bug#28139: 25.2; TRAMP vs bash 4.4 / readline 7.0 "bracketed paste" mode

bug#28139: 25.2; TRAMP vs bash 4.4 / readline 7.0 "bracketed paste" mode

[Daniel Pittman]

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After upgrading a remote system to a version of GNU/Linux that includes bash
4.4 (from Debian/testing), with the readline option `set
enable-bracketed-paste on` in /etc/inputrc, and no personal inputrc,
tramp breaks.

The exact version of `/bin/sh --version` is:
GNU bash, version 4.4.12(1)-release (x86_64-pc-linux-gnu)

Specifically, it breaks because bash emits "enable bracketed paste" and
"disable bracketed paste" CSI control sequences to the terminal around the
shell prompt.

That results in TRAMP trying to read `<ESC> [ 2 0 0 4 h "..."` as a Lisp
expression, when reading the remote `uname -sr` output, which doesn't work.

Passing the `--noediting` option to the remote shell command resolves the
problem, by disabling readline entirely, but it should also be possible to
augment the `tramp-open-connection-setup-interactive-shell` to issue,
unconditionally, the command:

    bind 'set enable-bracketed-paste off'

That will fail on some variants of /bin/sh (dash, posh, tested, but non-GNU
systems may also show this.)

Ignoring the failure should be harmless, however, both when this is not a
valid internal command, and when it is not known to the bash /
readline version.


In GNU Emacs 25.2.1 (x86_64-apple-darwin16.7.0, NS appkit-1504.83 Version
10.12.6 (Build 16G29))
 of 2017-08-08 built on slippycheeze-macbookpro.roam
Windowing system distributor 'Apple', version 10.3.1504
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bug#28139: 25.2; TRAMP vs bash 4.4 / readline 7.0 "bracketed paste" mode

[Michael Albinus]

Daniel Pittman <slippycheeze@google.com> writes:

Hi Daniel,

> After upgrading a remote system to a version of GNU/Linux that
> includes bash
> 4.4 (from Debian/testing), with the readline option `set
> enable-bracketed-paste on` in /etc/inputrc, and no personal inputrc,
> tramp breaks.

Many different shells are busy to break Tramp.

> Passing the `--noediting` option to the remote shell command resolves
> the problem, by disabling readline entirely, but it should also be
> possible to augment the
> `tramp-open-connection-setup-interactive-shell` to issue,
> unconditionally, the command:
>
>     bind 'set enable-bracketed-paste off'

Does it help to add the following line into your remote ~/.bashrc:

[ $TERM = "dumb" ] && bind 'set enable-bracketed-paste off'

Best regards, Michael.

bug#28139: 25.2; TRAMP vs bash 4.4 / readline 7.0 "bracketed paste" mode

[Daniel Pittman]

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On Sat, Aug 19, 2017 at 1:59 PM, Michael Albinus <michael.albinus@gmx.de>
wrote:

> > After upgrading a remote system to a version of GNU/Linux that
> > includes bash
> > 4.4 (from Debian/testing), with the readline option `set
> > enable-bracketed-paste on` in /etc/inputrc, and no personal inputrc,
> > tramp breaks.
>
> Many different shells are busy to break Tramp.
>

Believe me, I know the pain.  This isn't my first time poking into the
internals of how TRAMP hits remote shells.


> > Passing the `--noediting` option to the remote shell command resolves
> > the problem, by disabling readline entirely, but it should also be
> > possible to augment the
> > `tramp-open-connection-setup-interactive-shell` to issue,
> > unconditionally, the command:
> >
> >     bind 'set enable-bracketed-paste off'
>
> Does it help to add the following line into your remote ~/.bashrc:
>
> [ $TERM = "dumb" ] && bind 'set enable-bracketed-paste off'
>

Alas, no, and the bash(1) man page "INVOCATION" section makes it clear why:

    Since a shell invoked as sh does not attempt to read and
    execute commands from any other startup files,
    the --rcfile option has no effect.

Interactive testing confirms this: if I invoke the shell the as TRAMP does,
with:

env ENV='' HISTFILE='' HISTFILESIZE=0 HISTSIZE=0 PROMPT_COMMAND=''
PS1=\#\$\  PS2='' PS3='' /bin/sh

...then strace confirms that no init files are read, other than /etc/inputrc

So, it's not possible to work around this issue without injecting
additional code into the shell setup process, using `/bin/sh --noediting`,
or using an interactive shell and adding that to the .profile or equivalent.

note: --noediting has been present since bash 2.0 according to their
changelog, so it may be reasonable to add by default to the non-interactive
shell invocations.

Ultimately, though, perhaps adding the ability to run additional commands
during the interactive shell setup process and/or consuming any CSI
sequences prior to matching, would be a more future-proof solution to this.

