I'm uploading a file with XMLHttprequest.
Here is the JS function, that uploads a file:

var upload = function(file) {

    // Create form data

    var formData = new FormData();

    formData.append('file', file);



    var xhr = new XMLHttpRequest();



    // Open

    xhr.open('POST', this.options.action);



    // Set headers

    xhr.setRequestHeader(Cache-Control, no-cache);

    xhr.setRequestHeader(X-Requested-With, XMLHttpRequest);

    xhr.setRequestHeader(Content-Type, multipart/form-data);

    xhr.setRequestHeader(X-File-Name, file.fileName);

    xhr.setRequestHeader(X-File-Size, file.fileSize);

    xhr.setRequestHeader(X-File-Type, file.type);



    // Send

    xhr.send(formData);

}

On the server side, in upload.php I read the file this way:

file_put_contents($filename, (file_get_contents('php://input')));

Everything works fine, except that I get a PHP Warning:

Missing boundary in multipart/form-data POST data in Unknown on line 0.

If I remove this line:
xhr.setRequestHeader(Content-Type, multipart/form-data); the warning goes away.

What should be the problem here?