Hide password in batch mode

* doc/lispref/minibuf.texi (Intro to Minibuffers, Reading a Password):
Password hiding is available in batch mode, do not mention it in
the exclusion list.  Mention `read-hide-char'. 

* lisp/subr.el (read-passwd): Use `read-hide-char' if non-nil.  Bind it
when calling `read-string'.

* src/minibuf.c (top): Include systty.h.  Declare external
emacs_get_tty and emacs_set_tty.
(Vread_hide_char): New lisp variable.
(read_minibuf_noninteractive): Hide characters with
Vread_hide_char if it is a character.

* src/sysdep.c (emacs_get_tty, emacs_set_tty): Make them externally visible.

Fixes: debbugs:17839

1 files changed, 35 insertions, 0 deletions

diff --git a/src/minibuf.c b/src/minibuf.c
index 3042b13b7d6..122f77fff96 100644
--- a/src/minibuf.c
+++ b/src/minibuf.c
@@ -35,6 +35,10 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 #include "keymap.h"
 #include "termhooks.h"
 
+#include "systty.h"
+extern void emacs_get_tty (int, struct emacs_tty *);
+extern int emacs_set_tty (int, struct emacs_tty *, bool);
+
 /* List of buffers for use as minibuffers.
    The first element of the list is used for the outermost minibuffer
    invocation, the next element is used for a recursive minibuffer
@@ -224,6 +228,22 @@ read_minibuf_noninteractive (Lisp_Object map, Lisp_Object initial,
   char *line;
   Lisp_Object val;
   int c;
+  unsigned char hide_char = 0;
+  struct emacs_tty old, new;
+
+  /* Check, whether we need to suppress echoing.  */
+  if (CHARACTERP (Vread_hide_char))
+    hide_char = XFASTINT (Vread_hide_char);
+
+  /* Manipulate tty.  */
+  if (hide_char)
+    {
+      emacs_get_tty (fileno (stdin), &old);
+      new = old;
+      new.main.c_lflag &= ~ICANON;	/* Disable buffering */
+      new.main.c_lflag &= ~ECHO;	/* Disable echoing */
+      emacs_set_tty (fileno (stdin), &new, 0);
+    }
 
   fprintf (stdout, "%s", SDATA (prompt));
   fflush (stdout);
@@ -242,6 +262,8 @@ read_minibuf_noninteractive (Lisp_Object map, Lisp_Object initial,
 	}
       else
 	{
+	  if (hide_char)
+	    fprintf (stdout, "%c", hide_char);
 	  if (len == size)
 	    {
 	      if (STRING_BYTES_BOUND / 2 < size)
@@ -253,6 +275,13 @@ read_minibuf_noninteractive (Lisp_Object map, Lisp_Object initial,
 	}
     }
 
+  /* Reset tty.  */
+  if (hide_char)
+    {
+      fprintf (stdout, "\n");
+      emacs_set_tty (fileno (stdin), &old, 0);
+    }
+
   if (len || c == '\n')
     {
       val = make_string (line, len);
@@ -2079,6 +2108,12 @@ properties.  */);
      initialization-order problems.  */
   Vminibuffer_prompt_properties = list2 (intern_c_string ("read-only"), Qt);
 
+  DEFVAR_LISP ("read-hide-char", Vread_hide_char,
+	       doc: /* Whether to hide input characters in noninteractive mode.
+It must be a character, which will be used to mask the input
+characters.  This variable should never be set globally.  */);
+  Vread_hide_char = Qnil;
+
   defsubr (&Sactive_minibuffer_window);
   defsubr (&Sset_minibuffer_window);
   defsubr (&Sread_from_minibuffer);