Debian Bug report logs - #711758
buffers not cleaned before creating full screen

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Package: xterm; Maintainer for xterm is Debian X Strike Force <debian-x@lists.debian.org>; Source for xterm is src:xterm.

Reported by: jidanni@jidanni.org

Date: Sun, 9 Jun 2013 13:42:01 UTC

Severity: minor

Found in version xterm/293-1

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Report forwarded to debian-bugs-dist@lists.debian.org, Debian X Strike Force <debian-x@lists.debian.org>:
Bug#711758; Package xterm. (Sun, 09 Jun 2013 13:42:06 GMT) Full text and rfc822 format available.

Acknowledgement sent to jidanni@jidanni.org:
New Bug report received and forwarded. Copy sent to Debian X Strike Force <debian-x@lists.debian.org>. (Sun, 09 Jun 2013 13:42:06 GMT) Full text and rfc822 format available.

Message #5 received at submit@bugs.debian.org (full text, mbox):

From: jidanni@jidanni.org
To: submit@bugs.debian.org
Subject: buffers not cleaned before creating full screen
Date: Sun, 09 Jun 2013 21:39:10 +0800
Package: xterm
Version: 293-1
Severity: minor

I have no idea where to submit this.
xterm, bash, icewm, nodm, linux, terminfo?
A very very very heavily loaded system is the only place you can see
this, and only if you are lucky.
There I was in xterm,

I did
$ w3m file.html
$ ls; etc.
$ top

As the top(1) command starts 'painting' the screen,
one sees the beginning contents of the previous w3m screen momentarily,
and those contents were supposedly cleaned off the screen upon close of w3m.
even though w3m is no longer running.

I bet it is using some 'kernel buffers' or maybe just bad Terminfo
sequences. But please clear the buffer before making the "frame", even
if those first few characters will flash only momentarily.



Information forwarded to debian-bugs-dist@lists.debian.org, Debian X Strike Force <debian-x@lists.debian.org>:
Bug#711758; Package xterm. (Sun, 09 Jun 2013 14:21:30 GMT) Full text and rfc822 format available.

Acknowledgement sent to dickey@his.com:
Extra info received and forwarded to list. Copy sent to Debian X Strike Force <debian-x@lists.debian.org>. (Sun, 09 Jun 2013 14:21:30 GMT) Full text and rfc822 format available.

Message #10 received at 711758@bugs.debian.org (full text, mbox):

From: Thomas Dickey <dickey@his.com>
To: jidanni@jidanni.org, 711758@bugs.debian.org
Subject: Re: Bug#711758: buffers not cleaned before creating full screen
Date: Sun, 09 Jun 2013 10:12:28 -0400
[Message part 1 (text/plain, inline)]
On Sun, Jun 09, 2013 at 09:39:10PM +0800, jidanni@jidanni.org wrote:
> Package: xterm
> Version: 293-1
> Severity: minor
> 
> I have no idea where to submit this.
> xterm, bash, icewm, nodm, linux, terminfo?

Sounds like xterm.  To keep the logic simple (this is long ago...), xterm does
the clear-screen operation right after switching between normal/alternate
screens.  The simplification is by reusing existing functions that do each
piece rather than write a special function that clears the buffer contents
while it is inactive.

-- 
Thomas E. Dickey <dickey@invisible-island.net>
http://invisible-island.net
ftp://invisible-island.net
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Information forwarded to debian-bugs-dist@lists.debian.org, Debian X Strike Force <debian-x@lists.debian.org>:
Bug#711758; Package xterm. (Sun, 09 Jun 2013 15:33:04 GMT) Full text and rfc822 format available.

Acknowledgement sent to jidanni@jidanni.org:
Extra info received and forwarded to list. Copy sent to Debian X Strike Force <debian-x@lists.debian.org>. (Sun, 09 Jun 2013 15:33:04 GMT) Full text and rfc822 format available.

Message #15 received at 711758@bugs.debian.org (full text, mbox):

From: jidanni@jidanni.org
To: dickey@his.com
Cc: 711758@bugs.debian.org
Subject: Re: Bug#711758: buffers not cleaned before creating full screen
Date: Sun, 09 Jun 2013 23:28:42 +0800
>>>>> "T" == Thomas Dickey <dickey@his.com> writes:

T> Sounds like xterm.  To keep the logic simple (this is long ago...), xterm does
T> the clear-screen operation right after switching between normal/alternate
T> screens.  The simplification is by reusing existing functions that do each
T> piece rather than write a special function that clears the buffer contents
T> while it is inactive.

Well ... call in security! The user thought that the contents of w3m had
safely disappeared from the screen before leaving the room, never
expecting that they would be shown to the next user, no matter how
briefly.

So do clear the contents please. It can't be that expensive.



Information forwarded to debian-bugs-dist@lists.debian.org, Debian X Strike Force <debian-x@lists.debian.org>:
Bug#711758; Package xterm. (Sun, 07 Jul 2013 15:15:09 GMT) Full text and rfc822 format available.

Acknowledgement sent to Sven Joachim <svenjoac@gmx.de>:
Extra info received and forwarded to list. Copy sent to Debian X Strike Force <debian-x@lists.debian.org>. (Sun, 07 Jul 2013 15:15:09 GMT) Full text and rfc822 format available.

