How to Control File Display (View or Download) in ASP.NET MVC?

Controlling File Display Options (View or Download) in ASP.NET MVC

ASP.NET MVC applications often need to serve files stored in a database to users. A key challenge is providing users with control over how these files are handled – whether they're viewed directly in the browser or downloaded.

While FileResult offers a simple solution, it can be unreliable for unknown file types, often defaulting to a download. For more robust control, consider using FileStreamResult or manipulating the ContentDisposition header.

Using FileStreamResult offers a compromise:

<code class="language-csharp">// Opens known types, downloads unknown types (incorrect filename/extension)
return new FileStreamResult(new MemoryStream(document.Data), document.ContentType);</code>

To consistently force a download, regardless of file type, utilize the File method with a customized ContentDisposition header:

<code class="language-csharp">public ActionResult Download()
{
    var document = ...;
    var cd = new System.Net.Mime.ContentDisposition
    {
        FileName = document.FileName,
        Inline = false, // Forces download
    };
    Response.AppendHeader("Content-Disposition", cd.ToString());
    return File(document.Data, document.ContentType);
}</code>

For improved international character support, the ContentDispositionHeaderValue class is recommended:

<code class="language-csharp">public IActionResult Download()
{
    var document = ...;
    var cd = new ContentDispositionHeaderValue("attachment")
    {
        FileNameStar = document.FileName // Use FileNameStar for better encoding
    };
    Response.Headers.Add(HeaderNames.ContentDisposition, cd.ToString());
    return File(document.Data, document.ContentType);
}</code>

These methods allow developers to precisely manage file delivery, ensuring a consistent and predictable user experience, whether the user intends to view or download the file.

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