（Wordpress）联系表格7 - file_get_contents不起作用

After submission of the contact form I hook in on the submission. The file, uploaded on the contact form, need to be send to a SOAP service. In order to receive the filedata I do the following:

Returns empty:
$base64string = base64_encode(file_get_contents($_FILES["cv"]["tmp_name"]));

My $_FILES is not empty, so the file is in place. file_get_contents always returns an empty string. also, allow_url_fopen is on "On"

When I test this on a single PHP file (no Wordpress) it returns the BASE_64 string so it has to do something with Wordpress:

Working code:

<form action="" method="POST" enctype="multipart/form-data">
    <input type="file" name="cv">
    <input type="submit" name="formsubmit">
</form>
<?

if(isset($_POST['formsubmit'])){
    print_r(base64_encode(file_get_contents($_FILES["cv"]["tmp_name"])));
}

Any ideas?

Alright, not much magic going on here. All the code above is correct. Apparently you cannot use file_get_contents within the hook of Contact Form 7. I placed my code outside the scope of the function and put the datafile in a session variable, so I could use it in my function.

Long story short: no file_get_contents in Contact Form 7, put it outside the scope of the hook.

if(!empty($_FILES['cv'])){
    $file = file_get_contents($_FILES["cv"]["tmp_name"]);
    $_SESSION['filestring'] = $file;
}

function wpcf7_soap_service($contact_form) {
  $submission = WPCF7_Submission::get_instance();

  if ( $submission ) {
      //Use session variable here
  }
}