Message #20 received at 711758@bugs.debian.org (full text, mbox):

From: Sven Joachim <svenjoac@gmx.de>
To: jidanni@jidanni.org
Cc: 711758@bugs.debian.org, dickey@his.com
Subject: Re: Bug#711758: buffers not cleaned before creating full screen
Date: Sun, 07 Jul 2013 17:12:25 +0200
On 2013-06-09 17:28 +0200, jidanni@jidanni.org wrote:

>>>>>> "T" == Thomas Dickey <dickey@his.com> writes:
>
> T> Sounds like xterm.  To keep the logic simple (this is long ago...), xterm does
> T> the clear-screen operation right after switching between normal/alternate
> T> screens.  The simplification is by reusing existing functions that do each
> T> piece rather than write a special function that clears the buffer contents
> T> while it is inactive.
>
> Well ... call in security! The user thought that the contents of w3m had
> safely disappeared from the screen before leaving the room, never
> expecting that they would be shown to the next user, no matter how
> briefly.

If the next user is going to use your xterm, you most likely have bigger
problems than that, and they could also get the contents by choosing
"Show Alternate Screen" from the menu (Ctrl+mouse-2).

> So do clear the contents please. It can't be that expensive.

The alternate screen buffer can be cleared with the commands 
"tput smcup; tput rmcup".  Or maybe you want to set the
Xterm*titeInhibit resource to false to disable the alternate screen
altogether.

Cheers,
       Sven



Information forwarded to debian-bugs-dist@lists.debian.org, Debian X Strike Force <debian-x@lists.debian.org>:
Bug#711758; Package xterm. (Sun, 07 Jul 2013 16:45:04 GMT) Full text and rfc822 format available.

Acknowledgement sent to jidanni@jidanni.org:
Extra info received and forwarded to list. Copy sent to Debian X Strike Force <debian-x@lists.debian.org>. (Sun, 07 Jul 2013 16:45:04 GMT) Full text and rfc822 format available.

Message #25 received at 711758@bugs.debian.org (full text, mbox):

From: jidanni@jidanni.org
To: svenjoac@gmx.de
Cc: 711758@bugs.debian.org, dickey@his.com
Subject: Re: Bug#711758: buffers not cleaned before creating full screen
Date: Mon, 08 Jul 2013 00:41:20 +0800
>>>>> "SJ" == Sven Joachim <svenjoac@gmx.de> writes:
SJ> "Show Alternate Screen" from the menu (Ctrl+mouse-2).
Wow, I looked in there and found an old mutt session...!



Information forwarded to debian-bugs-dist@lists.debian.org, Debian X Strike Force <debian-x@lists.debian.org>:
Bug#711758; Package xterm. (Sun, 07 Jul 2013 18:57:09 GMT) Full text and rfc822 format available.

Acknowledgement sent to dickey@his.com:
Extra info received and forwarded to list. Copy sent to Debian X Strike Force <debian-x@lists.debian.org>. (Sun, 07 Jul 2013 18:57:09 GMT) Full text and rfc822 format available.

Message #30 received at 711758@bugs.debian.org (full text, mbox):

From: Thomas Dickey <dickey@his.com>
To: Sven Joachim <svenjoac@gmx.de>
Cc: jidanni@jidanni.org, 711758@bugs.debian.org, dickey@his.com
Subject: Re: Bug#711758: buffers not cleaned before creating full screen
Date: Sun, 07 Jul 2013 14:55:41 -0400
[Message part 1 (text/plain, inline)]
On Sun, Jul 07, 2013 at 05:12:25PM +0200, Sven Joachim wrote:
> On 2013-06-09 17:28 +0200, jidanni@jidanni.org wrote:
> 
> >>>>>> "T" == Thomas Dickey <dickey@his.com> writes:
> >
> > T> Sounds like xterm.  To keep the logic simple (this is long ago...), xterm does
> > T> the clear-screen operation right after switching between normal/alternate
> > T> screens.  The simplification is by reusing existing functions that do each
> > T> piece rather than write a special function that clears the buffer contents
> > T> while it is inactive.
> >
> > Well ... call in security! The user thought that the contents of w3m had
> > safely disappeared from the screen before leaving the room, never
> > expecting that they would be shown to the next user, no matter how
> > briefly.
> 
> If the next user is going to use your xterm, you most likely have bigger
> problems than that, and they could also get the contents by choosing
> "Show Alternate Screen" from the menu (Ctrl+mouse-2).

yes (I would have thought everyone knew that, but the level of discussion
on alternate screen tends to stop with titeInhibit).
 
> > So do clear the contents please. It can't be that expensive.
> 
> The alternate screen buffer can be cleared with the commands 
> "tput smcup; tput rmcup".  Or maybe you want to set the
> Xterm*titeInhibit resource to false to disable the alternate screen
> altogether.

that's a simple solution

(my change in #294 is still useful, of course)

-- 
Thomas E. Dickey <dickey@invisible-island.net>
http://invisible-island.net
ftp://invisible-island.net
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