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bug#28139: 25.2; TRAMP vs bash 4.4 / readline 7.0 "bracketed paste" mode

[Michael Albinus]

Daniel Pittman <slippycheeze@google.com> writes:

Hi Daniel,

> So, it's not possible to work around this issue without injecting
> additional code into the shell setup process, using `/bin/sh -
> -noediting`, or using an interactive shell and adding that to the .
> profile or equivalent.
>
> note: --noediting has been present since bash 2.0 according to their
> changelog, so it may be reasonable to add by default to the
> non-interactive shell invocations.
>
> Ultimately, though, perhaps adding the ability to run additional
> commands during the interactive shell setup process and/or consuming
> any CSI sequences prior to matching, would be a more future-proof
> solution to this.

Well, we have `tramp-sh-extra-args' for ages. But this doesn't work
usually, because I don't know a bullet-proof way to detect a bash shell
prior invocation, unless "*bash" is called.

Let me contemplate about. With Emacs 26 / Tramp 2.3, we have
connection-local variables. Maybe we could use it for your case.

Best regards, Michael.

bug#28139: 25.2; TRAMP vs bash 4.4 / readline 7.0 "bracketed paste" mode

[Daniel Pittman]

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On Mon, Aug 21, 2017 at 11:45 AM, Michael Albinus <michael.albinus@gmx.de>
wrote:
>
> Well, we have `tramp-sh-extra-args' for ages. But this doesn't work
> usually, because I don't know a bullet-proof way to detect a bash shell
> prior invocation, unless "*bash" is called.
>

*nod*  The best I can think of, since we already have the "outer" shell,
would be to invoke `/bin/sh --version -c exit`, which should work on any
basic posix shell, and will emit a bash version string for bash, then wait
for the prompt, and scan the output for the appropriate version data.

Let me contemplate about. With Emacs 26 / Tramp 2.3, we have
> connection-local variables. Maybe we could use it for your case.
>

FWIW, I already extend `tramp-actions-before-shell`, so something similarly
low level would be fine by me, to handle the custom stuff.

However, `ansi-color-filter-region` and friends from the shipped ANSI
SGR->face handling library can strip all control sequences out of a region,
or string, and might be useful here; that would allow TRAMP to become
insensitive to ANSI control codes injected anywhere into the output, which
will also fix the next time a shell decides to add some additional terminal
integration like bracketed paste mode.

If you want to apply this to streaming output, because that will rewrite
the buffer fragment with a smaller number of characters in the presence of
control codes, throw a marker at your endpoint, and retrieve the position
after the stripping, to avoid getting confused about the new offset.

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bug#28139: 25.2; TRAMP vs bash 4.4 / readline 7.0 "bracketed paste" mode

[Michael Albinus]

Daniel Pittman <slippycheeze@google.com> writes:

> However, `ansi-color-filter-region` and friends from the shipped ANSI
> SGR->face handling library can strip all control sequences out of a
> region, or string, and might be useful here; that would allow TRAMP to
> become insensitive to ANSI control codes injected anywhere into the
> output, which will also fix the next time a shell decides to add some
> additional terminal integration like bracketed paste mode.

Tramp does already something like this on its own, using
`tramp-display-escape-sequence-regexp' and
`tramp-device-escape-sequence-regexp'. Let me check, whether I could
rewrite this to the more general `ansi-color-filter-region`.

(I wouldn't reject a patch from your side :-)

Best regards, Michael.

bug#28139: 25.2; TRAMP vs bash 4.4 / readline 7.0 "bracketed paste" mode

[Daniel Pittman]

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On Mon, Aug 21, 2017 at 12:17 PM, Michael Albinus <michael.albinus@gmx.de>
wrote:

> Tramp does already something like this on its own, using
> `tramp-display-escape-sequence-regexp' and
> `tramp-device-escape-sequence-regexp'. Let me check, whether I could
> rewrite this to the more general `ansi-color-filter-region`.
>

So it does, in versions newer than what is shipped with Emacs.  Is the
current release of TRAMP available through any ELPA style package
repository, or do I need obtain and compile it myself to use it ahead of
the built-in?  I'll certainly do that, but I'm lazy.


> (I wouldn't reject a patch from your side :-)
>

If I confirm it still exists in the current version I'll try and cut a
patch for this, but my contribution time is limited, I'm afraid.

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bug#28139: 25.2; TRAMP vs bash 4.4 / readline 7.0 "bracketed paste" mode

[Michael Albinus]

Daniel Pittman <slippycheeze@google.com> writes:

Hi Daniel,

> Is the current release of TRAMP available through any ELPA style
> package repository, or do I need obtain and compile it myself to use
> it ahead of the built-in?  I'll certainly do that, but I'm lazy.

