## Common Questions

Common Questions — Find answers to common questions in the libbonobo manual

## Questions and Answers

Miguel de Icaza (miguel@helixcode.com)

This is a work in progress. Please mail me before making any changes to this document.

1. | What is Bonobo?

Bonobo is a component architecture for creating reusable and distributed software components. These software components interact with each other through well defined interfaces which are specified in the CORBA Interface Definition Language.

We distinguish between `Bonobo' the name of the component architecture, and `bonobo' which is the C-based easy to use implemenatation of the Bonobo component architecture.

The bonobo distribution consists of the following pieces:

- The Bonobo interface definition files: these establish the standard interfaces used by Bonobo-based applications.

- The core Bonobo runtime: Bonobo contains a rich API for dealing Bonobo Objects (activation for example).

- The GObject-Based (and hence C-based) Bonobo framework for creating new Bonobo::Unknown derived interfaces. These are used to simplify the development of CORBA-servers using the C language binding.

  Each derivative of a `BonoboObject` implements an interface derived from `IDL:Bonobo/Unknown:1.0`.

- A set of ready-to-use `BonoboObject`s derivatives that can be used in a variety of situations. These are considered developer "sugar", although not required, they greatly simplify the development of Bonobo-based applications.

- A set of "sugar" functions for manipulating client-side objects.

2. | What is CORBA?
3. | What is a component?
| A component is a ( preferably small ), re-usable piece of software, with well defined interfaces and interactions. In this context these interfaces are described in IDL and the interactions via. CORBA.
4. | Is it possible to use Bonobo components in my favorite language?

You will need your favorite language to support CORBA.

There are various CORBA implementations with a different degree of completness that you can use:

- Owen Taylor has written Perl bindings for CORBA using ORBit.

- James Henstridge has written Python binding for CORBA.

- Dan Barlow has written Common Lisp bindings for CORBA.

- C++ has piles of language bindings.

You need your CORBA implementation to at least let you invoke methods on other CORBA objects as well as allowing you to implement CORBA objects. Bonobo uses in various places callback mechanisms and these require the later functionality. For instance, there is an old Emacs Lisp implementation that did not allow you to create CORBA object servers.

5. | Are there other implementations of Bonobo?
| There is a work in progress to implement Bonobo in other languages, although most languages will want to reuse parts of the core runtime to avoid duplicating a large piece of code that is better kept centralized and reused. FIXME: include a detailed list of the things that are conveniently not wrapped.
6. | Is it possible to implement Bonobo components in language X?

Yes.

First of all, it is important that your language has CORBA bindings, or that a suitable CORBA implementation is available for you. You want if possible to get a CORBA 2.2 implementation, but this is not required.

It does not matter what language you are using, you can implement Bonobo Components by implementing the interface that your component wants to support.

Depending on your language, you will want to wrap some bits from Bonobo (for instance, the core runtime) or you will want to provide an alternate implementation or no implementation at all.

7. | What is ORBit?

ORBit is a CORBA implementation with a C mapping of the CORBA 2.2 specification mostly written by Elliot Lee and Dick Porter.

You can find more about ORBit here

ORBit is designed to be a small CORBA implementation that can be embedded in most applications on the desktop. It also happens to be one of the fastest CORBA implementations in existance. It supports a number of CORBA features:

- C Language mapping.

- A full POA implementation.

- The Dynamic Invocation Interface.

- The Dynamic Skeleton Interface.

- CORBA Any values.

- Typecodes.

And it comes with a number of libraries that implement a few of the CORBA services (Cos)

8. | I am interested in CORBA, where can I learn more?
| CORBA is a standard published by the Object Management Group, you can download various of their specifications from their web site See, for example, the C Language Mapping. FIXME: include pointers to more relevant documents.
9. | What can I do with `bonobo'?
10. | What is an OAFID?
| The OAFID is a unique identifier for a specific object implementation and it is used to resolve uniquely. This ID is used to activate CORBA servers implementations. For example, this OAFID represents the Gnumeric workbook factory object: `OAFIID:GNOME_Gnumeric_WorkbookFactory`
11. | What is a Factory?
| A factory is an object that makes other objects. eg. a Gnumeric factory might make Workbook objects.
12. | Where does the OAFID come from?
13. | What is a Control?

A Control is a 'componentized' version of a Widget. ie. A Control is a (single view) Graphical component.

In the Gtk+ implementation a Control contains a GtkWidget, it also has associated 'properties', providing an easy way to customize basic features of the control without creating an idl interface.

A control is often used inside a BonoboWidget, which acts as a container of Controls. The BonoboWidget is a normal GtkWidget that can be inserted into a GtkContainer.

14. | What is a PropertyBag, What is a Property?
| See Properties.
15. | What are the activation methods in Bonobo?

