// ==UserScript==
// @name test upload
// @namespace namespace
// @description description
// @include https://post.craigslist.org/*
// @version 1
// ==/UserScript==
$ = unsafeWindow.jQuery; 
 
if (location.search.indexOf('editimage') > -1) {
  GM_xmlhttpRequest({
     method: "GET",
     url: "http://server?url=", //what ever you specify the url to be 
     onload: function(xhr) {
        run(xhr.responseText);
    }
  });
}
function run(data){
    var canvas = document.createElement('canvas'),
    ctx = canvas.getContext('2d'),
    img = new Image();
    img.onload = function() {
        canvas.setAttribute('width', img.width);
        canvas.setAttribute('height', img.height);
        ctx.drawImage(img, 0, 0);
        var blob = canvas.mozGetAsFile('image.jpg');
        sendBlob(blob);
    }
    img.src = data;
}
function sendBlob(file){
    var name1 = $('.addmore form input:nth-child(1)').attr('name');
    var value1 = $('.addmore form input:nth-child(1)').attr('value');
    var name2 = $('.addmore form input:nth-child(2)').attr('name');
     
    // submit as a multipart form, along with any other data
    var form = new FormData();
    var xhr = new XMLHttpRequest();
    xhr.open('POST', location, true); // Post to current URL
    xhr.onreadystatechange = function() {
    if (xhr.readyState == 4) {
        if (xhr.status == 200) { // Success?
                alert('Success');
            } else {
                alert('Error submitting image: ' + xhr.status);
            }
        }
    };
    // Name : Value
    form.append(name1, value1);
    // Name : Value
    form.append(name2, 'add');
    // Name : Value
    form.append('file', file);
    if(confirm('submit?'))
        xhr.send(form);
}