GIO socket-server / -client example

Question

I would like to create a server and client application that communicate via sockets using GIO. GSocketService and GSocketClient seem be perfect for this purpose but unfortunately I couldn't find some tutorial or example code (that a GLib, GIO,... newbie can understand). Does anybody know some good resources or can post example code here?

Answer 1

I finally managed to create both a simple server and client using glib and gio.
My server looks like this:

#include <glib.h>
#include <gio/gio.h>

/* this function will get called everytime a client attempts to connect */
gboolean
incoming_callback  (GSocketService *service,
                    GSocketConnection *connection,
                    GObject *source_object,
                    gpointer user_data)
{
  g_print("Received Connection from client!\n");
  GInputStream * istream = g_io_stream_get_input_stream (G_IO_STREAM (connection));
  gchar message[1024];
  g_input_stream_read  (istream,
                        message,
                        1024,
                        NULL,
                        NULL);
  g_print("Message was: \"%s\"\n", message);
  return FALSE;
}

int
main (int argc, char **argv)
{
  /* initialize glib */
  g_type_init();

  GError * error = NULL;

  /* create the new socketservice */
  GSocketService * service = g_socket_service_new ();

  /* connect to the port */
  g_socket_listener_add_inet_port ((GSocketListener*)service,
                                    1500, /* your port goes here */
                                    NULL,
                                    &error);

  /* don't forget to check for errors */
  if (error != NULL)
  {
      g_error (error->message);
  }

  /* listen to the 'incoming' signal */
  g_signal_connect (service,
                    "incoming",
                    G_CALLBACK (incoming_callback),
                    NULL);

  /* start the socket service */
  g_socket_service_start (service);

  /* enter mainloop */
  g_print ("Waiting for client!\n");
  GMainLoop *loop = g_main_loop_new(NULL, FALSE);
  g_main_loop_run(loop);
  return 0;
}

and this is the corresponding client:

#include <glib.h>
#include <gio/gio.h>

int
main (int argc, char *argv[])
{
   /* initialize glib */
  g_type_init ();

  GError * error = NULL;

  /* create a new connection */
  GSocketConnection * connection = NULL;
  GSocketClient * client = g_socket_client_new();

  /* connect to the host */
  connection = g_socket_client_connect_to_host (client,
                                               (gchar*)"localhost",
                                                1500, /* your port goes here */
                                                NULL,
                                                &error);

  /* don't forget to check for errors */
  if (error != NULL)
  {
      g_error (error->message);
  }
  else
  {
      g_print ("Connection successful!\n");
  }

  /* use the connection */
  GInputStream * istream = g_io_stream_get_input_stream (G_IO_STREAM (connection));
  GOutputStream * ostream = g_io_stream_get_output_stream (G_IO_STREAM (connection));
  g_output_stream_write  (ostream,
                          "Hello server!", /* your message goes here */
                          13, /* length of your message */
                          NULL,
                          &error);
  /* don't forget to check for errors */
  if (error != NULL)
  {
      g_error (error->message);
  }
  return 0;
}

Note though, that I am still new to glib, gio and even C, so double check my code before using it.

Answer 2

The callback from incoming should not block, from gio documentation: "The handler must initiate the handling of connection , but may not block; in essence, asynchronous operations must be used."

I had some issue with connection in the async version, it has to be referred by the user or the connection will close after the incoming callback returns.

A full example of a server that does not block, based on the example given before:

#include <gio/gio.h>
#include <glib.h>

#define BLOCK_SIZE 1024
#define PORT 2345

struct ConnData {
  GSocketConnection *connection;
  char message[BLOCK_SIZE];
};

void message_ready (GObject * source_object,
    GAsyncResult *res,
    gpointer user_data)
{
  GInputStream *istream = G_INPUT_STREAM (source_object);
  GError *error = NULL;
  struct ConnData *data = user_data;
  int count;

  count = g_input_stream_read_finish (istream,
      res,
      &error);

  if (count == -1) {
    g_error ("Error when receiving message");
    if (error != NULL) {
      g_error ("%s", error->message);
      g_clear_error (&error);
    }
  }
  g_message ("Message was: \"%s\"\n", data->message);
  g_object_unref (G_SOCKET_CONNECTION (data->connection));
  g_free (data);
}

static gboolean
incoming_callback (GSocketService *service,
    GSocketConnection * connection,
    GObject * source_object,
    gpointer user_data)
{
  g_message ("Received Connection from client!\n");
  GInputStream *istream = g_io_stream_get_input_stream (G_IO_STREAM (connection));
  struct ConnData *data = g_new (struct ConnData, 1);

  data->connection = g_object_ref (connection);

  g_input_stream_read_async (istream,
      data->message,
      sizeof (data->message),
      G_PRIORITY_DEFAULT,
      NULL,
      message_ready,
      data);
  return FALSE;
}

int main ()
{
  GSocketService *service;
  GError *error = NULL;
  gboolean ret;

  service = g_socket_service_new ();
  ret = g_socket_listener_add_inet_port (G_SOCKET_LISTENER (service),
      PORT, NULL, &error);

  if (ret && error != NULL)
  {
    g_error ("%s", error->message);
    g_clear_error (&error);
    return 1;
  }

  g_signal_connect (service,
      "incoming",
      G_CALLBACK (incoming_callback),
      NULL);

  g_socket_service_start (service);
  GMainLoop *loop = g_main_loop_new(NULL, FALSE);
  g_main_loop_run(loop);

  /* Stop service when out of the main loop*/
  g_socket_service_stop (service);
  return 0;
}