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Subject: Re: *cause of* screen writing over restored buffer on detach/exit
To: cygwin@cygwin.com
References: <1554907871.14124.ezmlm@cygwin.com> <1919747550.7813512.1554926603758.JavaMail.zimbra@his.com>
From: Thomas Wolff <towo@towo.net>
Message-ID: <73451c62-b4ef-854c-8974-1963b05f7128@towo.net>
Date: Wed, 10 Apr 2019 23:51:34 +0200
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Hi Thomas,

Thomas Dickey wrote:
> ----- Original Message -----
> | From: "Shaddy Baddah" <lithium-cygwin@shaddybaddah.name>
> | To: "cygwin" <cygwin@cygwin.com>
> | Sent: Tuesday, April 9, 2019 11:18:19 PM
> | Subject: Re: *cause of* screen writing over restored buffer on detach/exit
>
> | On 9/4/19 4:07 pm, Shaddy Baddah wrote:
> |>
> |> This helped with screen when using Putty to a Cygwin ssh session. For
> |> some reason, it isn't helping for running screen locally in a mintty
> |> session. And it's not mintty either, because I can ssh to a Debian
> |> stretch server within mintty and I can use its screen without this
> |> issue happening. Back to the drawing board for me.
> |
> | I understand the cause of the issue now, by capturing and comparing the
> | escape characters used to control the terminal by screen on Cygwin and
> | Debian.
> |
> | It is not so much the detach/exit is the issue, although the escape
> | sequence for Cygwin includes a couple of extra xterm OSC Set Text
> | Parameters -> Change Icon Name and Window Title outputs. I misdiagnosed
> | this somehow. I can suppress the extra utmp error one of these OSC
> | outputs, but it didn't/doesn't really make a difference.
> |
> | The issue is in the escape sequences sent to the terminal by Cygwin
> | screen to switch to new windows buffer, as compared to Debian.
> |
> | Debian uses xterm sequence DECSET / ESC[?1049h in the switch to the new
> | window. Cygwin uses the two sequences ESC7 / Save Cursor (DECSC) and
> | ESC[?47l / DEC Private Mode Reset (DECRST) -> Use Normal Screen Buffer.
> |
> |
> | The reason seems to be that the Debian screen package packages a custom
> | /etc/screenrc that does not include this explicit term capability:
> |
> |
> | #
> | # Do not use xterms alternate window buffer.
> | # This one would not add lines to the scrollback buffer.
> | termcap xterm|xterms|xs ti=\E7\E[?47l
> | terminfo xterm|xterms|xs ti=\E7\E[?47l
> |
> |
> |
> | If I comment these out, my screen issue is resolved.
> |
> | I'm not suggesting this is a problem with Cygwin screen... it is using
> | the upstream settings. In fact, I am not confident to say where the
> | fault lies. Perhaps screen is right to use these sequences, but the
> | xterms used (putty and mintty) aren't doing the right thing?
>
> yes - that's one of a half-dozen cases where PuTTY has never matched xterm's behavior.
I've tested the CSI?1049h and CSI?1049l pair on xterm, pterm, mintty and 
see no difference. In what way would it not match? And what are the 
cases, do you have a list?
Thanks
Thomas

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