Re: Crash when restoring screen

[Thomas Dickey]

On Mon, Oct 18, 2021 at 05:33:23AM +0000, Frank Tkalcevic wrote:
> I’m porting an application from Solaris/curses to Linux/ncurses.
> 
> The applications uses scr_dump() and scr_restore() a lot when popping up
> boxes, or launching child applications.
> 
> If the terminal is made bigger by the user between the scr_dump() and
> scr_restore(), the application will crash in the ncurses library – sometimes

(I can reproduce this, have a fix)

I don't suppose this case ever worked, since even before my rewrite a few
years ago, ncurses always read into the same window size for restore as
the dump.  The getch() does the internal screen-sizing as a side-effect.

> it displays rubbish in the extended area then crashes.  It works fine on
> Solaris/curses.  I’m using xterm and teraterm.

"fine" is relative: Solaris curses won't detect the screen size-change,
so it'll continue using the same dimensions.  In some cases (particularly
if shrinking the screen), you'll get odd repainting due to wrapping.
ncurses won't wrap.

Solaris curses would "see" the size-change if you put an endwin between
the two parts (just before the getch loop).  However (reading the source
code in illumos-gate), it seems that if it does notice the size-change,
the getwin/scr_restore will return an error:

        /* if get here, everything is ok, read the curscr image */              
        if (((win = getwin(filep)) == NULL) ||                                  
            ((type == 2) && ((win1 = dupwin(win)) == NULL)) ||                  
            (win->_maxy != curscr->_maxy) || (win->_maxx != curscr->_maxx) ||   
            /* soft labels */                                                   
            (fread((char *)&magic, sizeof (int), 1, filep) != 1))               
                goto err;
 
> Sample…
> 
> 
> #include <ncurses.h>
> 
> 
> void
> main(int argc, char *argv[] )
> {
>         WINDOW *win = initscr();
> 
>         erase();
>         mvprintw(3, 10, "This is the main screen.");
> 
>         const char *filename = "scr_dump.dmp";
>         scr_dump(filename);
> 
>         erase();
>         mvprintw(5, 10, "Make the screen bigger, then press a to continue");
> 
>         while ( getch() != 'a' )
>                 continue;
> 
>         scr_restore(filename);
>         doupdate();
> 
>         mvprintw(8,10,"Press a to exit");
>         while ( getch() != 'a' )
>                 continue;
> 
>         endwin();
> }
> 
> 
> 
> 
> 
> 
> Frank Tkalcevic
> Senior Software Engineer
> T   +61 3 8610 2480
> 
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-- 
Thomas E. Dickey <dickey@invisible-island.net>
https://invisible-island.net
ftp://ftp.invisible-island.net

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