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GTK+ - Chat between Python y C: GIOChannel and Internet Sockets

A good exercise to get to know and practice the intricacies of handling communication channels is brewing a chat program. This example shows an example of how to realize such a 'chat' application between two windows. To make the example more exciting (and to learn a little more), I wrote the client application in Python and the server in C (though I used g++ to compile, I didn't use classes).

The main challenge was the requirement that reception be implemented asynchronously - without a wait loop - as the program was just a test for a larger control program.

There's another version available which uses FIFOs instead of sockets.

The user interface (common for Python/C)

The diagram left shows the elements used to construct the users interface:
  • GtkTextView: Used to show the conversation
  • GtkEntry: To contain the transmit buffer. It will be send when 'Enter' is pressed.
  • GtkLabel: Show the system state messages
  • GtkButton: Program Quit button

The green rectangle is the container (GtkVBox) for the entire GUI, while the GtkLabel and GtkButton are located in a GtkHBox (blue rectangle).

Client code in Python

#!/usr/bin/env python
# -*- coding: utf-8 -*-
#
#  client.py
#  
#  Copyright 2014 John Coppens <john@jcoppens.com>
#  
#  This program is free software; you can redistribute it and/or modify
#  it under the terms of the GNU General Public License as published by
#  the Free Software Foundation; either version 2 of the License, or
#  (at your option) any later version.
#  
#  This program is distributed in the hope that it will be useful,
#  but WITHOUT ANY WARRANTY; without even the implied warranty of
#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#  GNU General Public License for more details.
#  
#  You should have received a copy of the GNU General Public License
#  along with this program; if not, write to the Free Software
#  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
#  MA 02110-1301, USA.
#  
#  

import gtk
import pygtk
import socket as skt
import sys
import gobject, glib

HOST = "localhost"
PORT = 5000

class Client():
    """ The Client class takes care of our communications by socket.
    """
    def __init__(self, host, port):
        """ Create the socket, but do NOT connect yet. That way we
            can still change some parameters of the 
        """
        self.host = host
        self.port = port
        self.socket = skt.socket(skt.AF_INET, skt.SOCK_STREAM)
                                                   # Construir el zocalo
        self.show_status_cb = None
        self.show_data_cb = None
        self.data = '\n'

    def connect(self):
        """ Now really try to connect to the server.
            I really need to add an exception handler in case the server
            is not on-line.
        """
        self.socket.connect((HOST, PORT))
        self.socket.setblocking(False)
        self.fd = self.socket.fileno()             # Obtener el file descriptor
        self.show_status("Connected to " + self.host)
        glib.io_add_watch(self.fd, glib.IO_IN, self.process_input)
                                                   # Instalar la funcion en caso
                                                   # de datos recibidos

    def process_input(self, skt, cond):
        """ This function is called asynchronously when data is received.
        """
        msg = self.socket.recv(100)                # Recibir el mensage de la red
        self.show_data(msg)                        # Enviar los datos a MainWindow
        return True                                # Queremos quedar activos

    def send(self, msg):
        self.socket.send(msg)

    def show_status(self, msg):
        """ Show status changes from this class, either on the terminal,
            or else by calling the callback installed by set_status_show().
        """
        if self.show_status_cb == None:
            print "Status: ", msg
        else:
            self.show_status_cb(msg)

    def show_data(self, msg):
        """ Show received messages, either on the terminal,
            or else by calling the callback installed by set_data_show().
        """
        if self.show_data_cb == None:
            print "Data: ", msg
        else:
            self.show_data_cb(msg)

    def set_status_show(self, show_status_cb):
        self.show_status_cb = show_status_cb

    def set_data_show(self, show_data_cb):
        self.show_data_cb = show_data_cb


class MainWindow(gtk.Window):
    def __init__(self):
        gtk.Window.__init__(self);
        self.connect("delete-event", self.destroy);
        self.set_size_request(400, 300)

        # Make the upper window, which the received text.
        txtview = gtk.TextView()
        self.txtbff = gtk.TextBuffer()
        txtview.set_buffer(self.txtbff)
        txtview.set_can_focus(False)

        # This is where the text to be transmitted is typed.
        # Pressing the 'Enter' key transmits the string.
        entry = gtk.Entry()
        entry.connect("activate", self.entry_activated);

        # And the button to exit the chat program
        button = gtk.Button("Quit")
        button.set_border_width(4)
        button.set_can_focus(False)
        button.connect("clicked", self.quit_clicked)

