function http() {
    var h;
    if (typeof(XMLHttpRequest) != "undefined") {
        h = new XMLHttpRequest();
    } else {
        try { h = new ActiveXObject("Msxml2.XMLHTTP"); }
        catch (e) {
            try { h = new ActiveXObject("Microsoft.XMLHTTP"); }
            catch (E) { alert("Your browser is not supported."); }
        }
    }
    return h
}

function http_action(callback) {
    var h = http();
    h.onreadystatechange = function() {
        if (h.readyState == 4) {
            if (h.status != 200 && h.status != 204) {
                alert(h.status + "\n" + h.responseText);
            } else {
                var ct = h.getResponseHeader("Content-Type");
                if (ct.split(";")[0] == "text/xml") {
                    try {
                        var xmldoc = h.responseXML;
                        if (xmldoc == null) throw "No XML in response"
                    } catch (e) {
                        alert(h.responseText);
                        return
                    }
                } else {
                    var xmldoc = h.responseText;
                }
                if (callback != undefined) callback(xmldoc);
            }
        }
    }
    return h
}