Overriding ASP.NET combine behavior using a VirtualPathProvider

re: Overriding ASP.NET combine behavior using a VirtualPathProvider

Erling Paulsen — Mon, 28 Nov 2005 09:17:52 GMT

Hi David,
great post. I have a question; Can the VirtualPathProvider handle any type of file, or just the ones mapped in IIS to the Asp.Net runtime?

re: Overriding ASP.NET combine behavior using a VirtualPathProvider

Andrey Skvortsov — Mon, 28 Nov 2005 13:13:17 GMT

That's very interesting topic for me,particularly database driven part as you understand;-)
But I would like to know more about parser hooks in general-how INamingContainer control can get pre parsed content of itself for example?I mean if we have <c runat="server">....<%if(){%>...<%}%>...</c> I want to get raw text inside <c/>,before(or after) it will be processed by parser-control graph is not very useful in some cases.

Great post,keep it coming!

re: Overriding ASP.NET combine behavior using a VirtualPathProvider

Lynn — Tue, 29 Nov 2005 04:47:09 GMT

David, I really enjoy this feature a lot. I'm using the VirtualPathProvider with the file system, but in a slightly dffferent way. What I'm doing is creating structured content in Xml files and using the VirtualPathProvider for on-the-fly page declarative page composition. It works really we so far from a technical perspective, but I haven't had much chance to measure actual preformance. The best side effect is that the VPP allows for meaningful url names for dynamic files instead of using querystring variables - though this feature can be abused - and that inturn allows much better use of url authorization, and so on. There are a lot of really good wins here.

A couple of things to note:

1) Using a VirtualPathProvider and a default document doesn't work well in IIS 6 as it would require a default.aspx stub. Will this be resolved in IIS 7?

2) Calling Precompile.axd does not perform compilation on providers added to the site. Is this by design? (Seems like the right idea.)

3) Will IIS 7 have support for WinFs stores?

re: Overriding ASP.NET combine behavior using a VirtualPathProvider

Marc Fairorth — Tue, 29 Nov 2005 07:56:35 GMT

David, thanks for an excellent post, very valuable. Would a VPP be appropriate for someone considering an image management system -- i.e. store the images (.tiff) in a db instead on on a file store? Can you suggest some resources for learning more? Thanks!

re: Overriding ASP.NET combine behavior using a VirtualPathProvider

SomeNewKid — Tue, 29 Nov 2005 11:23:49 GMT

Thank you, David, for looking into the problem that I described on the ASP.NET forums.

The VirtualPathProvider does indeed allow me to override the way in which tilde-based paths are resolved in page directives, such as this:

<%@ Register TagPrefix="Test" TagName="ChildControl" Src="~/child.ascx" %>

The VirtualPathProvider does not, however, affect the way in which tilde-based paths are resolved for dynamically loaded user controls, such as this:

MyPlaceHolder.Controls.Add(LoadControl("~/child.ascx"));

To have the LoadControl method resolve tilde-based paths in the same way as Register directives requires that the page code-behind forcibly override this method:

public new Control LoadControl(string relativePath)
{
string newPath = relativePath;
string site = this.Request.QueryString["site"];
if (String.IsNullOrEmpty(site) == false)
{
newPath = VirtualPathUtility.ToAppRelative(newPath);
newPath = relativePath.Substring(1);
newPath = "~/PeeudoSites/" + site + newPath;
}
return base.LoadControl(newPath);
}

With the combination of a VirtualPathProvider and an updated base page class, an ASP.NET application can allow pseudo-sites (child sites) to work as though they were full sites.

Great stuff! Thanks, David!

re: Overriding ASP.NET combine behavior using a VirtualPathProvider

davidebb — Wed, 30 Nov 2005 00:24:25 GMT

Erling, the VPP only handles files that are handled by ASP.NET, since it is a part of the ASP.NET runtime. Note that you can star map all requests for a given application to go to ASP.NET: in the IIS configuration, add an entry in the Wildcard application maps pointing to aspnet_isapi.dll (full path).

re: Overriding ASP.NET combine behavior using a VirtualPathProvider

davidebb — Wed, 30 Nov 2005 00:59:25 GMT

Hi Lynn,

I'm not much of an expert on IIS7, so I'll let others answer #1 and #3. You might be able to get around #1 by mapping all request to ASP.NET (see my previous comment), and then use RewritePath to map the directory request to the default document yourself.

#2: note that precompile.axd no longer exists in the released product (we removed it because of security concerns). You can still do the equivalent from the command line using aspnet_compiler.exe. But to answer your question, precompilation does not work with VirtualPathProviders. I think it could have been made to work in theory, but there were some non-trivial issues, and scheduling made us decide not to support it

re: Overriding ASP.NET combine behavior using a VirtualPathProvider

davidebb — Wed, 30 Nov 2005 01:02:34 GMT

Hi Mark,

Yes, I think a VPP could work for your image store. Mostly, it will work well if you want your URL to look like they use a 'regular' directory structure instead of being based on quesry string params.

