Why is GM_xmlhttpRequest ignoring its data parameter?

Question

According to its documentation, GM_xmlhttpRequest should be able to take a data parameter as part of its argument.

However, I can't seem to get it to work.

I have a simple server that echoes the parameters given to it:

require 'sinatra'
require 'json'
get '/' do
  JSON.dump params
end
post '/' do
  JSON.dump params
end

And a simple greasemonkey script that just tries to POST some data to the server. It tries to pass data as query parameters in the URL and as postdata:

// ==UserScript==
// @name        PostDataTest
// @namespace   Test
// @description Simple test of GM_xmlhttpRequest's data parameter
// @include     http://localhost:4567/
// @version     1
// @require     http://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js
// @grant       metadata
// @grant       GM_xmlhttpRequest
// ==/UserScript==

var url = '/?q0=0&q1=1';
var data = 'd0=0&d1=1'

GM_xmlhttpRequest({ method: 'POST', url: url, data: data, onload: function(r){
  console.log('gm:' + r.responseText);
}});
$.post(url, data, function(d,s,r){
  console.log('jq:' + r.responseText);
});

When I POST postdata using jQuery, it works fine, but any postdata I POST using GM_xmlhttpRequest is ignored:

jq:{"q0":"0","q1":"1","d0":"0","d1":"1"}
gm:{"q0":"0","q1":"1"}

This leads me to believe that GM_xmlhttpRequest isn't actually using the data parameter I'm giving it. (I'm not sure b/c I can't monitor GM_xmlhttpRequest's network activity in Firebug).

What's going on here? Did I screw something up? Did the API shift? How can I use GM_xmlhttpRequest to post data without packing it into the URL?

Answer 1

Ok, I used the TamperData firefox add-on to monitor my GM_xmlhttpRequests (which were sending the postdata) to see what they were doing differently.

The difference was four headers. Where jQuery sent

Accept:             */*
Content-Type:       application/x-www-form-urlencoded; charset=UTF-8
X-Requested-With:   XMLHttpRequest
Referer:            http://localhost:4567/

GM_xmlhttpRequest sent:

Accept:             text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Content-Type:       text/plain; charset=UTF-8

Using the headers: parameter I was able to specify the Content-Type of my GM_xmlhttpRequest, which got it to work.

// ==UserScript==
// @name        PostDataTest
// @namespace   Test
// @description Simple test of GM_xmlhttpRequest's data parameter
// @include     http://localhost:4567/
// @version     1
// @require     http://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js
// @grant       metadata
// @grant       GM_xmlhttpRequest
// ==/UserScript==

var url = '/?q0=0&q1=1';
var data = 'd0=0&d1=1'

GM_xmlhttpRequest({
  method: 'POST',
  url: url+'gm',
  data: data+'gm',
  headers: { 'Content-Type': 'application/x-www-form-urlencoded; charset=UTF-8' },
  onload: function(r){
    console.log('gm:' + r.responseText);
}});
$.post(url+'jq', data+'jq', function(d,s,r){
  console.log('jq:' + r.responseText);
});