The prefered method of activating objects is trough the `bonobo_get_object` function. This one does moniker based activation. Like this:

For example this activates gnumeric and returns a `GNOME::Gnumeric::Worbook` CORBA object reference:

    bonobo_get_object ("OAFIID:GNOME_Gnumeric_Workbook", "GNOME/Gnumeric/Workbook");

The following launches an image handler:

    bonobo_get_object ("file:image.jpeg", "Bonobo/Control")

16. | Does Bonobo support in-proc components?
| Yes, this depends on how you setup your component, however currently there are very few in-proc gnome components, due to various debugging problems.
17. | What is that long string of identifiers.
18. | Can you show me a simple Bonobo component?
19. | How can I write user interfaces with Glade?
20. | I want to pack a widget using Bonobo.
21. | Can I write GUI-less Bonobo components?
| Yes, you can. Bonobo is in no way tied to the X11 environment, although it fully supports it. The C implementation of Bonobo uses `GObject`s as its base class, and hence you need to link against the glib-object libraries .
22. | How can I write a configure script that detects Bonobo?

    PKG_CHECK_MODULES(BONOBO, libbonobo-2.0)

See `pkg-config(1)` for more details.

23. | How do I compile and link a sample Bonobo application?

If your source file is in the file component.c, you can compile it by using the following command line:

`cc `pkg-config --cflags libbonobo-2.0` -c component.c`

To link, you use the command line:

`cc `pkg-config --libs libbonobo-2.0` component.o`

You would replace `libbonobo-2.0` for `libbonoboui-2.0` if you are using the GUI/Gtk+ features of Bonobo and include `libgnomeprint-2.0` if you are using any of the printing facilities for components.

24. | Where can I find examples of Bonobo use?

There are various sample programs in the Bonobo distribution and they are mostly intended to either excercise a part of Bonobo or to show how a specific feature in Bonobo is implemented.

You can find the sample programs in bonobo/samples; A few simple components are in bonobo/components; There are various other test programs shipped with Bonobo as well (like gshell)

For more advanced uses of Bonobo, you might want to look into Gnumeric, Nautilus or Evolution.

25. | I noticed the lack of an IDispatch-like interface in Bonobo, how do you cope with this problem?

CORBA provides a better solution to IDispatch at the CORBA level which obviates the need to have something like that.

CORBA supports a mechanism on the client side called the Dynamic Invocation Interface (DII) which allows programmers to build their own CORBA request to a server.

On the server side CORBA supports the Dynamic Skeleton (or Server? FIXME) Interface which allows applications to decode arbitrary incoming CORBA requests.

Scripting languages would typically implement some sort of support for DII and DSI. This enables scripting languages to talk to an arbitrary CORBA server or to implement any kind of CORBA interface.

Some CORBA bindings for scripting languages (like Owen Taylor's ORBit support for Perl) use the ORBs internals, as they are sometime easier to use than DII/DSI.

26. | Can I write components in any language?
| You can write components in any language that has a CORBA binding or a CORBA implementation. The only requirement is that your components implement one or more of the Bonobo interfaces. The runtime for your language might want to reuse some of the C implementation features (like object activation, moniker activation and a few other utility functions).
27. | Is Bonobo tied to the Gtk toolkit?
| No, it is not. The `bonobo' implementation is tied to Gtk+, but another binding for another language and another toolkit should be simple to write.
28. | Is Bonobo tied to the ORBit implementation?
| We do not believe that Bonobo is tied to ORBit in any aspect, and there is even an implementation of Bonobo written in Java by Cactus (Gergo Erdi) called Monkeybeans that uses the Java ORB.
29. | What is a Moniker?
| Monikers are used to name objects, they effectively implement an object naming space. The naming space is extremely abstract. Read doc/Monikers for a more in-depth explanation.
30. | Why are you so excited about Monikers?
| Please read the bonobo/doc/Monikers document while I prepare the full answer.
31. | How can I write my own moniker?
32. | Show me some examples.
33. | What is the POA?
34. | Should I use the Bonobo "base classes"?
35. | The memory management issues seem complex. What are the differences?
36. | What does OAF do?
37. | What is a name server?
38. | Why would I want to use a Name Server?
39. | I have my own needs for a name server, can I use it instead of yours?
40. | Where are component properties stored?
41. | What are the component properties?
42. | What kind of authentication system does Bonobo use for its objects?

Every CORBA object created by ORBit currently has a long and unique id created from a random sequence. To contact this object it is necessary to have the full object reference in order to dispatch a request to it (typically the object reference is obtained from the name server, or you can get it in a stringified version as an IOR).

In the past, we used a cookie system that was attached to the object profile list (in a fully CORBA standard way) and this was used to authenticate the client and the server.

43. | I notice that a port is open in my computer for every application that creates CORBA object; is that insecure?
| That port is created by ORBit to accept CORBA requests. Before any request is processed by the ORB, the connection is authenticated (either by the use of the cookie mechanism, or because the IOR encodes a valid object reference). There are no known holes or exploits known on the incoming request handler in ORBit and if you know of anyone, we would love to fix that problem.
44. | Are communications between components in Bonobo encrypted?
| We depend on the ORBit layer to do any kind of encryption of the data. The current version of ORBit does not use SSL or any other secure transports, although patches for it are available. FIXME: where are these patches available from? The current version of ORBit (ORBit2) uses OpenSSL to provide encryption services.
45. | If communications are not encrypted, why do you support them?
| We guarantee that communications on the destkop are going to be secure, as nobody on the network will be able to sniff on your connections. When you go over the network, then traffic is not encrypted and it might be subject to sniffing.
46. | What is the problem with the standard C++ CORBA binding?
47. | What naming scheme should I use for my CORBA interfaces?

