GUIS - a GUI widget server
release 1.6 on Thu, 30 Dec 2004 14:14:05 +0100
prcsproj 1.62

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Table of Contents

Software Description
License GNU General Public License
Author Basile Starynkevitch
Version 1.6
Development system Linux/Debian/Sid x86
Programming Language C
Software Dependencies
GTK 2.4 (or 2.2)
and related libraries
(Glib, Pango, Atk) required
Python 2.3 (or 2.2) recommended
PyGTK 2.2 recommended
Ruby 1.8 recommended
Ryby-Gnome2 0.11.x recommended
Slang 1.4.x optional
Slgtk 0.5.x optional

Please be nice to send me ( an email if you use this information and this Guis software.

Guis is available (as a gnuzipped source tarball) from and this document is on See also my home page on or Guis page on Freshmeat for announcement of newer versions. Please feel free to send suggestions, patches, criticisms, etc...

1  Overview and usage

This section gives a short overview with the classical adder example. Then the usage details are given.

1.1  Motivations and related stuff

Guis is a small widget server. It is a gtk2 (see based program listening on a pipe for widget requests (requests are Python [or Ruby] scripts - see using the PyGTK 2.0 binding of GTK2 to Python - see and outputting events or replies Guis is useful for programs (in particular, setuid programs or (ruby,ocaml,perl...) scripts) which do not want to link in a full widget toolkit but prefer to delegate the user interface to another process.

The choice of the scripting language is not critical provided it does have a full Gtk2 binding. Porting Guis to another scripting language should be easy.

(Many years ago, I was a satisfied user of Sun OpenWindows system with its programmable NeWS [widget] server. I still miss that widget server (see a message I posted in october 1993 on which is copied on I don't understead why the NeWS team, which also probably designed Java, did not consider to embed the JVM inside the X11 server, as a standard X11 extension, and embedding a toolkit inside Java, like Swing does, is not an answer.)

A similar project is entity - see The major difference between entity and guis is that guis is a server (listening for orders on a pipe...) while entity is a script engine.

The IRAF widget server - see had similar goals. And PicoGui is also server based.

The XUL system of mozilla (see also describes an interface with XML.

The (previously Berlin, now) Fresco server should be a corba server for widgets - which seems nearly dormant. see

1.2  Introduction

Guis is a graphical user interface program communication with a client application (using separate protocols). The application send widget building requests to Guis (so these requests are input for Guis) and handles widget events sent from Guis. Usually Guis is started with a small Python initial script which defines common functions and build some widgets. The requests are Python source code chunks. The replies (i.e. events sent back from Guis to the application) are just some textual lines sent (by some Python code calling guis_send).

Actually, Guis is strongly dependent on GTK2, and depends less of Python. The code is designed to make Guis easily portable1 to any other scripting interpreter able to evaluate requests in textual strings, provided this interpreter has a binding to GTK2. The only reason I use Python here is the availability of a nearly complete binding of Python to GTK2. (I would prefer some other scripting languages). To remind that Guis is using Python its binary is called pyguis.

Since version 1.3, Guis is also interfaced to Ruby. See section 4 below.

1.2.1  callbacks

The initial script (or the application) is responsible for installing appropriate callbacks with the connect primitive (or equivalent) of the scripting language (Python or Ruby).

IMPORTANT Callbacks in Guis should be robust: callbacks cannot raise uncaught exceptions (because they are run by the gtk_main_loop in Guis, outside of the (Python or Ruby...) interpreter. Applications should encapsulate callbacks with the appropriate mechanism (catch ... ) in the scripts.

1.2.2  initial script

Usually, Guis runs an initial script (in Python or Ruby) which is interpreted by the scripting language before entering the gtk_main_loop. This initial script usually builds the widget and defines some application specific functions (to implement the protocol specific to your application).

The initial script is run once. It is specified with the -s option or with the -scripter trick. See below 2.2 and the man page.

