feat: Improve the stanza await system

This fixes an issue where publishing an avatar would fail, if returned
an error where the "from" attribute is missing from the stanza.

packages/moxxmpp/lib/src/awaiter.dart

@@ -0,0 +1,94 @@
+import 'dart:async';
+import 'package:meta/meta.dart';
+import 'package:moxxmpp/src/jid.dart';
+import 'package:moxxmpp/src/stringxml.dart';
+import 'package:synchronized/synchronized.dart';
+
+/// A surrogate key for awaiting stanzas.
+@immutable
+class _StanzaSurrogateKey {
+  const _StanzaSurrogateKey(this.sentTo, this.id, this.tag);
+
+  /// The JID the original stanza was sent to. We expect the result to come from the
+  /// same JID.
+  final String sentTo;
+
+  /// The ID of the original stanza. We expect the result to have the same ID.
+  final String id;
+
+  /// The tag name of the stanza.
+  final String tag;
+  
+  @override
+  int get hashCode => sentTo.hashCode ^ id.hashCode ^ tag.hashCode;
+
+  @override
+  bool operator==(Object other) {
+    return other is _StanzaSurrogateKey &&
+           other.sentTo == sentTo &&
+           other.id == id &&
+           other.tag == tag;
+  }
+}
+
+/// This class handles the await semantics for stanzas. Stanzas are given a "unique"
+/// key equal to the tuple (to, id, tag) with which their response is identified.
+///
+/// That means that when sending ```<iq to="example@some.server.example" id="abc123" />```,
+/// the response stanza must be from "example@some.server.example", have id "abc123" and
+/// be an iq stanza.
+///
+/// This class also handles some "edge cases" of RFC 6120, like an empty "from" attribute.
+class StanzaAwaiter {
+  /// The pending stanzas, identified by their surrogate key.
+  final Map<_StanzaSurrogateKey, Completer<XMLNode>> _pending = {};
+
+  /// The critical section for accessing [StanzaAwaiter._pending].
+  final Lock _lock = Lock();
+
+  /// Register a stanza as pending.
+  /// [to] is the value of the stanza's "to" attribute.
+  /// [id] is the value of the stanza's "id" attribute.
+  /// [tag] is the stanza's tag name.
+  ///
+  /// Returns a future that might resolve to the response to the stanza.
+  Future<Future<XMLNode>> addPending(String to, String id, String tag) async {
+    final completer = await _lock.synchronized(() {
+      final completer = Completer<XMLNode>();
+      _pending[_StanzaSurrogateKey(to, id, tag)] = completer;
+      return completer;
+    });
+
+    return completer.future;
+  }
+
+  /// Checks if the stanza [stanza] is being awaited. [bareJid] is the bare JID of
+  /// the connection.
+  /// If [stanza] is awaited, resolves the future and returns true. If not, returns
+  /// false.
+  Future<bool> onData(XMLNode stanza, JID bareJid) async {
+    assert(bareJid.isBare(), 'bareJid must be bare');
+
+    final id = stanza.attributes['id'] as String?;
+    if (id == null) return false;
+    
+    final key = _StanzaSurrogateKey(
+      // Section 8.1.2.1 § 3 of RFC 6120 says that an empty "from" indicates that the
+      // attribute is implicitly from our own bare JID.
+      stanza.attributes['from'] as String? ?? bareJid.toString(),
+      id,
+      stanza.tag,
+    );
+
+    return _lock.synchronized(() {
+      final completer = _pending[key];
+      if (completer != null) {
+        _pending.remove(key);
+        completer.complete(stanza);
+        return true;
+      }
+
+      return false;
+    });
+  }
+}

packages/moxxmpp/lib/src/connection.dart

@@ -2,6 +2,7 @@ import 'dart:async';
 import 'package:logging/logging.dart';
 import 'package:meta/meta.dart';
 import 'package:moxlib/moxlib.dart';
+import 'package:moxxmpp/src/awaiter.dart';
 import 'package:moxxmpp/src/buffer.dart';
 import 'package:moxxmpp/src/errors.dart';
 import 'package:moxxmpp/src/events.dart';
@@ -89,29 +90,6 @@ class XmppConnectionResult {
   final XmppError? error;
 }
 
