@@ -1,3 +1,7 @@
+## 0.3.0
+
+* Migrate package to null safety.
+
 ## 0.2.2
 * Fixes parsing of TXT records. Continues parsing on non-utf8 strings.
 
 
@@ -48,14 +48,13 @@ class MDnsClient {
 
   bool _starting = false;
   bool _started = false;
-  RawDatagramSocket _incoming;
   final List<RawDatagramSocket> _sockets = <RawDatagramSocket>[];
   final LookupResolver _resolver = LookupResolver();
   final ResourceRecordCache _cache = ResourceRecordCache();
   final RawDatagramSocketFactory _rawDatagramSocketFactory;
 
-  InternetAddress _mDnsAddress;
-  int _mDnsPort;
+  InternetAddress? _mDnsAddress;
+  int? _mDnsPort;
 
   /// Find all network interfaces with an the [InternetAddressType] specified.
   static NetworkInterfacesFactory allInterfacesFactory =
@@ -82,14 +81,14 @@ class MDnsClient {
   /// for the mDNS query. If not provided, defaults to either `224.0.0.251` or
   /// or `FF02::FB`.
   Future<void> start({
-    InternetAddress listenAddress,
-    NetworkInterfacesFactory interfacesFactory,
+    InternetAddress? listenAddress,
+    NetworkInterfacesFactory? interfacesFactory,
     int mDnsPort = mDnsPort,
-    InternetAddress mDnsAddress,
+    InternetAddress? mDnsAddress,
   }) async {
     listenAddress ??= InternetAddress.anyIPv4;
     interfacesFactory ??= allInterfacesFactory;
-    _mDnsPort = mDnsPort;
+    final int selectedMDnsPort = _mDnsPort = mDnsPort;
     _mDnsAddress = mDnsAddress;
 
     assert(listenAddress.address == InternetAddress.anyIPv4.address ||
@@ -101,32 +100,32 @@ class MDnsClient {
     _starting = true;
 
     // Listen on all addresses.
-    _incoming = await _rawDatagramSocketFactory(
+    final RawDatagramSocket incoming = await _rawDatagramSocketFactory(
       listenAddress.address,
-      _mDnsPort,
+      selectedMDnsPort,
       reuseAddress: true,
       reusePort: true,
       ttl: 255,
     );
 
     // Can't send to IPv6 any address.
-    if (_incoming.address != InternetAddress.anyIPv6) {
-      _sockets.add(_incoming);
+    if (incoming.address != InternetAddress.anyIPv6) {
+      _sockets.add(incoming);
     }
 
-    _mDnsAddress ??= _incoming.address.type == InternetAddressType.IPv4
+    _mDnsAddress ??= incoming.address.type == InternetAddressType.IPv4
         ? mDnsAddressIPv4
         : mDnsAddressIPv6;
 
     final List<NetworkInterface> interfaces =
-        await interfacesFactory(listenAddress.type);
+        (await interfacesFactory(listenAddress.type)).toList();
 
     for (NetworkInterface interface in interfaces) {
       // Create a socket for sending on each adapter.
       final InternetAddress targetAddress = interface.addresses[0];
       final RawDatagramSocket socket = await _rawDatagramSocketFactory(
         targetAddress,
-        _mDnsPort,
+        selectedMDnsPort,
         reuseAddress: true,
         reusePort: true,
         ttl: 255,
@@ -147,9 +146,9 @@ class MDnsClient {
         ));
       }
       // Join multicast on this interface.
-      _incoming.joinMulticast(_mDnsAddress, interface);
+      incoming.joinMulticast(_mDnsAddress!, interface);
     }
-    _incoming.listen(_handleIncoming);
+    incoming.listen((RawSocketEvent event) => _handleIncoming(event, incoming));
     _started = true;
     _starting = false;
   }
@@ -186,7 +185,8 @@ class MDnsClient {
     ResourceRecordQuery query, {
     Duration timeout = const Duration(seconds: 5),
   }) {
-    if (!_started) {
+    final int? selectedMDnsPort = _mDnsPort;
+    if (!_started || selectedMDnsPort == null) {
       throw StateError('mDNS client must be started before calling lookup.');
     }
     // Look for entries in the cache.
@@ -207,18 +207,21 @@ class MDnsClient {
     // Send the request on all interfaces.
     final List<int> packet = query.encode();
     for (RawDatagramSocket socket in _sockets) {
-      socket.send(packet, _mDnsAddress, _mDnsPort);
+      socket.send(packet, _mDnsAddress!, selectedMDnsPort);
     }
     return results;
   }
 
