[Kde-bindings] How to unserialize types defined in other Qt apps in QtRuby?

[Yaohan Chen]

(I'm sorry for the multiple posts; I'm learning new things but not sure
if I'm moving in the right direction.)

I added a method in the extension to unserialize data as below, hoping
that since it's linked to the Quassel C++ files, it will be able to
unserialize the custom types correctly. Unfortunately, looking at QDebug
output of the variants, it's still not recognizing the custom types. Also,
I don't know how to transfer the unserialized objects from C++ to Ruby,
converting them like QtRuby's Qt::Variant#value does.

VALUE unserialize(VALUE self, VALUE string)
{
  Check_Type(string, T_STRING);

  QByteArray byte_array(RSTRING_PTR(string), RSTRING_LEN(string));
  QDataStream data_stream(byte_array);
  QVariant variant;
  data_stream >> variant;

  // FIXME return a Ruby object for the variant instead of its qDebug
  QString output;
  QDebug debug(&output);

  debug << variant;

  VALUE result = rb_str_new2(output.toUtf8().data());
  rb_enc_associate_index(string, rb_enc_find_index("UTF-8"));
  return result;
}


Yaohan Chen

On Thursday, February 23, 2012 02:00:14 AM you wrote:
> I compiled several of Quassel's C++ files which define 
> the custom types
> (most files under "src/common" at 
> <http://git.quassel-
> irc.org/?p=quassel.git;a=tree;f=src/common;hb=HEAD>),
> into an extension, and loaded it in my QtRuby client, 
> and unserialization
> still doesn't work for the types. I didn't think this 
> would be enough,
> but I'm not sure what else I need to do now, or if I'm 
> going in the right
> direction. These C++ files, for example BufferInfo.
> {h,cpp}, do define
> operator>> and operator<<(QDataStream, type), and use 
> Q_DECLARE_METATYPE
> and qRegisterMetaType with them.
> 
> Paolo's link as well as Richard Dale's 
> <https://blogs.kde.org/node/2679>
> talk about the ability to call a C++ QObject's slots 
> in QtRuby, but I'm
> not sure how to adapt the technique in my application. 
> I don't have
> the objects of Quassel types yet, because they're 
> serialized in the
> stream. If I arbitrarily instantiate one in the 
> extension, it doesn't
> seem helpful in unserializing other instances. And is 
> it possible to
> use operator>> as a slot?
> 
> 
> Yaohan Chen
> 
> On Wednesday, February 22, 2012 04:50:50 PM Arno Rehn 
> wrote:
> > On Tuesday 21 February 2012 22:35:42 Yaohan Chen 
> wrote:
> > > Hello,
> > > 
> > > How can I unserialize objects of types defined in 
> a C++ Qt app, through a
> > > Qt::DataStream in QtRuby?
> > > 
> > > I am trying to create a scripting interface for 
> the Qt IRC client Quassel
> > > <http://quasselirc.org>. Quassel'score connects to 
> IRC networks, and its
> > > client
> > > displays its user interface. The two communicate 
> through a socket, sending
> > > QVariant maps and lists to each other, and each 
> map or list is prefixed
> > > with a uint32 indicating its size in the socket. 
> My QtRuby client is able
> > > to read some of the messages sent by core, but not 
> the ones containing
> > > types defined by Quassel. These messages show up 
> as empty Qt maps. My
> > > code is at <https://github.com/hagabaka/Quassel-
> Ruby> if it's of any
> > > interest.
> > > 
> > > It seems that normally qRegisterMetaType would be 
> used for this, but I'm
> > > not sure how to call a template function QtRuby. I 
> don't have much
> > > experience with C++ Qt programming either, but I 
> would appreciate any
> > > pointers.
> > If the types in question are custom Quassel types, 
> you're pretty much out of
> > luck, I'm afraid.
> > Quassel then uses custom operator<< and operator>> 
> for serializing these
> > types which the QtRuby runtime can't know about.
> > You could create a wrapper C++ library for those 
> operators only and then
> > call them from Ruby - Paolo has written a nice blog 
> entry about easy C++
> > interop:
> > 
> http://pcapriotti.wordpress.com/2010/12/06/effective-
> qt-in-ruby-part-3-2/
> > 
> > I can't think of any other quick solution now.
>