Wordpress frontend file uploading

functions.php

<?php 
// simple frontend file upload
// written by Arūnas Liuiza | tinyStudio | wp.tribuna.lt
// Usage: use [tiny_upload] shortcode or get_tiny_upload()/the_tiny_upload() template tags
 
// Localization: replace 'theme' with your text domain string.
 
// ======= UPLOAD FORM =====>
 
// return form #1
// usage: $result = get_tiny_upload();
function get_tiny_upload($redirect=false) {
  $return = "<form action=\"\" method=\"post\" class=\"tiny_form tiny_upload\"  enctype=\"multipart/form-data\" >\r\n";
  $return .= "  <p>
    <label for=\"tiny_upload\">".__('File','theme')."</label>
    <input type=\"file\" id=\"tiny_upload\" name=\"tiny_upload\"/>
  </p>\r\n";

// where to redirect on success
  if ($redirect)
    $return .= "  <input type=\"hidden\" name=\"redirect\" value=\"{$redirect}\">\r\n";

  $return .= "  <input type=\"hidden\" name=\"tiny_action\" value=\"upload\">\r\n";
  $return .= "  <button type=\"submit\">".__('Upload','theme')."</button>\r\n";
  $return .= "</form>\r\n";
  return $return;
}
// print form #1
/* usage: <?php the_tiny_upload(); ?> */
function the_tiny_upload($redirect=false) {
  echo get_tiny_upload($redirect);
}
// shortcode for form #1
// usage: [tiny_upload] in post/page content
add_shortcode('tiny_upload','tiny_upload_shortcode');
function tiny_upload_shortcode ($atts,$content=false) {
  $atts = shortcode_atts(array(
    'redirect' => false
  ), $atts);
  return get_tiny_upload($atts['redirect']);
}
// <============== UPLOAD FORM

// ============ FORM SUBMISSION HANDLER
add_action('init','tiny_handle');
function tiny_handle() {
  if (isset($_POST['tiny_action'])) {
    switch ($_POST['tiny_action']) {
      case 'upload':
        require_once(ABSPATH . 'wp-admin/includes/admin.php');
        // step one upload file to server
        $file_return = wp_handle_upload($_FILES['tiny_upload'], array('test_form' => false));

        if(isset($file_return['error']) || isset($file_return['upload_error_handler'])) {
            // echo 'not working again :(';
        }
        else {
          $filename = $file_return['file'];
          // do something with the uploaded file
          $success = true;
        }
        break;
    }

    // if redirect is set and action was successful
    if (isset($_POST['redirect']) && $_POST['redirect'] && $success) {
      wp_redirect($_POST['redirect']);
    }      
  }
}

?>