You might (if possible) end your initial script with a call to gtk_main_loop as provided by the (Python or Ruby) GTK2 binding. Calling it will make the request evaluation better under control and might permit exceptions in callbacks (see your documentation of the GTK binding you are using). Then you have to exit explicitly Guis (by calling the exit primitive of Python or Ruby) or tell Guis (using guis_main_loop_in_script) that you call the main loop.

I still strongly advise against uncaught exceptions in callbacks.

1.2.3  protocols

Every request sent from the application to Guis should end with two consecutive newline2 characters coded in C as \n\n or with a formfeed (coded in C as \f, decimal 12).

Obviously requests cannot contain (inside) a double newline which is a convention suitable for most scripting languages (including Python, Ruby, Ocaml, Lua, Rep-Lisp, Slang, ...).

A convenient way to debug Guis initial scripts is to run pyguis with an explicit FIFO input: make it with mkfifo /tmp/fifo and then run pyguis -s yourscript -i /tmp/fifo -o -; in another xterm, run cat >> /tmp/fifo and don't forget to end every request with a double newline (ie return) character.

Events or replies sent from Guis to the application are single lines (maybe very long) ended with a newline. They should not contain any control character (eg newline or formfeed) inside. Requests and replies are asynchronous (a request can be sent without any replies and vice versa).

The driving idea of Guis is that the input and output protocols are tailored to your application. On the input side (requests from your application to Guis) the protocol is usually made of calls to specific functions defined in the initial script. On the output side (replies or events from Guis to your application) the protocol is defined by sending (thru an appropriate primitive, usually guis_send, of the scripting language) arbitrary lines to your application from callbacks.

1.2.4  other toolkits (Qt3)?

It would be interesting to have a similar approach with QT3. I tried, and leave some (bad, incomplete, not even compilable) C++ code under the bad_qt_stuff/ directory of this Guis. Feel free to reuse this code (under a GNU license). My main problem was lack of good binding to QT3 and threading problems (notably threads are nearly incompatible with an embedded Python).

1.3  Small example

For illustration purpose, suppose we have an application which computes the sum of 2 integers, and we want to give it a nice graphical interface containing two (editable) textual entry widgets, a quit button, and a label widget displaying the sum.

Figure 1: Simple example demo window

1.3.1  protocols

We have to think first about the messages sent from the application to Guis. We need first to start the interface (giving some nice title). We will need to display a sum using displaysum and to display an error message using displayerror. And we need to stop the demo, thru a stopdemo function. All these functions are Python functions defined in the initial script file.

We also need to define the messages sent from Guis back to the application. We will send a plain END for end, and a more complex message starting with ADD to ask the application to make an addition (displaying the result with a displaysum request. The ADD message should contain the textual content of the two entry widgets. Since the textual content can be anything (it could even contain control characters like newlines) it should be encoded. We use a C like encoding convention, so will usually send ADD "1" "3" -or even ADD "\t1" "3" if the first entry starts with a tab3. The application is in charge of checking that the entries contain valid numbers.

The Guis server program buffers all input (python requests) and output (event replies), reading and writing as soon as possible.

A typical exchange between the application and Guis might be as follow; first the application starts and sends
start("pid 1234")
Then Guis shows the window and let the user interact with it. Some user interaction makes Guis send back messages like
ADD "2" "5"
To which the application responds with
When the user closes the window, Guis send back
To which the application responds with
and then exits.

When run with the -T flag, Guis opens a window to show the trace of all requests and replies (this is useful for script and application debugging):

Figure 2: Protocol trace window

1.3.2  initial Python script

We write a small Python initial script. A special trick in Guis is that if Guis is invoked with a name (i.e. argv[0] in C parlance) ending with -scripter then the next (second) argument is the initial script name. Hence we can start our script with
#! /usr/bin/env pyguis-scripter
# file guisdemo_script in -*- python -*-
With such a trick, our initial script can be invoked by any pyguis-scripter found in our $PATH. We make it a symbolic link to the pyguis executable.

