Unable to Upload File Via POST From Qt to PHP Script - php

Question

I'm trying to upload a file via POST from a Qt (C++) application to my webserver, running a LAMP stack.
All seems to go well, but for some reason, the script's $_POST and $_FILES arrays are completely empty. I've tried uploading the same file with a plain HTML form, and it works.
Here's how I construct the request inside my Qt program:
request.setUrl(ServerAddress);
request.setHeader(request.ContentTypeHeader, "application/x-www-form-urlencoded");
reply = nam.post(request, file);
And the PHP:
<?php
var_dump($_POST);
var_dump($_FILES);
?>
Where request is a QNetworkRequest, reply is a QNetworkReply, nam is a QNetworkAccessManager, and file is the open QFile for my file.
The request sends fine, and I've even tried to see if somehow the request got messed up by using Wireshark. Here's the output:
POST /upload.php HTTP/1.1
Content-Type: application/x-www-form-urlencoded
Content-Length: 8
Connection: Keep-Alive
Accept-Encoding: gzip, deflate
Accept-Language: en-US,*
User-Agent: Mozilla/5.0
Host: mysite.com
My data!HTTP/1.1 200 OK
Date: Wed, 03 Jul 2013 15:16:37 GMT
Server: Apache/2.2.22 (Ubuntu)
X-Powered-By: PHP/5.4.17RC1
Vary: Accept-Encoding
Content-Encoding: gzip
Content-Length: 36
Keep-Alive: timeout=5, max=100
Connection: Keep-Alive
Content-Type: text/html
array(0) {
}
array(0) {
}
It's a very small text file, and only contains "'My data!". I just don't get why the PHP script isn't seeing the file. Any ideas where I'm going wrong?