card: Let the APDU command prints a description of the status word.

* tools/card-call-scd.c (scd_apdu_strerror): New.
* tools/gpg-card.c (cmd_apdu): Print a description.
--

Pretty convenient to explore smartcards.

tools/card-call-scd.c

@@ -1709,3 +1709,33 @@ agent_get_s2k_count (void)
 
   return count;
 }
+
+
+/* Return a malloced string describing the statusword SW.  On error
+ * NULL is returned.  */
+char *
+scd_apdu_strerror (unsigned int sw)
+{
+  gpg_error_t err;
+  char line[ASSUAN_LINELENGTH];
+  membuf_t data;
+  char *buf;
+
+  err = start_agent (0);
+  if (err)
+    return NULL;
+
+  init_membuf (&data, 64);
+  snprintf (line, sizeof line, "SCD GETINFO apdu_strerror 0x%x", sw);
+  err = assuan_transact (agent_ctx, line, put_membuf_cb, &data,
+                         NULL, NULL, NULL, NULL);
+  if (err)
+    {
+      xfree (get_membuf (&data, NULL));
+      return NULL;
+    }
+
+  put_membuf (&data, "", 1);
+  buf = get_membuf (&data, NULL);
+  return buf;
+}

tools/gpg-card.c

@@ -3501,7 +3501,16 @@ cmd_apdu (card_info_t info, char *argstr)
   if (err)
     goto leave;
   if (!with_atr)
-    log_info ("Statusword: 0x%04x\n", sw);
+    {
+      if (opt.interactive || opt.verbose)
+        {
+          char *p = scd_apdu_strerror (sw);
+          log_info ("Statusword: 0x%04x (%s)\n", sw, p? p: "?");
+          xfree (p);
+        }
+      else
+        log_info ("Statusword: 0x%04x\n", sw);
+    }
   for (i=0; i < resultlen; )
     {
       size_t save_i = i;

tools/gpg-card.h

@@ -242,6 +242,9 @@ gpg_error_t scd_checkpin (const char *serialno);
 
 unsigned long agent_get_s2k_count (void);
 
+char *scd_apdu_strerror (unsigned int sw);
+
+
 /*-- card-yubikey.c --*/
 gpg_error_t yubikey_commands (card_info_t info,
                               estream_t fp, int argc, const char *argv[]);