fix(network_info_plus): Fix subnet mask and broadcast on Linux

packages/network_info_plus/network_info_plus/lib/src/network_info_plus_linux.dart

@@ -97,7 +97,7 @@ class NetworkInfoPlusLinuxPlugin extends NetworkInfoPlatform {
 
   String? _getSubnetMask(List<Map<String, dynamic>>? data) {
     final prefix = data?.firstOrNull?['prefix'] as int;
-    final mask = 0xffffffff >> (32 - prefix);
+    final mask = (0xffffffff << (32 - prefix)) & 0xffffffff;
     return mask.toIpString();
   }
 
@@ -113,17 +113,26 @@ class NetworkInfoPlusLinuxPlugin extends NetworkInfoPlatform {
 }
 
 extension _IpInt on int {
-  int byteAt(int i) => (this >> (i * 8)) & 0xff;
-  String toIpString() => '${byteAt(0)}.${byteAt(1)}.${byteAt(2)}.${byteAt(3)}';
+  /// Returns the i-th octet in network (big-endian) order.
+  /// i must be 0..3.
+  int octet(int i) {
+    assert(i >= 0 && i <= 3);
+    return (this >> (24 - i * 8)) & 0xff;
+  }
+
+  String toIpString() {
+    final v = this & 0xFFFFFFFF;
+    return '${v.octet(0)}.${v.octet(1)}.${v.octet(2)}.${v.octet(3)}';
+  }
 }
 
 extension _IpString on String {
   int toIpInt() {
     final parts = split('.');
-    return parts.intAtOrZero(3) << 24 |
-        parts.intAtOrZero(2) << 16 |
-        parts.intAtOrZero(1) << 8 |
-        parts.intAtOrZero(0);
+    return parts.intAtOrZero(0) << 24 |
+        parts.intAtOrZero(1) << 16 |
+        parts.intAtOrZero(2) << 8 |
+        parts.intAtOrZero(3);
   }
 }
 

packages/network_info_plus/network_info_plus/test/network_info_plus_linux_test.dart

@@ -1,13 +1,79 @@
-@TestOn('linux')
-library;
-
 import 'package:flutter_test/flutter_test.dart';
 import 'package:network_info_plus/network_info_plus.dart';
 import 'package:network_info_plus_platform_interface/network_info_plus_platform_interface.dart';
+import 'package:nm/nm.dart';
 
 void main() {
   test('registered instance', () {
     NetworkInfoPlusLinuxPlugin.registerWith();
     expect(NetworkInfoPlatform.instance, isA<NetworkInfoPlusLinuxPlugin>());
   });
+
+  group('IPv4 subnet mask and broadcast', () {
+    // address, prefix, expected mask, expected broadcast
+    const cases = [
+      ('192.168.1.10', 24, '255.255.255.0', '192.168.1.255'),
+      ('192.168.1.10', 22, '255.255.252.0', '192.168.3.255'),
+      ('192.168.1.10', 25, '255.255.255.128', '192.168.1.127'),
+      ('10.1.2.3', 8, '255.0.0.0', '10.255.255.255'),
+      ('172.16.5.4', 12, '255.240.0.0', '172.31.255.255'),
+      ('200.100.50.25', 20, '255.255.240.0', '200.100.63.255'),
+      ('10.0.0.1', 30, '255.255.255.252', '10.0.0.3'),
+      ('192.168.1.10', 32, '255.255.255.255', '192.168.1.10'),
+      ('192.168.1.10', 0, '0.0.0.0', '255.255.255.255'),
+    ];
+
+    for (final (address, prefix, mask, broadcast) in cases) {
+      test('$address/$prefix', () async {
+        final plugin = NetworkInfoPlusLinuxPlugin()
+          ..createClient = () => _FakeClient(address: address, prefix: prefix);
+
+        expect(await plugin.getWifiSubmask(), mask);
+        expect(await plugin.getWifiBroadcast(), broadcast);
+      });
+    }
+  });
+
+  test('wifi IP and gateway are passed through', () async {
+    final plugin = NetworkInfoPlusLinuxPlugin()
+      ..createClient = () => _FakeClient(address: '192.168.1.10', prefix: 22);
+
+    expect(await plugin.getWifiIP(), '192.168.1.10');
+    expect(await plugin.getWifiGatewayIP(), '192.168.0.1');
+  });
+}
+
+class _FakeClient extends Fake implements NetworkManagerClient {
+  _FakeClient({required String address, required int prefix})
+    : primaryConnection = _FakeConnection(
+        _FakeIp4Config([
+          {'address': address, 'prefix': prefix},
+        ]),
+      );
+
+  @override
+  final NetworkManagerActiveConnection? primaryConnection;
+
+  @override
+  Future<void> connect() async {}
+
+  @override
+  Future<void> close() async {}
+}
+
+class _FakeConnection extends Fake implements NetworkManagerActiveConnection {
+  _FakeConnection(this.ip4Config);
+
+  @override
+  final NetworkManagerIP4Config? ip4Config;
+}
+
+class _FakeIp4Config extends Fake implements NetworkManagerIP4Config {
+  _FakeIp4Config(this.addressData);
+
+  @override
+  final List<Map<String, dynamic>> addressData;
+
+  @override
+  String get gateway => '192.168.0.1';
 }