Running Exchange EWS on Mono LdapException

Question

I'm trying to experiment with using Exchange EWS 2 on debian via Mono (Version 2.10.8.1 & 3.0.6) I'm developing on windows 8 using vs2012.

The program works just fine on windows and i get the expected output.

On mono however I keep getting the following output and exception.

<Trace Tag="AutodiscoverConfiguration" Tid="1" Time="2013-03-07 19:09:05Z">
Starting SCP lookup for domainName='example.com', root path=''
</Trace>
Connect Error

Unhandled Exception: LdapException: (91) Connect Error
System.Net.Sockets.SocketException: No such host is known
  at System.Net.Dns.hostent_to_IPHostEntry (System.String h_name, System.String[]          h_aliases, System.String[] h_addrlist) [0x00000] in <filename unknown>:0
  at System.Net.Dns.GetHostByName (System.String hostName) [0x00000] in <filename unknown>:0
  at System.Net.Dns.GetHostEntry (System.String hostNameOrAddress) [0x00000] in <filename unknown>:0
  at System.Net.Dns.GetHostAddresses (System.String hostNameOrAddress) [0x00000] in <filename unknown>:0
  at System.Net.Sockets.TcpClient.Connect (System.String hostname, Int32 port) [0x00000] in <filename unknown>:0
  at System.Net.Sockets.TcpClient..ctor (System.String hostname, Int32 port) [0x00000] in <filename unknown>:0
  at Novell.Directory.Ldap.Connection.connect (System.String host, Int32 port, Int32 semaphoreId) [0x00000] in <filename unknown>:0
[ERROR] FATAL UNHANDLED EXCEPTION: LdapException: (91) Connect Error
System.Net.Sockets.SocketException: No such host is known
  at System.Net.Dns.hostent_to_IPHostEntry (System.String h_name, System.String[] h_aliases, System.String[] h_addrlist) [0x00000] in <filename unknown>:0
  at System.Net.Dns.GetHostByName (System.String hostName) [0x00000] in <filename unknown>:0
  at System.Net.Dns.GetHostEntry (System.String hostNameOrAddress) [0x00000] in <filename unknown>:0
  at System.Net.Dns.GetHostAddresses (System.String hostNameOrAddress) [0x00000] in <filename unknown>:0
  at System.Net.Sockets.TcpClient.Connect (System.String hostname, Int32 port) [0x00000] in <filename unknown>:0
  at System.Net.Sockets.TcpClient..ctor (System.String hostname, Int32 port) [0x00000] in <filename unknown>:0
  at Novell.Directory.Ldap.Connection.connect (System.String host, Int32 port, Int32 semaphoreId) [0x00000] in <filename unknown>:0

Apparently it is attempting to look up a host which it can't find. Both my windows and linux systems are using the same dns server so it isn't that causing the problem.

I read through the trace on windows when it works - and the trace shows that the lookups fail a few times and the autodiscover method tries a few different urls until it hits on one that works - on mono however it seems to fall over after the first failure and that's the end of it.

I've tried googling for using ews on mono but i haven't found anyone who is doing it so i'm not really sure what else to try.

The code used is below - pretty much all of it is taken from code examples on http://msdn.microsoft.com/en-us/library/exchange/dd633709(v=exchg.80).aspx

class Program
{
    private static int verbose = 10;
    private static string loginEmail = "[email protected]";
    private static string password = "#############";

    static void Main(string[] args)
    {
        try
        {

            ServicePointManager.ServerCertificateValidationCallback = CertificateValidationCallBack;

            ExchangeService service = new ExchangeService(ExchangeVersion.Exchange2010_SP2);

            service.Credentials = new WebCredentials(loginEmail, password);

            if (verbose >= 10)
            {

                service.TraceEnabled = true;
                service.TraceFlags = TraceFlags.All;

            }

            service.AutodiscoverUrl(loginEmail, RedirectionUrlValidationCallback);

            Console.WriteLine("AutoDiscover Completed");

            getContacts(service);

            Console.ReadLine();

        }
        catch (Exception e) {
            Console.WriteLine(e.Message);
            foreach (string key in e.Data.Keys)
            {
                Console.WriteLine(String.Format("{0}: {1}",key, e.Data[key]));
            }
            throw e;
        }

    }

    private static void getContacts(ExchangeService service){


        // Get the number of items in the Contacts folder.
        ContactsFolder contactsfolder = ContactsFolder.Bind(service, WellKnownFolderName.Contacts);

