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

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 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 GetUsersRecursively(DirectoryEntry searchRoot, string groupDn) {
        List searchedGroups = new List();
        List searchedUsers = new List();
        return GetUsersRecursively(searchRoot, groupDn, searchedGroups, searchedUsers);
    }

    static IEnumerable GetUsersRecursively(
        DirectoryEntry searchRoot,
        string groupDn,
        List searchedGroups,
        List 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]);
            }
        }
    }

}