.NET autogenerated web-service client: How do I avoid requesting schemas from w3.org?

Question

I have a .NET web-service client that has been autogenerated from a wsdl-file using the wsdl.exe tool.

When I first instantiate the generated class, it begins to request a bunch of documents from w3.org and others. The first one being http://www.w3.org/2001/XMLSchema.dtd

Besides not wanting to cause unnecessary traffic to w3.org, I need to be able to run the application without a connection to the Internet (the web-service is a "Intra-web-service").

Anyone know the solution?

If it helps, here is the stacktrace I get when I do not have Internet:

"An error has occurred while opening external DTD 'http://www.w3.org/2001/XMLSchema.dtd': The remote name could not be resolved: 'www.w3.org'"

   at System.Net.HttpWebRequest.GetResponse()
   at System.Xml.XmlDownloadManager.GetNonFileStream(Uri uri, ICredentials credentials)
   at System.Xml.XmlDownloadManager.GetStream(Uri uri, ICredentials credentials)
   at System.Xml.XmlUrlResolver.GetEntity(Uri absoluteUri, String role, Type ofObjectToReturn)
   at System.Xml.XmlTextReaderImpl.OpenStream(Uri uri)
   at System.Xml.XmlTextReaderImpl.DtdParserProxy_PushExternalSubset(String systemId, String publicId)

   at System.Xml.XmlTextReaderImpl.Throw(Exception e)
   at System.Xml.XmlTextReaderImpl.DtdParserProxy_PushExternalSubset(String systemId, String publicId)
   at System.Xml.XmlTextReaderImpl.DtdParserProxy.System.Xml.IDtdParserAdapter.PushExternalSubset(String systemId, String publicId)
   at System.Xml.DtdParser.ParseExternalSubset()
   at System.Xml.DtdParser.ParseInDocumentDtd(Boolean saveInternalSubset)
   at System.Xml.DtdParser.Parse(Boolean saveInternalSubset)
   at System.Xml.XmlTextReaderImpl.DtdParserProxy.Parse(Boolean saveInternalSubset)
   at System.Xml.XmlTextReaderImpl.ParseDoctypeDecl()
   at System.Xml.XmlTextReaderImpl.ParseDocumentContent()
   at System.Xml.XmlTextReaderImpl.Read()
   at System.Xml.Schema.Parser.StartParsing(XmlReader reader, String targetNamespace)
   at System.Xml.Schema.Parser.Parse(XmlReader reader, String targetNamespace)
   at System.Xml.Schema.XmlSchemaSet.ParseSchema(String targetNamespace, XmlReader reader)
   at System.Xml.Schema.XmlSchemaSet.Add(String targetNamespace, XmlReader schemaDocument)
   at [...]WebServiceClientType..cctor() in [...]

Answer 1

I needed the XmlResolver, so tamberg's solution did not quite work. I solved it by implementing my own XmlResolver that read the necessary schemas from embedded resources instead of downloading them.

The problem did not have anything to do with the autogenerated code, by the way.

The web-service-client had another implementation file that contained something like this:

public partial class [...]WebServiceClientType
  {
    private static readonly XmlSchemaSet _schema;

    static KeyImportFileType()
    {
      _schema = new XmlSchemaSet();
      _schema.Add(null, XmlResourceResolver.GetXmlReader("http://www.w3.org/TR/2002/REC-xmldsig-core-20020212/xmldsig-core-schema.xsd"));
      _schema.Add(null, XmlResourceResolver.GetXmlReader("http://www.w3.org/TR/2002/REC-xmlenc-core-20021210/xenc-schema.xsd"));
      _schema.Compile();
    }

and it was this class-constructor that failed.

Answer 2

if you have access to the XmlReader (or XmlTextReader) you can do the following:

XmlReader r = ...
r.XmlResolver = null; // prevent xsd or dtd parsing

Regards, tamberg

Answer 3

Here's my solution. I hope it saves someone from having to debug through the .NET framework like I had to to work out the underpinnings of XmlUrlResolver. It will either load from a local resource (resx text file), cache, or use XmlUrlResolver default behavior:

using System;
using System.Text;
using System.Text.RegularExpressions;
using System.Xml;
using System.Net;
using System.Net.Cache;
using System.IO;
using System.Resources;

namespace AxureExport {

    //
    // redirect URL resolution to local resource (or cache)
    public class XmlCustomResolver : XmlUrlResolver {