We need to tell python to use the gtk module (provided by pygtk) and the guis module (builtin inside pyguis).
import gtk
import guis
Next, we need to define a callback used by the quit button; it just sends back the END string to the application

def end_cb(*args):
We also define a callback used when text entries are updated. It uses the guis.to_guis primitive to convert a C string to its textual representation but we could have used Python repr function.

We need to define the start function, invoked by the application in its first request, to build the graphical widgets and connect them to callbacks. It first builds a window and its contained vertical box (using GTK2 calls in Python):

def start(welcomsg):
    global window, xent, yent, sumlab
    window = gtk.Window(gtk.WINDOW_TOPLEVEL)
    window.set_title("Guis Demo")
    vbox = gtk.VBox(gtk.FALSE,2)
Then it builds the other widgets (details deleted here, see the source of guisdemo_script file). At last, it makes the quit button, connect it to the end_cb callback, add it into vbox and show all of the window:

    # ...
    quitbut = gtk.Button("quit")
    quitbut.connect("clicked", end_cb)
We need to define the displaysum function

def displaysum(x,y,sum):
    sumlab.set_markup(('<i>%d</i> + <i>%d</i>' % (x,y))
                       + (' = <big>%d</big>' % sum))
We need to define the displayerror function. To avoid messing the Gtk2 (pango provided) XML-like markup, we convert the message to its XML representation (i.e. using &lt; for < etc...) using the guis.xml_coded primitive.

def displayerror(message):
    sumlab.set_markup('<b>ERROR:</b> '
                      + (guis.xml_coded(message)))
A stopdemo function is also needed (see the source file).

1.3.3  client application

We suppose the client application is written in C. You can code it in any language able to communicate on channels in a textual way. We comment here parts of the file guisdemo_client.c. You don't need to link any Guis specific library to it!

We declare a big line buffer, and the requests and replies files. We could also use the glibc specific getline function which dynamically allocates the line buffer.

  char linbuf[1024];
  FILE *toguis = stdout;
  FILE *fromguis = stdin;
At first, we want to send a request like start("<b>guis</b> demo"). Requests may start with a comment used to help identify them in error messages4.

  fprintf (toguis, "#initial start\n"
           "start(\"pid %d\")\n\n",
           (int) getpid ());
  fflush (toguis);
Never forget to flush your request channel very often, and to end every request with two newlines.

Of course we need a loop to read events (or replies) messages from Guis - each of them is a single (sometimes very long) line ended with a single newline.

  while (!feof (fromguis)) {
    fgets (linbuf, sizeof (linbuf) - 1, fromguis);
if the reply line starts with ADD we scan it appropriately and ask to display a fancy line like ``2 + 3 = 5'' otherwise (bad scan because of non-numeric entries) we display ``invalid input''

    if (!strncmp (linbuf, "ADD", 3)) {
      int x=0,  y=0,  pos=0;
      if (sscanf (linbuf, "ADD \"%d\" \"%d\" %n", 
                  &x, &y, &pos) > 0 && pos > 0) {
        fprintf (toguis, "#good sum\n"
                 x, y, x + y);
      } else {
        fprintf (toguis, "#bad input\n"
                 "displayerror(\"bad input\")\n\n");
If the reply is END we stop gently (by sending a stopdemo() request and exiting):

    } else if (!strncmp (linbuf, "END", 3)) {
      fprintf (toguis, "#stop\n" "stopdemo()\n\n");
      fflush (toguis);
      sleep (1);
      exit (0);
After warning against unexpected input lines, we flush the request channel and end the loop.

    fflush (toguis);
  }; // end of while feof
Normally the while loop should never be ended, since our guis python script should signal termination with END (handled above).

