bug#60499: 28.2; tramp: Remote host name not always accounted when computing multi-hops

bug#60499: 28.2; tramp: Remote host name not always accounted when computing multi-hops

[Jani Juhani Sinervo]

When using a custom TRAMP method with a program that expects the host
name to be passed in as an argument to a command-line switch, the
natural way of writing the `tramp-login-args' like (("--switch" "%h"))
does not work, since `tramp-compute-multi-hops' only considers the host
name to have been used within the command template, if it is in its own
list, as in (("--switch") ("%h")).

This is a problem, because there are tools, like Toolbox[0], which
allow running the command within a specific container. For example with
Toolbox, it would look something like the following:

`toolbox run -c container-name-here command'

This can be turned into a TRAMP method relatively easily, and the most
natural way to write the `tramp-login-args' would be the following:

(tramp-login-args (("run") ("-c" "%h") ("sh")))

This however will not work for the aforementioned bug in
`tramp-compute-multi-hops'. While splitting the "-c" and "%h" into
their own lists works, and would work for the usecase of
`C-x C-f /toolbox:container-name-here:', there is a reasonable
interpretation for `C-x C-f /toolbox::', entering the default
container, in which case splitting the optional "-c"-flag from the
"host name" would not be the valid thing to do.

[0]: https://containertoolbx.org/

Steps to reproduce from `emacs -Q':

1. Evaluate the following Lisp in the scratch buffer:

(require 'tramp)
(add-to-list 'tramp-methods
             (cons "ssh4"
                   '((tramp-login-program "ssh")
                     (tramp-login-args (("-l" "%u")
                                        ("-p" "%p")
                                        ("%c")
                                        ("-e" "none")
                                        ("-t" "-t")
                                        ("-o" "RemoteCommand=\"%l\"")
                                        ("-4" "%h")))
                     (tramp-remote-shell "/bin/sh")
                     (tramp-remote-shell-login
                      ("-l"))
                     (tramp-remote-shell-args
                      ("-c")))))

2. Try to connect somewhere with this method, for example by doing:

`C-x C-f /ssh4:example.org: TAB'

Expected behavior:

TRAMP should try to connect to the host according to the method
definition.

Actual behavior:

TRAMP gives the error message:

Host name ‘example.org’ does not match
‘\`\(127\.0\.0\.1\|::1\|hostname\|localhost6?\)\'’

The code responsible can be found in `lisp/net/tramp.el' and within the
function `tramp-compute-multi-hops'. Excerpt:

;; Some methods ("su", "sg", "sudo", "doas", "ksu") do not use the
;; host name in their command template.  In this case, the remote
;; file name must use either a local host name (first hop), or a
;; host name matching the previous hop.
(let ((previous-host (or tramp-local-host-regexp "")))
  (setq choices target-alist)
  (while (setq item (pop choices))
    (let ((host (tramp-file-name-host item)))
      (unless
          (or
           ;; The host name is used for the remote shell command.
           (member
            '("%h") (tramp-get-method-parameter item 'tramp-login-
args))
           ;; The host name must match previous hop.
           (string-match-p previous-host host))
        (setq tramp-default-proxies-alist saved-tdpa)
        (tramp-user-error
         vec "Host name `%s' does not match `%s'" host previous-host))
      (setq previous-host (concat "^" (regexp-quote host) "$")))))

We notice that the culprit here is the call to `member', where it
erroneously checks for the host name being used by the command template
by only checking whether the literal list '("%h") is within the
`tramp-login-args'.

My proposed fix would be the go through the `tramp-login-args' method
parameter, and go through each of the list-of-lists to check whether
there is a string "%h" there.


In GNU Emacs 28.2 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.35,
cairo version 1.16.0)
 of 2022-12-09 built on cncf-x86-3
Windowing system distributor 'The X.Org Foundation', version
11.0.12201007
System Description: Freedesktop.org SDK 22.08 (Flatpak runtime)

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bug#60499: 28.2; tramp: Remote host name not always accounted when computing multi-hops

[Michael Albinus]

[-- Attachment #1: Type: text/plain, Size: 1987 bytes --]

Jani Juhani Sinervo <jani@sinervo.fi> writes:

Hi Jani,

> When using a custom TRAMP method with a program that expects the host
> name to be passed in as an argument to a command-line switch, the
> natural way of writing the `tramp-login-args' like (("--switch" "%h"))
> does not work, since `tramp-compute-multi-hops' only considers the host
> name to have been used within the command template, if it is in its own
> list, as in (("--switch") ("%h")).
>
> This is a problem, because there are tools, like Toolbox[0], which
> allow running the command within a specific container. For example with
> Toolbox, it would look something like the following:
>
> `toolbox run -c container-name-here command'
>
> This can be turned into a TRAMP method relatively easily, and the most
> natural way to write the `tramp-login-args' would be the following:
>
> (tramp-login-args (("run") ("-c" "%h") ("sh")))

Thanks for the bug report.

> The code responsible can be found in `lisp/net/tramp.el' and within the
> function `tramp-compute-multi-hops'. Excerpt:
>
> We notice that the culprit here is the call to `member', where it
> erroneously checks for the host name being used by the command template
> by only checking whether the literal list '("%h") is within the
> `tramp-login-args'.
>
> My proposed fix would be the go through the `tramp-login-args' method
> parameter, and go through each of the list-of-lists to check whether
> there is a string "%h" there.

I've pushed a slightly simpler fix to the emacs-29 branch, see
appended. It will appear with the upcoming Emacs 29.1.

Until it is released, you could also try to apply it in Emacs 28.2 (I
didn't check myself). Or you wait for the next GNU ELPA release of
Tramp, 2.6.0.1, which will appear later this month.

Btw, the idea with toolbox looks good. I'll see whether I could add it
to Tramp 2.7, living in the Emacs master branch. However, I'd prefer to say

(tramp-login-args (("enter") ("-c" "%h")))

Best regards, Michael.


[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #2: Type: text/x-patch, Size: 588 bytes --]

diff --git a/lisp/net/tramp.el b/lisp/net/tramp.el
index 61a606c3383..f0b17ef3934 100644
--- a/lisp/net/tramp.el
+++ b/lisp/net/tramp.el
@@ -4694,7 +4694,8 @@ tramp-compute-multi-hops
 	      (or
 	       ;; The host name is used for the remote shell command.
 	       (member
-		'("%h") (tramp-get-method-parameter item 'tramp-login-args))
+		"%h" (tramp-compat-flatten-tree
+		      (tramp-get-method-parameter item 'tramp-login-args)))
 	       ;; The host name must match previous hop.
 	       (string-match-p previous-host host))
 	    (setq tramp-default-proxies-alist saved-tdpa)

bug#60499: 28.2; tramp: Remote host name not always accounted when computing multi-hops

[Michael Albinus]

Version: 29.1

Michael Albinus <michael.albinus@gmx.de> writes:

Hi Jani,

> Btw, the idea with toolbox looks good. I'll see whether I could add it
> to Tramp 2.7, living in the Emacs master branch.

I've added this to Emacs master (Tramp 2.7).

> However, I'd prefer to say
>
> (tramp-login-args (("enter") ("-c" "%h")))

This didn't work, so I'm using "toolbox run ..." as proposed.

Since there's nothing left to do, I'm closing the bug.

Best regards, Michael.