Re: suppressed ACS characters, ignpar, brkint, and imaxbel

[G. Branden Robinson]

At 2024-09-28T22:59:44-0500, G. Branden Robinson wrote:
> From time to time over the years I've noticed that sometimes terminal
> emulators (usually xterm in my case) get screwed into some state where
> ACS characters just don't work.  I get the ugly 'qqqqqqqqx' nonsense
> where box borders should be.
> 
> I've tracked it down this far:
> 
> $ diff -u /tmp/{good,bad}
> --- /tmp/good   2024-09-28 22:49:05.858771398 -0500
> +++ /tmp/bad    2024-09-28 22:49:13.826766470 -0500
> @@ -3,8 +3,8 @@
>  eol2 = <undef>; swtch = <undef>; start = ^Q; stop = ^S; susp = ^Z; rprnt = 
> ^R;
>  werase = ^W; lnext = ^V; discard = ^O; min = 1; time = 0;
>  -parenb -parodd -cmspar cs8 -hupcl -cstopb cread -clocal -crtscts
> --ignbrk brkint ignpar -parmrk -inpck -istrip -inlcr -igncr icrnl ixon -ixoff
> --iuclc -ixany imaxbel iutf8
> +-ignbrk -brkint -ignpar -parmrk -inpck -istrip -inlcr -igncr icrnl -ixon 
> -ixoff
> +-iuclc -ixany -imaxbel iutf8
>  opost -olcuc -ocrnl onlcr -onocr -onlret -ofill -ofdel nl0 cr0 tab0 bs0 vt0 
> ff0
>  isig icanon iexten echo echoe echok -echonl -noflsh -xcase -tostop -echoprt
>  echoctl echoke -flusho -extproc

This may have been a red herring, or at least an incomplete indication
of the trouble.  I've isolated the following further details:

1.  The state xterm gets screwed into can be caused by catting a binary
    file to the terminal.  What I think happens is that some of this
    binary content masquerades as a terminal-control escape sequence.

2.  The same binary file, once it's done being output, leaves garbage at
    the shell prompt which will be read as input.  I thought these
    problems had been found and fixed years ago?

These seem to be separate problems; some PDFs seem to cause problem #2
but not #1.

I'm attaching a PDF that does only #2 (grodvi.1.2024-09-27.pdf) and one
that does both #1 and #2 (meintro.2024-09-27.pdf).

I'd like to know if (a) anything more can be done to prevent problem #2,
and (b) what terminal capability seems to be disabling group switching
in UTF-8 mode.  (There's an "enacs" [for "enable ACS"] but no
counterpart to disable it?)

Regards,
Branden

grodvi.1.2024-09-27.pdf
Description: Adobe PDF document

meintro.2024-09-27.pdf
Description: Adobe PDF document

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