    XMLNode nonza,
+  ) async {
+    _supported = true;
+    return const Result(NegotiatorState.done);
+  }
+
+  @override
+  void reset() {
+    _supported = false;
+
+    super.reset();
+  }
+}
+
 /// A mandatory manager that handles initial presence sending, sending of subscription
 /// request management requests and triggers events for incoming presence stanzas.
 class PresenceManager extends XmppManagerBase {

packages/moxxmpp/test/xmpp_test.dart

@@ -794,4 +794,20 @@ void main() {
     expect(fakeSocket.getState(), 9);
     expect(await stanzaFuture != null, true);
   });
+
+  test('Test subscription pre-approval parsing', () async {
+    final rawFeatures = XMLNode.fromString(
+      '''
+<top-level>
+  <test-feature-1 xmlns="invalid:urn:features:1" />
+  <test-feature-2 xmlns="invalid:urn:features:2" />
+  <test-feature-3 xmlns="invalid:urn:features:3" />
+  <test-feature-4 xmlns="invalid:urn:features:4" />
+  <sub xmlns='urn:xmpp:features:pre-approval' />
+</top-level>
+      ''',
+    );
+
+    expect(PresenceNegotiator().matchesFeature(rawFeatures.children), true);
+  });
 }