Question

I’m trying to implement storing an Azure web site’s Themes in the Azure CDN.

I’ve copied the files into the CDN retaining the folder structure as it was in the original App_Themes folder.

I’ve created a VirtualPathProvider and the necessary Virtualdirectory and VirtualFile classes. The provider is registered in global.asax.

My problem is that the only file that seems to come from the CDN is the skin file. All the images, css etc are still refernced as if they are in the standard App_Themes structure. If I put a break point in my code then my VirtualTheme’s Open method is only ever called for the skin file.

Has anyone managed to implement a solution like this?

Any ideas what I’m doing wrong?

[AspNetHostingPermission(SecurityAction.Demand, Level = AspNetHostingPermissionLevel.Medium)]
[AspNetHostingPermission(SecurityAction.InheritanceDemand, Level = AspNetHostingPermissionLevel.High)]
public class RedirectAppThemes : VirtualPathProvider
{

    private bool IsPathVirtual(string virtualPath)
    {
        String checkPath = VirtualPathUtility.ToAppRelative(virtualPath);
        return checkPath.StartsWith("~/App_Themes/", StringComparison.InvariantCultureIgnoreCase);
    }

    public override bool FileExists(string virtualPath)
    {
        if (IsPathVirtual(virtualPath))
        {
            VirtualThemeFile file = new VirtualThemeFile(virtualPath);
            return file.Exists;
        }
        else
        {
            return Previous.FileExists(virtualPath);
        }
    }

    public override VirtualFile GetFile(string virtualPath)
    {
        if (IsPathVirtual(virtualPath))
        {
            return new VirtualThemeFile(virtualPath);
        }
        else
        {
            return Previous.GetFile(virtualPath);
        }
    }

    public override bool DirectoryExists(string virtualDir)
    {
        if (IsPathVirtual(virtualDir))
        {
            VirtualThemeDirectory dir = new VirtualThemeDirectory(virtualDir);
            return dir.Exists;
        }
        else
        {
            return Previous.DirectoryExists(virtualDir);
        }
    }

    public override VirtualDirectory GetDirectory(string virtualDir)
    {
        if (IsPathVirtual(virtualDir))
        {
            return new VirtualThemeDirectory(virtualDir);
        }
        else
        {
            return Previous.GetDirectory(virtualDir);
        }
    }

    public override CacheDependency GetCacheDependency(string virtualPath, IEnumerable virtualPathDependencies, DateTime utcStart)
    {
        if (IsPathVirtual(virtualPath))
        {
            return null;
        }
        else
        {
            return Previous.GetCacheDependency(virtualPath, virtualPathDependencies, utcStart);
        }
    }


}

 [AspNetHostingPermission(SecurityAction.Demand, Level = AspNetHostingPermissionLevel.Minimal)]
[AspNetHostingPermission(SecurityAction.InheritanceDemand, Level = AspNetHostingPermissionLevel.Minimal)]
public class VirtualThemeDirectory : VirtualDirectory
{
    private string cdnPath = "http://xxxxxxxxx.blob.core.windows.net/";

    public VirtualThemeDirectory(string virtualPath) : base(virtualPath)
    {
    }

    public override IEnumerable Children
    {
        get
        {
            List<object> children = new List<object>();

            string dir = this.VirtualPath.Replace("/App_Themes/", String.Empty);
            CloudBlobClient client = new CloudBlobClient(cdnPath);

            var blobs = client.ListBlobsWithPrefix(@"webinterfacethemes/" + dir );

            foreach (CloudBlobDirectory directory in blobs.OfType<CloudBlobDirectory>())
            {
                VirtualThemeDirectory vtd = new VirtualThemeDirectory(directory.Uri.AbsolutePath.Replace("/webinterfacethemes/", "/App_Themes/"));
                children.Add(vtd);
            }
            foreach (CloudBlob file in blobs.OfType<CloudBlob>())
            {
                VirtualThemeFile vtf = new VirtualThemeFile(file.Uri.AbsolutePath.Replace("/webinterfacethemes/", "/App_Themes/"));
                children.Add(vtf);
            }                

            return children;
        }
    }

    public override IEnumerable Directories
    {
        get
        {
            List<object> children = new List<object>();

            string dir = this.VirtualPath.Replace("/App_Themes/", String.Empty);
            CloudBlobClient client = new CloudBlobClient(cdnPath);

            var blobs = client.ListBlobsWithPrefix(@"webinterfacethemes/" + dir);

            foreach (CloudBlobDirectory directory in blobs.OfType<CloudBlobDirectory>())
            {
                VirtualThemeDirectory vtd = new VirtualThemeDirectory(directory.Uri.AbsolutePath.Replace("/webinterfacethemes/", "/App_Themes/"));
                children.Add(vtd);
            }

            return children;
        }
    }

    public override IEnumerable Files
    {
        get
        {
            List<object> children = new List<object>();

            string dir = this.VirtualPath.Replace("/App_Themes/", String.Empty);
            CloudBlobClient client = new CloudBlobClient(cdnPath);

            var blobs = client.ListBlobsWithPrefix(@"webinterfacethemes/" + dir);

            foreach (CloudBlob file in blobs.OfType<CloudBlob>())
            {
                VirtualThemeFile vtf = new VirtualThemeFile(file.Uri.AbsolutePath.Replace("/webinterfacethemes/", "/App_Themes/"));
                children.Add(vtf);
            }

            return children;
        }
    }

    public bool Exists
    {
        get
        {
            string dir = this.VirtualPath.Replace("/App_Themes/", String.Empty);
            CloudBlobClient client = new CloudBlobClient(cdnPath);

            if (client.ListBlobsWithPrefix("webinterfacethemes/" + dir).Count() > 0)
                return true;
            else
                return false;