        // Set the number of items to the number of items in the Contacts folder or 1000, whichever is smaller.
        int numItems = contactsfolder.TotalCount < 1000 ? contactsfolder.TotalCount : 1000;

        // Instantiate the item view with the number of items to retrieve from the Contacts folder.
        ItemView view = new ItemView(numItems);

        // To keep the request smaller, request only the display name property.
        //view.PropertySet = new PropertySet(BasePropertySet.IdOnly, ContactSchema.DisplayName);

        // Retrieve the items in the Contacts folder that have the properties that you selected.
        FindItemsResults<Item> contactItems = service.FindItems(WellKnownFolderName.Contacts, view);

        // Display the list of contacts. 
        foreach (Item item in contactItems)
        {
            if (item is Contact)
            {
                Contact contact = item as Contact;

                Console.WriteLine();
                Console.WriteLine(contact.DisplayName);
                if (verbose >= 2)
                {
                    Console.WriteLine("    " + contact.Id);
                }

                try
                {
                    Console.WriteLine("    " + contact.EmailAddresses[EmailAddressKey.EmailAddress1].ToString());
                }
                catch (Exception e) 
                {
                    if (verbose >= 5)
                    {
                        Console.WriteLine("    " + "Email Address 1 Not Available : " + e.Message);
                    }
                }
            }
        }

    }

    #region taken from tutorial

    private static bool CertificateValidationCallBack(
        object sender,
        System.Security.Cryptography.X509Certificates.X509Certificate certificate,
        System.Security.Cryptography.X509Certificates.X509Chain chain,
        System.Net.Security.SslPolicyErrors sslPolicyErrors)
    {
        // If the certificate is a valid, signed certificate, return true.
        if (sslPolicyErrors == System.Net.Security.SslPolicyErrors.None)
        {
            return true;
        }

        // If there are errors in the certificate chain, look at each error to determine the cause.
        if ((sslPolicyErrors & System.Net.Security.SslPolicyErrors.RemoteCertificateChainErrors) != 0)
        {
            if (chain != null && chain.ChainStatus != null)
            {
                foreach (System.Security.Cryptography.X509Certificates.X509ChainStatus status in chain.ChainStatus)
                {
                    if ((certificate.Subject == certificate.Issuer) &&
                       (status.Status == System.Security.Cryptography.X509Certificates.X509ChainStatusFlags.UntrustedRoot))
                    {
                        // Self-signed certificates with an untrusted root are valid. 
                        continue;
                    }
                    else
                    {
                        if (status.Status != System.Security.Cryptography.X509Certificates.X509ChainStatusFlags.NoError)
                        {
                            // If there are any other errors in the certificate chain, the certificate is invalid,
                            // so the method returns false.
                            return false;
                        }
                    }
                }
            }

            // When processing reaches this line, the only errors in the certificate chain are 
            // untrusted root errors for self-signed certificates. These certificates are valid
            // for default Exchange server installations, so return true.
            return true;
        }
        else
        {
            // In all other cases, return false.
            return false;
        }
    }

    private static bool RedirectionUrlValidationCallback(string redirectionUrl)
    {
        // The default for the validation callback is to reject the URL.
        bool result = false;

        Uri redirectionUri = new Uri(redirectionUrl);

        // Validate the contents of the redirection URL. In this simple validation
        // callback, the redirection URL is considered valid if it is using HTTPS
        // to encrypt the authentication credentials. 
        if (redirectionUri.Scheme == "https")
        {
            result = true;
        }
        return result;
    }

    #endregion

}

---

The answer from BeepBeep helped me to solve this.

After using BeepBeep's suggestion i then had a problem that Mono appeared not to have dnsapi.dll (according to the exceptions). I resolved this by skipping autodiscover for now.

In order to do that, i replaced

service.AutodiscoverUrl(loginEmail, RedirectionUrlValidationCallback);

with

service.Url = new Uri("https://blah.com/ews/exchange.asmx");

Then I had an error with the certificate (the exception said something like 'error with request or decryption') - suffice to say, you need to know that mono doesn't include any root ca certificates by default, more info here: Mono FAQ about Security

I chose the lazier way to get the certs i wanted, using mozroots tool. This however did not work as expected and the error persisted.

I then used the tlstest also from the above FAQ to determine the problem - it was related to the certificate chain i was using (the root was accepted, but the intermediate was not being accepted). I then used the third tool documented in the FAQ (certmgr) to install the certificates.

Following that, it all works.

Answer 1

Same problem and solved using this code :

ExchangeService service = new ExchangeService();
service.EnableScpLookup = false;