    /*
     * call-seq:
     *  read_io(io, url, encoding, options)
     *
     * Create a new document from an IO object
     */
    static VALUE read_io( VALUE klass,
                          VALUE io,
                          VALUE url,
                          VALUE encoding,
                          VALUE options )
    {
      const char * c_url    = NIL_P(url)      ? NULL : StringValuePtr(url);
      const char * c_enc    = NIL_P(encoding) ? NULL : StringValuePtr(encoding);
      VALUE error_list      = rb_ary_new();
      VALUE document;
      xmlDocPtr doc;

      xmlResetLastError();
      xmlSetStructuredErrorFunc((void *)error_list, Nokogiri_error_array_pusher);

      doc = xmlReadIO(
          (xmlInputReadCallback)io_read_callback,
          (xmlInputCloseCallback)io_close_callback,
          (void *)io,
          c_url,
          c_enc,
          (int)NUM2INT(options)
      );
      xmlSetStructuredErrorFunc(NULL, NULL);

      if(doc == NULL) {
        xmlErrorPtr error;

        xmlFreeDoc(doc);

        error = xmlGetLastError();
        if(error)
          rb_exc_raise(Nokogiri_wrap_xml_syntax_error((VALUE)NULL, error));
        else
          rb_raise(rb_eRuntimeError, "Could not parse document");

        return Qnil;
      }

      document = Nokogiri_wrap_xml_document(klass, doc);
      rb_iv_set(document, "@errors", error_list);
      return document;
    }