Re: Unset ICRNL in CBREAK mode in stty(1) following X/Open Curses

[Pádraig Brady]

On 21/01/2024 04:01, Soumendra Ganguly wrote:
> Respected maintainers,
>
> In X/Open Curses, Issue 7 (
> https://pubs.opengroup.org/onlinepubs/9699909599/toc.pdf), the following is
> mentioned about the cbreak mode:
>
> This mode achieves the same effect as non-canonical-mode, Case B input
> processing (with
> MIN set to 1 and *ICRNL cleared*) as specified in the XBD specification.
>
> For example, ncurses does this in NCURSES_SP_NAME(cbreak):
> https://github.com/mirror/ncurses/blob/87c2c84cbd2332d6d94b12a1dcaf12ad1a51a938/ncurses/tinfo/lib_raw.c#L177
>
> My question is this: I understand that the standard linked above is NOT a
> specification for stty but rather for curses, and therefore the Coreutils
> implementation of stty need not follow it. *But*, would this be a welcome
> change in stty for the sake of sticking to *some* standard? Or could this
> potentially break lots of existing projects?
>
> ---------------------------------------------
>
> Some context: I had made some changes in the tty library of Python to make
> it more standard compliant: https://github.com/python/cpython/pull/101832
>
> This is a part of a series of changes:
> https://github.com/python/cpython/issues/85984
>
> The particular change of concern is that in `tty.setcbreak()`, I unset
> ICRNL. Because of this change , some old behavior is broken:
> https://github.com/python/cpython/issues/114328
>
> Sincerely,
> Soumendra

cbreak is a mode between raw and cooked.
I.e. input _is_ sent character at a time rather than line at a time,
though there is still some processing done on some input chars.
Being somewhere between the raw/cooked extremes makes the cbreak "definition"
somewhat fuzzy as you've seen.

If I was implementing from scratch I _would_ have cbreak
clear line oriented settings like icrnl.

However given that the unix stty implementations (and python) agree
that cbreak doesn't touch icrnl, I wouldn't change it at this stage.
Also one generally has the control to easily set icrnl independently from 
cbreak,
so it's not too onerous to do that where needed.

thanks,
Pádraig.