How to determine if file has downloaded?

Question

I have the following code that allows a user to download a file. I need to know (if possible) if they downloaded the file successfully. Is there any kind of callback that I can tie into to know whether or not they were successful in downloading it?

string filename = Path.GetFileName(url);
context.Response.Buffer = true;
context.Response.Charset = "";
context.Response.Cache.SetCacheability(HttpCacheability.NoCache);
context.Response.ContentType = "application/x-rar-compressed";
context.Response.AddHeader("content-disposition", "attachment;filename=" + filename);
context.Response.TransmitFile(context.Server.MapPath(url));
context.Response.Flush();

Answer 1

Why not add one more line that lets you know it's finished? After the context.Response.Flush(), it should be done.

Answer 2

I guess this is not possible.

Response is just a memory object which interacts with IIS. You cannot know whether the browser completely downloaded a file, since the user might cancel just before the last byte arrived, but after IIS finished sending the whole stream.

You might try to implement an IHttpHandler, continuously write chunks of the file to context.Response in the Process() method, and Flush() and check like this

context.Response.Flush();
if (!context.Response.IsClientConnected)
// handle disconnect

That's the closest thing I can think of solving your problem.

Answer 3

You can do something like this:

try
{
    Response.Buffer = false;
    Response.AppendHeader("Content-Disposition", "attachment;filename=" + file.Name);
    Response.AppendHeader("Content-Type", "application/octet-stream");
    Response.AppendHeader("Content-Length", file.Length.ToString());

    int offset = 0;
    byte[] buffer = new byte[64 * 1024]; // 64k chunks
    while (Response.IsClientConnected && offset < file.Length)
    {
        int readCount = file.GetBytes(buffer, offset,
            (int)Math.Min(file.Length - offset, buffer.Length));
        Response.OutputStream.Write(buffer, 0, readCount);
        offset += readCount;
    }

    if(!Response.IsClientConnected)
    {
        // Cancelled by user; do something
    }
}
catch (Exception e)
{
    throw new HttpException(500, e.Message, e);
}
finally
{
    file.Close();
}