How-to create, get, update, and delete a UW Groups Web Service resource with .NET

Purpose of document

• This document provides sample .NET code to create, get, update, and delete a UW Groups web service resource
• It does not provide an example of how to modify the membership, though this should be fairly straightforward once you have the .NET code and read the Groups Service API v2.

Alternatives

• The forthcoming ASP.NET 3.5 Extensions offers a .NET web client for consuming RESTful web resources. This library makes querying and updating web resources behave like other LINQ operations, and may be of interest.

Requirements

• .NET 2.0/3.0/3.5
• UWCA certificate, that has been authorized to the UW Groups Web Service
• UW Groups web service v1

Refer to Groups Service API v2 to understand the resources.

The steps below outline what you need to do to get and parse the XHTML from a group resource.

To see how to create, update, and delete, please download the following Visual Studio .NET 2008 C# solution. That solution also contains a simple RESTful client which is used in the test code.

1. Include namespaces

   using System.Security.Cryptography.X509Certificates;
   using System.Web;
   using System.Net;
   using System.Xml;
   using System.IO;
   

2. Construct the URI

   string uri = "https://iam-ws.u.washington.edu:7443/group_sws/v2/group/u_nebula_gca";
   

3. Create a GET request

   HttpWebRequest _request = (HttpWebRequest)HttpWebRequest.Create(uri);
   _request.AllowAutoRedirect = true;
   _request.Method = "GET";
   

4. Find the certificate in the certificate store

   If you get a runtime exception stating "The request was aborted: Could not create SSL/TLS secure channel." this is is usually related to permissions on the private key (or lack of private key) in the Windows certificate store. See Certificates and Private Key Permissions for tips and tools on investigating further.

   string subject = "[MyCertificateSubjectName]";
   X509Certificate cert = null;
   
   X509Store store = new X509Store(StoreName.My, StoreLocation.LocalMachine);
   store.Open(OpenFlags.ReadOnly);
   X509Certificate2Collection col =
          store.Certificates.Find(X509FindType.FindBySubjectName,
                          subject, true);
   try {
       cert = col[0];
   }
   catch (Exception ex) {
       throw new Exception(String.Format("Certificate '{0}' not found", subject), ex);
   }
   
    

5. Attach the certificate

   _request.ClientCertificates.Add(_cert);
   

6. Get the response, and cast it to a HttpWebResponse
   
   If the HttpWebRequest encounters an error accessing the resource (HttpStatusCode > 200), it throws a WebException
   To be able to determine what kind of error happened, it is neccessary to handle that exception, retrieve
   the WebResponse object, cast it to an HttpWebResponse, and inspect the HttpStatusCode

   WebResponse webResponse = null;
   HttpWebResponse _response = null;
   
   try {
       webResponse = request.GetResponse();
       _response = (HttpWebResponse)webResponse;
   }
   catch (WebException ex) {
       webResponse = ex.Response;
       _response = (HttpWebResponse)webResponse;
   }
   

7. Handle any exceptional status codes

   if (_response.HttpStatusCode > 200) {
   // if the server was busy, wait and try again
   // was there a redirect?
   ...
   }
   

8. Load the response stream into an XmlDocument object

   XmlDocument xmlDoc = null;
   using (Stream responseStream = _response.GetResponseStream()) {
       xmlDoc = new XmlDocument();
       xmlDoc.Load(responseStream);
   }
   

9. Retrieve values from the XmlDocument using xPath query

   // in order to do xPath, we need to add any namespaces from the xhtml document with prefixes
   XmlNamespaceManager nsmgr = new XmlNamespaceManager(xmlDoc.NameTable);
   nsmgr.AddNamespace(String.Empty, "http://www.w3.org/1999/xhtml");
   nsmgr.AddNamespace("t", "http://www.w3.org/1999/xhtml");
   
   // Regid
   XmlElement regidEl = (XmlElement)xmlDoc.SelectSingleNode("//t:*[@class='regid']", nsmgr);
   this.Regid = regidEl.InnerText;
   
   // Description
   XmlElement descEl = (XmlElement)xmlDoc.SelectSingleNode("//t:*[@class='description']", nsmgr);
   if (descEl != null) {
       this.Description = descEl.InnerText;
   }
   
   // Names
   this.Names = null;
   XmlNodeList nameList = (XmlNodeList)xmlDoc.SelectNodes("//t:*[@class='name']", nsmgr);
   foreach (XmlElement nameEl in nameList) {
       this.Names.Add(nameEl.InnerText);
   }
   

Resources

• Groups Service API v2