title: axios does not append Content-Lenght when sending formdata
body: <p>I am trying to use <code>axios</code> to send file to the PHP server. Unfortunately <code>$_FILES</code> global variable is empty, but I can clearly see multipart data sent using <code>file_get_contents('php://input')</code>. I already set <code>file_uploads</code>, <code>post_max_size</code>, <code>upload_max_filesize</code> in php.ini. I tracked down the problem to the fact that axios never sends <code>content-length</code>. This is an example</p>
  <pre><code>import FormData from 'form-data';
  let formData = new FormData();
  formData.append(&quot;screenshot&quot;, fs.createReadStream(absoluteOutputFile), relativeOutputFile);
  let headers = {&quot;Content-Type&quot;: &quot;multipart/form-data&quot;}
  
  axios(
         {
            method:&quot;POST&quot;,
            url:serverPathIsHere,
            data:formData,
            headers:headers
         }).then(response=&gt;{
              console.log(response.request); // no content length send
              console.log(response.data);// Content-Length header is not present in echoed response
                 
          }).catch(error=&gt;{});
  </code></pre>
  <p>On the server side I just echo back all <code>$_SERVER</code> variables with <code>echo json_encode($_SERVER)</code>; to verify that content-length is not sent. What am I doing wrong?</p>
  <p><strong>UPDATE</strong></p>
  <p>I added content length header manually as suggested:</p>
  <pre><code>    let formDataLength = await new Promise&lt;number&gt;((resolve,reject)=&gt;{
          formData.getLength((error,length)=&gt;{
              resolve(length);
          })
      });
  
  
  let headers = {
      &quot;Content-Type&quot;: &quot;multipart/form-data&quot;,
      &quot;Content-Length&quot;: formDataLenght,
  }
  </code></pre>
  <p>Content-Length is now sent successfully, but <code>$_FILES</code> is still empty. I am not sure if the length calculated is actually the one sent over the wire. Compression comes to mind..</p>