Re-land "Extend the mDNS package with a native extension used on Mac OS"

pkg/mdns/lib/src/native_extension_client.dart

+// Copyright (c) 2015, the Fletch project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE.md file.
+
+library mdns.src.native_extension_client;
+
+import 'dart:async';
+import 'dart:io';
+import 'dart:isolate';
+
+import 'package:mdns/mdns.dart';
+import 'package:mdns/src/lookup_resolver.dart';
+import 'package:mdns/src/native_extension_api.dart'
+    deferred as native_extension_api;
+import 'package:mdns/src/packet.dart';
+
+// Requests Ids. This should be aligned with the C code.
+enum RequestType {
+  echoRequest,  // 0
+  lookupRequest,  // 1
+}
+
+// Implementation of mDNS client using a native extension.
+class NativeExtensionMDnsClient implements MDnsClient {
+  bool _starting = false;
+  bool _started = false;
+  SendPort _service;
+  ReceivePort _incoming;
+  final LookupResolver _resolver = new LookupResolver();
+
+  /// Start the mDNS client.
+  Future start() async {
+    if (_started && _starting) {
+      throw new StateError('mDNS client already started');
+    }
+    _starting = true;
+
+    await native_extension_api.loadLibrary();
+    _service = native_extension_api.servicePort();
+    _incoming = new ReceivePort();
+    _incoming.listen(_handleIncoming);
+
+    _starting = false;
+    _started = true;
+  }
+
+  void stop() {
+    if (!_started) return;
+    if (_starting) {
+      throw new StateError('Cannot stop mDNS client wile it is starting');
+    }
+
+    _incoming.close();
+
+    _started = false;
+  }
+
+  Future<InternetAddress> lookup(
+      String hostname, {Duration timeout: const Duration(seconds: 5)}) {
+    if (!_started) {
+      throw new StateError('mDNS client is not started');
+    }
+
+    // Add the pending request before sending the query.
+    var future = _resolver.addPendingRequest(hostname, timeout);
+
+    // Send the request.
+    _service.send([_incoming.sendPort,
+                   RequestType.lookupRequest.index,
+                   hostname]);
+
+    return future;
+  }
+
+  // Process incoming responses.
+  _handleIncoming(response) {
+    // Right not the only response we can get is the response to a
+    // lookupRequest where the response looks like this:
+    //
+    //  response[0]: hostname (String)
+    //  response[1]: IPv4 address (Uint8List)
+    if (response is List && response.length == 2) {
+      if (response[0] is String &&
+          response[1] is List && response[1].length == 4) {
+        response = new DecodeResult(response[0],
+                                    new InternetAddress(response[1].join('.')));
+        _resolver.handleResponse([response]);
+      } else {
+        // TODO(sgjesse): Improve the error handling.
+        print('mDNS Response not understood');
+      }
+    }
+  }
+}
+
+Future nativeExtensionEchoTest(dynamic message) async {
+  await native_extension_api.loadLibrary();
+  SendPort service = native_extension_api.servicePort();
+  ReceivePort port = new ReceivePort();
+  try {
+    service.send([port.sendPort, RequestType.echoRequest.index, message]);
+    return await port.first;
+  } finally {
+    port.close();
+  }
+}