feat(example): Add a very simple client example

examples_dart/bin/simple_client.dart

@@ -0,0 +1,112 @@
+import 'package:logging/logging.dart';
+import 'package:moxxmpp/moxxmpp.dart';
+import 'package:moxxmpp_socket_tcp/moxxmpp_socket_tcp.dart';
+
+/// The JID we want to authenticate as.
+final xmppUser = JID.fromString('jane@example.com');
+
+/// The password to authenticate with.
+const xmppPass = 'secret';
+
+/// The [xmppHost]:[xmppPort] server address to connect to.
+/// In a real application, one might prefer to use [TCPSocketWrapper]
+/// with a custom DNS implementation to let moxxmpp resolve the XMPP
+/// server's address automatically. However, if we just provide a host
+/// and a port, then [TCPSocketWrapper] will just skip the resolution and
+/// immediately use the provided connection details.
+const xmppHost = 'localhost';
+const xmppPort = 5222;
+
+void main(List<String> args) async {
+  Logger.root.level = Level.ALL;
+  Logger.root.onRecord.listen((record) {
+    print('${record.level.name}|${record.time}: ${record.message}');
+  });
+
+  // This class manages every aspect of handling the XMPP stream.
+  final connection = XmppConnection(
+    // A reconnection policy tells the connection how to handle an error
+    // while or after connecting to the server. The [TestingReconnectionPolicy]
+    // immediately triggers a reconnection. In a real implementation, one might
+    // prefer to use a smarter strategy, like using an exponential backoff.
+    TestingReconnectionPolicy(),
+
+    // A connectivity manager tells the connection when it can connect. This is to
+    // ensure that we're not constantly trying to reconnect because we have no
+    // Internet connection. [AlwaysConnectedConnectivityManager] always says that
+    // we're connected. In a real application, one might prefer to use a smarter
+    // strategy, like using connectivity_plus to query the system's network connectivity
+    // state.
+    AlwaysConnectedConnectivityManager(),
+
+    // This kind of negotiator tells the connection how to handle the stream
+    // negotiations. The [ClientToServerNegotiator] allows to connect to the server
+    // as a regular client. Another negotiator would be the [ComponentToServerNegotiator] that
+    // allows for connections to the server where we're acting as a component.
+    ClientToServerNegotiator(),
+
+    // A wrapper around any kind of connection. In this case, we use the [TCPSocketWrapper], which
+    // uses a dart:io Socket/SecureSocket to connect to the server. If you want, you can also
+    // provide your own socket to use, for example, WebSockets or any other connection
+    // mechanism.
+    TCPSocketWrapper(false),
+  )..connectionSettings = ConnectionSettings(
+      jid: xmppUser,
+      password: xmppPass,
+      host: xmppHost,
+      port: xmppPort,
+    );
+
+  // Register a set of "managers" that provide you with implementations of various
+  // XEPs. Some have interdependencies, which need to be met. However, this example keeps
+  // it simple and just registers a [MessageManager], which has no required dependencies.
+  await connection.registerManagers([
+    // The [MessageManager] handles receiving and sending <message /> stanzas.
+    MessageManager(),
+  ]);
+
+  // Feature negotiators are objects that tell the connection negotiator what stream features
+  // we can negotiate and enable. moxxmpp negotiators always try to enable their features.
+  await connection.registerFeatureNegotiators([
+    // This negotiator authenticates to the server using SASL PLAIN with the provided
+    // credentials.
+    SaslPlainNegotiator(),
+    // This negotiator attempts to bind a resource. By default, it's always a random one.
+    ResourceBindingNegotiator(),
+    // This negotiator attempts to do StartTLS before authenticating.
+    StartTlsNegotiator(),
+  ]);
+
+  // Set up a stream handler for the connection's event stream. Managers and negotiators
+  // may trigger certain events. The [MessageManager], for example, triggers a [MessageEvent]
+  // whenever a message is received. If other managers are registered that parse a message's
+  // contents, then they can add their data to the event.
+  connection.asBroadcastStream().listen((event) {
+    if (event is! MessageEvent) {
+      return;
+    }
+
+    // The text body (contents of the <body /> element) are returned as a
+    // [MessageBodyData] object. However, a message does not have to contain a
+    // body, so it is nullable.
+    final body = event.extensions.get<MessageBodyData>()?.body;
+    print('[<-- ${event.from}] $body');
+  });
+
+  // Connect to the server.
+  final result = await connection.connect(
+    // This flag indicates that we want to reconnect in case something happens.
+    shouldReconnect: true,
+    // This flag indicates that we want the returned Future to only resolve
+    // once the stream negotiations are done and no negotiator has any feature left
+    // to negotiate.
+    waitUntilLogin: true,
+  );
+
+  // Check if the connection was successful. [connection.connect] can return a boolean
+  // to indicate success or a [XmppError] in case the connection attempt failed.
+  if (!result.isType<bool>()) {
+    print('Failed to connect to server');
+    return;
+  }
+}