   // Process incoming datagrams.
-  void _handleIncoming(RawSocketEvent event) {
+  void _handleIncoming(RawSocketEvent event, RawDatagramSocket incoming) {
     if (event == RawSocketEvent.read) {
-      final Datagram datagram = _incoming.receive();
+      final Datagram? datagram = incoming.receive();
+      if (datagram == null) {
+        return;
+      }
 
       // Check for published responses.
-      final List<ResourceRecord> response = decodeMDnsResponse(datagram.data);
+      final List<ResourceRecord>? response = decodeMDnsResponse(datagram.data);
       if (response != null) {
         _cache.updateRecords(response);
         _resolver.handleResponse(response);
 
@@ -14,20 +14,20 @@ final InternetAddress mDnsAddressIPv6 = InternetAddress('FF02::FB');
 const int mDnsPort = 5353;
 
 /// Enumeration of supported resource record class types.
-class ResourceRecordClass {
+abstract class ResourceRecordClass {
   // This class is intended to be used as a namespace, and should not be
   // extended directly.
-  factory ResourceRecordClass._() => null;
+  ResourceRecordClass._();
 
   /// Internet address class ("IN").
   static const int internet = 1;
 }
 
 /// Enumeration of DNS question types.
-class QuestionType {
+abstract class QuestionType {
   // This class is intended to be used as a namespace, and should not be
   // extended directly.
-  factory QuestionType._() => null;
+  QuestionType._();
 
   /// "QU" Question.
   static const int unicast = 0x8000;
 
@@ -25,7 +25,7 @@ class PendingRequest extends LinkedListEntry<PendingRequest> {
   final StreamController<ResourceRecord> controller;
 
   /// The timer for the request.
-  Timer timer;
+  Timer? timer;
 }
 
 /// Class for keeping track of pending lookups and processing incoming
@@ -89,7 +89,7 @@ class LookupResolver {
     while (_pendingRequests.isNotEmpty) {
       final PendingRequest request = _pendingRequests.first;
       request.unlink();
-      request.timer.cancel();
+      request.timer?.cancel();
       request.controller.close();
     }
   }
 
@@ -29,7 +29,7 @@ class ResourceRecordCache {
     for (final SplayTreeMap<String, List<ResourceRecord>> map
         in _cache.values) {
       for (final List<ResourceRecord> records in map.values) {
-        count += records?.length;
+        count += records.length;
       }
     }
     return count;
@@ -45,14 +45,15 @@ class ResourceRecordCache {
       // TODO(dnfield): Update this to use set literal syntax when we're able to bump the SDK constraint.
       seenRecordTypes[record.resourceRecordType] ??=
           Set<String>(); // ignore: prefer_collection_literals
-      if (seenRecordTypes[record.resourceRecordType].add(record.name)) {
+      if (seenRecordTypes[record.resourceRecordType]!.add(record.name)) {
         _cache[record.resourceRecordType] ??=
             SplayTreeMap<String, List<ResourceRecord>>();
 
-        _cache[record.resourceRecordType]
-            [record.name] = <ResourceRecord>[record];
+        _cache[record.resourceRecordType]![record.name] = <ResourceRecord>[
+          record
+        ];
       } else {
-        _cache[record.resourceRecordType][record.name].add(record);
+        _cache[record.resourceRecordType]![record.name]!.add(record);
       }
     }
   }
@@ -62,12 +63,12 @@ class ResourceRecordCache {
       String name, int type, List<T> results) {
     assert(ResourceRecordType.debugAssertValid(type));
     final int time = DateTime.now().millisecondsSinceEpoch;
-    final SplayTreeMap<String, List<ResourceRecord>> candidates = _cache[type];
+    final SplayTreeMap<String, List<ResourceRecord>>? candidates = _cache[type];
     if (candidates == null) {
       return;
     }
 
-    final List<ResourceRecord> candidateRecords = candidates[name];
+    final List<ResourceRecord>? candidateRecords = candidates[name];
     if (candidateRecords == null) {
       return;
     }
 
