bug#28622: 25.1; EasyPG conflicts with tar-mode

bug#28622: 25.1; EasyPG conflicts with tar-mode

[lawfullazy]

I start from 'emacs -Q' and I create an empty, encrypted tar file,
insert a file into it, and save it like so:

C-x C-f n e w . t a r . g p g <RET> I h e l l o . t x t <RET> C-x
C-s C-s O K <RET> <RET>

At this point, I enter a symmetric key from an external popup dialog:

t h i n g <RET> t h i n g <RET>

I then continue in emacs:

q C-x k <RET>

I open the encrypted tar file like so:

C-x C-f n e w . t a r . g p g <RET>

GPG Agent decrypts the file. What I expect to find is a buffer in
tar-mode, but I instead find a buffer in Fundamental mode with the
following message:

File mode specification error: (error Malformed Tar header)

Instead of a tar file encrypted with GPG, I instead have an encrypted
ASCII file with the same text as what was in the tar-mode buffer.



In GNU Emacs 25.1.1 (x86_64-pc-linux-gnu, GTK+ Version 3.22.11)
of 2017-09-19, modified by Debian built on lgw01-amd64-019
Windowing system distributor 'The X.Org Foundation', version 11.0.11903000
System Description: Ubuntu 17.04

Configured using:
'configure --build x86_64-linux-gnu --prefix=/usr
--sharedstatedir=/var/lib --libexecdir=/usr/lib
--localstatedir=/var/lib --infodir=/usr/share/info
--mandir=/usr/share/man --with-pop=yes
--enable-locallisppath=/etc/emacs25:/etc/emacs:/usr/local/share/emacs/25.1/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/25.1/site-lisp:/usr/share/emacs/site-lisp

--with-sound=alsa --build x86_64-linux-gnu --prefix=/usr
--sharedstatedir=/var/lib --libexecdir=/usr/lib
--localstatedir=/var/lib --infodir=/usr/share/info
--mandir=/usr/share/man --with-pop=yes
--enable-locallisppath=/etc/emacs25:/etc/emacs:/usr/local/share/emacs/25.1/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/25.1/site-lisp:/usr/share/emacs/site-lisp

--with-sound=alsa --with-x=yes --with-x-toolkit=gtk3
--with-toolkit-scroll-bars 'CFLAGS=-g -O2
-fdebug-prefix-map=/build/emacs25-i5Rf44/emacs25-25.1+1=.
-fstack-protector-strong
-Wformat -Werror=format-security -Wall' 'CPPFLAGS=-Wdate-time
-D_FORTIFY_SOURCE=2' 'LDFLAGS=-Wl,-Bsymbolic-functions -Wl,-z,relro''

Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND GPM DBUS GSETTINGS NOTIFY
ACL LIBSELINUX GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB
TOOLKIT_SCROLL_BARS GTK3 X11

Important settings:
value of $LANG: en_US.UTF-8
locale-coding-system: utf-8-unix

Major mode: Fundamental

Minor modes in effect:
tooltip-mode: t
global-eldoc-mode: t
electric-indent-mode: t
mouse-wheel-mode: t
tool-bar-mode: t
menu-bar-mode: t
file-name-shadow-mode: t
global-font-lock-mode: t
font-lock-mode: t
blink-cursor-mode: t
auto-composition-mode: t
auto-encryption-mode: t
auto-compression-mode: t
line-number-mode: t
transient-mark-mode: t

Recent messages:
Checking 57 files in /usr/share/emacs/25.1/lisp/calendar...
Checking 87 files in /usr/share/emacs/25.1/lisp/calc...
Checking 120 files in /usr/share/emacs/25.1/lisp/obsolete...
Checking for load-path shadows...done
You can run the command ‘report-emacs-bug’ with M-x r-em RET
Checking for load-path shadows...done
Undo!
mwheel-scroll: Beginning of buffer [6 times]
mwheel-scroll: End of buffer [4 times]
next-line: End of buffer
previous-line: Beginning of buffer

Load-path shadows:
None found.