        }
    }
}

[AspNetHostingPermission(SecurityAction.Demand, Level = AspNetHostingPermissionLevel.Minimal)]
[AspNetHostingPermission(SecurityAction.InheritanceDemand, Level = AspNetHostingPermissionLevel.Minimal)]
public class VirtualThemeFile : VirtualFile
{
    private string cdnPath = "http://xxxxxxx.vo.msecnd.net/webinterfacethemes/";

    public VirtualThemeFile(string VirtualPath) : base(VirtualPath)
    {

    }

    public override Stream Open()
    {
        string url = this.VirtualPath.Replace("/App_Themes/", cdnPath);
        HttpWebRequest myReq = (HttpWebRequest)WebRequest.Create(url);
        WebResponse myResp = myReq.GetResponse();
        Stream stream = myResp.GetResponseStream();
        return stream;
    }

    public bool Exists
    {
        get
        {
            //Check if the file exists
            //do this with a HEAD only request so we don't download the whole file
            string url = this.VirtualPath.Replace("/App_Themes/", cdnPath);
            HttpWebRequest myReq = (HttpWebRequest)WebRequest.Create(url);
            myReq.Method = "HEAD";
            HttpWebResponse myResp = (HttpWebResponse)myReq.GetResponse();
            if (myResp.StatusCode == HttpStatusCode.OK)
            {
                return true;
            }
            else
            {
                return false;
            }
        }
    }
}

And in Global.asax Application_start:

RedirectAppThemes redirect = new RedirectAppThemes();
        HostingEnvironment.RegisterVirtualPathProvider(redirect);

Answer 1

Mucho Googling eventually found this similar problem

I’ve added the following to my web.config inside the <system.webServer> tags and now the image and css files are calling the methods in my code.

<handlers>
  <add name="Images" path="*.png" verb="GET,HEAD,POST" type="System.Web.StaticFileHandler" modules="ManagedPipelineHandler" resourceType="Unspecified" />
  <add name="Stylesheets" path="*.css" verb="GET,HEAD,POST" type="System.Web.StaticFileHandler" modules="ManagedPipelineHandler" resourceType="Unspecified" />
</handlers>

If anyone is looking for a complete solution to putting their Themes in the CDN using this method I’ve also changed the following from the original code posted above and it now works:

the VirtualFile class is as follows:

[AspNetHostingPermission(SecurityAction.Demand, Level = AspNetHostingPermissionLevel.Minimal)]
[AspNetHostingPermission(SecurityAction.InheritanceDemand, Level = AspNetHostingPermissionLevel.Minimal)]
public class VirtualThemeFile : VirtualFile
{
    private string cdnPath = "https://xxxxxx.vo.msecnd.net/webinterfacethemes/";
    private string blobURL;

    public VirtualThemeFile(string VirtualPath) : base(VirtualPath)
    {
        blobURL = this.VirtualPath.Replace("/App_Themes/", cdnPath);
    }

    public override Stream Open()
    {
        CloudBlobClient client = new CloudBlobClient(cdnPath);
        CloudBlob blob = client.GetBlobReference(blobURL);
        MemoryStream stream = new MemoryStream();
        blob.DownloadToStream(stream);
        stream.Seek(0, SeekOrigin.Begin);
        return stream;
    }

    public bool Exists
    {
        get
        {
            CloudBlobClient client = new CloudBlobClient(cdnPath);
            CloudBlob blob = client.GetBlobReference(blobURL);
            try
            {
                blob.FetchAttributes();
                return true;
            }
            catch (StorageClientException e)
            {
                if (e.ErrorCode == StorageErrorCode.ResourceNotFound)
                {
                    return false;
                }
                else
                {
                    throw;
                }
            }
        }
    }
}

And I’ve changed my global.asax code so that the VirtualPathProvider is invoked if the site is pre-compiled:

HostingEnvironment hostingEnvironmentInstance = (HostingEnvironment)typeof(HostingEnvironment).InvokeMember("_theHostingEnvironment", BindingFlags.NonPublic | BindingFlags.Static | BindingFlags.GetField, null, null, null);
        MethodInfo mi = typeof(HostingEnvironment).GetMethod("RegisterVirtualPathProviderInternal", BindingFlags.NonPublic | BindingFlags.Static);
        mi.Invoke(hostingEnvironmentInstance, new object[] { new RedirectAppThemes() });