Download Dynamically Generated File in ASP.NET MVC

Question

I need to implement a file download in ASP.NET MVC. Searching the Web, I found code like this:

public ActionResult GetFile()
{
    return File(filename, "text/csv", Server.UrlEncode(filename));
}

That's nice, but I want to create the contents of this file dynamically.

I realize I could dynamically create the file, and then use the syntax above to download that file. But wouldn't it be more efficient if I could simply write my contents directly to the response? Is this possible in MVC?

Answer 1

Here's an overly simplified version of the code I ended up using. It meets my needs.

[HttpGet]
public ActionResult GetFile()
{
    Response.Clear();
    Response.AddHeader("Content-Disposition", "attachment; filename=myfile.csv");
    Response.ContentType = "text/csv";

    // Write all my data
    Response.Write(...);
    Response.End();

    // Not sure what else to do here
    return Content(String.Empty);
}

Answer 2

An alternative solution is to use the overload for File() that accepts a stream.

In my case, it's a csv that I need to generate from a Controller Action, so it's a bit like this:

[HttpGet]
public ActionResult DownloadInvalidData(int fileId)
{
    string invalidDataCsv = this.importService.GetInvalidData(fileId);
    string downloadFileName = "error.csv";

    var stream = new MemoryStream();
    var writer = new StreamWriter(stream);

    writer.Write(invalidDataCsv);
    writer.Flush();
    stream.Position = 0;

    return File(stream, "text/csv", downloadFileName);
}

Note you should not dispose of the Stream or the StreamWriter before passing it to the File() function because disposing of either will close the stream making it unusable.