ASP.NET XMLHTTPREQUEST download file using Handler - asp.net

Question

am trying to implement file download using xmlhttprequest... But am not getting the file dialog or any response. I have debug the handler, no error.
function download(id)
{
try
{
var xmlHttp=new XMLHttpRequest();
xmlHttp.open("GET","DownloadFileHandler.ashx?id=" + id,false);
xmlHttp.send();
xmlHttp.onreadystatechange=function()
{
//if request has been entertained and response is returned from server
if(xmlHttp.readyState==4)
{
alert("aq");
}
}
}
catch (ex)
{
alert("Browser does not support ajax");
}
}
}
my handler
context.Response.AppendHeader("content-disposition", "attachment; filename=" + name);
context.Response.ContentType = type;
context.Response.WriteFile(path);
context.Response.End();

Answer 1

So, clearly AJAX uses a XML based http requests. This is a different
protocol than a file download request. A file download is a binary
http request.
First, while the XmlHttpRequest object can parse the data to XML, you can also get the full data, be it binary or not. You can parse it into whatever you want.
Second, it is not a different protocol. The protocol is HTTP. HTTP is transferring the data, and doing content negotiation, in both cases.
Third, HTTP GET requests (the same kind of request in both cases) can return binary or textual data entirely independent on how the request is generated. A request can be generated through an tag, or a user clicking an link, or an XMLHttpRequest, and the content type (binary or text) is totally independent of how the request was generated.
The real reason you can't download a file using XMLHttpRequest, but instead have to use browser-specific extensions such as nsIWebBrowserPersist, is that browsers have chosen to not pay attention to the Content-Disposition header when reading data returned from an XMLHttpRequest, the way they do when reading data for a top-level page (or -- you can trigger a download by getting data through an invisible iframe)
Personally, I think this is a poor choice by web browsers, because there is no extra security, only inconvenience for developers. There's no way to send Accept: headers or verbs other than GET by issuing requests with an IFRAME or IMG element, so you can't control content negotiation. Instead, you have to escape the HTTP protocol into GET parameters, which I find sad and un-REST-ful.
For more information on nsIWebBrowserPersist, see https://developer.mozilla.org/en/Code_snippets/Downloading_Files

Answer 2

Notice in your code you have:
var xmlHttp=new XMLHttpRequest();
So, clearly AJAX uses a XML based http requests. This is a different protocol than a file download request. A file download is a binary http request.
Kinda like speaking two different languages when there is no translator. Doesn't work...
So, one solution is to create a link which points to a .ashx handler which can get the file and send it to the client