[multicast_dns] Optimized Socket Binding: Always bind to 0.0.0.0 for simplicity and efficiency - #79772

packages/multicast_dns/CHANGELOG.md

@@ -1,5 +1,6 @@
-## NEXT
+## 0.3.2+7
 
+* Optimized Socket Binding: Always bind to 0.0.0.0 for simplicity and efficiency.
 * Updates minimum supported SDK version to Flutter 3.16/Dart 3.2.
 
 ## 0.3.2+6

packages/multicast_dns/README.md

@@ -1,5 +1,7 @@
 # Multicast DNS package
 
+Based on [RFC 6762 Multicast DNS](https://datatracker.ietf.org/doc/html/rfc6762).
+
 [![pub package](https://img.shields.io/pub/v/multicast_dns.svg)](
 https://pub.dartlang.org/packages/multicast_dns)
 

packages/multicast_dns/lib/multicast_dns.dart

@@ -48,8 +48,8 @@ class MDnsClient {
 
   bool _starting = false;
   bool _started = false;
-  final List<RawDatagramSocket> _sockets = <RawDatagramSocket>[];
-  final List<RawDatagramSocket> _toBeClosed = <RawDatagramSocket>[];
+  RawDatagramSocket? _incomingIPv4;
+  final List<RawDatagramSocket> _ipv6InterfaceSockets = <RawDatagramSocket>[];
   final LookupResolver _resolver = LookupResolver();
   final ResourceRecordCache _cache = ResourceRecordCache();
   final RawDatagramSocketFactory _rawDatagramSocketFactory;
@@ -117,9 +117,9 @@ class MDnsClient {
 
     // Can't send to IPv6 any address.
     if (incoming.address != InternetAddress.anyIPv6) {
-      _sockets.add(incoming);
+      _incomingIPv4 = incoming;
     } else {
-      _toBeClosed.add(incoming);
+      _ipv6InterfaceSockets.add(incoming);
     }
 
     _mDnsAddress ??= incoming.address.type == InternetAddressType.IPv4
@@ -130,30 +130,25 @@ class MDnsClient {
         (await interfacesFactory(listenAddress.type)).toList();
 
     for (final NetworkInterface interface in interfaces) {
-      // Create a socket for sending on each adapter.
       final InternetAddress targetAddress = interface.addresses[0];
-      final RawDatagramSocket socket = await _rawDatagramSocketFactory(
-        targetAddress,
-        selectedMDnsPort,
-        reuseAddress: true,
-        reusePort: true,
-        ttl: 255,
-      );
-      _sockets.add(socket);
+
       // Ensure that we're using this address/interface for multicast.
-      if (targetAddress.type == InternetAddressType.IPv4) {
-        socket.setRawOption(RawSocketOption(
-          RawSocketOption.levelIPv4,
-          RawSocketOption.IPv4MulticastInterface,
-          targetAddress.rawAddress,
-        ));
-      } else {
+      if (targetAddress.type == InternetAddressType.IPv6) {
+        final RawDatagramSocket socket = await _rawDatagramSocketFactory(
+          targetAddress,
+          selectedMDnsPort,
+          reuseAddress: true,
+          reusePort: true,
+          ttl: 255,
+        );
+        _ipv6InterfaceSockets.add(socket);
         socket.setRawOption(RawSocketOption.fromInt(
           RawSocketOption.levelIPv6,
           RawSocketOption.IPv6MulticastInterface,
           interface.index,
         ));
       }
+
       // Join multicast on this interface.
       incoming.joinMulticast(_mDnsAddress!, interface);
     }
@@ -171,15 +166,13 @@ class MDnsClient {
       throw StateError('Cannot stop mDNS client while it is starting.');
     }
 
-    for (final RawDatagramSocket socket in _sockets) {
-      socket.close();
-    }
-    _sockets.clear();
+    _incomingIPv4?.close();
+    _incomingIPv4 = null;
 
-    for (final RawDatagramSocket socket in _toBeClosed) {
+    for (final RawDatagramSocket socket in _ipv6InterfaceSockets) {
       socket.close();
     }
-    _toBeClosed.clear();
+    _ipv6InterfaceSockets.clear();
 
     _resolver.clearPendingRequests();
 
@@ -219,11 +212,17 @@ class MDnsClient {
     final Stream<T> results = _resolver.addPendingRequest<T>(
         query.resourceRecordType, query.fullyQualifiedName, timeout);
 
