Reported on the mailinglist:
"
I discovered recently that if an application running inside st tries to
send a DCS string, subsequent Unicode characters get messed up. For
example, consider the following test-case:
printf '\303\277\033P\033\\\303\277'
...where:
- \303\277 is the UTF-8 encoding of U+00FF LATIN SMALL LETTER Y WITH
DIAERESIS (ÿ).
- \033P is ESC P, the token that begins a DCS string.
- \033\\ is ESC \, a token that ends a DCS string.
- \303\277 is the same ÿ character again.
If I run the above command in a VTE-based terminal, or xterm, or
QTerminal, or pterm (PuTTY), I get the output:
ÿÿ
...which is to say, the empty DCS string is ignored. However, if I run
that command inside st (as of commit 9ba7ecf), I get:
ÿÿ
...where those last two characters are \303\277 interpreted as ISO8859-1
characters, instead of UTF-8.
I spent some time tracing through the state machines in st.c, and so far
as I can tell, this is how it works currently:
- ESC P sets the "ESC_DCS" and "ESC_STR" flags, indicating that
incoming bytes should be collected into the strescseq buffer, rather
than being interpreted.
- ESC \ sets the "ESC_STR_END" flag (when ESC is received), and then
calls strhandle() (when \ is received) to interpret the collected
bytes.
- If the collected bytes begin with 'P' (i.e. if this was a DCS
string) strhandle() sets the "ESC_DCS" flag again, confusing the
state machine.
If my understanding is correct, fixing the problem should be as easy as
removing the line that sets ESC_DCS from strhandle():
diff --git a/st.c b/st.c
index ef8abd5..b5b805a 100644
--- a/st.c
+++ b/st.c
@@ -1897,7 +1897,6 @@ strhandle(void)
xsettitle(strescseq.args[0]);
return;
case 'P': /* DCS -- Device Control String */
- term.mode |= ESC_DCS;
case '_': /* APC -- Application Program Command */
case '^': /* PM -- Privacy Message */
return;
I've tried the above patch and it fixes my problem, but I don't know if
it introduces any others.
"
Similar to the xterm AllowWindowOps option, this is an option to allow or
disallow certain (non-interactive) operations that can be insecure or
exploited.
NOTE: xsettitle() is not guarded by this because st does not support printing
the window title. Else this could be exploitable (arbitrary code execution).
Similar problems have been found in the past in other terminal emulators.
The sequence for base64-encoded clipboard copy is now guarded because it allows
a sequence written to the terminal to manipulate the clipboard of the running
user non-interactively, for example:
printf '\x1b]52;0;ZWNobyBoaQ0=\a'
Add the functionality back in for xterm compatibility, but do not expose the
capability in st.info (yet).
Some notes:
It was reverted because it caused some issues with ncurses in some
configurations, namely when using BSD padding (--enable-bsdpad, BSD_TPUTS) in
ncurses it caused issues with repeating digits.
A fix has been upstreamed in ncurses since snapshot 20200523. The fix is also
backported to OpenBSD -current.
This reverts commit e8392b282c.
There is currently a bug in older ncurses versions (like on OpenBSD) where a
fix for a bug with REP is not backported yet. Most likely in tty/tty_update.c:
Noticed while using lynx (which uses ncurses/curses).
To reproduce using lynx: echo "Z0000000" | lynx -stdin
or using the program:
int
main(void)
{
WINDOW *win;
win = initscr();
printw("Z0000000");
refresh();
sleep(5);
return 0;
}
This prints "ZZZZZZZ" (incorrectly).
The sequence \e[Nb prints the last printed char N (more) times if it's
printable, and it's ignored after newline or other control chars.
This is Ecma-048/ANSI-X3.6 sequence and not DEC VT. It's supported by
xterm, and ncurses uses it when possible, e.g. when TERM is xterm* (and
with this commit also st*).
xterm supports only codepoints<=255, possibly due to internal limits.
We support any value/codepoint which was placed in a cell.
To test:
- tput rep 65 4 -> prints 'AAAA'
- printf "\342\225\246\033[4b" -> prints U+2566 1+4 times.
St uses a very good hack where mouse wheel genereates ^Y and ^E,
that are the same keys that less and vi uses for backward and
fordward scrolling. Scroll, as many terminal emulators, use
shift+Prev/Next for scrolling, but it is also using ^E and ^Y
for scroling, characters that are reserved in the POSIX shell
in emacs mode for end of line and yanking, making scroll unsable
in st.
This patch adds a new hack, making shift+wheel returning the
same sequences than shift+Prev/Next, meaning that scroll or
any other similar program will not be able to differentiate
between them.
Fix an issue with incorrect (partial) written sequences when libc wcwidth() ==
-1. The sequence is updated to on wcwidth(u) == -1:
c = "\357\277\275"
but len isn't.
A way to reproduce in practise:
* st -o dump.txt
* In the terminal: printf '\xcd\xb8'
- This is codepoint 888, on OpenBSD it reports wcwidth() == -1.
- Quit the terminal.
- Look in dump.txt (partial written sequence of "UTF_INVALID").
This was introduced in:
" commit 11625c7166
Author: czarkoff@gmail.com <czarkoff@gmail.com>
Date: Tue Oct 28 12:55:28 2014 +0100
Replace character with U+FFFD if wcwidth() is -1
Helpful when new Unicode codepoints are not recognized by libc."
Change:
Remove setting the sequence. If this happens to break something, another
solution could be setting len = 3 for the sequence.
st could easily tear/flicker with animation or other unattended
output. This commit eliminates most of the tear/flicker.
Before this commit, the display timing had two "modes":
- Interactively, st was waiting fixed `1000/xfps` ms after forwarding
the kb/mouse event to the application and before drawing.
- Unattended, and specifically with animations, the draw frequency was
throttled to `actionfps`. Animation at a higher rate would throttle
and likely tear, and at lower rates it was tearing big frames
(specifically, when one `read` didn't get a full "frame").
The interactive behavior was decent, but it was impossible to get good
unattended-draw behavior even with carefully chosen configuration.
This commit changes the behavior such that it draws on idle instead of
using fixed latency/frequency. This means that it tries to draw only
when it's very likely that the application has completed its output
(or after some duration without idle), so it mostly succeeds to avoid
tear, flicker, and partial drawing.
The config values minlatency/maxlatency replace xfps/actionfps and
define the range which the algorithm is allowed to wait from the
initial draw-trigger until the actual draw. The range enables the
flexibility to choose when to draw - when least likely to flicker.
It also unifies the interactive and unattended behavior and config
values, which makes the code simpler as well - without sacrificing
latency during interactive use, because typically interactively idle
arrives very quickly, so the wait is typically minlatency.
While it only slighly improves interactive behavior, for animations
and other unattended-drawing it improves greatly, as it effectively
adapts to any [animation] output rate without tearing, throttling,
redundant drawing, or unnecessary delays (sounds impossible, but it
works).
Stein Gunnar Bakkeby
Loic Coyle
Kipras Melnikovas