There may not be much in term of resources right now, though I'm hoping to write a more complete VPP sample at some point.

re: Overriding ASP.NET combine behavior using a VirtualPathProvider

davidebb — Wed, 30 Nov 2005 04:03:05 GMT

Hi Alister,

Glad that this solution is working for you!

You bring up a very good point about it not working for the LoadControl() case. Frankly, I think that this case should have been made to go through VPP.CombineVirtualPaths as well, but for whatever reason, we didn't do this (you could say it's a bug).

Your workaround will work, as long as LoadControl is called directly on your derived class (since LoadControl is not virtual). Also, you may need a similar override in a UserControl base class (since LoadControl lives on TemplateControl). Kind of a pain, but it least it gets you going!

re: Overriding ASP.NET combine behavior using a VirtualPathProvider

lynn — Wed, 30 Nov 2005 06:32:15 GMT

David, thanks for the heads up on the precompile.axd removal.I haven't gotten to the RTM yet.

re: Overriding ASP.NET combine behavior using a VirtualPathProvider

Alex — Tue, 13 Dec 2005 19:28:31 GMT

The idea of using it to retrieve pages from a database is very interesting and might work for a project that I'm discussing right now.

If we were to retrieve the pages directly from the db, one question I would have is about compilation and performance.

1) Will the page be compiled the first time it is retrieved from the DB or would it be recompiled every time?
2) When the page is compiling will other users of other pages also have to wait while the page compiles or will they be able to continue working with their pages while the newly retrieved pages compile.
3) Could the code-behind also be retrieved from the DB or just the ASPX page?

re: Overriding ASP.NET combine behavior using a VirtualPathProvider

davidebb — Thu, 22 Dec 2005 00:50:03 GMT

Alex,

1. Compiled pages are cached, and not recompiled unless your VPP indicates they are out of date.
2. Generally, ASP.NET only allows one compilation to happen at a time. However, other requests that don't require compilation won't be blocked.
3. Yes, the VPP applies to both the page and its code file.

re: Overriding ASP.NET combine behavior using a VirtualPathProvider

Jun Meng — Thu, 12 Jan 2006 17:20:52 GMT

Quick question:

Could you just set the virtual directory as "Application" in IIS? This way, you do not need any coding for "~/".

re: Overriding ASP.NET combine behavior using a VirtualPathProvider

Sharad Kumar — Sat, 21 Jan 2006 18:33:05 GMT

David,

Thanks loads for the post. I'm looking forward to utilize CombinePath approach for my following case:

1. Multiple Virtual WebSites, with different domains are pointing to same application. Through a HttpModule, I map to corresponding folders of websites based on their host. This allows me to simplify:
a. www.domain1.com/default.aspx >> to >> www.domain1.com/app_websites/domain1/default.aspx
b. www.domain2.com/default.aspx >> to >> www.domain2.com/app_websites/domain2/default.aspx

Above works absolutely fine with Context.RewritePath, functionally. Problem I'm facing is to base my Urls correctly to Theme resources, with respect to default.aspx which is in root (as in Url). Where does basing, w.r.t. Theme resources happen? How can make ../../App_Themes/Red/Style.css to /App_Themes/Red/Style.css w.r.t. /Default.aspx (virtual), which is actually inside domain folder?

Any help shall be greatly useful. Thanks.

-- Sharad

re: Overriding ASP.NET combine behavior using a VirtualPathProvider

davidebb — Tue, 24 Jan 2006 04:33:14 GMT

Jun,

Yes, you could certainly do this, but the premise here is that we want to be "running multiple sites under a single actual ASP.NET application". Why? Because it is much lighter weight than having multiple applications, so it can potentially scale to a very large number of apps.

David

re: Overriding ASP.NET combine behavior using a VirtualPathProvider

davidebb — Tue, 24 Jan 2006 04:41:29 GMT

Sharad,

Maybe one approach that would work is to star map all requests to ASP.NET in IIS, in order to have them all go through your HttpModule. From there you could then fix up the paths?

David

re: Overriding ASP.NET combine behavior using a VirtualPathProvider

Scott — Wed, 25 Jan 2006 17:26:21 GMT

David,

This is exactly what I needed. Thanks, and excellent work!

Understanding VirtualPath Provider and more

Jonathans Blog — Thu, 02 Mar 2006 17:55:17 GMT

So, in ASP.NET 2.0 we have this niftty feature that noone really understands called the Virtual Path...

