FileResult

FileResult is a type in the ASP.NET Core MVC framework that represents a file to be downloaded by the client. It is an action result that, when returned from a controller action, instructs the browser to download a file. This is distinct from returning a view, which renders HTML content.

When a controller action returns a FileResult, the response sent back to the client includes specific HTTP headers that tell the browser how to handle the content. The Content-Disposition header is crucial, typically set to "attachment" along with a filename, which prompts the browser to display a save-as dialog. Other headers like Content-Type are also set to indicate the MIME type of the file being sent, such as "application/pdf" for a PDF document or "image/jpeg" for a JPEG image.

There are several concrete implementations of FileResult available, including FileContentResult, FilePathResult, and FileStreamResult. FileContentResult allows you to return a file directly from a byte array. FilePathResult enables returning a file from a specified path on the server. FileStreamResult is useful for returning files from a stream, which is efficient for large files as it avoids loading the entire file into memory.

Using FileResult is a common pattern for implementing file download functionality in web applications, such as for downloading reports, images, or any other type of document. It provides a structured way for the server to deliver binary content to the client for them to save or open.