NAME

       nbd_set_tls_psk_file - set the TLS Pre-Shared Keys (PSK) filename

SYNOPSIS

        #include <libnbd.h>

        int nbd_set_tls_psk_file (struct nbd_handle *h,
                                  const char *filename);

DESCRIPTION

       Set the TLS Pre-Shared Keys (PSK) filename.  This is used if trying to authenticate to the
       server using with a pre-shared key.  There is no default so if this is not set then PSK
       authentication cannot be used to connect to the server.

       This function may be called regardless of whether TLS is supported, but will have no
       effect unless nbd_set_tls(3) is also used to request or require TLS.

RETURN VALUE

       If the call is successful the function returns 0.

ERRORS

       On error "-1" is returned.

       Refer to "ERROR HANDLING" in libnbd(3) for how to get further details of the error.

HANDLE STATE

       The handle must be newly created, otherwise this call will return an error.

VERSION

       This function first appeared in libnbd 1.0.

       If you need to test if this function is available at compile time check if the following
       macro is defined:

        #define LIBNBD_HAVE_NBD_SET_TLS_PSK_FILE 1

EXAMPLE

       This example is also available as examples/encryption.c in the libnbd source code.

        /* An example showing how to connect to a server which is
         * using TLS encryption.
         *
         * This requires nbdkit, and psktool from gnutls.
         *
         * Both libnbd and nbdkit support TLS-PSK which is a
         * simpler-to-deploy form of encryption.  (Of course
         * certificate-based encryption is also supported, but
         * it’s harder to make a self-contained example).
         */

        #include <stdio.h>
        #include <stdlib.h>
        #include <string.h>
        #include <unistd.h>

        #include <libnbd.h>

        #define TMPDIR "/tmp/XXXXXX"
        #define KEYS "keys.psk"
        #define USERNAME "alice"

        static char dir[] = TMPDIR;
        static char keys[] = TMPDIR "/" KEYS;
        static char cmd[] =
          "psktool -u " USERNAME " -p " TMPDIR "/" KEYS;

        /* Remove the temporary keys file when the program
         * exits.
         */
        static void
        cleanup_keys (void)
        {
          unlink (keys);
          rmdir (dir);
        }

        /* Create the temporary keys file to share with the
         * server.
         */
        static void
        create_keys (void)
        {
          size_t i;

          if (mkdtemp (dir) == NULL) {
            perror ("mkdtemp");
            exit (EXIT_FAILURE);
          }
          i = strlen (cmd) - strlen (TMPDIR) - strlen (KEYS) - 1;
          memcpy (&cmd[i], dir, strlen (TMPDIR));
          memcpy (keys, dir, strlen (TMPDIR));

          if (system (cmd) != 0) {
            fprintf (stderr, "psktool command failed\n");
            exit (EXIT_FAILURE);
          }

          atexit (cleanup_keys);
        }

        int
        main (int argc, char *argv[])
        {
          struct nbd_handle *nbd;
          char buf[512];

          create_keys ();

          /* Create the libnbd handle. */
          nbd = nbd_create ();
          if (nbd == NULL) {
            fprintf (stderr, "%s\n", nbd_get_error ());
            exit (EXIT_FAILURE);
          }

          /* Enable TLS in the client. */
          if (nbd_set_tls (nbd, LIBNBD_TLS_REQUIRE) == -1) {
            fprintf (stderr, "%s\n", nbd_get_error ());
            exit (EXIT_FAILURE);
          }

          /* Enable TLS-PSK and pass the keys filename. */
          if (nbd_set_tls_psk_file (nbd, keys) == -1) {
            fprintf (stderr, "%s\n", nbd_get_error ());
            exit (EXIT_FAILURE);
          }

          /* Set the local username for authentication. */
          if (nbd_set_tls_username (nbd, USERNAME) == -1) {
            fprintf (stderr, "%s\n", nbd_get_error ());
            exit (EXIT_FAILURE);
          }

          /* Run nbdkit as a subprocess, enabling and requiring
           * TLS-PSK encryption.
           */
          char *args[] = {
            "nbdkit", "-s", "--exit-with-parent",
            "--tls", "require", "--tls-psk", keys,
            "pattern", "size=1M", NULL
          };
          if (nbd_connect_command (nbd, args) == -1) {
            fprintf (stderr, "%s\n", nbd_get_error ());
            exit (EXIT_FAILURE);
          }

          /* Read the first sector. */
          if (nbd_pread (nbd, buf, sizeof buf, 0, 0) == -1) {
            fprintf (stderr, "%s\n", nbd_get_error ());
            exit (EXIT_FAILURE);
          }

          /* TLS connections must be shut down. */
          if (nbd_shutdown (nbd, 0) == -1) {
            fprintf (stderr, "%s\n", nbd_get_error ());
            exit (EXIT_FAILURE);
          }

          /* Close the libnbd handle. */
          nbd_close (nbd);

          exit (EXIT_SUCCESS);
        }

SEE ALSO

       nbd_create(3), libnbd(3).

AUTHORS

       Eric Blake

       Richard W.M. Jones

COPYRIGHT

       Copyright (C) 2019 Red Hat Inc.

LICENSE

       This library is free software; you can redistribute it and/or modify it under the terms of
       the GNU Lesser General Public License as published by the Free Software Foundation; either
       version 2 of the License, or (at your option) any later version.

       This library 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 Lesser General Public License for more details.

       You should have received a copy of the GNU Lesser General Public License along with this
       library; if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth
       Floor, Boston, MA 02110-1301 USA