Returning Files from .NET Core or ASP.NET MVC Controllers
In ASP.NET MVC, the File helper method built into your controller gives you multiple options for retrieving the file you want to send to the client. You can pass the File helper method an array of bytes, a FileStream or the path name to a file depending on whether you want to return something in memory (the array of bytes), an open file (FileStream) or a file on your server's hard disk (a path).
In .NET Core, you still have the File helper method, but it has one limitation: It assumes that any file path you pass it is a virtual path (a relative path within your Web site). To compensate, this new version of the File method simplifies two common operations that require additional code in ASP.NET MVC: checking for new content and returning part of the file when the client includes a Range header in its request.
To handle physical path names in .NET Core, you'll want to switch to using the PhysicalFile helper method. Other than assuming any file name is a physical path to somewhere on your server, this method works just like the new File helper method.
Posted by Peter Vogel on 02/22/2019