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ASP.Net MVC File Stream, Initiated From Javascript Post

I was recently working on a page that does an AJAX post to an MVC controller passing quite a lot of parameters in the request. I needed to find a way to stream a file back to the browser as a result of a that Javascript call, for obvious reasons a file download can't be started from a stream sent in the response to an AJAX call.

To solve this I ended up swapping the AJAX post out for a form post, the response of which can be a file stream. The code looked a bit like this....

MVC Controller

public FileResult Download()  
{
    //Fake file
    byte[] fileBytes = new byte[10];
    string fileName = "hello.pdf";
    return File(fileBytes, MediaTypeNames.Application.Octet, fileName);
}

Javascript to replace AJAX call

var form = document.createElement("form");  
form.setAttribute("method", "post");  
form.setAttribute("action", "DownloadFile/Download");  
var hiddenField = document.createElement("input");  
hiddenField.setAttribute("type", "hidden");  
hiddenField.setAttribute("name", "Param1");  
hiddenField.setAttribute("value", "HelloWorld");  
form.appendChild(hiddenField);  
document.body.appendChild(form);  
form.submit();  

 
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