From b953b3f84a328ce7819d660bc101781b240f2f31 Mon Sep 17 00:00:00 2001
From: mikisoq <mikisoq@mikisoq.cc>
Date: Wed, 29 Jul 2026 01:56:08 -0100
Subject: [PATCH] Add DNS-based domain/DC auto-discovery

---
 ADBulkTool.csproj           |   1 +
 MainWindow.axaml            |   5 +-
 MainWindow.axaml.cs         |  68 ++++++++++
 Models/DiscoveryResult.cs   |   9 ++
 Services/DomainDiscovery.cs | 253 ++++++++++++++++++++++++++++++++++++
 5 files changed, 335 insertions(+), 1 deletion(-)
 create mode 100644 Models/DiscoveryResult.cs
 create mode 100644 Services/DomainDiscovery.cs

diff --git a/ADBulkTool.csproj b/ADBulkTool.csproj
index bd04cb1..3420104 100644
--- a/ADBulkTool.csproj
+++ b/ADBulkTool.csproj
@@ -13,5 +13,6 @@
     <PackageReference Include="Avalonia.Fonts.Inter" Version="12.0.5" />
     <PackageReference Include="CsvHelper" Version="33.1.0" />
     <PackageReference Include="Novell.Directory.Ldap.NETStandard" Version="4.0.0" />
+    <PackageReference Include="DnsClient" Version="1.8.0" />
   </ItemGroup>
 </Project>
diff --git a/MainWindow.axaml b/MainWindow.axaml
index 1970d13..1578f66 100644
--- a/MainWindow.axaml
+++ b/MainWindow.axaml
@@ -18,7 +18,10 @@
       <Grid ColumnDefinitions="*,90,130,210" RowDefinitions="Auto,Auto,Auto,Auto" ColumnSpacing="10" RowSpacing="8">
         <StackPanel Grid.Row="0" Grid.Column="0">
           <TextBlock Text="Domain controller / LDAP host" />
-          <TextBox x:Name="LdapHostBox" PlaceholderText="dc01.contoso.local" />
+          <Grid ColumnDefinitions="*,Auto" ColumnSpacing="6">
+            <TextBox x:Name="LdapHostBox" PlaceholderText="dc01.contoso.local" />
+            <Button Grid.Column="1" x:Name="DiscoverButton" Content="Discover" Click="Discover_Click" />
+          </Grid>
         </StackPanel>
 
         <StackPanel Grid.Row="0" Grid.Column="1">
diff --git a/MainWindow.axaml.cs b/MainWindow.axaml.cs
index 2d9a513..e4cb0fa 100644
--- a/MainWindow.axaml.cs
+++ b/MainWindow.axaml.cs
@@ -29,6 +29,74 @@ public partial class MainWindow : Window
 
         RefreshConnectionHelp();
         RefreshActionHelp();
+
+        _ = AutoDiscoverAsync();
+    }
+
+    private async void Discover_Click(object? sender, RoutedEventArgs e)
+    {
+        DiscoverButton.IsEnabled = false;
+        SetStatus("Discovering domain and domain controller from DNS...");
+
+        try
+        {
+            var result = await DomainDiscovery.DiscoverAsync(TimeSpan.FromSeconds(10));
+
+            if (result.LdapHost is not null)
+            {
+                LdapHostBox.Text = result.LdapHost;
+            }
+
+            if (result.SearchBaseDn is not null)
+            {
+                SearchBaseBox.Text = result.SearchBaseDn;
+            }
+
+            if (result.Domain is not null)
+            {
+                var domainUpper = result.Domain.ToUpperInvariant();
+                var domainParts = result.Domain.Split('.');
+                var netbios = domainParts.Length > 0 ? domainParts[0].ToUpperInvariant() : domainUpper;
+                var userPlaceholder = $@"{netbios}\adminuser or adminuser@{result.Domain}";
+                BindUserBox.PlaceholderText = userPlaceholder;
+            }
+
+            SetStatus(result.Message ?? "Discovery did not return a result.");
+        }
+        catch (Exception ex)
+        {
+            SetStatus($"Discovery failed: {ex.Message}");
+        }
+        finally
+        {
+            DiscoverButton.IsEnabled = true;
+        }
+    }
+
+    private async Task AutoDiscoverAsync()
+    {
+        try
+        {
+            var result = await DomainDiscovery.DiscoverAsync(TimeSpan.FromSeconds(5));
+
+            if (result.LdapHost is not null && string.IsNullOrWhiteSpace(LdapHostBox.Text))
+            {
+                LdapHostBox.Text = result.LdapHost;
+            }
+
+            if (result.SearchBaseDn is not null && string.IsNullOrWhiteSpace(SearchBaseBox.Text))
+            {
+                SearchBaseBox.Text = result.SearchBaseDn;
+            }
+
+            if (result.LdapHost is not null || result.SearchBaseDn is not null)
+            {
+                SetStatus("Auto-discovered AD domain from DNS. Adjust if needed, then enter credentials.");
+            }
+        }
+        catch
+        {
+        }
     }
 