-/// A surrogate key for awaiting stanzas.
-@immutable
-class _StanzaAwaitableData {
-  const _StanzaAwaitableData(this.sentTo, this.id);
-
-  /// The JID the original stanza was sent to. We expect the result to come from the
-  /// same JID.
-  final String sentTo;
-
-  /// The ID of the original stanza. We expect the result to have the same ID.
-  final String id;
-
-  @override
-  int get hashCode => sentTo.hashCode ^ id.hashCode;
-
-  @override
-  bool operator==(Object other) {
-    return other is _StanzaAwaitableData &&
-           other.sentTo == sentTo &&
-           other.id == id;
-  }
-}
-
 /// This class is a connection to the server.
 class XmppConnection {
   XmppConnection(
@@ -151,9 +129,8 @@ class XmppConnection {
   /// A policy on how to reconnect 
   final ReconnectionPolicy _reconnectionPolicy;
 
-  /// A list of stanzas we are tracking with its corresponding critical section lock
-  final Map<_StanzaAwaitableData, Completer<XMLNode>> _awaitingResponse = {};
-  final Lock _awaitingResponseLock = Lock();
+  /// A helper for handling await semantics with stanzas
+  final StanzaAwaiter _stanzaAwaiter = StanzaAwaiter();
   
   /// Sorted list of handlers that we call or incoming and outgoing stanzas
   final List<StanzaHandler> _incomingStanzaHandlers = List.empty(growable: true);
@@ -544,13 +521,12 @@ class XmppConnection {
     _log.fine('Attempting to acquire lock for ${data.stanza.id}...');
     // TODO(PapaTutuWawa): Handle this much more graceful
     var future = Future.value(XMLNode(tag: 'not-used'));
-    await _awaitingResponseLock.synchronized(() async {
-      _log.fine('Lock acquired for ${data.stanza.id}');
-
-      _StanzaAwaitableData? key;
     if (awaitable) {
-        key = _StanzaAwaitableData(data.stanza.to!, data.stanza.id!);
-        _awaitingResponse[key] = Completer();
+      future = await _stanzaAwaiter.addPending(
+        data.stanza.to!,
+        data.stanza.id!,
+        data.stanza.tag,
+      );
     }
 
     // This uses the StreamManager to behave like a send queue
@@ -575,13 +551,6 @@ class XmppConnection {
     );
     _log.fine('Done');
 
-      if (awaitable) {
-        future = _awaitingResponse[key]!.future;
-      }
-
-      _log.fine('Releasing lock for ${data.stanza.id}');
-    });
-
     return future;
   }
 
@@ -744,21 +713,10 @@ class XmppConnection {
       '';
     _log.finest('<== $prefix${incomingPreHandlers.stanza.toXml()}');
 
-    // See if we are waiting for this stanza
-    final id = incomingPreHandlers.stanza.attributes['id'] as String?;
-    var awaited = false;
-    await _awaitingResponseLock.synchronized(() async {
-      if (id != null && incomingPreHandlers.stanza.from != null) {
-        final key = _StanzaAwaitableData(incomingPreHandlers.stanza.from!, id);
-        final comp = _awaitingResponse[key];
-        if (comp != null) {
-          comp.complete(incomingPreHandlers.stanza);
-          _awaitingResponse.remove(key);
-          awaited = true;
-        }
-      }
-    });
-
+    final awaited = await _stanzaAwaiter.onData(
+      incomingPreHandlers.stanza,
+      _connectionSettings.jid.toBare(),
+    );
     if (awaited) {
       return;
     }

packages/moxxmpp/lib/src/jid.dart

@@ -51,7 +51,11 @@ class JID {
   bool isFull() => resource.isNotEmpty;
 
