/*
 * call-seq:
 *  read_memory(string, url, encoding, options)
 *
 * Create a new document from a String
 */
static VALUE read_memory( VALUE klass,
                          VALUE string,
                          VALUE url,
                          VALUE encoding,
                          VALUE options )
{
  const char * c_buffer = StringValuePtr(string);
  const char * c_url    = (url == Qnil) ? NULL : StringValuePtr(url);
  const char * c_enc    = (encoding == Qnil) ? NULL : StringValuePtr(encoding);
  int len               = NUM2INT(rb_funcall(string, rb_intern("length"), 0));

  xmlInitParser();
  xmlDocPtr doc = xmlReadMemory(c_buffer, len, c_url, c_enc, NUM2INT(options));

  if(doc == NULL) {
    xmlFreeDoc(doc);
    rb_raise(rb_eRuntimeError, "Couldn't create a document");
    return Qnil;
  }

  return Nokogiri_wrap_xml_document(klass, doc);
}