Get members of an Active Directory group recursively, i.e. including subgroups

Question

Given a group like this in Active Directory:

MainGroup
  GroupA
    User1
    User2
  GroupB
    User3
  User4

I can easily determine if Us

Answer 1

    static List<SearchResult> ad_find_all_members(string a_sSearchRoot, string a_sGroupDN, string[] a_asPropsToLoad)
    {
        using (DirectoryEntry de = new DirectoryEntry(a_sSearchRoot))
            return ad_find_all_members(de, a_sGroupDN, a_asPropsToLoad);
    }

    static List<SearchResult> ad_find_all_members(DirectoryEntry a_SearchRoot, string a_sGroupDN, string[] a_asPropsToLoad)
    {
        string sDN = "distinguishedName";
        string sOC = "objectClass";
        string sOC_GROUP = "group";
        string[] asPropsToLoad = a_asPropsToLoad;
        Array.Sort<string>(asPropsToLoad);
        if (Array.BinarySearch<string>(asPropsToLoad, sDN) < 0)
        {
            Array.Resize<string>(ref asPropsToLoad, asPropsToLoad.Length+1);
            asPropsToLoad[asPropsToLoad.Length-1] = sDN;
        }
        if (Array.BinarySearch<string>(asPropsToLoad, sOC) < 0)
        {
            Array.Resize<string>(ref asPropsToLoad, asPropsToLoad.Length+1);
            asPropsToLoad[asPropsToLoad.Length-1] = sOC;
        }

        List<SearchResult> lsr = new List<SearchResult>();

        using (DirectorySearcher ds = new DirectorySearcher(a_SearchRoot))
        {
            ds.Filter = "(&(|(objectClass=group)(objectClass=user))(memberOf=" + a_sGroupDN + "))";
            //ds.PropertiesToLoad.Clear();
            ds.PropertiesToLoad.AddRange(asPropsToLoad);
            //ds.PageSize = 1000;
            //ds.SizeLimit = 0;
            foreach (SearchResult sr in ds.FindAll())
                lsr.Add(sr);
        }

        for(int i=0;i<lsr.Count;i++)
            if (lsr[i].Properties.Contains(sOC) && lsr[i].Properties[sOC].Contains(sOC_GROUP))
                lsr.AddRange(ad_find_all_members(a_SearchRoot, (string)lsr[i].Properties[sDN][0], asPropsToLoad));

        return lsr;
    }

    static void Main(string[] args)
    {
    foreach (var sr in ad_find_all_members("LDAP://DC=your-domain,DC=com", "CN=your-group-name,OU=your-group-ou,DC=your-domain,DC=com", new string[] { "sAMAccountName" }))
        Console.WriteLine((string)sr.Properties["distinguishedName"][0] + " : " + (string)sr.Properties["sAMAccountName"][0]);
    }

Answer 2

Just in case this might benefit someone else: here is the solution I ended up with. It is just a recursive search, with some extra checks to avoid checking the same group or user twice, e.g. if groupA is member of groupB and groupB is member of groupA or a user is member of more than one group.

using System;
using System.DirectoryServices;
using System.Collections.Generic;

static class Program {

    static IEnumerable<SearchResult> GetMembers(DirectoryEntry searchRoot, string groupDn, string objectClass) {
        using (DirectorySearcher searcher = new DirectorySearcher(searchRoot)) {
            searcher.Filter = "(&(objectClass=" + objectClass + ")(memberOf=" + groupDn + "))";
            searcher.PropertiesToLoad.Clear();
            searcher.PropertiesToLoad.AddRange(new string[] { 
                "objectGUID",
                "sAMAccountName",
                "distinguishedName"});
            searcher.Sort = new SortOption("sAMAccountName", SortDirection.Ascending);
            searcher.PageSize = 1000;
            searcher.SizeLimit = 0;
            foreach (SearchResult result in searcher.FindAll()) {
                yield return result;
            }
        }
    }

    static IEnumerable<SearchResult> GetUsersRecursively(DirectoryEntry searchRoot, string groupDn) {
        List<string> searchedGroups = new List<string>();
        List<string> searchedUsers = new List<string>();
        return GetUsersRecursively(searchRoot, groupDn, searchedGroups, searchedUsers);
    }

    static IEnumerable<SearchResult> GetUsersRecursively(
        DirectoryEntry searchRoot,
        string groupDn,
        List<string> searchedGroups,
        List<string> searchedUsers) {
        foreach (var subGroup in GetMembers(searchRoot, groupDn, "group")) {
            string subGroupName = ((string)subGroup.Properties["sAMAccountName"][0]).ToUpperInvariant();
            if (searchedGroups.Contains(subGroupName)) {
                continue;
            }
            searchedGroups.Add(subGroupName);
            string subGroupDn = ((string)subGroup.Properties["distinguishedName"][0]);
            foreach (var user in GetUsersRecursively(searchRoot, subGroupDn, searchedGroups, searchedUsers)) {
                yield return user;
            }
        }
        foreach (var user in GetMembers(searchRoot, groupDn, "user")) {
            string userName = ((string)user.Properties["sAMAccountName"][0]).ToUpperInvariant();
            if (searchedUsers.Contains(userName)) {
                continue;
            }
            searchedUsers.Add(userName);
            yield return user;
        }
    }

    static void Main(string[] args) {
        using (DirectoryEntry searchRoot = new DirectoryEntry("LDAP://DC=x,DC=y")) {
            foreach (var user in GetUsersRecursively(searchRoot, "CN=MainGroup,DC=x,DC=y")) {
                Console.WriteLine((string)user.Properties["sAMAccountName"][0]);
            }
        }
    }

}