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How to give URL for a file stored in app_data folder in asp.net

I have a zip file stored in app_data folder .I want to give the path ofthat file as URL for a hyperlink.How to assign it
Server.Mappath(~/App_Data/Test.zip) will give the physical location as D:/Projects/Mnv/App_Data/Test.zip , but i want to give it as URL like http://..../test.zip, so user can download

You should not use App_Data available to the users.
This is a special folder used to store internal data only (XML, sdf, etc..).
By default, this folder is not even available via Http.
Yo can create an Action in your Asp.Net MVC and use it to retun some file from this folder. A direct download, however, it is not recommended.

Translate known physical path into virtual path

I want to take files from a known location on disk and have ASP redirect to them from code-behind, allowing the browser/app/device to control how the content is displayed.
I tried using:
Server.Redirect(pathToFile);
But got the following exception: Invalid path for child request 'C:\ContentFolder\testImage.png'. A virtual path is expected.
How can I allow my site to redirect users to these files? I am storing the base directory in the web config, and the file names are stored in a database.

If the files reside outside of your website directory you can't redirect to them. Think about the security implications if that was possible. You have a few options
Move the files inside the website directory (or a sub-directory of it). Then you can redirect your users to them using a virtual path e.g. Server.Redirect("~/files/somefile.zip").
Set up a virtual directory in IIS that maps to the physical location of the files on disk. Then you can redirect to them using the virtual path. You can do this through the GUI or config file.
Create a HttpHandler that loads the file from disk and returns them in the response. You can use a querystring to identify the file to load e.g. /filehandler.ashx?filename=somefile.zip. A quick google revealed this example.

Unable to access images stored inside my App_Data folder

I have the following link inside my asp.net mvc web application :-
#Model.Name
But when I click on this link, I get the following error :
HTTP Error 404.8 - Not Found
The request filtering module is configured to deny a path in the URL that contains a hiddenSegment section.
So what is causing this problem , and how I can solve it ?
Thanks

Create a Controller (e.g. "Streamer") and Action (e.g. "StreamUploadedImage") that streams the image (the Action will typically return a FileResult).
Change the url to reference your action, passing the image id as a parameter, e.g. (from memory so syntax may not be accurate):
#Html.ActionLink(Model.Name, "StreamUploadedImage", "Streamer", new {id = "38" })
An alternative would be to put the uploaded image in a location where it can be accessed from the client, e.g. in a subfolder of the Content folder:
#Model.Name
But using a controller gives you more control, e.g. to implement authorization.

The path is blocked by your IIS. To resolve, move the files to an other location ("~/Uploads/Images/" perhaps?).
The reason why IIS is blocking some folders is beacause they can contain importent data or files, which the user should not have access to. To avoid hackers from getting this information, the IIS is denying access to any of the files in those folders.
For more information: http://www.iis.net/configreference/system.webserver/security/requestfiltering/hiddensegments

Restrict unauthorized access to file download using handler

I am working on a website where the images and other files are handled by a handler named resources.ashx. These files are not stored in any folder but are fetched from database.
The problem is the access to some of the files is restricted, whereas some images and files are open to all.
Lets say the path to one of the restricted image is :
../website/resources.ashx/restrictedimage.jpg
If an unauthenticated user types in this url, he will have access to the image straight away.
I want to restrict that.
P.S. -> I can't change the handler as I am referencing it from some other project.

May be an HttpModule can help you out. Handle the AuthenticateRequest event, parse/compare requested url and users/roles.

You can use authorization rules in your web.config to control access to the files (ie urls) or your choosing based on user/group membership.
See:
using multiple authorization elements in web.config

resource sharing in asp.net mvc

I have 2 asp.net mvc2 projects in a solution. One is normal site for visitors use and the other one is admin back-end which is going to be separated by sub-domains like test.com and admin.test.com. The scenario is like admin will add a new item(e.g product) with image and test.com will use that image to display product. Both application are sharing one db. so there is no problem to get the item details that is coming from the db. but for item image that has been uploaded in admin directory(admin.test.com) - any idea how to get it from general domain(test.com) to display??
Also what is the best way of separating the resources like image files or even css or js files across sites and how to access them?
p.s.I'm using shared hosting.
Thanks!

You can upload to a third sub-domain or to the front end domain.
You upload to a physical folder. This folder can be an appSetting value or so.
So, you get similar settings to those in web.config appSettings:
<add key="ProductImagesPhysicalFolder" value="x:\websites\frontend\product-images" />
<add key="ProductImagesFolderUrl" value="http://frontend.com/product-images" />
Upload to the physical folder (given you setup permission in ISS to allow write access to that folder), and have a helper method like GetProductImageUrl(string imageFilename) to get the URL of the image given its filename (saved in DB).