bug#35639: 27.0.50; tramp fails to use ssh on LibreCMC (no base64 encoder available, and not mentioned in tramp manual)

[Jeronimo Pellegrini]

Hello. I believe I have found a bug in either tramp.texi or 
tramp-sh.el.

How to reproduce:

[1] set up a vanilla installation of LibreCMC (or OpenWRT, I've
reproduced this on both) on a wireless router. Suppose it's IP
it's 192.168.1.1.

[2] ssh into the router as root and create a file,

cat > test
whatever
^D

[3] from another machine, fire up emacs,

emacs -Q

[4] try to use tramp to access the file using ssh:

C-x X-f  /ssh:root@192.168.1.1:/root/test
(or using the IP address, or host name, of the router, whatever it is)


Emacs will respond with an error, complaining about a "wrong method".

This is because line 3174 of rtamp.el was reached. It is the default
case of a COND expression that has other two cases:
- (or (tramp-local-host-p v)
      (tramp-method-out-of-band-p v size))
- (rem-enc ...)

The rem-enc function should use a base64 encoding program on the
router (but LibreCMC and OpenWRT do not have it!).

If, on the router, I install base64:

# opkg install coreutils-base64

then tramp succeeds.

So, I believe this should be mentioned in the manual
(in the info node Configuration -> Remote Programs
there is a list of required programs, but neither uuencode nor
base64 are mentioned)

I'm willing to send a patch to the manual - however:
reading  lisp/net/tramp-sh.el  I get the impression that tramp
actually *should* be able to encode/decode using busybox/awk, 
which *is* available in LibreCMC (or did I get it wrong?).

So, I'm not sure if this is a tramp bug (can't use awk to encode/decode
files in base64 format) or bug in its manual (doesn't mention that
a base64 binary is needed on the remote side).

Thank you!
J.



In GNU Emacs 27.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.5)
 of 2019-05-08 built on mitra
Repository revision: 8b789755b45e6e10ed2809d7a7b89146b28452fc
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12003000
System Description: Debian GNU/Linux buster/sid

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Making completion list...

Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND DBUS GSETTINGS GLIB NOTIFY
INOTIFY LIBSELINUX GNUTLS LIBXML2 FREETYPE XFT ZLIB TOOLKIT_SCROLL_BARS
GTK3 X11 XDBE XIM THREADS LIBSYSTEMD JSON PDUMPER LCMS2 GMP

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

Major mode: Fundamental

Minor modes in effect:
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  global-eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
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  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  buffer-read-only: t
  line-number-mode: t
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Load-path shadows:
None found.

Features:
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custom widget hashtable-print-readable backquote threads dbusbind
inotify lcms2 dynamic-setting system-font-setting font-render-setting
move-toolbar gtk x-toolkit x multi-tty make-network-process emacs)

Memory information:
((conses 16 46847 6151)
 (symbols 48 5968 1)
 (strings 32 15091 1308)
 (string-bytes 1 495765)
 (vectors 16 9664)
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