2  Reference

2.1  installing Guis

You need Python (2.2.x or 2.3.y from, GTK (2.2 or better from and PyGTK (1.99.18 or 2.0 or better from to build pyguis (the Python version of Guis). You need Ruby (1.8.x) from and ruby-gnome 0.9.1 or later from to build ruguis (the Ruby version of Guis). I built a thread-less Python-2.25 which works with Guis. I am using GNU gcc (3.3) and GNU make (3.80). You may add a local file containing definitions for your installation, such as PREFIX=/usr, CC=gcc-3.3, PYTHONCFLAGS=-I/usr/include/python2.2 or PYTHONLDFLAGS=-lpython2.2 RUBY=ruby etc... you may even edit the Makefile.

First configure, either with make config or with the ./Configure script. Run it with -help to get usage information.

Then run make then make install (which usually requires to be root).

You may build only the Ruby version with make ruguis or only the Python version with make pyguis.

To run the demo, you probably need to add . or the Guis source directory to your $PATH before running or you can run the guisdemo_script -p guisdemo_client -T command. use guisdemo_rubyscript to run the Ruby version.

2.2  invoking Guis

See the man page in the source distribution for complete reference of invocation, or invoke the binay with the --help option.

Guis is usually invoked as pyguis command, or indirectly as pyguis-scripter if started by its initial script.

Guis can be started in a slave fashion (after the application has started) by specifing its input and output channels (thru the -i and -o options). You may specify file descriptors or paths as channels.

Guis can also be started as a master, by giving the application command as argument with -p. You usually need to quote this argument (because of your shell) unless the command has no spaces!

The -T option is interesting to show the exchange between guis and its application in a separate window. This is very useful to debug your initial script or your application.

The -D option (disabled with -DNDEBUG compile flag) show lots of debugging information (to debug pyguis itself).

The -L option writes all requests into a log file.

the -I or --input-enconding option set the input encoding (as supported by GLib2 on input channels). Likewise for -O or --output-enconding

3  Guis for Python

3.1  invocation

as usual, see section 2.2 above.

3.1.1  added Python primitives

In alphabetical order, here are the names wired in the guis builtin Python module. You need of course to learn and use the modules provided by pygtk to actually build any GTK2 widget! You should not explicitly call gtk_main_loop from Python, since it is is already called by pyguis

3.1.2  end_of_input_hook

With a callable argument, sets the hook called at end of input. Always return the previous hook (even without any arguments). You probably also need to set the end timeout using end_timeout below.

3.1.3  end_timeout

Get (without arguments) or set (with an integer argument) the timeout in milliseconds after which pyguis exits at end of input. Useful with end_of_input_hook above.

3.1.4  guis_send

Send the string argument on the output channel to the application. The string should not contain control characters (this is not checked) otherwise the application might have trouble scanning it. A newline is added if needed. (You may use many Python packages to build the sent string; eg you could send XML stuff).

3.1.5  main_loop_in_script

Get (without argument) or set (with a truth-value argument) the flag telling Guis that the main loop gtk_main was called from the initial script.

3.1.6  nb_replies

Get (without arguments) the number of sent replies (event lines sent to application). You might set this number with an integer argument (but I see no reason to do this).

3.1.7  nb_requests

Get the number of processed Python requests. You might set this number with an integer argument (but I see no reason to do this).

3.1.8  pipe_check_period

Get (without arguments) or set (with an integer argument) the period in milliseconds (should be 0 or 50 to 10000) to check for application termination (in master mode). Useful with end_of_input_hook above.

3.1.9  to_guis

Convert an object (or many of them, considered as a tuple) to a string sendable to the application using the following algorithm:

3.1.10  xml_coded

Quickly convert a Python string or unicode to its XML representation (so the 3 characters string a<b is converted to the 6 characters string a&lt;b), escaping characters per XML requirements: The result of guis.xml_coded is a string with only ASCII printable characters (coded 32-126).