A while ago, I've started to transform Tramp into an ELPA package. There
were some non-trivial problems, this task is stalled for the moment.

So you must use Tramp's git repository:

git clone git://git.savannah.gnu.org/tramp.git

>     (I wouldn't reject a patch from your side :-)
>
> If I confirm it still exists in the current version I'll try and cut a
> patch for this, but my contribution time is limited, I'm afraid.

Take your time, there's no rush. The next regular Tramp release is
scheduled for end of the year.

If it helps you, I could also add your login to the Tramp repo. You
would need a Savannah account, maybe you have already.

Best regards, Michael.

bug#28139: 25.2; TRAMP vs bash 4.4 / readline 7.0 "bracketed paste" mode

[Daniel Pittman]

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On Fri, Aug 25, 2017 at 3:31 AM, Michael Albinus <michael.albinus@gmx.de>
wrote:

> Daniel Pittman <slippycheeze@google.com> writes:
> >     (I wouldn't reject a patch from your side :-)
> >
> > If I confirm it still exists in the current version I'll try and cut a
> > patch for this, but my contribution time is limited, I'm afraid.
>
> Take your time, there's no rush. The next regular Tramp release is
> scheduled for end of the year.
>

Please find attached a patch that resolves the bracketed paste issues
nicely for me.  It does so by setting two environment variables when
initially establishing the remote shell: `EMACS=t`, which bash interprets
to disable line editing, and `TERM=dumb`, which is a better match than the
default interactive terminal type I get.

Google own the copyright on this change, such as it is, but they have
papers on file with the FSF.  (As do I, for TRAMP, though I have not
contributed since 2000 or so, haha.)

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From 57859c8daad54b895a2f50ce97db9be9e4267ff3 Mon Sep 17 00:00:00 2001
From: Daniel Pittman  <slippycheeze@google.com>
Date: Tue, 31 Oct 2017 16:02:26 -0400
Subject: [PATCH] Inform shells to avoid fancy features more vigorously

Setting the environment variable `EMACS=t` triggers bash(1) to disable
various line editing features - critically, including bracketed paste
mode, which TRAMP doesn't work with.

In addition, setting `TERM=dumb` provides additional feedback to tools
that they should avoid fancy outputs and features, while again, better
matching how TRAMP expects to interact with the shell.
---
 lisp/tramp-sh.el | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lisp/tramp-sh.el b/lisp/tramp-sh.el
index 52a6b8fa..3c2ae348 100644
--- a/lisp/tramp-sh.el
+++ b/lisp/tramp-sh.el
@@ -3950,7 +3950,7 @@ file exists and nonzero exit status otherwise."
       ;; $HISTFILE is set according to `tramp-histfile-override'.
       (tramp-send-command
        vec (format
-	    "exec env ENV=%s %s PROMPT_COMMAND='' PS1=%s PS2='' PS3='' %s %s"
+	    "exec env EMACS=t TERM=dumb ENV=%s %s PROMPT_COMMAND='' PS1=%s PS2='' PS3='' %s %s"
             (or (getenv-internal "ENV" tramp-remote-process-environment) "")
 	    (if (stringp tramp-histfile-override)
 		(format "HISTFILE=%s"
-- 
2.15.0

bug#28139: 25.2; TRAMP vs bash 4.4 / readline 7.0 "bracketed paste" mode

[Michael Albinus]

Daniel Pittman <slippycheeze@google.com> writes:

Hi Daniel,

> Please find attached a patch that resolves the bracketed paste issues
> nicely for me.

Thanks!

> It does so by setting two environment variables when
> initially establishing the remote shell: `EMACS=t`, which bash
> interprets to disable line editing, and `TERM=dumb`, which is a better
> match than the default interactive terminal type I get.

Well, TERM=dumb setting is not needed. It is already set, inherited from
the outer environment. I've just cross-checked this.

The EMACS=t setting is much more problematic. It has been thrown away
from Emacs years ago, and it was expected that bash 4.4 honors the
replacement INSIDE_EMACS. Furthermore, it was reported that EMACS=t
settings have damaged other packages. See Emacs bug#20484 for a related
discussion.

It doesn't seem to be applicable for Tramp. So I'm kind of undecided how
to continue ...

Best regards, Michael.

bug#28139: 25.2; TRAMP vs bash 4.4 / readline 7.0 "bracketed paste" mode

[Daniel Pittman]

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Michael, you are completely right that my previous change was not
necessary.  I blame my prehistoric knowledge of Emacs here, as I wasn't
aware of the change to use INSIDE_EMACS.  On testing, it seems that EMACS=t
just happened to work in bash (for legacy reasons, probably other dinosaurs
like me), and INSIDE_EMACS also disables editing, and fixes my problem.

