Post Body to Javascript Fail

gistfile1.js

function doRequest(request, headers, http_method, request_body, successCallback, failureCallback){
    $.ajax({
	url: api+request,
	headers: headers,
	data:JSON.stringify(request_body),
	//data:request_body,
	processData:false,
	type: http_method,
	contentType: "application/json",
	error: function(XMLHttpRequest, textStatus, errorThrown){
	    failureCallback(textStatus, errorThrown);
	},
	success: function(data){
	    successCallback(data);
	}
    });
}