nbd_set_tls_username3

Usage

 #include <libnbd.h>
 int nbd_set_tls_username (
       struct nbd_handle *h, const char *username
     );

Overview

Set the TLS client username. This is used if authenticating with PSK over TLS is enabled. If not set then the local username is used.

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.

The following parameters must not be NULL: "h", "username". For more information see "Non-NULL parameters" in libnbd(3).

Handle state

nbd_set_tls_username can be called when the handle is in the following state:

 ┌─────────────────────────────────────┬─────────────────────────┐
 │ Handle created, before connecting   │ ✅ allowed              │
 │ Connecting                          │ ❌ error                │
 │ Connecting & handshaking (opt_mode) │ ❌ error                │
 │ Connected to the server             │ ❌ error                │
 │ Connection shut down                │ ❌ error                │
 │ Handle dead                         │ ❌ 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_USERNAME 1

Examples

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);
 }