        ICredentials _credentials;
        ResourceManager _resourceManager;

        public enum ResolverType { useDefault, useCache, useResource };
        ResolverType _resolverType;

        public XmlCustomResolver(ResolverType rt, ResourceManager rm = null) {
            _resourceManager = rm != null ? rm : AxureExport.Properties.Resources.ResourceManager;
            _resolverType = rt;
        }

        public override ICredentials Credentials {
            set {
                _credentials = value;
                base.Credentials = value;
            }
        }

        public override object GetEntity(Uri absoluteUri, string role, Type ofObjectToReturn) {
            object response = null;

            if (absoluteUri == null)
                throw new ArgumentNullException(@"absoluteUri");

            switch (_resolverType) {
                default:
                case ResolverType.useDefault:                   // use the default behavior of the XmlUrlResolver
                    response = defaultResponse(absoluteUri, role, ofObjectToReturn);
                    break;

                case ResolverType.useCache:                     // resolve resources thru cache
                    if (!isExternalRequest(absoluteUri, ofObjectToReturn)) {
                        response = defaultResponse(absoluteUri, role, ofObjectToReturn);
                        break;
                    }

                    WebRequest webReq = WebRequest.Create(absoluteUri);
                    webReq.CachePolicy = new HttpRequestCachePolicy(HttpRequestCacheLevel.Default);
                    if (_credentials != null)
                        webReq.Credentials = _credentials;

                    WebResponse wr = webReq.GetResponse();
                    response = wr.GetResponseStream();
                    break;

                case ResolverType.useResource:                  // get resource from internal resource
                    if (!isExternalRequest(absoluteUri, ofObjectToReturn)) {
                        response = defaultResponse(absoluteUri, role, ofObjectToReturn);    // not an external request
                        break;
                    }

                    string resourceName = uriToResourceKey(absoluteUri);
                    object resource = _resourceManager.GetObject(resourceName);
                    if (resource == null)
                        throw new ArgumentException(@"Resource not found.  Uri=" + absoluteUri + @" Local resourceName=" + resourceName);

                    if (resource.GetType() != typeof(System.String))
                        throw new ArgumentException(resourceName + @" is an unexpected resource type.  (Are you setting resource FileType=Text?)");

                    response = ObjectToUTF8Stream(resource);
                    break;
            }

            return response;
        }

        //
        // convert object to stream
        private static object ObjectToUTF8Stream(object o) {
            MemoryStream stream = new MemoryStream();

            StreamWriter writer = new StreamWriter(stream, Encoding.UTF8);
            writer.Write(o);
            writer.Flush();
            stream.Position = 0;

            return stream;
        }

        //
        // default response is to call tbe base resolver
        private object defaultResponse(Uri absoluteUri, string role, Type ofObjectToReturn) {
            return base.GetEntity(absoluteUri, role, ofObjectToReturn);
        }

        //
        // determine whether this is an external request
        private static bool isExternalRequest(Uri absoluteUri, Type ofObjectToReturn) {
            return absoluteUri.Scheme == @"http" && (ofObjectToReturn == null || ofObjectToReturn == typeof(Stream));
        }

        //
        // translate uri to format compatible with reource manager key naming rules
        // see: System.Resources.Tools.StronglyTypedResourceBuilder.VerifyResourceName Method
        //   from http://msdn.microsoft.com/en-us/library/ms145952.aspx:
        private static string uriToResourceKey(Uri absoluteUri) {
            const string repl = @"[ \xA0\.\,\;\|\~\@\#\%\^\&\*\+\-\/\\\<\>\?\[\]\(\)\{\}\" + "\"" + @"\'\:\!]+";
            return Regex.Replace(Path.GetFileNameWithoutExtension(absoluteUri.LocalPath), repl, @"_");
        }
    }
}

Answer 4

Thanks Tamberg, you saved me a great deal of time with your succinct and correct answer. I didn't realise the default resolver would go to the web. Checking MSDN is states -

XmlResolver is the default resolver for all classes in the System.Xml namespace. You can also create your own resolver...

I've implemented your answer, setting the resolver to NULL which solves the problem and reduces the network overhead.

XmlReader r = ...r.XmlResolver = null; // prevent xsd or dtd parsing

Thanks again, Andy