   /// Converts the JID into a bare JID.
-  JID toBare() => JID(local, domain, '');
+  JID toBare() {
+    if (isBare()) return this;
+    
+    return JID(local, domain, '');
+  }
 
   /// Converts the JID into one with a resource part of [resource].
   JID withResource(String resource) => JID(local, domain, resource);

packages/moxxmpp/lib/src/stringxml.dart

@@ -1,7 +1,6 @@
 import 'package:xml/xml.dart';
 
 class XMLNode {
-
   XMLNode({
     required this.tag,
     this.attributes = const <String, dynamic>{},

packages/moxxmpp/test/awaiter_test.dart

@@ -0,0 +1,104 @@
+import 'package:moxxmpp/moxxmpp.dart';
+import 'package:moxxmpp/src/awaiter.dart';
+import 'package:test/test.dart';
+
+void main() {
+  final bareJid = JID('moxxmpp', 'server3.example', '');
+
+  test('Test awaiting an awaited stanza with a from attribute', () async {
+    final awaiter = StanzaAwaiter();
+
+    // "Send" a stanza
+    final future = await awaiter.addPending('user1@server.example', 'abc123', 'iq');
+
+    // Receive the wrong answer
+    final result1 = await awaiter.onData(
+      XMLNode.fromString('<iq from="user3@server.example" id="abc123" type="result" />'),
+      bareJid,
+    );
+    expect(result1, false);
+    final result2 = await awaiter.onData(
+      XMLNode.fromString('<iq from="user1@server.example" id="lol" type="result" />'),
+      bareJid,
+    );
+    expect(result2, false);
+
+    // Receive the correct answer
+    final stanza = XMLNode.fromString('<iq from="user1@server.example" id="abc123" type="result" />');
+    final result3 = await awaiter.onData(
+      stanza,
+      bareJid,
+    );
+    expect(result3, true);
+    expect(await future, stanza);
+  });
+
+  test('Test awaiting an awaited stanza without a from attribute', () async {
+    final awaiter = StanzaAwaiter();
+
+    // "Send" a stanza
+    final future = await awaiter.addPending(bareJid.toString(), 'abc123', 'iq');
+
+    // Receive the wrong answer
+    final result1 = await awaiter.onData(
+      XMLNode.fromString('<iq id="lol" type="result" />'),
+      bareJid,
+    );
+    expect(result1, false);
+   
+    // Receive the correct answer
+    final stanza = XMLNode.fromString('<iq id="abc123" type="result" />');
+    final result2 = await awaiter.onData(
+      stanza,
+      bareJid,
+    );
+    expect(result2, true);
+    expect(await future, stanza);
+  });
+
+  test('Test awaiting a stanza that was already awaited', () async {
+    final awaiter = StanzaAwaiter();
+
+    // "Send" a stanza
+    final future = await awaiter.addPending(bareJid.toString(), 'abc123', 'iq');
+
+    // Receive the correct answer
+    final stanza = XMLNode.fromString('<iq id="abc123" type="result" />');
+    final result1 = await awaiter.onData(
+      stanza,
+      bareJid,
+    );
+    expect(result1, true);
+    expect(await future, stanza);
+
+    // Receive it again
+    final result2 = await awaiter.onData(
+      stanza,
+      bareJid,
+    );
+    expect(result2, false);
+  });
+
+  test('Test ignoring a stanza that has the wrong tag', () async {
+    final awaiter = StanzaAwaiter();
+
+    // "Send" a stanza
+    final future = await awaiter.addPending(bareJid.toString(), 'abc123', 'iq');
+
+    // Receive the wrong answer
+    final stanza = XMLNode.fromString('<iq id="abc123" type="result" />');
+    final result1 = await awaiter.onData(
+      XMLNode.fromString('<message id="abc123" type="result" />'),
+      bareJid,
+    );
+    expect(result1, false);
+
+    // Receive the correct answer
+    final result2 = await awaiter.onData(
+      stanza,
+      bareJid,
+    );
+    expect(result2, true);
+    expect(await future, stanza);
+  });
+}