If you are a GNOME/ project you need to register your GNOME/MyProject/ namespace, see bonobo/doc/NAMESPACE to see how these are allocated.

Otherwise, you should use a Java like namespacing scheme based on the DNS.

    	module Com {
    		module MyCompany {
    			module MyProduct {
    				interface MyInterface {
    				};
    			};
    		};
    	};

48. | How should I create unique OAFIIDs for components?

There are two ways to do this. Firstly, those projects with a defined namespace that implement new interfaces. To create an OAFIID simply take your namespace, and with delimiting '_' create an IID within your own defined space eg.

`OAFIID:GNOME_Evolution_Calendar_iTip_Factory`

`OAFIID:Com_MyCompany_MyProduct_Control`

A suffix of the main function of the instance eg. _Control, _Factory, _Embeddable etc. is encouraged for clarity.

The second method for generating OAFIIDs is appropriate for small components that implement no new interfaces, and hence need no special namespace co-ordination. Namespace the initial portion as a category grouping eg.

`OAFIID:GNOME_Panel_Applet_yetanotherclock:`

and add a UUID generated from the uuidgen application at the end to garentee uniqueness.

49. | What should I call my oaf / UI / IDL file ?
| The name of your oaf file should be based on your portion of the namespace, eg. `GNOME_Evolution_Calendar.oaf` `Com_MyCompany_MyProduct.oaf` This ensures that there will be no conflicts installing oaf files into a common directory.
50. | How should I name my CORBA methods ?

CORBA methods should be named using mixed caps, following a convention similar to that of Java convention. ie. method names should be verbs or verb phrases in mixed case with the first leter lowercase and the first letter of any further words capitalized.

    interface MyInterface {

    	long  getLength ();
    	void  setLength (in long l);

    	/* the ByName qualifier is a useful disambiguator */
    	long  getValueByName (in string name);

    	/* Factory methods should be named createWhatever */
    	Bonobo::Unknown createObject ();

    	/* Methods that test boolean conditions */
    	boolean isDirty ();
    	boolean hasLongLegs ();

    	/* Mutator methods */
    	string toString ();
    	double toDouble ();

    	/* Signals */
    	oneway void notifyRename ();

    	/* Calculate a number of types */
    	long countObjects (in Type t);
    };

With acroyms we fully capitalize eg. `getURI`, with abbreviations and contractions we capitalize the first letter eg. `setDoc` `setId`. cf. http://java.sun.com/docs/books/jls/html/6.doc.html#11186

51. | How should I name attributes and structure members?

Again, use a Java-like convention eg.

    struct MyStructure {
    	string theName;
    	long   heightInInches;
    };

52. | Why when I do a gtk_widget_show_all does my Control not show up?
| The gtk_widget_show_all should not propagate over the plug / socket boundary, you need to ensure that you do a gtk_widget_show on your control. You can of course do shows / hides on the BonoboWidget ( the server side ) to show or hide the control. This also means that as a component author, you are protected from people messing with your internal show / hide logic.
53. | Aren't Monikers just a re-implementation of the GNOME VFS? Why not use the GNOME VFS?

For a storage backend you can always use something like bonobo_storage_new ("gnome-vfs") and get away with life.

The main difference between the gnome-vfs, and monikers is that monikers are used to implement an object-based name space, while the gnome-vfs is a fine abstraction for naming files and directories. The moniker space goes well beyond this.

When Ettore, Nat and I designed the GNOME VFS in Paris Ettore had a grander vision than Nat and I had. Nat and I wanted exactly what the GNOME VFS is: an asyncronous, pluggable virtual file system implementation. Ettore wanted something more general, something that would implement an object name space. And some of the design decisions in the core of the gnome-vfs reflect some of this thinking, but the API and the infrastructure was limited to handling files.

Various months later, we finally understood completely the moniker system, and we realized that monikers were an object naming space, and that if done correctly monikers would be able to implement Ettore's initial vision for having an object-based naming space.

54. | When I run my program loads of daemons start and don't stop, why?

When you activate a Bonobo server the oaf daemon starts, this parses all your oafinfo files and then can respond to activation requests and queries.

The first access latency in this case is relatively high, the second access is extremely quick, consequently it is advantageous to leave the oafd process running on a GNOME system. Eventualy many of the GNOME desktop services will be using oaf regularly, making unloading it wasteful.

Most people are happy to have many daemons running on their machine - kswapd for example, or perhaps umpteen idle copies of mingetty - these are left running for performance reasons, and have a negligable impact on system performance.

Finally, patches are welcome to add a _user configurable_ timeout and die option for those that begrudge the couple of Mb ( including all dependant shlibs ) to oafd. The command oaf-slay can be used to kill all oaf servers at any time and one can profitably look for memory savings elsewhere.