4  Guis with Ruby

Guis has been ported to Ruby 1.8. See for more on Ruby. The binary name is ruguis (including the ruguis-scripter trick) and has the same invocation as the pyguis (Python) version. The Ruby port is in the file ru_gguis.c

This port uses the ruby-gnome2 binding of GTK2. See

The demo works in a Ruby way - it is in the guisdemo_rubyscript file and can be run as ruguis -T -D -s guisdemo_rubyscript -p guisdemo_client (provided that . is inside your $PATH)

4.1  open questions

I don't know if a builtin module can have virtual variables (as defined by the rb_define_virtual_variable C function of the Ruby runtime).

I would like to print more (e.g. the current environment in debug_extra) but I don't know how to code it.

4.2  Ruby API

There is a builtin Guis Ruby module. It contains the guis_send primitive to send a string back to the application.

$guis_nbreq, $guis_nbsend and $guis_pipecheckperiod are (global) virtual variables (implemented thru rb_define_virtual_variable C function).

$guis_main_loop_in_script is a global variable which when set to a true value avoid calling gtk_main after interpreting the initial script (which should hence call Gtk.main explicitly).

Conversion to XML notation is done by the to_xml method added to the existing String class.

Conversion to a C-like notation (like to_guis in Python above 3.1.9) is done by the to_guis method with built-in implementations for arrays, strings, integers, floats, symbols. The user could add other methods to existing classes by Ruby code like

ExistingClass.class_eval { 
  def to_guis
    return "result"
Then end of input hook is settable with

Guis::on_end_of_input do |timeout|
  # user end input hook
To remove the end of input hook, just do

#removing end of input hook

5  experimental and incomplete Slang version of GUIS using slgtk

See for the Slang interpreter. See for the Slgtk binding of Slang to GTK.

The GUIS port to Slang is incomplete and barely tested. See the source code for details. Feedback is welcome.

6  Feedback

6.1  Feedback welcome

Please send comments, criticisms, suggestions and patches to (but remove the _NOSPAM and .invalid from the email) mentioning guis in the subject line. Feel free to suggestion new features. Tell me about any success stories (ie Guis use) in your applications!

I am interested by your feedback (to this guisdoc page)

Did you find this page:
Highly Interesting (1);   Interesting (2);   Uninteresting (3);   Awefully Uninteresting (4)

6.2  Change log

version 1.6
(december 30, 2004) - minor code clean.

version 1.5
(may 10, 2004) - ported to Gtk2.2, added Slang preliminary port (and non-working port to Perl).

version 1.4
(september 5, 2003) bugfix (read buffer uses GString) and added guis_main_loop_in_script), with both Python2.2 and Python2.3 support.

version 1.3
(september 2, 2003) contains the experimental Ruby port (and warns against exception in callbacks).

version 1.2
(august 31, 2003) minor fixes: just added the guis.xml_coded primitive and updated the demo and the documentation.

version 1.1
(august 30, 2003) made a major switch to Python using PyGTK previous versions used Lua).

versions <= 0.3
(march 22, 2003) and older was Lua based (with a Gtk binding to Lua generated by a CommonLisp script)

To port Guis to another language you just have to link gguis.c with a file similar to py_guis.c for your scripting language which provides the following functions : guis_initialize_interpreter(void) (called once to initialise the interpreter), guis_load_initial_script(char* scriptname) (called once with either the initial script name -a file path- or NULL), guis_interpret_request(char* request) (called for every request), and guis_end_of_input_hook(int timeout) (called at end of input with a timeout in milliseconds). These last 3 functions should return 0 if successful, or a static C string describing the error.
The newline is coded decimal 10 in ASCII or IsoLatin1
How to enter a tab character inside a Gtk entry widget is left as an exercise to the reader.
Actually requests are identified by their first line in error messages.
I passed the -disable-threads option to Python's configure script
Distinguishing floating numbers from integers with a prefix should make parsing easier for the application.

This document was translated from LATEX by HEVEA.

This article is translated to Serbo-Croatian language by Jovana Milutinovich from Geeks Education.