feat(xep): Allow changing the SASL2 user agent

integration_tests/test/sasl2_test.dart

@@ -44,13 +44,12 @@ void main() {
       FASTSaslNegotiator(),
       Bind2Negotiator(),
       StartTlsNegotiator(),
-      Sasl2Negotiator(
-        userAgent: const UserAgent(
+      Sasl2Negotiator()
+        ..userAgent = const UserAgent(
           id: 'd4565fa7-4d72-4749-b3d3-740edbf87770',
           software: 'moxxmpp',
           device: "PapaTutuWawa's awesome device",
         ),
-      ),
     ]);
 
     final result = await conn.connect(

packages/moxxmpp/lib/src/xeps/xep_0388/user_agent.dart

@@ -1,6 +1,6 @@
 import 'package:moxxmpp/src/stringxml.dart';
 
-/// A data class describing the user agent. See https://dyn.eightysoft.de/final/xep-0388.html#initiation
+/// A data class describing the user agent. See https://xmpp.org/extensions/xep-0388.html#initiation.
 class UserAgent {
   const UserAgent({
     this.id,
@@ -24,11 +24,9 @@ class UserAgent {
     );
     return XMLNode(
       tag: 'user-agent',
-      attributes: id != null
-          ? {
-              'id': id,
-            }
-          : {},
+      attributes: {
+        if (id != null) 'id': id,
+      },
       children: [
         if (software != null)
           XMLNode(

packages/moxxmpp/lib/src/xeps/xep_0388/xep_0388.dart

@@ -20,12 +20,10 @@ enum Sasl2State {
 /// A negotiator that implements XEP-0388 SASL2. Alone, it does nothing. Has to be
 /// registered with other negotiators that register themselves against this one.
 class Sasl2Negotiator extends XmppFeatureNegotiatorBase {
-  Sasl2Negotiator({
-    this.userAgent,
-  }) : super(100, false, sasl2Xmlns, sasl2Negotiator);
+  Sasl2Negotiator() : super(100, false, sasl2Xmlns, sasl2Negotiator);
 
   /// The user agent data that will be sent to the server when authenticating.
-  final UserAgent? userAgent;
+  UserAgent? userAgent;
 
   /// List of callbacks that are registered against us. Will be called once we get
   /// SASL2 features.

packages/moxxmpp/test/xeps/xep_0198_test.dart

@@ -850,13 +850,12 @@ void main() {
       SaslPlainNegotiator(),
       ResourceBindingNegotiator(),
       StreamManagementNegotiator()..resource = 'test-resource',
-      Sasl2Negotiator(
-        userAgent: const UserAgent(
+      Sasl2Negotiator()
+        ..userAgent = const UserAgent(
           id: 'd4565fa7-4d72-4749-b3d3-740edbf87770',
           software: 'moxxmpp',
           device: "PapaTutuWawa's awesome device",
         ),
-      ),
     ]);
 
     final result = await conn.connect(
@@ -948,13 +947,12 @@ void main() {
       ResourceBindingNegotiator(),
       StreamManagementNegotiator()..resource = 'test-resource',
       Bind2Negotiator(),
-      Sasl2Negotiator(
-        userAgent: const UserAgent(
+      Sasl2Negotiator()
+        ..userAgent = const UserAgent(
           id: 'd4565fa7-4d72-4749-b3d3-740edbf87770',
           software: 'moxxmpp',
           device: "PapaTutuWawa's awesome device",
         ),
-      ),
     ]);
 
     final result = await conn.connect(
@@ -1051,13 +1049,12 @@ void main() {
       ResourceBindingNegotiator(),
       smn,
       Bind2Negotiator(),
-      Sasl2Negotiator(
-        userAgent: const UserAgent(
+      Sasl2Negotiator()
+        ..userAgent = const UserAgent(
           id: 'd4565fa7-4d72-4749-b3d3-740edbf87770',
           software: 'moxxmpp',
           device: "PapaTutuWawa's awesome device",
         ),
-      ),
     ]);
 
     final result = await conn.connect(

packages/moxxmpp/test/xeps/xep_0280_test.dart

@@ -114,13 +114,12 @@ void main() {
       ResourceBindingNegotiator(),
       CarbonsNegotiator(),
       Bind2Negotiator(),
-      Sasl2Negotiator(
-        userAgent: const UserAgent(
+      Sasl2Negotiator()
+        ..userAgent = const UserAgent(
           id: 'd4565fa7-4d72-4749-b3d3-740edbf87770',
           software: 'moxxmpp',
           device: "PapaTutuWawa's awesome device",
         ),
-      ),
     ]);
 
     final result = await conn.connect(

packages/moxxmpp/test/xeps/xep_0352_test.dart

@@ -184,13 +184,12 @@ void main() {
       FASTSaslNegotiator(),
       Bind2Negotiator(),
       CSINegotiator(),
-      Sasl2Negotiator(
-        userAgent: const UserAgent(
+      Sasl2Negotiator()
+        ..userAgent = const UserAgent(
           id: 'd4565fa7-4d72-4749-b3d3-740edbf87770',
           software: 'moxxmpp',
           device: "PapaTutuWawa's awesome device",
         ),
-      ),
     ]);
 