Features:
(pp shadow sort mail-extr emacsbug message dired format-spec rfc822 mml
mml-sec password-cache gnus-util mm-decode mm-bodies mm-encode
mail-parse rfc2231 mailabbrev gmm-utils mailheader sendmail rfc2047
rfc2045 ietf-drums mm-util mail-prsvr mail-utils misearch multi-isearch
apropos thingatpt help-fns help-mode easymenu wid-edit cl-loaddefs pcase
cl-lib epa-file epa derived epg epg-config jka-compr tar-mode time-date
mule-util tooltip eldoc electric uniquify ediff-hook vc-hooks
lisp-float-type mwheel x-win term/common-win x-dnd tool-bar dnd fontset
image regexp-opt fringe tabulated-list newcomment elisp-mode lisp-mode
prog-mode register page menu-bar rfn-eshadow timer select scroll-bar
mouse jit-lock font-lock syntax facemenu font-core frame cl-generic cham
georgian utf-8-lang misc-lang vietnamese tibetan thai tai-viet lao
korean japanese eucjp-ms cp51932 hebrew greek romanian slovak czech
european ethiopic indian cyrillic chinese charscript case-table epa-hook
jka-cmpr-hook help simple abbrev minibuffer cl-preloaded nadvice
loaddefs button faces cus-face macroexp files text-properties overlay
sha1 md5 base64 format env code-pages mule custom widget
hashtable-print-readable backquote dbusbind inotify dynamic-setting
system-font-setting font-render-setting move-toolbar gtk x-toolkit x
multi-tty make-network-process emacs)

Memory information:
((conses 16 97865 13559)
(symbols 48 20624 1)
(miscs 40 71 279)
(strings 32 16766 4531)
(string-bytes 1 473696)
(vectors 16 13410)
(vector-slots 8 446423 9809)
(floats 8 175 104)
(intervals 56 773 0)
(buffers 976 27))

bug#28622: 25.1; EasyPG conflicts with tar-mode

[Adam Tack]

The issue is also present in emacs 24.5.1 and 26.1 (latest from git -
5659b2fe843627aa4b6d450758f71920143ac173).

I think that the problem is caused by the fact that
`epa-file-write-region' (which is used when saving buffers
corresponding to `.gpg' files), does not call any of the
`write-region-annotate-functions', directly or indirectly.

`tar-mode' normally uses `tar-write-region-annotate' (which is added
to `write-region-annotate-functions') to select the tar data buffer
instead of the buffer containing the file listing, when saving.

Adam

bug#28622: 25.1; EasyPG conflicts with tar-mode

[Lars Ingebrigtsen]

Adam Tack <adam.tack.513@gmail.com> writes:

> The issue is also present in emacs 24.5.1 and 26.1 (latest from git -
> 5659b2fe843627aa4b6d450758f71920143ac173).
>
> I think that the problem is caused by the fact that
> `epa-file-write-region' (which is used when saving buffers
> corresponding to `.gpg' files), does not call any of the
> `write-region-annotate-functions', directly or indirectly.
>
> `tar-mode' normally uses `tar-write-region-annotate' (which is added
> to `write-region-annotate-functions') to select the tar data buffer
> instead of the buffer containing the file listing, when saving.

Indeed.

The documentation of `write-region-annotate-functions' is nice...

----

A list of functions to be called at the start of ‘write-region’.
Each is passed two arguments, START and END as for ‘write-region’.
These are usually two numbers but not always; see the documentation
for ‘write-region’.  The function should return a list of pairs
of the form (POSITION . STRING), consisting of strings to be effectively
inserted at the specified positions of the file being written (1 means to
insert before the first byte written).  The POSITIONs must be sorted into
increasing order.

If there are several annotation functions, the lists returned by these
functions are merged destructively.  As each annotation function runs,
the variable ‘write-region-annotations-so-far’ contains a list of all
annotations returned by previous annotation functions.

An annotation function can return with a different buffer current.
Doing so removes the annotations returned by previous functions, and
resets START and END to ‘point-min’ and ‘point-max’ of the new buffer.

----

... but the only implementation of this algorithm is in C, spread out
over build_annotations and a_write.  :-/

Exposing any of that to the Lisp level doesn't seem practical (after
looking at the code for a couple of minutes), so if this is to work for
epa, then a Lisp implementation has to be written.

Before embarking on that -- has anybody looked at this before?  And
hopefully have an implementation somewhere they've just forgotten to
push?  :-)

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no