Add DNS-based domain/DC auto-discovery
This commit is contained in:
mikisoq
@@ -0,0 +1,253 @@
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using System.Net;
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using ADBulkTool.Models;
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using DnsClient;
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namespace ADBulkTool.Services;
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public static class DomainDiscovery
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{
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public static async Task<DiscoveryResult> DiscoverAsync(TimeSpan timeout)
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{
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var steps = new List<string>();
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try
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{
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var domain = await GetSystemDomainAsync(timeout);
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if (string.IsNullOrWhiteSpace(domain))
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{
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return new DiscoveryResult(null, null, null, null, null,
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"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.");
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}
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steps.Add($"Detected domain: {domain}");
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var searchBase = DomainToSearchBase(domain);
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steps.Add($"Derived search base: {searchBase}");
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var dnsServers = GetDnsServers();
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var dnsServer = dnsServers.FirstOrDefault();
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steps.Add(dnsServer is not null
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? $"DNS server from /etc/resolv.conf: {dnsServer}"
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: "No DNS server found in /etc/resolv.conf, using system default.");
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var ldapHost = await FindDomainControllerViaSrvAsync(domain, dnsServer, timeout);
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if (ldapHost is not null)
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{
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steps.Add($"Found DC via SRV record: {ldapHost}");
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return new DiscoveryResult(domain, dnsServer, ldapHost, 636, searchBase,
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string.Join(" | ", steps));
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}
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ldapHost = await FindDomainControllerViaLdapSrvAsync(domain, dnsServer, timeout);
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if (ldapHost is not null)
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{
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steps.Add($"Found DC via generic LDAP SRV: {ldapHost}");
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return new DiscoveryResult(domain, dnsServer, ldapHost, 636, searchBase,
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string.Join(" | ", steps));
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}
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var guessedHost = $"dc01.{domain}";
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steps.Add($"SRV lookup failed. Guessed DC: {guessedHost}");
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return new DiscoveryResult(domain, dnsServer, guessedHost, 636, searchBase,
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string.Join(" | ", steps));
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}
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catch (Exception ex)
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{
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return new DiscoveryResult(null, null, null, null, null,
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$"Discovery failed: {ex.Message}");
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}
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}
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public static List<string> GetDnsServers()
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{
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var servers = new List<string>();
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try
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{
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var lines = File.ReadAllLines("/etc/resolv.conf");
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foreach (var line in lines)
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{
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var trimmed = line.Trim();
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if (trimmed.StartsWith("nameserver ", StringComparison.OrdinalIgnoreCase))
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{
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var parts = trimmed.Split(' ', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries);
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if (parts.Length >= 2 && IPAddress.TryParse(parts[1], out _))
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{
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servers.Add(parts[1]);
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}
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}
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}
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}
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catch
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{
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}
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return servers;
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}
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public static string? DomainToSearchBase(string? domain)
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{
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if (string.IsNullOrWhiteSpace(domain))
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{
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return null;
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}
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var parts = domain.Split('.', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries);
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if (parts.Length == 0)
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{
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return null;
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}
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return string.Join(",", parts.Select(p => $"DC={p}"));
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}
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private static async Task<string?> GetSystemDomainAsync(TimeSpan timeout)
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{
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try
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{
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using var cts = new CancellationTokenSource(timeout);
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var resolvDomain = await Task.Run(() => GetDomainFromResolvConf(), cts.Token);
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if (!string.IsNullOrWhiteSpace(resolvDomain))
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{
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return resolvDomain;
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}
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var hostDomain = await Task.Run(() => GetDomainFromHostname(), cts.Token);
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if (!string.IsNullOrWhiteSpace(hostDomain))
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{
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return hostDomain;
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}
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var ipDomain = await Task.Run(() =>
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{
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try { return System.Net.NetworkInformation.IPGlobalProperties.GetIPGlobalProperties().DomainName; }
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catch { return string.Empty; }
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}, cts.Token);