-    // Send the request on all interfaces.
     final List<int> packet = query.encode();
-    for (final RawDatagramSocket socket in _sockets) {
-      socket.send(packet, _mDnsAddress!, selectedMDnsPort);
+
+    if (_mDnsAddress?.type == InternetAddressType.IPv4) {
+      // Send and listen on same "ANY" interface
+      _incomingIPv4?.send(packet, _mDnsAddress!, selectedMDnsPort);
+    } else {
+      for (final RawDatagramSocket socket in _ipv6InterfaceSockets) {
+        socket.send(packet, _mDnsAddress!, selectedMDnsPort);
+      }
     }
+
     return results;
   }
 

packages/multicast_dns/pubspec.yaml

@@ -2,7 +2,7 @@ name: multicast_dns
 description: Dart package for performing mDNS queries (e.g. Bonjour, Avahi).
 repository: https://github.com/flutter/packages/tree/main/packages/multicast_dns
 issue_tracker: https://github.com/flutter/flutter/issues?q=is%3Aissue+is%3Aopen+label%3A%22p%3A+multicast_dns%22
-version: 0.3.2+6
+version: 0.3.2+7
 
 environment:
   sdk: ^3.2.0

packages/multicast_dns/test/client_test.dart

@@ -86,6 +86,78 @@ void main() {
     await client.start();
     await client.lookup(ResourceRecordQuery.serverPointer('_')).toList();
   });
+
+  group('Bind a single socket to ANY IPv4 and more than one when IPv6', () {
+    final List<Map<String, Object>> testCases = <Map<String, Object>>[
+      <String, Object>{
+        'name': 'IPv4',
+        'datagramSocketType': InternetAddress.anyIPv4,
+        'interfacePrefix': '192.168.2.'
+      },
+      <String, Object>{
+        'name': 'IPv6',
+        'datagramSocketType': InternetAddress.anyIPv6,
+        'interfacePrefix': '2001:0db8:85a3:0000:0000:8a2e:7335:030'
+      }
+    ];
+
+    for (final Map<String, Object> testCase in testCases) {
+      test('Bind a single socket to ANY ${testCase["name"]}', () async {
+        final FakeRawDatagramSocket datagramSocket = FakeRawDatagramSocket();
+
+        datagramSocket.address =
+            testCase['datagramSocketType']! as InternetAddress;
+
+        final List<dynamic> selectedInterfacesForSendingPackets = <dynamic>[];
+        final MDnsClient client = MDnsClient(rawDatagramSocketFactory:
+            (dynamic host, int port,
+                {bool reuseAddress = true,
+                bool reusePort = true,
+                int ttl = 1}) async {
+          selectedInterfacesForSendingPackets.add(host);
+          return datagramSocket;
+        });
+
+        const int numberOfFakeInterfaces = 10;
+        Future<Iterable<NetworkInterface>> fakeNetworkInterfacesFactory(
+            InternetAddressType type) async {
+          final List<NetworkInterface> fakeInterfaces = <NetworkInterface>[];
+
+          // Generate "fake" interfaces
+          for (int i = 0; i < numberOfFakeInterfaces; i++) {
+            fakeInterfaces.add(FakeNetworkInterface(
+              'inetfake$i',
+              <InternetAddress>[
+                InternetAddress("${testCase['interfacePrefix']! as String}$i")
+              ],
+              0,
+            ));
+          }
+
+          // ignore: always_specify_types
+          return Future.value(fakeInterfaces);
+        }
+
+        final InternetAddress listenAddress =
+            testCase['datagramSocketType']! as InternetAddress;
+
+        await client.start(
+            listenAddress: listenAddress,
+            mDnsPort: 1234,
+            interfacesFactory: fakeNetworkInterfacesFactory);
+        client.stop();
+
+        if (testCase['datagramSocketType'] == InternetAddress.anyIPv4) {
+          expect(selectedInterfacesForSendingPackets.length, 1);
+        } else {
+          // + 1 because of unspecified address (::)
+          expect(selectedInterfacesForSendingPackets.length,
+              numberOfFakeInterfaces + 1);
+        }
+        expect(selectedInterfacesForSendingPackets[0], listenAddress.address);
+      });
+    }
+  });
 }
 
 class FakeRawDatagramSocket extends Fake implements RawDatagramSocket {
@@ -113,4 +185,30 @@ class FakeRawDatagramSocket extends Fake implements RawDatagramSocket {
   int send(List<int> buffer, InternetAddress address, int port) {
     return buffer.length;
   }
+
+  @override
+  void joinMulticast(InternetAddress group, [NetworkInterface? interface]) {
+    // nothing to do here
+  }
+  @override
+  void setRawOption(RawSocketOption option) {
+    // nothing to do here
+  }
+}
+
+class FakeNetworkInterface implements NetworkInterface {
+  FakeNetworkInterface(this._name, this._addresses, this._index);
+
+  final String _name;
+  final List<InternetAddress> _addresses;
+  final int _index;
+
+  @override
+  List<InternetAddress> get addresses => _addresses;
+
+  @override
+  String get name => _name;
+
+  @override
+  int get index => _index;
 }