     private async void LoadCsv_Click(object? sender, RoutedEventArgs e)
diff --git a/Models/DiscoveryResult.cs b/Models/DiscoveryResult.cs
new file mode 100644
index 0000000..17b88e8
--- /dev/null
+++ b/Models/DiscoveryResult.cs
@@ -0,0 +1,9 @@
+namespace ADBulkTool.Models;
+
+public sealed record DiscoveryResult(
+    string? Domain,
+    string? DnsServer,
+    string? LdapHost,
+    int? LdapPort,
+    string? SearchBaseDn,
+    string? Message);
diff --git a/Services/DomainDiscovery.cs b/Services/DomainDiscovery.cs
new file mode 100644
index 0000000..16f611d
--- /dev/null
+++ b/Services/DomainDiscovery.cs
@@ -0,0 +1,253 @@
+using System.Net;
+using ADBulkTool.Models;
+using DnsClient;
+
+namespace ADBulkTool.Services;
+
+public static class DomainDiscovery
+{
+    public static async Task<DiscoveryResult> DiscoverAsync(TimeSpan timeout)
+    {
+        var steps = new List<string>();
+
+        try
+        {
+            var domain = await GetSystemDomainAsync(timeout);
+            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.");
+            }
+
+            steps.Add($"Detected domain: {domain}");
+
+            var searchBase = DomainToSearchBase(domain);
+            steps.Add($"Derived search base: {searchBase}");
+
+            var dnsServers = GetDnsServers();
+            var dnsServer = dnsServers.FirstOrDefault();
+            steps.Add(dnsServer is not null
+                ? $"DNS server from /etc/resolv.conf: {dnsServer}"
+                : "No DNS server found in /etc/resolv.conf, using system default.");
+
+            var ldapHost = await FindDomainControllerViaSrvAsync(domain, dnsServer, timeout);
+
+            if (ldapHost is not null)
+            {
+                steps.Add($"Found DC via SRV record: {ldapHost}");
+                return new DiscoveryResult(domain, dnsServer, ldapHost, 636, searchBase,
+                    string.Join(" | ", steps));
+            }
+
+            ldapHost = await FindDomainControllerViaLdapSrvAsync(domain, dnsServer, timeout);
+
+            if (ldapHost is not null)
+            {
+                steps.Add($"Found DC via generic LDAP SRV: {ldapHost}");
+                return new DiscoveryResult(domain, dnsServer, ldapHost, 636, searchBase,
+                    string.Join(" | ", steps));
+            }
+
+            var guessedHost = $"dc01.{domain}";
+            steps.Add($"SRV lookup failed. Guessed DC: {guessedHost}");
+            return new DiscoveryResult(domain, dnsServer, guessedHost, 636, searchBase,
+                string.Join(" | ", steps));
+        }
+        catch (Exception ex)
+        {
+            return new DiscoveryResult(null, null, null, null, null,
+                $"Discovery failed: {ex.Message}");
+        }
+    }
+
+    public static List<string> GetDnsServers()
+    {
+        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;
+    }
+
+    public static string? DomainToSearchBase(string? domain)
+    {
+        if (string.IsNullOrWhiteSpace(domain))
+        {
+            return null;
+        }
+
+        var parts = domain.Split('.', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries);
+        if (parts.Length == 0)
+        {
+            return null;
+        }
+
+        return string.Join(",", parts.Select(p => $"DC={p}"));
+    }
+
+    private static async Task<string?> GetSystemDomainAsync(TimeSpan timeout)
+    {
+        try
+        {
+            using var cts = new CancellationTokenSource(timeout);
+
+            var resolvDomain = await Task.Run(() => GetDomainFromResolvConf(), cts.Token);
+            if (!string.IsNullOrWhiteSpace(resolvDomain))
+            {
+                return resolvDomain;
+            }
+
+            var hostDomain = await Task.Run(() => GetDomainFromHostname(), cts.Token);
+            if (!string.IsNullOrWhiteSpace(hostDomain))
+            {
+                return hostDomain;
+            }
+
+            var ipDomain = await Task.Run(() =>
+            {
+                try { return System.Net.NetworkInformation.IPGlobalProperties.GetIPGlobalProperties().DomainName; }
+                catch { return string.Empty; }
+            }, cts.Token);