     final result = await conn.connect(

packages/moxxmpp/test/xeps/xep_0386_test.dart

@@ -59,13 +59,12 @@ void main() {
       SaslPlainNegotiator(),
       ResourceBindingNegotiator(),
       Bind2Negotiator(),
-      Sasl2Negotiator(
-        userAgent: const UserAgent(
+      Sasl2Negotiator()
+        ..userAgent = const UserAgent(
           id: 'd4565fa7-4d72-4749-b3d3-740edbf87770',
           software: 'moxxmpp',
           device: "PapaTutuWawa's awesome device",
         ),
-      ),
     ]);
 
     final result = await conn.connect(
@@ -129,13 +128,12 @@ void main() {
       SaslPlainNegotiator(),
       ResourceBindingNegotiator(),
       Bind2Negotiator()..tag = 'moxxmpp',
-      Sasl2Negotiator(
-        userAgent: const UserAgent(
+      Sasl2Negotiator()
+        ..userAgent = const UserAgent(
           id: 'd4565fa7-4d72-4749-b3d3-740edbf87770',
           software: 'moxxmpp',
           device: "PapaTutuWawa's awesome device",
         ),
-      ),
     ]);
 
     final result = await conn.connect(

packages/moxxmpp/test/xeps/xep_0388_test.dart

@@ -115,13 +115,12 @@ void main() {
     await conn.registerFeatureNegotiators([
       SaslPlainNegotiator(),
       ResourceBindingNegotiator(),
-      Sasl2Negotiator(
-        userAgent: const UserAgent(
+      Sasl2Negotiator()
+        ..userAgent = const UserAgent(
           id: 'd4565fa7-4d72-4749-b3d3-740edbf87770',
           software: 'moxxmpp',
           device: "PapaTutuWawa's awesome device",
         ),
-      ),
     ]);
 
     final result = await conn.connect(
@@ -199,13 +198,12 @@ void main() {
         ScramHashType.sha256,
       ),
       ResourceBindingNegotiator(),
-      Sasl2Negotiator(
-        userAgent: const UserAgent(
+      Sasl2Negotiator()
+        ..userAgent = const UserAgent(
           id: 'd4565fa7-4d72-4749-b3d3-740edbf87770',
           software: 'moxxmpp',
           device: "PapaTutuWawa's awesome device",
         ),
-      ),
     ]);
 
     final result = await conn.connect(
@@ -276,13 +274,12 @@ void main() {
         ScramHashType.sha256,
       ),
       ResourceBindingNegotiator(),
-      Sasl2Negotiator(
-        userAgent: const UserAgent(
+      Sasl2Negotiator()
+        ..userAgent = const UserAgent(
           id: 'd4565fa7-4d72-4749-b3d3-740edbf87770',
           software: 'moxxmpp',
           device: "PapaTutuWawa's awesome device",
         ),
-      ),
     ]);
 
     final result = await conn.connect(
@@ -356,13 +353,12 @@ void main() {
       SaslPlainNegotiator(),
       ResourceBindingNegotiator(),
       ExampleNegotiator(),
-      Sasl2Negotiator(
-        userAgent: const UserAgent(
+      Sasl2Negotiator()
+        ..userAgent = const UserAgent(
           id: 'd4565fa7-4d72-4749-b3d3-740edbf87770',
           software: 'moxxmpp',
           device: "PapaTutuWawa's awesome device",
         ),
-      ),
     ]);
 
     final result = await conn.connect(
@@ -439,13 +435,12 @@ void main() {
       SaslPlainNegotiator(),
       ResourceBindingNegotiator(),
       ExampleNegotiator(),
-      Sasl2Negotiator(
-        userAgent: const UserAgent(
+      Sasl2Negotiator()
+        ..userAgent = const UserAgent(
           id: 'd4565fa7-4d72-4749-b3d3-740edbf87770',
           software: 'moxxmpp',
           device: "PapaTutuWawa's awesome device",
         ),
-      ),
     ]);
 
     final result = await conn.connect(

packages/moxxmpp/test/xeps/xep_xxxx_fast_test.dart

@@ -121,13 +121,12 @@ void main() {
       SaslPlainNegotiator(),
       ResourceBindingNegotiator(),
       FASTSaslNegotiator(),
-      Sasl2Negotiator(
-        userAgent: const UserAgent(
+      Sasl2Negotiator()
+        ..userAgent = const UserAgent(
           id: 'd4565fa7-4d72-4749-b3d3-740edbf87770',
           software: 'moxxmpp',
           device: "PapaTutuWawa's awesome device",
         ),
-      ),
     ]);
 
     final result1 = await conn.connect(
@@ -238,13 +237,12 @@ void main() {
           'WXZzciBwYmFmdmZnZiBqdmd1IGp2eXFhcmZm',
           '2020-03-12T14:36:15Z',
         ),
-      Sasl2Negotiator(
-        userAgent: const UserAgent(
+      Sasl2Negotiator()
+        ..userAgent = const UserAgent(
           id: 'd4565fa7-4d72-4749-b3d3-740edbf87770',
           software: 'moxxmpp',
           device: "PapaTutuWawa's awesome device",
         ),
-      ),
     ]);
 
     final result1 = await conn.connect(