How return 304 status with FileResult in ASP.NET MVC RC1

Question

As you may know we have got a new ActionResult called FileResult in RC1 version of ASP.NET MVC.

Using that, your action methods can return image to browser dynamically. Something like this:

public ActionResult DisplayPhoto(int id)
{
   Photo photo = GetPhotoFromDatabase(id);
   return File(photo.Content, photo.ContentType);
}

In the HTML code, we can use something like this:

<img src="http://mysite.com/controller/DisplayPhoto/657">

Since the image is returned dynamically, we need a way to cache the returned stream so that we don't need to read the image again from database. I guess we can do it with something like this, I'm not sure:

Response.StatusCode = 304;

This tells the browser that you already have the image in your cache. I just don't know what to return in my action method after setting StatusCode to 304. Should I return null or something?

Answer 1

This blog answered the question for me; http://weblogs.asp.net/jeff/archive/2009/07/01/304-your-images-from-a-database.aspx

Basically, you need to read the request header, compare the last modified dates and return 304 if they match, otherwise return the image (with a 200 status) and set the cache headers appropriately.

Code snippet from the blog:

public ActionResult Image(int id)
{
    var image = _imageRepository.Get(id);
    if (image == null)
        throw new HttpException(404, "Image not found");
    if (!String.IsNullOrEmpty(Request.Headers["If-Modified-Since"]))
    {
        CultureInfo provider = CultureInfo.InvariantCulture;
        var lastMod = DateTime.ParseExact(Request.Headers["If-Modified-Since"], "r", provider).ToLocalTime();
        if (lastMod == image.TimeStamp.AddMilliseconds(-image.TimeStamp.Millisecond))
        {
            Response.StatusCode = 304;
            Response.StatusDescription = "Not Modified";
            return Content(String.Empty);
        }
    }
    var stream = new MemoryStream(image.GetImage());
    Response.Cache.SetCacheability(HttpCacheability.Public);
    Response.Cache.SetLastModified(image.TimeStamp);
    return File(stream, image.MimeType);
}