        # Left of the button is a label, which can be used to
        # show status messages.
        hbox = gtk.HBox()
        self.statlbl = gtk.Label("")
        hbox.pack_start(self.statlbl, expand = True, fill = True)
        hbox.pack_start(button, expand = False)

        # Pack everything into a VBox, then that into the window.
        vbox = gtk.VBox()
        vbox.set_spacing(4)
        vbox.pack_start(txtview)
        vbox.pack_start(entry, expand = False)
        vbox.pack_start(hbox, expand = False)
        self.add(vbox)

        entry.grab_focus()
        self.show_all()

    def destroy(self, window, data):
        """ Called when the MainWindow is closed - this stops the
            GTK+ main loop, and terminates the program
        """
        gtk.main_quit()

    def entry_activated(self, widget):
        self.client.send(widget.get_text() + "\n")
        widget.set_text("")

    def show_status(self, msg):
        self.statlbl.set_text(msg)    

    def show_data(self, msg):
        self.txtbff.insert(self.txtbff.get_end_iter(), msg)    

    def set_client(self, client):
        """ The client is the communication system which wants to show
            things here, and get strings to transmit from the GtkEntry
        """
        self.client = client
        # We connect callbacks to get news from the client
        client.set_status_show(self.show_status)
        client.set_data_show(self.show_data)

    def quit_clicked(self, widget):
        gtk.main_quit()

    def run(self):
        gtk.main()


def main():
    main = MainWindow()                # Prepare the main window,
    client = Client(HOST, PORT)        # and the communications package
    main.set_client(client)            # Announce the client to the main window
    client.connect()                   # and try to do the real connection

    main.run()

    return 0

if __name__ == '__main__':
    main()
Code: gtk_socket_chat_client.py

Server code in C(++)

The server code consists of three parts: The main program: main.cc, and the header and code part for the communications section: fifocom.h, y fifocom.cc. The complete package compile and install: fifo_test-0.1.tar.gz

/* -*- Mode: C; indent-tabs-mode: t; c-basic-offset: 8; tab-width: 8 -*-  */
/*
 * main.cc
 * Copyright (C) 2014 John Coppens <root@on6jc>
 * 
 * socket_test is free software: you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the
 * Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 * 
 * socket_test is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 * See the GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License along
 * with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#include <gtk/gtk.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <string.h>

#include "config.h"
#include "socketcom.h"


#ifdef ENABLE_NLS
#  include <libintl.h>
#endif

/* For testing propose use the local (not installed) ui file */
/* #define UI_FILE PACKAGE_DATA_DIR"/ui/socket_test.ui" */
#define UI_FILE "src/socket_test.ui"

#define TCP_HOST "127.0.0.1"
#define TCP_PORT 5000 

GtkWidget *MainWindow,
	  *entry;
GtkTextBuffer *txtbuffer;


extern "C" gboolean
quit_button_clicked_cb(GtkButton *btn)
{
  gtk_main_quit();
}

extern "C" void
on_main_window_delete_event(GtkWidget *w)
{
  gtk_main_quit();
}

extern "C" void
tx_entry_activate(GtkEntry *entry)
{
  network_write_chars(channel, (char *) gtk_entry_get_text(entry));
  network_write_chars(channel, (char *) "\n");
  gtk_entry_set_text(entry, "");
}

void
add_to_textbuffer(char *message)
{
  GtkTextIter iter;
  
  gtk_text_buffer_get_end_iter(txtbuffer, &iter);
  gtk_text_buffer_insert(txtbuffer, &iter, message, strlen(message));
}

int
main (int argc, char *argv[])
{
  GtkWidget *txtview;
  GError *error = NULL;
  int listenfd;
	
  gtk_init(&argc, &argv);

  GtkBuilder *builder = gtk_builder_new();

  gtk_builder_add_from_file(builder, UI_FILE, &error);
  gtk_builder_connect_signals(builder, NULL);
	
  MainWindow = GTK_WIDGET(gtk_builder_get_object(builder, "main_window"));
  txtview  = GTK_WIDGET(gtk_builder_get_object(builder, "textview1"));
  MainWindow = GTK_WIDGET(gtk_builder_get_object(builder, "tx_entry"));
  
  txtbuffer = gtk_text_buffer_new(NULL);
  gtk_text_view_set_buffer(GTK_TEXT_VIEW(txtview), txtbuffer);
  
  g_object_unref(G_OBJECT(builder));

  gtk_widget_show_all(MainWindow);
	
  start_socket(TCP_HOST, TCP_PORT, add_to_textbuffer);
	
  gtk_main();
	
  close_socket(listenfd);

  return 0;
}

/* -*- Mode: C; indent-tabs-mode: t; c-basic-offset: 8; tab-width: 8 -*-  */
/*
 * socketcom.h
 * Copyright (C) 2014 Unknown <root@on6jc>
 *
 * socket_test is free software: you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the
 * Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 * 
 * socket_test is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 * See the GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License along
 * with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#ifndef _SOCKETCOM_H_
#define _SOCKETCOM_H_

typedef void (*netread_callback)(char *);

