Writing file to HttpResponse, browser not prompting to save

Question

I have an ashx file with an IHttpHandler. When I POST some data to this IHttpHandler, I do some work, create a file, and then want that file returned to the user so that they may save the file via their browser.

With the file created, this is how I attempt to write the file back to the response:

HttpResponse response = context.Response;
response.ClearContent();
response.Clear();
response.ContentType = "application/octet-stream";
response.AddHeader("Content-Disposition", "attachment; filename=MYFILE.EXT");
response.WriteFile("C:\tempstuff\MYFILE.EXT");

In a finally block later on, I will call:

response.End()

When I call this Handler, nothing happens. Response 200 is returned, no errors are thrown - but the browser will not prompt the user to save this file.

Here is what the response, as captured by Fiddler, looks like:

HTTP/1.1 200 OK
Server: ASP.NET Development Server/10.0.0.0
Date: Thu, 23 Aug 2012 12:12:19 GMT
X-AspNet-Version: 4.0.30319
Content-Disposition: attachment; filename=MYFILE.EXT
Cache-Control: private
Content-Type: application/octet-stream
Content-Length: 781053
Connection: Close

[raw content of the file here]

This response looks correct to me. It contains the content of the file - however under any of the major browsers, no file dialog prompts me to save the file.

What am I doing wrong here?

Update: In case it helps, here is where I am using JavaScript from my web application to call this HttpHandler.

$.ajax({
    type: 'POST',
       url: ashxUrl,
       data: postData,
       success: function (result) {
           // Doin' stuff on success
       },
       error: function (error) {
           // Doin' stuff on error.
        }
});

Answer 1

You've said that you want the results of the web-call to be made available to your javascript. It would be extremely annoying if that caused the browser to prompt you to save it, as then all AJAX would be impossible.

You want the browser itself to make the call. For a GET that would be a simple matter of setting self.location.href. For a POST the easiest way is normally to fill out a hidden form with the data, and then submit() it.