feat: add example for sendMulticast method

example/get_resource_multicast.dart

@@ -0,0 +1,41 @@
+// ignore_for_file: avoid_print
+
+/*
+ * Package : Coap
+ * Author : S. Hamblett <steve.hamblett@linux.com>
+ * Date   : 06/06/2018
+ * Copyright :  S.Hamblett
+ *
+ * Example for iterating over responses using sendMulticast().
+ *
+ * For this to work, you need at least one CoAP node reachable under the
+ * link-local IPv6 "All CoAP nodes" multicast address (ff02::fd), exposing its
+ * resources using `/.well-known/core`.
+ */
+
+import 'dart:async';
+import 'package:coap/coap.dart';
+import 'config/coap_config.dart';
+
+FutureOr<void> main() async {
+  final conf = CoapConfig();
+  final uri = Uri(
+    scheme: 'coap',
+    host: CoapDefinedAddress.allCOAPNodesLinkLocalIPV6,
+    port: conf.defaultPort,
+  );
+  final client = CoapClient(uri, conf);
+
+  try {
+    final request = CoapRequest.newGet()..uriPath = './well-known/core';
+
+    await for (final response in client.sendMulticast(request)) {
+      print(response.payloadString);
+      break;
+    }
+  } on Exception catch (e) {
+    print('CoAP encountered an exception: $e');
+  }
+
+  client.close();
+}