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+;;; tramp-docker.el --- Tramp integration for Docker containers  -*- lexical-binding: t; -*-
+
+;; Copyright © 2022 Free Software Foundation, Inc.
+
+;; Author: Brian Cully <bjc@kublai.com>
+;; Maintainer: Brian Cully <bjc@kublai.com>
+;; URL: https://git.spork.org/tramp-docker
+;; Keywords: tramp, docker
+;; Version: 0.99.1
+;; Package-Requires: ((emacs "23"))
+
+;;; 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:
+
+;;
+;; ‘tramp-docker’ allows Tramp access to environments provided by
+;; Docker.
+;;
+;; ## Usage
+;;
+;; Call ‘tramp-docker-setup’ in your Emacs initialization.
+;;
+;;     (add-hook 'after-init-hook 'tramp-docker-setup)
+;;
+;; Open a file on a running systemd-docker container:
+;;
+;;     C-x C-f /docker:USER@CONTAINER:/path/to/file
+;;
+;; Where:
+;;     USER          is the user on the container to connect as (optional)
+;;     CONTAINER     is the container to connect to
+;;
+
+;;; Code:
+\f
+(require 'tramp)
+
+(defgroup tramp-docker nil
+  "Tramp integration for Docker containers."
+  :prefix "tramp-docker-"
+  :group 'applications
+  :link '(url-link :tag "repo" "https://git.spork.org/tramp-docker.git")
+  :link '(emacs-commentary-link :tag "Commentary" "tramp-docker"))
+
+(defcustom tramp-docker-program "docker"
+  "Name of the Docker client program."
+  :type '(choice (const "docker")
+                 (const "podman")
+                 (string))
+  :group 'tramp-docker)
+
+(defconst tramp-docker-method "docker"
+  "Tramp method name to use to connect to Docker containers.")
+
+(defun tramp-docker--completion-function (&rest _args)
+  "List Docker 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 tramp-docker-program
+                            " ps --format '{{.ID}}\t{{.Names}}'")))
+         (lines (split-string raw-list "\n"))
+         (names (mapcar (lambda (line)
+                          (let ((words (split-string line "\t")))
+                            (or (nth 1 words) (nth 0 words))))
+                        lines))
+         (machines (seq-take-while (lambda (name) name) names)))
+    (mapcar (lambda (m) (list nil m)) machines)))
+
+;; todo: check tramp-async-args and tramp-direct-async
+(defun tramp-docker--add-method ()
+  "Add Tramp method handler for Docker containers."
+  (push `(,tramp-docker-method
+          (tramp-login-program ,tramp-docker-program)
+          (tramp-login-args (("exec")
+                             ("-it")
+                             ("-u" "%u")
+                             ("%h")
+                            ("/bin/sh")))
+          (tramp-remote-shell "/bin/sh")
+          (tramp-remote-shell-login ("-l"))
+          (tramp-remote-shell-args ("-i" "-c")))
+        tramp-methods))
+
+(defun tramp-docker--remove-method ()
+  "Remove Tramp method handler for docker containers."
+  (setf (alist-get tramp-docker-method tramp-methods nil t 'string=) nil))
+
+(defun tramp-docker-unload-function ()
+  "Remove Tramp method handler and completion functions."
+  (tramp-set-completion-function tramp-docker-method nil)
+  (tramp-docker--remove-method)
+  nil)
+
+(when nil
+  (load-file (buffer-file-name))
+  (setq tramp-docker-program "doas podman")
+  (setq tramp-verbose 7) ;; default 3
+  (tramp-docker-setup)
+  (tramp-docker-unload-function))
+
+;;;###autoload
+(defun tramp-docker-setup ()
+  "Initialize Docker support for Tramp."
+  (tramp-docker--add-method)
+  (tramp-set-completion-function tramp-docker-method
+                                 '((tramp-docker--completion-function ""))))
+
+(provide 'tramp-docker)
+;;; tramp-docker.el ends here