Posting a file in Swift - swift

Question

I am trying to post a file to a web API from Swift. The request I send is received fine, but it doesn't have any file in it. I was able to peek at request from the C# controller and HttpContext.Current.Request.Files.Count is 0. I suspect that instead of attaching a file to the body of the request, it just puts in the file's contents as raw data.
Code creating request:
func upload(_ fileName:URL)
{
let requestUrl:URL = URL(string: uploadURL)!
let request = NSMutableURLRequest(url: requestUrl)
request.httpMethod = "POST"
request.httpBodyStream = InputStream(url: fileName)
let (data, response, error) = URLSession.shared.synchronousDataTaskWithRequest(request as URLRequest)
}
What am I doing wrong?
If it is helpful to understand what kind of request I am trying to build, this is the working code in JS which creates a FormData object from an HTML <input type='file'> element:
$.ajax({
url: $('#apiURL').val() + 'Upload'
type: 'POST',
contentType: false,
processData: false,
data: new FormData($('form')[0]),
success: function (data)
{
// doing successful things
},
error: function (jqXHR, textStatus, errorThrown)
{
alert("Failed");
}
});
I basically just want to send a file to the same controller it references but in swift...

Answer 1

My google-fu wasn't up to par. Copy-paste of the answer given with minor code changes to work with the data types I already had made it work:
https://stackoverflow.com/a/26163136/6825722