admin-ajax.php do not recognizes 'action'. $_REQUEST is empty - ajax

Question

After two days of fruitless research, I decided to join the community. I hope to get a solution. I develop a plug-in that, among other things, must implement the upload of documents. this should be done using ajax technology. the problem is that the request is approved, but admin_ajax.php reacts like no action was taken. Outside of wp this piece of code works fine, as it was thought out. The problems come with installing this code in wp. Below is my code
PHP. This code in the main class that will call from main modul of plugin
class main{
//other activation methods
private function register_scripts(){
add_action('wp_enqueue_scripts', array($this,'re_add_script'));
}
public function re_add_script() {
wp_enqueue_script('re_upload',plugins_url('re'.'/js/re_upload.js'),array('jquery'));
wp_localize_script('re_upload',"re_ajax",array(
'ajaxurl'=>admin_url("admin-ajax.php")));
add_action( 'wp_ajax_upload', 'processingUpload');
}
}//end of class
//callback function
function processingUpload(){
$clsUpload = new UploadsDocs();
$clsUpload->setRequestedData($_FILES,$_POST['doc_id']);
$clsUpload->checkUploadsFiles();
$clsUpload->outputFilesList();
wp_die();
}
jQuery 're_upload.js'
jQuery(document).ready(function (e) {
jQuery('#bt_upload').on('click', function () {
var toUpload=getFileListToUpload();
var form_data = new FormData();
var ins = input.files.length;
for (var x = 0; x < ins; x++) {
if (isFileToUpload(input.files[x],toUpload)){
form_data.append("files[]", input.files[x]);
}
}
form_data.append("doc_id", jQuery('#doc_id')[0].value);
var data_to_sent={
action: 'upload',
datas: form_data
};
jQuery.ajax({
url: re_ajax.ajaxurl, // point to server-side PHP script
dataType: 'text', // what to expect back from the PHP script
cache: false,
contentType: false,
processData: false,
data: data_to_sent,
type: 'post',
success: function (response) {
// do something
},
error: function (response) {
// do something
},
xhr: function(){
//upload Progress
var xhr = jQuery.ajaxSettings.xhr();
if (xhr.upload) {
xhr.upload.addEventListener('progress', function(event) {
var percent = 0;
var position = event.loaded || event.position;
var total = event.total;
if (event.lengthComputable) {
percent = Math.ceil(position / total * 100);
}
//update progressbar
jQuery('#bt_upload').css("display","none");
jQuery('#progress-wrp').css("display","block");
jQuery('#progress-wrp' +" .progress-bar").css("width", + percent +"%");
(percent<50)? jQuery('#progress-status').addClass('status-less-then-50'): jQuery('.status-less-then-50').removeClass('status-less-then-50').addClass('status-more-then-50');
jQuery('#progress-status').text("Uploading..."+percent +"%");
}, true);
}
return xhr;
},
mimeType:"multipart/form-data"
});
});
});
function getFileListToUpload(){
var list=[];
var elem = document.getElementsByClassName('preview');
var tag_li=elem[0].querySelectorAll('p');
for (var i=0;i<tag_li.length;i++){
list[i]=tag_li[i].textContent.split('(')[0];
}
return list;
}
function isFileToUpload(input_file,files_toUpload){
var res=false;
for(var i=0; i<files_toUpload.length;i++){
if (input_file.name==files_toUpload[i]){
res=true;
break;
}
}
return res;
}

Answer 1

The problem is
add_action( 'wp_ajax_upload', 'processingUpload');
is not called.
The upload is done in two separate invocations of the server. The first invocation displays the upload page to the user. The second invocation processes the AJAX request. Your call to
add_action( 'wp_ajax_upload', 'processingUpload');
is done in the first invocation where it is not needed but not in the second invocation where it is needed.
Please read https://codex.wordpress.org/AJAX_in_Plugins. (Observe carefully how the call to 'add_action( 'wp_ajax_...', ...) is done.) Further, you need to read about nonces.

Answer 2

Try to append action to your ajax url like:
url: re_ajax.ajaxurl?action=upload
and
data: form_data
or pass it to form_data like:
form_data.append('action', 'upload')