+            if (!string.IsNullOrWhiteSpace(ipDomain) && !string.Equals(ipDomain, "localdomain", StringComparison.OrdinalIgnoreCase))
+            {
+                return ipDomain.TrimEnd('.');
+            }
+
+            return null;
+        }
+        catch
+        {
+            return null;
+        }
+    }
+
+    private static string? GetDomainFromResolvConf()
+    {
+        try
+        {
+            var lines = File.ReadAllLines("/etc/resolv.conf");
+            foreach (var line in lines)
+            {
+                var trimmed = line.Trim();
+
+                if (trimmed.StartsWith("domain ", StringComparison.OrdinalIgnoreCase))
+                {
+                    var parts = trimmed.Split(' ', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries);
+                    if (parts.Length >= 2 && !string.IsNullOrWhiteSpace(parts[1]))
+                    {
+                        return parts[1].TrimEnd('.');
+                    }
+                }
+
+                if (trimmed.StartsWith("search ", StringComparison.OrdinalIgnoreCase))
+                {
+                    var parts = trimmed.Split(' ', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries);
+                    if (parts.Length >= 2 && !string.IsNullOrWhiteSpace(parts[1]))
+                    {
+                        return parts[1].TrimEnd('.');
+                    }
+                }
+            }
+        }
+        catch
+        {
+        }
+
+        return null;
+    }
+
+    private static string? GetDomainFromHostname()
+    {
+        try
+        {
+            var hostname = Dns.GetHostEntry("localhost").HostName;
+            var dotIndex = hostname.IndexOf('.');
+            if (dotIndex > 0 && dotIndex < hostname.Length - 1)
+            {
+                var domain = hostname[(dotIndex + 1)..].TrimEnd('.');
+                return string.IsNullOrWhiteSpace(domain) ? null : domain;
+            }
+        }
+        catch
+        {
+        }
+
+        try
+        {
+            var fullHostname = System.Net.NetworkInformation.IPGlobalProperties.GetIPGlobalProperties().HostName;
+            var dotIndex = fullHostname.IndexOf('.');
+            if (dotIndex > 0 && dotIndex < fullHostname.Length - 1)
+            {
+                var domain = fullHostname[(dotIndex + 1)..].TrimEnd('.');
+                return string.IsNullOrWhiteSpace(domain) ? null : domain;
+            }
+        }
+        catch
+        {
+        }
+
+        return null;
+    }
+
+    private static async Task<string?> FindDomainControllerViaSrvAsync(string domain, string? dnsServer, TimeSpan timeout)
+    {
+        try
+        {
+            var srvQuery = $"_ldap._tcp.dc._msdcs.{domain}";
+            var lookup = CreateLookup(dnsServer);
+            using var cts = new CancellationTokenSource(timeout);
+            var result = await lookup.QueryAsync(srvQuery, QueryType.SRV, QueryClass.IN, cts.Token);
+            var record = result.Answers.SrvRecords().FirstOrDefault();
+            return record?.DomainName.Value.TrimEnd('.');
+        }
+        catch
+        {
+            return null;
+        }
+    }
+
+    private static async Task<string?> FindDomainControllerViaLdapSrvAsync(string domain, string? dnsServer, TimeSpan timeout)
+    {
+        try
+        {
+            var srvQuery = $"_ldap._tcp.{domain}";
+            var lookup = CreateLookup(dnsServer);
+            using var cts = new CancellationTokenSource(timeout);
+            var result = await lookup.QueryAsync(srvQuery, QueryType.SRV, QueryClass.IN, cts.Token);
+            var record = result.Answers.SrvRecords().FirstOrDefault();
+            return record?.DomainName.Value.TrimEnd('.');
+        }
+        catch
+        {
+            return null;
+        }
+    }
+
+    private static LookupClient CreateLookup(string? dnsServer)
+    {
+        if (dnsServer is not null && IPAddress.TryParse(dnsServer, out var ip))
+        {
+            return new LookupClient(new LookupClientOptions(ip) { UseCache = false, Timeout = TimeSpan.FromSeconds(5) });
+        }
+
+        return new LookupClient(new LookupClientOptions { UseCache = false, Timeout = TimeSpan.FromSeconds(5) });
+    }
+}