Checking Client Download Success with ASP.NET MVC

Scenario: You want to know if a client completes a large download successfully.

Possible Solution: Create a custom ActionResult (perhaps derived from FileStreamResult) that streams the data and checks to see if the client remains connected.

public class CheckedFileStreamResult : FileStreamResult
{
    public CheckedFileStreamResult(FileStream stream, string contentType)
        :base(stream, contentType)
    {
        DownloadCompleted = false;
    }

    public bool DownloadCompleted { get; set; }

    protected override void WriteFile(HttpResponseBase response)
    {
        var outputStream = response.OutputStream;
        using (FileStream)
        {
            var buffer = new byte[_bufferSize];
            var count = FileStream.Read(buffer, 0, _bufferSize);
            while(count != 0 && response.IsClientConnected)
            {                 
                outputStream.Write(buffer, 0, count);
                count = FileStream.Read(buffer, 0, _bufferSize);
            }
            DownloadCompleted = response.IsClientConnected;
        }
    }
    
    private const int _bufferSize = 0x1000;
}

You can now log or audit the DownloadCompleted property of the result from an action filter. I'm sure this isn't 100% foolproof, but it seems to work reasonably well. Note: The IsClientConnected property of the response only tells the truth when running under IIS. With the WebDev server the property always returns true.