7.3.6 Client with Resume Capability Example

This is a modification of the simple client example. Here we demonstrate the use of session resumption. The client tries to connect once using TLS, close the connection and then try to establish a new connection using the previously negotiated data.

/* This example code is placed in the public domain. */

#ifdef HAVE_CONFIG_H
# include <config.h>
#endif

#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <gnutls/gnutls.h>

/* Those functions are defined in other examples.
 */
extern void check_alert (gnutls_session_t session, int ret);
extern int tcp_connect (void);
extern void tcp_close (int sd);

#define MAX_BUF 1024
#define CAFILE "ca.pem"
#define MSG "GET / HTTP/1.0\r\n\r\n"

int
main (void)
{
  int ret;
  int sd, ii;
  gnutls_session_t session;
  char buffer[MAX_BUF + 1];
  gnutls_certificate_credentials_t xcred;

  /* variables used in session resuming 
   */
  int t;
  char *session_data = NULL;
  size_t session_data_size = 0;

  gnutls_global_init ();

  /* X509 stuff */
  gnutls_certificate_allocate_credentials (&xcred);

  gnutls_certificate_set_x509_trust_file (xcred, CAFILE, GNUTLS_X509_FMT_PEM);

  for (t = 0; t < 2; t++)
    {				/* connect 2 times to the server */

      sd = tcp_connect ();

      gnutls_init (&session, GNUTLS_CLIENT);

      gnutls_priority_set_direct (session, "PERFORMANCE:!ARCFOUR-128", NULL);

      gnutls_credentials_set (session, GNUTLS_CRD_CERTIFICATE, xcred);

      if (t > 0)
	{
	  /* if this is not the first time we connect */
	  gnutls_session_set_data (session, session_data, session_data_size);
	  free (session_data);
	}

      gnutls_transport_set_ptr (session, (gnutls_transport_ptr_t) sd);

      /* Perform the TLS handshake
       */
      ret = gnutls_handshake (session);

      if (ret < 0)
	{
	  fprintf (stderr, "*** Handshake failed\n");
	  gnutls_perror (ret);
	  goto end;
	}
      else
	{
	  printf ("- Handshake was completed\n");
	}

      if (t == 0)
	{			/* the first time we connect */
	  /* get the session data size */
	  gnutls_session_get_data (session, NULL, &session_data_size);
	  session_data = malloc (session_data_size);

	  /* put session data to the session variable */
	  gnutls_session_get_data (session, session_data, &session_data_size);

	}
      else
	{			/* the second time we connect */

	  /* check if we actually resumed the previous session */
	  if (gnutls_session_is_resumed (session) != 0)
	    {
	      printf ("- Previous session was resumed\n");
	    }
	  else
	    {
	      fprintf (stderr, "*** Previous session was NOT resumed\n");
	    }
	}

      /* This function was defined in a previous example
       */
      /* print_info(session); */

      gnutls_record_send (session, MSG, strlen (MSG));

      ret = gnutls_record_recv (session, buffer, MAX_BUF);
      if (ret == 0)
	{
	  printf ("- Peer has closed the TLS connection\n");
	  goto end;
	}
      else if (ret < 0)
	{
	  fprintf (stderr, "*** Error: %s\n", gnutls_strerror (ret));
	  goto end;
	}

      printf ("- Received %d bytes: ", ret);
      for (ii = 0; ii < ret; ii++)
	{
	  fputc (buffer[ii], stdout);
	}
      fputs ("\n", stdout);

      gnutls_bye (session, GNUTLS_SHUT_RDWR);

    end:

      tcp_close (sd);

      gnutls_deinit (session);

    }				/* for() */

  gnutls_certificate_free_credentials (xcred);

  gnutls_global_deinit ();

  return 0;
}