Connecting to LDAP server throws NullReferenceException

Question

I am trying to connect to the online test LDAP server specified here using System.DirectoryServices.AccountManagement like this:

try
{
    using (PrincipalContext ctx = new PrincipalContext(ContextType.Domain, "ldap.forumsys.com:389", "dc=example,dc=com", "cn=read-only-admin,dc=example,dc=com", "password"))
    {
         using (var searcher = new PrincipalSearcher(new UserPrincipal(ctx )))
         {
              foreach (var result in searcher.FindAll().Take(usersCount))
              {
                 DirectoryEntry de = result.GetUnderlyingObject() as DirectoryEntry;
              }
        }
    }
}
catch(Exception ex)
{
    Console.WriteLine(ex.Message);
}

But it throws the following exception:

Object reference not set to an instance of an object.

Could you please tell what is wrong with my code and how to be able to connect to that LDAP server?

PS: I am able to connect to that server using Apache Directory Studio

Stack Trace :

at System.DirectoryServices.AccountManagement.PrincipalContext.ReadServerConfig(String serverName, ServerProperties& properties) at System.DirectoryServices.AccountManagement.PrincipalContext.DoServerVerifyAndPropRetrieval() at System.DirectoryServices.AccountManagement.PrincipalContext..ctor(ContextType contextType, String name, String container, ContextOptions options, String userName, String password) at System.DirectoryServices.AccountManagement.PrincipalContext..ctor(ContextType contextType, String name, String container, String userName, String password) at ConsoleApp1.Program.GetGroups(String userName) in C:\Users\Simple Code\source\repos\ConsoleApp1\ConsoleApp1\Program.cs:line 48

Possible duplicate of [What is a NullPointerException, and how do I fix it?](https://stackoverflow.com/questions/218384/what-is-a-nullpointerexception-and-how-do-i-fix-it) — Fildor, Jan 04 '18 at 11:10
in simple terms it failed to create ctx with the principalcontext you gave it — BugFinder, Jan 04 '18 at 11:10
@Fildor You mixed it up. NullPointerException => java, NullReferenceException => .NET — Camilo Terevinto, Jan 04 '18 at 11:11
@Simple Code can you share the real code of `// some code here`? — Ferus7, Jan 04 '18 at 11:12
@Ferus7 It's throwing that exception on PrincipalContext constructor — Simple Code, Jan 04 '18 at 11:14
Usually I use `DirectoryEntry` and `DirectorySearcher` to connect to LDAP — Ferus7, Jan 04 '18 at 11:14
Possible duplicate of [What is a NullReferenceException, and how do I fix it?](https://stackoverflow.com/questions/4660142/what-is-a-nullreferenceexception-and-how-do-i-fix-it) — BugFinder, Jan 04 '18 at 11:16
@BugFinder That duplicate doesn't work when the exception is thrown by the framework itself. The OP cannot debug nor change that code — Camilo Terevinto, Jan 04 '18 at 11:18
@CamiloTerevinto you can still check that ctx (in this case) is not null, or trap for it — BugFinder, Jan 04 '18 at 11:20
@BugFinder The OP commented that the constructor call throws the error, not that `ctx` is null — Camilo Terevinto, Jan 04 '18 at 11:21
in which exactly line is the exception fired? maybe is here `result.GetUnderlyingObject()`? — Ferus7, Jan 04 '18 at 11:24
@Ferus7 at "using (PrincipalContext ctx = new PrincipalContext(ContextType.Domain, "ldap.forumsys.com:389", "dc=example,dc=com", "cn=read-only-admin,dc=example,dc=com", "password"))" — Simple Code, Jan 04 '18 at 11:25
@CamiloTerevinto actually he didnt until 1 min ago ... but you can still place a try loop round the whole thing. — BugFinder, Jan 04 '18 at 11:27
@BugFinder not really: "@Ferus7 It's throwing that exception on PrincipalContext constructor – Simple Code 13 mins ago" — Camilo Terevinto, Jan 04 '18 at 11:28
@SimpleCode It seems (from a .NET Core issue, though) that it can throw a NRE if the domain cannot be found. Can you post the full stack trace? — Camilo Terevinto, Jan 04 '18 at 11:29
Possible duplicate of [PrincipalContext - I Can't connect to a local openldap server](https://stackoverflow.com/questions/28988638/principalcontext-i-cant-connect-to-a-local-openldap-server) — Ferus7, Jan 04 '18 at 11:37
@CamiloTerevinto language doesn't make a difference in this case. — Fildor, Jan 04 '18 at 12:02
@CamiloTerevinto yes about 1 min before I posted that he had 1 min ago... However a try/catch round that whole thing would still be valid — BugFinder, Jan 04 '18 at 12:22

