Make auto-discovery cross-platform (Windows + Linux)

Services/DomainDiscovery.cs

@@ -1,4 +1,6 @@
 using System.Net;
+using System.Net.NetworkInformation;
+using System.Runtime.InteropServices;
 using ADBulkTool.Models;
 using DnsClient;
 
@@ -16,7 +18,7 @@ public static class DomainDiscovery
             if (string.IsNullOrWhiteSpace(domain))
             {
                 return new DiscoveryResult(null, null, null, null, null,
-                    "Could not detect a DNS domain from this machine. Check that you are on a domain-joined network and that /etc/resolv.conf has a search or domain entry.");
+                    "Could not detect a DNS domain. Ensure the machine is on a domain network with a proper DNS configuration.");
             }
 
             steps.Add($"Detected domain: {domain}");
@@ -27,8 +29,8 @@ public static class DomainDiscovery
             var dnsServers = GetDnsServers();
             var dnsServer = dnsServers.FirstOrDefault();
             steps.Add(dnsServer is not null
-                ? $"DNS server from /etc/resolv.conf: {dnsServer}"
+                ? $"DNS server found: {dnsServer}"
-                : "No DNS server found in /etc/resolv.conf, using system default.");
+                : "No DNS server found, using system default resolver.");
 
             var ldapHost = await FindDomainControllerViaSrvAsync(domain, dnsServer, timeout);
 
@@ -62,29 +64,12 @@ public static class DomainDiscovery
 
     public static List<string> GetDnsServers()
     {
-        var servers = new List<string>();
+        if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
-
-        try
-        {
-            var lines = File.ReadAllLines("/etc/resolv.conf");
-            foreach (var line in lines)
-            {
-                var trimmed = line.Trim();
-                if (trimmed.StartsWith("nameserver ", StringComparison.OrdinalIgnoreCase))
-                {
-                    var parts = trimmed.Split(' ', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries);
-                    if (parts.Length >= 2 && IPAddress.TryParse(parts[1], out _))
-                    {
-                        servers.Add(parts[1]);
-                    }
-                }
-            }
-        }
-        catch
         {
+            return GetDnsServersWindows();
         }
 
-        return servers;
+        return GetDnsServersLinux();
     }
 
     public static string? DomainToSearchBase(string? domain)
@@ -109,11 +94,23 @@ public static class DomainDiscovery
         {
             using var cts = new CancellationTokenSource(timeout);
 
+            if (RuntimeInformation.IsOSPlatform(OSPlatform.Linux))
+            {
                 var resolvDomain = await Task.Run(() => GetDomainFromResolvConf(), cts.Token);
                 if (!string.IsNullOrWhiteSpace(resolvDomain))
                 {
                     return resolvDomain;
                 }
+            }
+
+            if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
+            {
+                var winDomain = await Task.Run(() => GetDomainFromWindows(), cts.Token);
+                if (!string.IsNullOrWhiteSpace(winDomain))
+                {
+                    return winDomain;
+                }
+            }
 
             var hostDomain = await Task.Run(() => GetDomainFromHostname(), cts.Token);
             if (!string.IsNullOrWhiteSpace(hostDomain))
@@ -123,8 +120,14 @@ public static class DomainDiscovery
 
             var ipDomain = await Task.Run(() =>
             {
-                try { return System.Net.NetworkInformation.IPGlobalProperties.GetIPGlobalProperties().DomainName; }
+                try
-                catch { return string.Empty; }
+                {
+                    return IPGlobalProperties.GetIPGlobalProperties().DomainName;
+                }
+                catch
+                {
+                    return string.Empty;
+                }
             }, cts.Token);
             if (!string.IsNullOrWhiteSpace(ipDomain) && !string.Equals(ipDomain, "localdomain", StringComparison.OrdinalIgnoreCase))
             {
@@ -139,6 +142,68 @@ public static class DomainDiscovery
         }
     }
 
+    private static List<string> GetDnsServersWindows()
+    {
+        var servers = new List<string>();
+
+        try
+        {
+            foreach (var ni in NetworkInterface.GetAllNetworkInterfaces())
+            {
+                if (ni.OperationalStatus != OperationalStatus.Up)
+                {
+                    continue;
+                }
+
+                var props = ni.GetIPProperties();
+                if (props is null)
+                {
+                    continue;
+                }
+
+                foreach (var dns in props.DnsAddresses)
+                {
+                    if (dns.AddressFamily == System.Net.Sockets.AddressFamily.InterNetwork && !servers.Contains(dns.ToString()))
+                    {
+                        servers.Add(dns.ToString());
+                    }
+                }
+            }
+        }
+        catch
+        {
+        }
+
+        return servers;
+    }
+
+    private static List<string> GetDnsServersLinux()
+    {
+        var servers = new List<string>();
+
+        try
+        {
+            var lines = File.ReadAllLines("/etc/resolv.conf");
+            foreach (var line in lines)
+            {
+                var trimmed = line.Trim();
+                if (trimmed.StartsWith("nameserver ", StringComparison.OrdinalIgnoreCase))
+                {
+                    var parts = trimmed.Split(' ', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries);
+                    if (parts.Length >= 2 && IPAddress.TryParse(parts[1], out _))
+                    {
+                        servers.Add(parts[1]);
+                    }
+                }
+            }
+        }
+        catch
+        {
+        }
+
+        return servers;
+    }
+
     private static string? GetDomainFromResolvConf()
     {
         try
@@ -174,6 +239,62 @@ public static class DomainDiscovery
         return null;
     }
 
+    private static string? GetDomainFromWindows()
+    {
+        try
+        {
+            foreach (var ni in NetworkInterface.GetAllNetworkInterfaces())
+            {
+                if (ni.OperationalStatus != OperationalStatus.Up)
+                {
+                    continue;
+                }
+
+                var props = ni.GetIPProperties();
+                if (props is null)
+                {
+                    continue;
+                }
+
+                var suffix = props.DnsSuffix;
+                if (!string.IsNullOrWhiteSpace(suffix))
+                {
+                    return suffix.TrimEnd('.');
+                }
+            }
+        }
+        catch
+        {
+        }
+
+#pragma warning disable CA1416 // Registry access is guarded by platform check
+        try
+        {
+            using var key = Microsoft.Win32.Registry.LocalMachine.OpenSubKey(
+                @"SYSTEM\CurrentControlSet\Services\Tcpip\Parameters");
+            if (key is not null)
+            {
+                var domain = key.GetValue("Domain") as string;
+                if (!string.IsNullOrWhiteSpace(domain))
+                {
+                    return domain.TrimEnd('.');
+                }
+
+                var dhcpDomain = key.GetValue("DhcpDomain") as string;
+                if (!string.IsNullOrWhiteSpace(dhcpDomain))
+                {
+                    return dhcpDomain.TrimEnd('.');
+                }
+            }
+        }
+        catch
+        {
+        }
+#pragma warning restore CA1416
+
+        return null;
+    }
+
     private static string? GetDomainFromHostname()
     {
         try
@@ -192,7 +313,7 @@ public static class DomainDiscovery
 
         try
         {
-            var fullHostname = System.Net.NetworkInformation.IPGlobalProperties.GetIPGlobalProperties().HostName;
+            var fullHostname = IPGlobalProperties.GetIPGlobalProperties().HostName;
             var dotIndex = fullHostname.IndexOf('.');
             if (dotIndex > 0 && dotIndex < fullHostname.Length - 1)
             {