bug#23883: 24.4.51; tramp sometimes reports "Args out of range" error when resuming editing a remote file after a period of inactivity

[Michael Albinus]

MICHAEL J MCCLENNEN <mmcclenn@geology.wisc.edu> writes:

> Hi Michael,

Hi Michael,

I have added 23883@debbugs.gnu.org to Cc, again, for the archives. Pls
keep it.

I'll remove all sensitive data in my replies. In case you send me traces
containing sensitive data, you might drop off the debbugs.gnu.org
address.

> I have now done as you asked.  The attached file contains the contents
> of the tramp debug buffer generated while reproducing the bug I
> reported, with tramp-verbose set to 10.

> 08:06:26.507825 tramp-maybe-open-connection (6) # /bin/sh -i

Here Tramp did detect that the connection was broken, and it tries to
reconnect. First it opens a local shell

> 08:06:26.711851 tramp-wait-for-regexp (6) #
> :100644 100644 cdbd4deb831678472fbf42ae92a141e68cd938a2 
> 0000000000000000000000000000000000000000 Mdoc/1.2/changelog_doc.ttdiff --git 
> a/doc/1.2/changelog_doc.tt b/doc/1.2/changelog_doc.tt
> index cdbd4de..d361f88 100644
> --- a/doc/1.2/changelog_doc.tt
> +++ b/doc/1.2/changelog_doc.tt

[...]

> -New output block B<countries> returns a list of the ISO-3166-1 country codes.
> +New output block B<C<countries>> returns a list of the ISO-3166-1 country 
> codes.
>  The output includes the continent on which each country is located.
>
>  =back
> Write failed: Broken pipe
> Write failed: Broken pipe
> #$

Wow, ~540 lines garbage from the previous session. And we also see the
"Write failed: Broken pipe" message. In 'tramp-maybe-open-connection',
the current position in that buffer is preserved.

> 08:06:26.826303 tramp-send-command (6) # exec ssh   -o 
> ControlPath=/var/folders/r4/fdb5rfz92fn2s0yg7yj897mr0000gs/T/tramp.897QcO.%r@%h:%p
>  -o ControlMaster=auto -o ControlPersist=no -e none synonymy

Now Tramp tries to reconnect to the remote host synonymy. First, it did
a cleanup of the connection buffer. The preserved position is not valid
anymore.

> 08:06:28.950301 tramp-process-actions (6) #
> Last login: Sat Jul 23 22:10:45 2016 from ice.geology.wisc.edu
> perl: warning: Setting locale failed.
> perl: warning: Please check that your locale settings:
>       LC_ALL = "en_US.utf8",
>       LANG = (unset)
>     are supported and installed on your system.
> perl: warning: Falling back to the standard locale ("C").
> perl: warning: Setting locale failed.
> perl: warning: Please check that your locale settings:
>       LC_ALL = "en_US.utf8",
>       LANG = (unset)
>     are supported and installed on your system.
> perl: warning: Falling back to the standard locale ("C").
> ====== synonymy ======
> ~ (501)$
> 08:06:28.950516 tramp-get-connection-property (7) # process-buffer nil
> 08:06:28.951307 tramp-process-actions (3) # Waiting for prompts from remote 
> shell...failed

And here we are. Tramp claims a problem. The preserved position from
above is given to `tramp-process-actions' as argument, for further
handling. And because it is not valid anymore (remember, a large value),
it is out of the scope of the current buffer contents. Error.

> You asked about the remote file name: they are mainly Perl source
> code, but the same thing happens with a variety of file types.  I am
> hoping that you can figure out what method is causing the problem from
> the debug trace.  If not, can you tell me which ones should be
> checked?  I can trace through the code while it is working and try to
> figure out which method is being called.

Well, likely it is sufficient to reset the preserved position when the
buffer is cleaned up. Something like this:

--8<---------------cut here---------------start------------->8---
*** 
/home/albinus/src/tramp/lisp/tramp-sh.el.~608444a67599b876fa6c861338e6ebe4b8468d31~
 2016-07-29 14:55:39.779097246 +0200
--- /home/albinus/src/tramp/lisp/tramp-sh.el    2016-07-29 14:51:04.279291259 
+0200
***************
*** 4668,4674 ****
            (tramp-error vec 'file-error "Awake did fail")))
        (file-error
         (tramp-cleanup-connection vec t)
!        (setq p nil)))
  
      ;; New connection must be opened.
      (condition-case err
--- 4668,4675 ----
            (tramp-error vec 'file-error "Awake did fail")))
        (file-error
         (tramp-cleanup-connection vec t)
!        (setq pos (with-current-buffer (tramp-get-connection-buffer vec) 
(point))
!            p nil)))
  
      ;; New connection must be opened.
      (condition-case err
--8<---------------cut here---------------end--------------->8---

The line numbers in tramp-sh.el might differ (I've applied the patch in
Tramp's master repo), but you shall find where to apply.

Could you, pls, tell whether it works for you?

>   -- Michael

Best regards, Michael.