thread-safety issue with webdav client library (and tip on connecting to Exchange 2K)

[Pete Heist]

Hello,

I am using Slide's WebDAV library to connect to Microsoft Exchange Server
2000. First of all, as a side note for those trying it be sure to upgrade to
service pack 1 of Exchange so that valid XML is generated in response to a
PROPFIND for all properties. Otherwise you won't be able to parse the XML
response to this query.

Nextly, there is an issue with thread-safety that appers to be in the Slide
WebDAV client library and is simple to reproduce. At the bottom of this
email is source code written to Slide 1.0.11 that causes the error. It
simply creates N number of threads to do a PROPFIND for all properties.
(This exerciser really doesn't need to connect to Exchange 2K- any WebDAV
server should be fine.) An example command line to run it with five threads
is as follows:

java ExchangeWebdavTest http://server/exchange/Mailbox/Inbox 5

Occasionally all five threads will succeed, but much of the time output will
be like:

-----
Making DAV Connection...
Making DAV Connection...
Making DAV Connection...
Making DAV Connection...
Making DAV Connection...
connect time = 3475
connect time = 4317
java.lang.NullPointerException
        at
org.apache.commons.httpclient.HttpMethodBase.generateRequestLine(HttpMethodB
ase.java:519)
        at
org.apache.commons.httpclient.HttpClient.sendRequestHeader(HttpClient.java:8
35)
        at
org.apache.commons.httpclient.HttpClient.executeMethod(HttpClient.java:422)
        at
org.apache.webdav.lib.WebdavResource.propfindMethod(WebdavResource.java:2388
)
        at
org.apache.webdav.lib.WebdavResource.propfindMethod(WebdavResource.java:2359
)
        at
ExchangeWebdavTest$ExchangeWebdavThread.run(ExchangeWebdavTest.java:110)
        at java.lang.Thread.run(Unknown Source)
-----

Looking at the source code for HttpMethodBase, it seems like the "state"
member variable is ending up null. It's almost as if these objects are
getting recycled before we finish using them. I would like to find and fix
this problem myself but it's unclear what revision of commons should be
pulled down to work with Slide 1.0.11 (there are no obvious tags in the
commons tree). Does anyone know what the issue could be? Or know how I can
get a buildable snapshot of the commons tree used as of the 1.0.11 Slide
release?

tx,
Pete

-----

/**
 *
 * Exchange 2K WebDAV test program. First argument is the URL to connect to
 * and second is the number of threads to create.
 *
 * @author      PHeist (07/01)
 */
public class    ExchangeWebdavTest
{

/**
 * Method description.
 *
 * @author      PHeist (07/01)
 */
public          ExchangeWebdavTest
(
)
    {
    }

/**
 * Main.
 *
 * @author      PHeist (07/01)
 */
public static   void    main
(
String[]        args
)
    {
    for (int i = 0; i < Integer.parseInt (args[1]); i++)
        {
        ExchangeWebdavTest test = new ExchangeWebdavTest();
        Thread thr = new Thread (test.new ExchangeWebdavThread (new String
(args[0])));
        thr.start ();
        }
    }

/**
 *
 * Exchange WebDAV thread.
 *
 * @author      PHeist (07/01)
 */
public class    ExchangeWebdavThread
implements      Runnable
{

private         String          i_sUrl;

/**
 * Constructor.
 *
 * @author      PHeist (07/01)
 */
public          ExchangeWebdavThread
(
String          sUrl
)
    {
    i_sUrl = sUrl;
    }

/**
 * Method description.
 *
 * @author      PHeist (07/101)
 */
public void     run
(
)
    {
    WebdavResource resource = null;

    try
        {
        System.out.println ("Making DAV Connection...");

        HttpURL url = new HttpURL (i_sUrl);
        url.setUserInfo ("CLUSTER\\PHeist", "pheist");

        long lStart = System.currentTimeMillis ();
        resource = new WebdavResource (url);

        Enumeration props = resource.propfindMethod(Integer.MAX_VALUE);

        int i = 0;
        while (props.hasMoreElements())
            {
            ResponseEntity entity = (ResponseEntity) props.nextElement();
            //System.out.println ((i++) + " (" + entity.getClass() + "): " +
entity);

            //System.out.println (i++);

            Enumeration responseProperties = entity.getProperties();
            while (responseProperties.hasMoreElements())
                {
                Property responseProp = (Property) responseProperties.nextElement();
                //System.out.println ("   " + responseProp.getName() + "| " +
                //    responseProp.getPropertyAsString());
                }
            }

        System.out.println ("connect time = " + (System.currentTimeMillis() -
lStart));
        }
    catch (Exception e)
        {
        e.printStackTrace ();
        }
    finally
        {
        if (null != resource)
            try
                {
                resource.close ();
                }
            catch (IOException ioe)
                {
                }
        }
    }

} // ExchangeWebdavThread

} // ExchangeWebdavTest