Drupal 7 : Flush () more than one response with Ajax

Question

I have a Drupal 7 form, where on submit i call a PHP function via Ajax like this :

$('input[id*="edit-validate"]').click(function (e) {
        var uploadcvPath = Drupal.settings.basePath + 'myfunction_submit';
        $.ajax({
            url: uploadcvPath,
            data: $('form').serialize(),
            xhrFields: {
                onprogress: function (e) {
                    var thisResponse, response = e.currentTarget.response;
                    if (lastResponseLen === false) {
                        thisResponse = response;
                        lastResponseLen = response.length;
                    } else {
                        thisResponse = response.substring(lastResponseLen);
                        lastResponseLen = response.length;
                    }
                    jsonResponse = JSON.parse(thisResponse);
                    $('.ajax-res p').text('Processed ' + jsonResponse.count + ' of ' + jsonResponse.total);
                    $(".progress-bar").css('width', jsonResponse.progress + '%').text(jsonResponse.progress + '%');
                }
            },
            success: function (response) {
                    alert('Success!!');
            },
            complete: function () {
                //Hide loading container
                alert('Done!!');
            },
            error: function (xmlhttp) {
                alert('An HTTP error ' + xmlhttp.status + ' occurred.\n' + uploadcvPath);
            },
        });
             e.preventDefault();
    });

What i want to do is to return responses to feed a progress bar, so my PHP function looks like this :

function myfunction_submit() {

  //First response
  drupal_json_output(array('progress' => 50, 'count' => 50, 'total' => 50));
  flush();
  ob_flush();
  sleep(2);

  //Seconde response
  drupal_json_output(array('progress' => 80, 'count' => 80, 'total' => 80));
  flush();
  ob_flush();
  sleep(2);

}

This works fine with just the first response, but when i add the seconde one i get the following error :

Uncaught SyntaxError: Unexpected token { in JSON at position 37 at JSON.parse () at XMLHttpRequest.onprogress

position 37 correspond to the seconde { in the JSON response

{"progress":1,"count":1,"total":2}{"progress":2,"count":2,"total":2}

which means the Json format is not valid. My question is : Is there a problem with flush() function in Drupal 7 ? because the code above works to the perfection outside Drupal.

Answer 1

In case someone is having this probleme, i solved it by using

ob_end_flush(); 
ob_flush(); 
flush(); 
ob_start()

instead of

flush();
ob_flush();

I hope this helps someone someday !!