title: XMLHttpRequest multipart/form-data: Invalid boundary in multipart
body: <p>I am sending post data via XMLHttpRequest:</p>
  
  <pre><code>var xmlHttp=new XMLHttpRequest();
  xmlHttp.open("POST", domain, true);
  xmlHttp.setRequestHeader("Content-type","multipart/form-data");
  var formData = new FormData();  
  formData.append("data", data_json_string);
  xmlHttp.send(formData);
  </code></pre>
  
  <p>In Python, I get an error if I try to get the POST (or FILES or anything) data:</p>
  
  <pre><code>MultiPartParserError: Invalid boundary in multipart: None
  </code></pre>
  
  <p>Can this never work?? Do I really need to create the form body as a single string where I loop through the parameters and place a boundary string before and after each one? And, if so, what should that look like? How do  I get it from my POST in Python?? Or is there an easier way. I'm looking around and not finding much on this.</p>
  
  <p>btw, I am using "multipart/form-data" because my string data is really long and this is a faster way to send it. It has worked for me when I create a form and post it, targeting it to an iframe. But here I much prefer xmlHttp.</p>