#include <gtk/gtk.h>

extern  GIOChannel *channel;

gboolean	network_read(GIOChannel *source, GIOCondition cond,
     			gpointer data);
gboolean	network_write_chars(GIOChannel *dest, char *message);
gboolean	new_connection(GSocketService *service,
			GSocketConnection *connection,
			GObject *source_object,
			gpointer user_data);
void		start_socket(const char *host, int port,
                netread_callback callback);
void		close_socket(int listenfd);

#endif // _SOCKETCOM_H_

/* -*- Mode: C; indent-tabs-mode: t; c-basic-offset: 8; tab-width: 8 -*-  */
/*
 * socketcom.cc
 * Copyright (C) 2014 Unknown <root@on6jc>
 *
 * socket_test is free software: you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the
 * Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 * 
 * socket_test is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 * See the GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License along
 * with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#include <string.h>

#include "socketcom.h"

GIOChannel *channel;

gboolean
network_read(GIOChannel *source,
             GIOCondition cond,
             gpointer data)
{
  char bff[100];
  GError  *error = NULL;
  gsize   bytes_read;
  GIOStatus ret;
  
  printf("Channel mon installed\n");
  ret = g_io_channel_read_chars(source, bff, sizeof(bff), &bytes_read, &error);
  
  if (ret == G_IO_STATUS_ERROR)
    g_error("Error reading: %s\n", error->message);
  else {
    bff[bytes_read] = 0;
    ((netread_callback) data)(bff);
    printf("Got: %s\n", bff);
  }
  return TRUE;
}

gboolean
network_write_chars(GIOChannel *dest, char *message)
{
  GError  *error = NULL;
  gsize   bytes_written;
  GIOStatus ret;
  
  printf("Trying to write %s\n", message);
  ret = g_io_channel_write_chars(dest, message, strlen(message), 
		&bytes_written, &error);
  
  if (ret == G_IO_STATUS_ERROR)
    g_error("Error writing: %s\n", error->message);

  g_io_channel_flush(dest, &error);	// Important! Else message stays
					// in the buffer
  
  return TRUE;
}

gboolean
new_connection(GSocketService *service,
               GSocketConnection *connection,
               GObject *source_object,
               gpointer user_data)
{
  g_object_ref(connection); 
 
  GSocketAddress *sockaddr;
  GInetAddress   *addr;
  guint16         port;
  
  sockaddr = g_socket_connection_get_remote_address(connection, NULL);
  addr     = g_inet_socket_address_get_address(G_INET_SOCKET_ADDRESS(sockaddr));
  port     = g_inet_socket_address_get_port(G_INET_SOCKET_ADDRESS(sockaddr));
  
  printf("New Connection from %s:%d\n", g_inet_address_to_string(addr), port);

  GSocket *socket = g_socket_connection_get_socket(connection);

  gint fd = g_socket_get_fd(socket);
  channel = g_io_channel_unix_new(fd);
  g_io_add_watch(channel, G_IO_IN, (GIOFunc) network_read, user_data);
  
  return TRUE;
}

void
start_socket(const char *host, int port, netread_callback callback)
{
  GSocketService *service;
  GInetAddress   *address;
  GSocketAddress *socket_address;
  
  service = g_socket_service_new();
  address = g_inet_address_new_from_string(host);
  socket_address = g_inet_socket_address_new(address, port);
  
  g_socket_listener_add_address(
		        G_SOCKET_LISTENER(service), 
		        socket_address, 
		        G_SOCKET_TYPE_STREAM,
		        G_SOCKET_PROTOCOL_TCP, 
		        NULL, NULL, NULL);
  g_object_unref(socket_address);
  g_object_unref(address);

  g_signal_connect(service, "incoming", G_CALLBACK(new_connection),
                (gpointer) callback);

  g_socket_service_start(service);
}


void
close_socket(int listenfd)
{
  close(listenfd);
}

Thanks

A special thanks to all those who share their code over the internet - some of which was used to implement these examples. And the people on the gtk+ IRC channel.

And to those at Pygments for the syntax coloring program.

Anjuta was used to write and test the C code, and Geany to edit the Python code.

9391


(c) John Coppens ON6JC/LW3HAZ mail