bug#24608: 26.0.50; PTY window size initially zero

bug#24608: 26.0.50; PTY window size initially zero

[Helmut Eller]

When a subprocess tries to read the window size of the tty with the
TIOCGWINSZ ioctl the result is initially zero.  This causes problems for
programs that aren't prepared for zero sized windows.  It would be
better if the size would be initialized correctly or at least not be
zero.

To reproduce the situation compile the attached C program and execute
Emacs like this:
 emacs -Q -nw -f shell \
   --eval '(progn (sit-for 1) (insert "getwinsize") (comint-send-input))' \
   --eval '(progn (sit-for 1) (insert "getwinsize") (comint-send-input))' \
   --eval '(progn (sit-for 1) (delete-other-windows) (insert "getwinsize") (comint-send-input))'

After that, the *shell* buffer look like so:

  helmut@caladan:/tmp> getwinsize
  Window size: 0 columns 0 rows
  helmut@caladan:/tmp> getwinsize
  Window size: 0 columns 0 rows
  helmut@caladan:/tmp> getwinsize
  Window size: 80 columns 21 rows
  helmut@caladan:/tmp> 

We see that the size is initially zero but after resizing the window the
size is no longer zero.  (Note: when typing the commands manually
tab-completion may create temporary windows and will initialize the
window size as side effect.)

Here the C programm to read the window size:

/* -*- compile-command:"cc getwinsize.c -o getwinsize" -*- */
#include <sys/ioctl.h>
#include <stdio.h>
#include <errno.h>
#include <stdlib.h>
#include <string.h>

int main(int argc, char **argv)
{
  struct winsize sz;
  if (ioctl (0, TIOCGWINSZ, &sz) == -1)
    {
      printf ("ioctl failed: %s", strerror (errno));
      exit (1);
    }
  printf ("Window size: %i columns %i rows\n", sz.ws_col, sz.ws_row);
  return 0;
}


In GNU Emacs 26.0.50.1 (x86_64-unknown-linux-gnu, GTK+ Version 3.14.5)
 of 2016-10-04 built on caladan
Repository revision: e2913dc880b9843bf69cf885270551bafeb46120
Windowing system distributor 'The X.Org Foundation', version 11.0.11604000
System Description:	Debian GNU/Linux 8.5 (jessie)

Configured using:
 'configure --with-xpm=no --with-jpeg=no --with-gif=no --with-tiff=no'

Configured features:
PNG SOUND DBUS GSETTINGS NOTIFY GNUTLS LIBXML2 FREETYPE XFT ZLIB
TOOLKIT_SCROLL_BARS GTK3 X11

Important settings:
  value of $LANG: C.UTF-8
  locale-coding-system: utf-8-unix

bug#24608: 26.0.50; PTY window size initially zero

[Lars Ingebrigtsen]

Helmut Eller <eller.helmut@gmail.com> writes:

> When a subprocess tries to read the window size of the tty with the
> TIOCGWINSZ ioctl the result is initially zero.  This causes problems for
> programs that aren't prepared for zero sized windows.  It would be
> better if the size would be initialized correctly or at least not be
> zero.
>
> To reproduce the situation compile the attached C program and execute
> Emacs like this:
>  emacs -Q -nw -f shell \
>    --eval '(progn (sit-for 1) (insert "getwinsize") (comint-send-input))' \
>    --eval '(progn (sit-for 1) (insert "getwinsize") (comint-send-input))' \
>    --eval '(progn (sit-for 1) (delete-other-windows) (insert "getwinsize") (comint-send-input))'
>
> After that, the *shell* buffer look like so:
>
>   helmut@caladan:/tmp> getwinsize
>   Window size: 0 columns 0 rows
>   helmut@caladan:/tmp> getwinsize
>   Window size: 0 columns 0 rows
>   helmut@caladan:/tmp> getwinsize
>   Window size: 80 columns 21 rows
>   helmut@caladan:/tmp> 

(This bug report unfortunately got no response at the time.)

I'm not getting exactly this (in Emacs 27):

arsi@xo:~/src/emacs/trunk$ /tmp/getwinsize
/tmp/getwinsize
/tmp/getwinsize
larsi@xo:~/src/emacs/trunk$ larsi@xo:~/src/emacs/trunk$ Window size: 0 columns \
0 rows
larsi@xo:~/src/emacs/trunk$ Window size: 0 columns 0 rows
larsi@xo:~/src/emacs/trunk$ Window size: 0 columns 0 rows

But it's still wrong.  However, in Emacs 28, I'm getting:

/tmp/getwinsize
/tmp/getwinsize
/tmp/getwinsize
larsi@xo:~/src/emacs/trunk$ larsi@xo:~/src/emacs/trunk$ larsi@xo:~/src/emacs/tr\
unk$ Window size: 79 columns 21 rows
larsi@xo:~/src/emacs/trunk$ Window size: 79 columns 21 rows
larsi@xo:~/src/emacs/trunk$ Window size: 79 columns 21 rows

So I'm going to go ahead and guess that this has been fixed now, and I'm
closing this bug report.  If this is still an issue, please respond to
the debbugs address and we'll reopen.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no