извлечение полного пути до файла в url

Determining Physical File Paths for the Current Web Site
In your application, you might need to determine the path of a file or other resource on the server. For example, if your application reads or writes a text file programmatically, you must supply the file's complete physical path to the methods used for reading and writing.

It is not a good practice to hard-code physical file paths (such as C:\Website\MyApplication) into your application, because the paths can change if you move or deploy your application. However, ASP.NET provides you with ways to get any physical file path within your application programmatically. You can then use the base file path to create a full path to the resource you need. The two most commonly used ASP.NET features for determining a file path are properties of the HttpRequest object that return path information, and the MapPath method.

Note
Physical file paths should not be sent to the client because they could be used by a malicious user to gain information about your application.