@@ -23,7 +23,6 @@ const int _kHeaderSize = 12;
 /// Will attempt to append 'local' if the name is something like '_http._tcp',
 /// and '._tcp.local' if name is something like '_http'.
 List<String> processDnsNameParts(String name) {
-  assert(name != null);
   final List<String> parts = name.split('.');
   if (parts.length == 1) {
     return <String>[parts[0], '_tcp', 'local'];
@@ -47,9 +46,7 @@ List<int> encodeMDnsQuery(
   int type = ResourceRecordType.addressIPv4,
   bool multicast = true,
 }) {
-  assert(name != null);
   assert(ResourceRecordType.debugAssertValid(type));
-  assert(multicast != null);
 
   final List<String> nameParts = processDnsNameParts(name);
   final List<List<int>> rawNameParts =
@@ -179,7 +176,7 @@ _FQDNReadResult _readFQDN(
 /// If decoding fails (e.g. due to an invalid packet), `null` is returned.
 ///
 /// See https://tools.ietf.org/html/rfc1035 for format.
-ResourceRecordQuery decodeMDnsQuery(List<int> packet) {
+ResourceRecordQuery? decodeMDnsQuery(List<int> packet) {
   final int length = packet.length;
   if (length < _kHeaderSize) {
     return null;
@@ -214,7 +211,7 @@ ResourceRecordQuery decodeMDnsQuery(List<int> packet) {
 /// If decoding fails (e.g. due to an invalid packet) `null` is returned.
 ///
 /// See https://tools.ietf.org/html/rfc1035 for the format.
-List<ResourceRecord> decodeMDnsResponse(List<int> packet) {
+List<ResourceRecord>? decodeMDnsResponse(List<int> packet) {
   final int length = packet.length;
   if (length < _kHeaderSize) {
     return null;
@@ -242,7 +239,7 @@ List<ResourceRecord> decodeMDnsResponse(List<int> packet) {
     }
   }
 
-  ResourceRecord readResourceRecord() {
+  ResourceRecord? readResourceRecord() {
     // First read the FQDN.
     final _FQDNReadResult result = _readFQDN(data, packetBytes, offset, length);
     final String fqdn = result.fqdn;
@@ -319,7 +316,6 @@ List<ResourceRecord> decodeMDnsResponse(List<int> packet) {
           priority: priority,
           weight: weight,
         );
-        break;
       case ResourceRecordType.serverPointer:
         checkLength(offset + readDataLength);
         final _FQDNReadResult result =
@@ -373,7 +369,7 @@ List<ResourceRecord> decodeMDnsResponse(List<int> packet) {
       offset += 4;
     }
     for (int i = 0; i < remainingCount; i++) {
-      final ResourceRecord record = readResourceRecord();
+      final ResourceRecord? record = readResourceRecord();
       if (record != null) {
         result.add(record);
       }
@@ -391,7 +387,7 @@ class MDnsDecodeException implements Exception {
   /// specified [offset].
   ///
   /// The [offset] parameter should not be null.
-  const MDnsDecodeException(this.offset) : assert(offset != null);
+  const MDnsDecodeException(this.offset);
 
   /// The offset in the packet at which the exception occurred.
   final int offset;
Original file line number	Diff line number	Diff line change
`@@ -25,7 +25,7 @@ class PendingRequest extends LinkedListEntry<PendingRequest> {`
`25`	`25`	`final StreamController<ResourceRecord> controller;`
`26`	`26`
`27`	`27`	`/// The timer for the request.`
`28`		`- Timer timer;`
	`28`	`+ Timer? timer;`
`29`	`29`	`}`
`30`	`30`
`31`	`31`	`/// Class for keeping track of pending lookups and processing incoming`
`@@ -89,7 +89,7 @@ class LookupResolver {`
`89`	`89`	`while (_pendingRequests.isNotEmpty) {`
`90`	`90`	`final PendingRequest request = _pendingRequests.first;`
`91`	`91`	`request.unlink();`
`92`		`- request.timer.cancel();`
	`92`	`+ request.timer?.cancel();`
`93`	`93`	`request.controller.close();`
`94`	`94`	`}`
`95`	`95`	`}`