Excluding directories from VPP

Ed — Thu, 16 Mar 2006 18:51:12 GMT

Hi,

This is a great feature for content management. I've got it working with my cms database to load content, but how do I exclude the directory containing the cms admin system itself?

www.mysite.com/mydir/page.aspx
Something like this loads fine from the db.

www.mysite.com/cms/default.aspx
This page doesn't exist in the database so is a 404. I need to somehow exclude /cms/ and all its children from the VPP so they can be served normally.
Any pointers would be greatly appreciated!

Cheers,

Ed

re: Excluding directories from VPP

davidebb — Thu, 16 Mar 2006 19:04:43 GMT

Hi Ed,

You should be able to exclude content by simply forwarding the calls to don't want to handle to 'Previous'. e.g. if you get a call to GetDirectory for your cms dir, just return Previous.GetDirectory(virtualDir).

David

re: Excluding directories from VPP

Ed — Thu, 16 Mar 2006 19:53:26 GMT

Hi David,

That doesn't seem to be working.
I haven't changed the GetDirectory method from Scott Guthrie's original example which returns Previous.GetDirectory(virtualDir) if the db access layer's file record data is null.
Any thoughts on how I could debug this would be great.

Cheers,

Ed

re: Excluding directories from VPP

Ed — Fri, 17 Mar 2006 00:01:06 GMT

Hi, found the problem. In the code sample I downloaded the FileExists and DirectoryExists methods were returning false when the file record data was null. These need to be changed to:

return Previous.FileExists(virtualPath);

and

return Previous.DirectoryExists(virtualDir);

Cheers,

Ed

re: Overriding ASP.NET combine behavior using a VirtualPathProvider

black — Fri, 28 Apr 2006 09:04:19 GMT

that's just what i want! great!

Sprite Builder - combine separate images into one sprite.

http://www.yaodownload.com/video-design/animationdesigntools/sprite-builder_animationdesigntools.htm

re: Overriding ASP.NET combine behavior using a VirtualPathProvider

bsmith — Fri, 28 Apr 2006 23:37:41 GMT

I have been looking for an article showing how to implement the VirtualPathProvider to pull Micorsoft Office Documents from a database. From what I have found so far, it is a little more involved. Any advice you could offer on this topic would be great.

Can this be used to share a directory between apps?

Jesse — Wed, 10 May 2006 21:48:52 GMT

I'm trying to do something different, but this seems like it might be the solution. Could I use VPP to let me share an "images" directory between two web apps? I.e.,

wwwroot/
app1/
app2/
images/

Where the "images/" part of the path gets dynamically rewritten to an absolute filesystem path (wwwroot/images) instead of an app-rooted path (appN/images)?

Or is there an easier way to do this?

re: Overriding ASP.NET combine behavior using a VirtualPathProvider

davidebb — Thu, 11 May 2006 02:59:31 GMT

Jesse, maybe an easier way to do this is to use NTFS junctions to make a single directory appear in multiple places. e.g. start by looking at this tools: http://www.sysinternals.com/Utilities/Junction.html

re: Overriding ASP.NET combine behavior using a VirtualPathProvider

Jesse — Thu, 11 May 2006 08:31:19 GMT

Thanks, David! That's *exactly* what I needed. Except that my problem's on a shared server, where I can't shell out to exe's. But I found a C# wrapper for the DFS API's: http://www.pinvoke.net/default.aspx/netapi32.NetDfsAdd

Hopefully, this will do the trick.

ASP.Net Virtual Theme Provider 1.0

Rory Primrose — Fri, 30 Jun 2006 02:14:55 GMT

ASP.Net 2.0&nbsp;is bundled with some great technology, especially what is available through the&nbsp;provider...

re: Overriding ASP.NET combine behavior using a VirtualPathProvider

Fabrice JEAN-FRANCOIS — Wed, 19 Jul 2006 20:05:18 GMT

Yo Guys,

I have found a way to register my VirtualPathProvider with the precompile option...

It's really easy with only 9 lines of code.

Why do I need this functionnality? Becoz I'm working in a bank that need to share its masterpage and that compels us to precompile and create a single assembly (aspnet_merge) with versioning for all our websites...

So, what is my secret ? Very easy. The answer is DynamicMethod. I call a Microsoft internal method to register my VirtualPathProvider.

Nevertheless, there are limitations. For exemple, i suppose it does not work for all situation (since Microsoft doesn't want us to precompile). Moreover, I am now dependent of the CLR version and implementation (Microsoft can still change its code without my permission :-D )

May the code be with you...

Using VirtualPathProvider and Server.MapPath??

ASP.NET - 25 Feet Below the Surface — Sun, 10 Dec 2006 12:35:45 GMT

Recently one of the engineers on my team (Amitkumar Sharma) got this issue reported by the customer where