How to download a file in ASP.NET Core

Question

In MVC, we have used following code to download a file. In ASP.NET core, how to achieve this?

HttpResponse response = HttpContext.Current.Response;                   


        

Answer 1

Your controller should return an IActionResult, and use the File method, such as this:

[HttpGet("download")]
public IActionResult GetBlobDownload([FromQuery] string link)
{
    var net = new System.Net.WebClient();
    var data = net.DownloadData(link);
    var content = new System.IO.MemoryStream(data);
    var contentType = "APPLICATION/octet-stream";
    var fileName = "something.bin";
    return File(content, contentType, fileName);
}

Answer 2

my way is quite short and I think it suits most people's need.

  [HttpPost]
  public ActionResult Download(string filePath, string fileName)
  {
      var fileBytes = System.IO.File.ReadAllBytes(filePath);
      new FileExtensionContentTypeProvider().TryGetContentType(Path.GetFileName(filePath), out var contentType);
      return File(fileBytes, contentType ?? "application/octet-stream", fileName);
  }

Answer 3

A relatively easy way to achieve this is to use the built-in PhysicalFile result, which is available to all controllers: MS Docs: PhysicalFile

A simple example:

public IActionResult DownloadFile(string filePath)
{
     return PhysicalFile(filePath, MimeTypes.GetMimeType(filePath), Path.GetFileName(filePath));
}

Now of course you should never expose this kind of API, due to security concerns.

I typically shield the actual file paths behind a friendly identifier, which I then use to lookup the real file path (or return a 404 if an invalid ID was passed in), ie:

[HttpGet("download-file/{fileId}")]
public IActionResult DownloadFile(int fileId)
{
    var filePath = GetFilePathFromId(fileId);
    if (filePath == null) return NotFound();

    return PhysicalFile(filePath, MimeTypes.GetMimeType(filePath), Path.GetFileName(filePath));
}

For those that are curious, the MimeTypes helper is a great little nuget package from the folks at MimeKit