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+;;; nspawn-tramp -- TRAMP integration for systemd-nspawn containers  -*- lexical-binding: t; -*-
+
+;; Copyright © 2021 Brian Cully <bjc@kublai.com>
+
+;; Author: Brian Cully <bjc@kublai.com>
+;; URL: https://github.com/bjc/nspawn-tramp
+;; Keywords: tramp, nspawn, machinectl, systemd, systemd-nspawn
+;; Version: 0.1
+;; Package-Requires: ((emacs "23"))
+
+;; This file is NOT part of GNU Emacs.
+
+;;; License:
+
+;; This program is free software; you can redistribute it and/or
+;; modify it under the terms of the GNU General Public License as
+;; published by the Free Software Foundation, either version 3 of the
+;; License, or (at your option) any later version.
+
+;; This program is distributed in the hope that it will be useful, but
+;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+;; General Public License for more details.
+
+;; You should have received a copy of the GNU General Public License
+;; along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+;;; Commentary:
+
+;;
+;; ‘nspawn-tramp’ allows TRAMP to work with containers provided by
+;; systemd-nspawn.
+;;
+;; ## Usage
+;;
+;; Open a file on a running systemd-nspawn container:
+;;
+;;     C-x C-f /nspawn:user@container:/path/to/file
+;;
+;; Where:
+;;     ‘user’          is the user on the container to connect as (optional)
+;;     ‘container’     is the container to connect to
+;;
+;; ## Privileges
+;;
+;; systemd-nspawn and its container utilities often require super user
+;; access to run, and this package does not do privilege escalation in
+;; order to accomplish that.
+;;
+;; One way of working around this using TRAMP’s built-in multi-hop
+;; facilities with doas or sudo to raise your privileges.
+;;
+;; Another possibility is using polkit(8) to allow specific users
+;; access to the requisite services (machinectl).
+;;
+
+;;; Code:
+
+(require 'tramp)
+
+(defgroup nspawn-tramp nil
+  "TRAMP integration for systemd-nspawn containers."
+  :prefix "nspawn-tramp-"
+  :group 'applications
+  :link '(url-link :tag "Github" "https://github.com/bjc/nspawn-tramp")
+  :link '(emacs-commentary-link :tag "Commentary" "nspawn-tramp"))
+
+(defcustom nspawn-tramp-machinectl-path "machinectl"
+  "Path to machinectl executable."
+  :type 'string
+  :group 'nspawn-tramp)
+
+;;;###autoload
+(defconst nspawn-tramp-method "nspawn"
+  "TRAMP method name to use to connect to systemd-nspawn containers.")
+
+;;;###autoload
+(defun nspawn-tramp--completion-function (&rest _args)
+  "List systemd-nspawn containers available for connection.
+
+This function is used by ‘tramp-set-completion-function’, please
+see its function help for a description of the format."
+  (let* ((raw-list (shell-command-to-string
+                    (concat nspawn-tramp-machinectl-path
+                            " list -q")))
+         (lines (cdr (split-string raw-list "\n")))
+         (first-words (mapcar (lambda (line) (car (split-string line)))
+                              lines))
+         (machines (seq-take-while (lambda (name) name) first-words)))
+    (mapcar (lambda (m) (list nil m)) machines)))
+
+;;;###autoload
+(defun nspawn-tramp--add-method ()
+  "Add TRAMP method handler for nspawn conainers."
+  (push `(,nspawn-tramp-method
+          (tramp-login-program ,nspawn-tramp-machinectl-path)
+          (tramp-login-args (("shell")
+                             ("-q")
+                             ("--uid" "%u")
+                             ("%h")))
+          (tramp-remote-shell "/bin/sh")
+          (tramp-remote-shell-login ("-l"))
+          (tramp-remote-shell-args ("-i" "-c")))
+        tramp-methods))
+
+;;;###autoload
+(defun nspawn-tramp--remove-method ()
+  "Remove TRAMP method handler for nspawn conainers."
+  (setf (alist-get nspawn-tramp-method tramp-methods nil t 'string=) nil))
+
+;;;###autoload
+(defun nspawn-tramp--init ()
+  "Initialize systemd-nspawn support for TRAMP."
+  (nspawn-tramp--remove-method)
+  (nspawn-tramp--add-method)
+  (tramp-set-completion-function nspawn-tramp-method
+                                 '((nspawn-tramp--completion-function ""))))
+
+;;;###autoload
+(eval-after-load 'tramp-remote-path
+  (nspawn-tramp--init))
+
+(provide 'nspawn-tramp)
+;;; nspawn-tramp.el ends here