You are also quite correct that INSIDE_EMACS was being set by tramp.  The
problem was that it was set at the wrong time: we need it set *before* we
start the shell, to disable readline bracketed paste (and other advanced
features) before we start, for example, interrogating the remote system for
the running version with `uname` during `tramp-open-shell`.

I have attached a patch that moves two variables, TERM and INSIDE_EMACS,
out of `tramp-remote-process-environment`, and instead, handles setting
them prior to shell execution.

This has two advantages:

First, INSIDE_EMACS is visible to the shell we are about to probe for
usability, which fixes my own problem with bracketed paste support in
libreadline / bash breaking, and which makes it uniformly available on the
remote host.

Second, changes to `tramp-terminal-type` (and the TRAMP version) are now
handled correctly without having to recompute the value of
`tramp-remote-process-environment`; previously this was not done, and a
restart or user intervention would be required to correct them.

Hopefully this meets with approval, so I append both the patch, and what I
think is the appropriate changelog entry for this, to be manually added:

2017-11-13  Daniel Pittman  <slippycheeze@google.com>

* tramp-sh.el: Set TERM and INSIDE_EMACS environment earlier.
(tramp-remote-process-environment): Remove TERM and INSIDE_EMACS.
(tramp-remote-process-environment): Document their special handling.
(tramp-open-shell): Set TERM and INSIDE_EMACS prior to starting the
initial remote shell, so that it is also aware of the environment
in which it is operating.

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[-- Attachment #2: emacs-tramp-no-editing.patch --]
[-- Type: application/octet-stream, Size: 2265 bytes --]

--- 26.0.90/lisp/net/tramp-sh.el.orig	2017-11-13 13:59:24.000000000 -0500
+++ 26.0.90/lisp/net/tramp-sh.el	2017-11-13 14:38:06.000000000 -0500
@@ -533,9 +533,7 @@
 
 ;;;###tramp-autoload
 (defcustom tramp-remote-process-environment
-  `("ENV=''" "TMOUT=0" "LC_CTYPE=''"
-    ,(format "TERM=%s" tramp-terminal-type)
-    ,(format "INSIDE_EMACS='%s,tramp:%s'" emacs-version tramp-version)
+  '("ENV=''" "TMOUT=0" "LC_CTYPE=''"
     "CDPATH=" "HISTORY=" "MAIL=" "MAILCHECK=" "MAILPATH=" "PAGER=cat"
     "autocorrect=" "correct=")
   "List of environment variables to be set on the remote host.
@@ -544,8 +542,15 @@
 entry ENVVARNAME= disables the corresponding environment variable,
 which might have been set in the init files like ~/.profile.
 
-Special handling is applied to the PATH environment, which should
-not be set here. Instead, it should be set via `tramp-remote-path'."
+Special handling is applied to some environment variables,
+which should not be set here:
+
+The PATH environment variable should be set via `tramp-remote-path'.
+
+The TERM environment variable should be set via `tramp-terminal-type'.
+
+The INSIDE_EMACS environment variable will automatically be set
+based on the TRAMP and Emacs versions, and should not be set here."
   :group 'tramp
   :version "26.1"
   :type '(repeat string)
@@ -3942,9 +3947,15 @@
       ;; file clobbering $PS1.  $PROMPT_COMMAND is another way to set
       ;; the prompt in /bin/bash, it must be discarded as well.
       ;; $HISTFILE is set according to `tramp-histfile-override'.
+      ;; TERM and INSIDE_EMACS set here to ensure they have the
+      ;; correct values when the shell starts, not just processes
+      ;; run within the shell. (Which processes include our
+      ;; initial probes to ensure the remote shell is usable.)
       (tramp-send-command
        vec (format
-	    "exec env ENV=%s %s PROMPT_COMMAND='' PS1=%s PS2='' PS3='' %s %s"
+	    "exec env TERM='%s' INSIDE_EMACS='%s,tramp:%s' ENV=%s %s PROMPT_COMMAND='' PS1=%s PS2='' PS3='' %s %s"
+            tramp-terminal-type
+            emacs-version tramp-version  ; INSIDE_EMACS
             (or (getenv-internal "ENV" tramp-remote-process-environment) "")
 	    (if (stringp tramp-histfile-override)
 		(format "HISTFILE=%s"

bug#28139: 25.2; TRAMP vs bash 4.4 / readline 7.0 "bracketed paste" mode

[Michael Albinus]

Version: 26.1

Daniel Pittman <slippycheeze@google.com> writes:

Hi Daniel,

> Hopefully this meets with approval, so I append both the patch, and
> what I think is the appropriate changelog entry for this, to be
> manually added:

Thanks, it looks good. I have applied it to the emacs-26 branch, with
some minor cosmetic changes.

Closing the bug.

Best regards, Michael.