I researched the issue and discovered that XDocument and XmlDocument can slow down during parsing when the document references one or more DTDs. Disabling DTDs wasn't an option for me so I played around a little and found that caching the DTDs locally gave me the performance I was looking for. It went from taking a little over 8 seconds to load to taking a little under a half a second (that's a bit of a difference).
When I took a look at the directory where I was putting these cached files I was surprised to find 41 files (DTDs, files the DTDs reference, etc...)!
The code for this solution is as follows:
// I hereby place this code in the public domain.
public class CachedXmlResolver : XmlUrlResolver
{
public static Dictionary<Uri, String> cache = new Dictionary<Uri, String>();
public const string Prefix = /* Directory for storing the cached files. */;
public override object GetEntity(Uri absoluteUri, string role, Type ofObjectToReturn)
{
if (!cache.ContainsKey(absoluteUri))
if (!doCache(absoluteUri))
return base.GetEntity(absoluteUri, role, ofObjectToReturn);
return new FileStream(cache[absoluteUri], FileMode.Open, FileAccess.Read, FileShare.Read);
}
private void addCache(Uri uri, string path)
{
if (cache.ContainsKey(uri))
cache[uri] = path;
else
cache.Add(uri, path);
}
private bool doCache(Uri absoluteUri)
{
try
{
string strUri = absoluteUri.ToString();
if (strUri.StartsWith("http://"))
{
int lindex = strUri.LastIndexOf('/');
string fname = Prefix + strUri.Substring(lindex + 1);
if (!File.Exists(fname))
{
WebRequest request = WebRequest.Create(absoluteUri);
WebResponse response = request.GetResponse();
Stream str = response.GetResponseStream();
byte[] buffer = new byte[8192];
Stream outs = new FileStream(fname, FileMode.Create, FileAccess.Write);
int count = 0;
while ((count = str.Read(buffer, 0, buffer.Length)) > 0)
outs.Write(buffer, 0, count);
outs.Flush();
outs.Close();
}
addCache(absoluteUri, fname);
return true;
}
}
catch { }
return false;
}
}
Using the fix is really simple:
XmlReaderSettings settings = new XmlReaderSettings();
settings.XmlResolver = new CachedXmlResolver();
XmlReader reader = XmlReader.Create(/* WEB SERVICE RESPONSE STREAM HERE */, settings);
XDocument xml = XDocument.Load(reader);NOTE: I had to manually cache (and hard-code the 'addCache' calls in the constructor) for the following:
- "-/W3C/DTD XHTML 1.0 Strict/EN" -> "xhtml1-strict.dtd"
- "-/W3C XHTML 1.0 Transitional/EN" -> "xhtml1-transitional.dtd"
- "-/W3C/DTD XHTML 1.0 Transitional/EN" -> "xhtml1-transitional.dtd"
- "-/W3C XHTML 1.0 Frameset/EN" -> "xhtml1-frameset.dtd"
- "-/W3C/DTD XHTML 1.1/EN" -> "xhtml11.dtd"
- "-/W3C/DTD XHTML 1.1/xhtml11-model-1.mod" -> "xhtml11-model-1.mod"
If you want to know more about 'XmlResolver' you can always check MSDN. Hope this helps someone!
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