Question

I am writing a Firefox extension. Right now I need to create a local copy of a XML file and I am almost successful. A File is read and a new one is created but this one is empty. Is there a special method for XML files or why does it not work?

Here are the functions:

function loadXMLDoc(dname) {
    if (window.XMLHttpRequest) {
        xhttp = new XMLHttpRequest();
    } else {
        xhttp = new ActiveXObject("Microsoft.XMLHTTP");
    }
    xhttp.open("GET", dname, false);
    xhttp.send("");
    return xhttp.responseXML;
}

and

function localcopy() {
    var url = content.document.location.href;
    var prefManagerr = Components.classes["@mozilla.org/preferences-service;1"]
        .getService(Components.interfaces.nsIPrefService)
        .getBranch("extensions.foafnet.");

    var prefStringx;
    if (prefManagerr.prefHasUserValue("stringpref1")) {
        prefStringx = prefManagerr.getCharPref("stringpref1");
    } else {
        // Preference is default value so use that
        prefStringx = "0"
    }
    if (prefStringx == url) {
        xml = loadXMLDoc(prefStringx);
        var file = Components.classes["@mozilla.org/file/directory_service;1"].
        getService(Components.interfaces.nsIProperties).
        get("TmpD", Components.interfaces.nsIFile);
        file.append("profiletemp.xml");
        file.createUnique(Components.interfaces.nsIFile.NORMAL_FILE_TYPE, 0666);
        // do whatever you need to the created file
        alert(file.path);
        //
        var stream = Components.classes["@mozilla.org/network/safe-file-output-stream;1"].
        createInstance(Components.interfaces.nsIFileOutputStream);
        stream.init(file, 0x04 | 0x08 | 0x20, 0600, 0); // readwrite, create, truncate

        stream.write(xml, xml.length);
        if (stream instanceof Components.interfaces.nsISafeOutputStream) {
            stream.finish();
        } else {
            stream.close();
        }
    }
}

The beginning of the second function just declares, that a local copy is only to be made if the called website hast the same url as a url defined in the preferences of the extension. this part works just fine.

Answer 1

The first parameter to nsIOutputStream.write() has to be a string – you are giving it an XML document instead. You can use XMLSerializer to convert XML into text and to write it to a stream directly:

new XMLSerializer().serializeToStream(xml, stream, "utf-8");