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if (!string.IsNullOrWhiteSpace(ipDomain) && !string.Equals(ipDomain, "localdomain", StringComparison.OrdinalIgnoreCase))
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{
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return ipDomain.TrimEnd('.');
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}
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return null;
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}
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catch
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{
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return null;
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}
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}
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private static string? GetDomainFromResolvConf()
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{
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try
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{
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var lines = File.ReadAllLines("/etc/resolv.conf");
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foreach (var line in lines)
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{
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var trimmed = line.Trim();
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if (trimmed.StartsWith("domain ", StringComparison.OrdinalIgnoreCase))
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{
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var parts = trimmed.Split(' ', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries);
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if (parts.Length >= 2 && !string.IsNullOrWhiteSpace(parts[1]))
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{
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return parts[1].TrimEnd('.');
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}
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}
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if (trimmed.StartsWith("search ", StringComparison.OrdinalIgnoreCase))
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{
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var parts = trimmed.Split(' ', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries);
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if (parts.Length >= 2 && !string.IsNullOrWhiteSpace(parts[1]))
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{
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return parts[1].TrimEnd('.');
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}
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}
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}
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}
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catch
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{
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}
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return null;
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}
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private static string? GetDomainFromHostname()
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{
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try
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{
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var hostname = Dns.GetHostEntry("localhost").HostName;
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var dotIndex = hostname.IndexOf('.');
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if (dotIndex > 0 && dotIndex < hostname.Length - 1)
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{
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var domain = hostname[(dotIndex + 1)..].TrimEnd('.');
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return string.IsNullOrWhiteSpace(domain) ? null : domain;
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}
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}
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catch
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{
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}
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try
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{
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var fullHostname = System.Net.NetworkInformation.IPGlobalProperties.GetIPGlobalProperties().HostName;
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var dotIndex = fullHostname.IndexOf('.');
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if (dotIndex > 0 && dotIndex < fullHostname.Length - 1)
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{
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var domain = fullHostname[(dotIndex + 1)..].TrimEnd('.');
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return string.IsNullOrWhiteSpace(domain) ? null : domain;
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}
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}
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catch
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{
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}
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return null;
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}
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private static async Task<string?> FindDomainControllerViaSrvAsync(string domain, string? dnsServer, TimeSpan timeout)
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{
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try
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{
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var srvQuery = $"_ldap._tcp.dc._msdcs.{domain}";
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var lookup = CreateLookup(dnsServer);
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using var cts = new CancellationTokenSource(timeout);
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var result = await lookup.QueryAsync(srvQuery, QueryType.SRV, QueryClass.IN, cts.Token);
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var record = result.Answers.SrvRecords().FirstOrDefault();
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return record?.DomainName.Value.TrimEnd('.');
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}
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catch
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{
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return null;
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}
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}
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private static async Task<string?> FindDomainControllerViaLdapSrvAsync(string domain, string? dnsServer, TimeSpan timeout)
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{
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try
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{
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var srvQuery = $"_ldap._tcp.{domain}";
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var lookup = CreateLookup(dnsServer);
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using var cts = new CancellationTokenSource(timeout);
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var result = await lookup.QueryAsync(srvQuery, QueryType.SRV, QueryClass.IN, cts.Token);
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var record = result.Answers.SrvRecords().FirstOrDefault();
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return record?.DomainName.Value.TrimEnd('.');
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}
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catch
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{
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return null;
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}
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}
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private static LookupClient CreateLookup(string? dnsServer)
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{
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if (dnsServer is not null && IPAddress.TryParse(dnsServer, out var ip))
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{
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return new LookupClient(new LookupClientOptions(ip) { UseCache = false, Timeout = TimeSpan.FromSeconds(5) });
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}
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return new LookupClient(new LookupClientOptions { UseCache = false, Timeout = TimeSpan.FromSeconds(5) });
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}
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}
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