Ferus7 · Accepted Answer · 2018-01-04T11:42:33.507

4

As said here, the problem could be that you try to connect to an Apache Directory Studio with the class PrincipalContext that not supports this OpenLDAP,

so one way to go is using the DirectoryEntry class

edited Jan 04 '18 at 11:42

answered Jan 04 '18 at 11:41

Ferus7

707
1
10
23

DirectoryEntry entry = new DirectoryEntry("ldap.forumsys.com:389", "cn=gauss,ou=mathematicians,dc=example,dc=com", "password"); DirectorySearcher searcher = new DirectorySearcher(entry) { PageSize = int.MaxValue, Filter = "(&(objectClass=user)(objectCategory=person))" }; searcher.PropertiesToLoad.Add("mail"); var result1 = searcher.FindOne(); – Simple Code Jan 04 '18 at 11:42
It throws "Unknown error (0x80005000)" on FindOne() – Simple Code Jan 04 '18 at 11:43
it doesn't work like that, [check](https://msdn.microsoft.com/en-us/library/39zxbb5w(v=vs.110).aspx) – Ferus7 Jan 04 '18 at 11:44
Thanks a lot. I would appreciate your help to help me out finding out the reason for that exception – Simple Code Jan 04 '18 at 12:25
@SimpleCode still getting that exception? – Ferus7 Jan 04 '18 at 12:29
I have posted my answer using DirectoryEntry and it's working now – Simple Code Jan 04 '18 at 12:30
@SimpleCode perfect! If my question helped you resolving =>`Connecting to LDAP server throws NullReferenceException`, feel free to mark as the correct one, glad to help you – Ferus7 Jan 04 '18 at 12:31

Simple Code · Answer 2 · 2018-01-04T12:23:08.467

Using DirectoryEntry it works for me as following:

using (var searcher = new DirectorySearcher(new DirectoryEntry("LDAP://ldap.forumsys.com:389/dc=example,dc=com", "", "", AuthenticationTypes.None)))
{
    searcher.Filter = "((objectClass=person))";
    searcher.PropertiesToLoad.Add("mail");//email
    searcher.PropertiesToLoad.Add("givenName");//first name
    searcher.PropertiesToLoad.Add("sn"); //last name
    searcher.PropertiesToLoad.Add("telephoneNumber");
    searcher.PropertiesToLoad.Add("description");
    searcher.PropertiesToLoad.Add("memberOf"); // groups

    var activeDirectoryStaffs = searcher.FindAll();
    if (activeDirectoryStaffs != null)
    {
        for (int i = 0; i < activeDirectoryStaffs.Count; i++)
        {
            SearchResult result = activeDirectoryStaffs[i];
            var Email = result.Properties.Contains("mail") ? (string)result.Properties["mail"][0]:null;
            var Mobile = result.Properties.Contains("telephoneNumber") ? (string)result.Properties["telephoneNumber"][0] : null;
            var FirstName = result.Properties.Contains("givenName") ? (string)result.Properties["givenName"][0] : null;
            var LastName = result.Properties.Contains("sn") ? (string)result.Properties["sn"][0] : null;
            var Description = result.Properties.Contains("description") ? (string)result.Properties["description"][0] : null;

        }
    }
}

Connecting to LDAP server throws NullReferenceException

2 Answers2