File name handler for http web URLs

[Lennart Borgman (gmail)]

I am getting so used to opening files with recentf-mode so I decided to 
see if it could be conveniently used for any files.

It looks quite easy to do so, at least on w32. I have attached an example.

However one thing that surprised me is that there is no file name 
handler for web URLs. (I am using Firefox.) Am I missing something? Is 
there perhaps such a file name handler? Or is there any obstacle against 
having one for opening web URL in external browsers?
;;; sex-mode.el --- Shell EXecute mode / Send to EXterna program
;;
;; Author: Lennart Borgman (lennart O borgman A gmail O com)
;; Created: 2008-06-01T18:41:50+0200 Sun
;; Version: 0.1
;; Last-Updated: 2008-06-01T20:21:06+0200 Sun
;; URL:
;; Keywords:
;; Compatibility:
;;
;; Features that might be required by this library:
;;
;;   None
;;
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;;
;;; Commentary:
;;
;; Open files in other programs, but add to recentf-mode etc.
;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;
;;; Change log:
;;
;;
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;;
;; 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 2, 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; see the file COPYING.  If not, write to
;; the Free Software Foundation, Inc., 51 Franklin Street, Fifth
;; Floor, Boston, MA 02110-1301, USA.
;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;
;;; Code:

(defcustom sex-open-alist
  '(
    "\\.pdf\\'"
    "\\.doc\\'"
    )
  "Alist of file name patterns to handle.
Adding to this list will cause those patterns to be added to to
`auto-mode-alist' and `file-name-handler-alist' when `sex-mode'
is on.

This means that opening those files will create a dummy buffer in
Emacs in `sex-file-mode' and an external program is called to
handle the file."
  :type '(repeat regexp)
  :group 'sex)

(defcustom sex-keep-dummy-buffer t
  "Keep dummy buffer after opening file.
See `sex-open-alist'."
  :type 'boolean
  :group 'sex)

(defvar sex-file-name nil)
(make-variable-buffer-local 'sex-file-name)

(defun sex-file-handler (operation &rest args)
  "Handler for `insert-file-contents'."
  (cond ((eq operation 'insert-file-contents)
         (unless (= 0 (buffer-size))
           (error "Buffer must be empty"))
         (let* ((name (nth 0 args))
                (exists (nth 1 args))
                (result (sex-handle-by-external name))
                (success (nth 0 result))
                (msg     (nth 1 result)))
           (setq buffer-file-name name)
           (if success
               (progn
                 (insert "This dummy buffer is used just for opening a file.\n"
                         "The file itself was sent to system for opening.\n\n"
                         "To open the file again click here:\n\n  ")
                 (save-excursion
                   (insert-text-button
                    buffer-file-name
                    'action (lambda (button)
                              (sex-handle-by-external buffer-file-name)))))
             (insert (propertize "Error\n\n" 'face 'font-lock-warning-face)
                     "Tried to send file\n\n\t"
                     buffer-file-name
                     "\n\nto system but it failed with message:\n"
                     msg))))
        ;; Handle any operation we don't know about.
        (t (let ((inhibit-file-name-handlers
                  (cons 'sex-file-handler
                        (and (eq inhibit-file-name-operation operation)
                             inhibit-file-name-handlers)))
                 (inhibit-file-name-operation operation))
             (apply operation args)))))

(defun sex-handle-by-external (&optional file)
  "Give file FILE to external program.
Return a list:

  (SUCCESS MESSAGE)

where SUCCESS is non-nil if operation succeeded and MESSAGE is an
informational message."
  (unless file (setq file buffer-file-name))
  (cond ((fboundp 'w32-shell-execute)
         (condition-case err
             (progn
               (w32-shell-execute "open" (convert-standard-filename file))
               (list t "Sent file to system"))
           (error
            (list nil (error-message-string err)))))
        (t
         (error "Don't know how to handle the file on your OS yet."))))

(define-derived-mode sex-file-mode nil
  "External"
  "Mode for files opened in external programs."
  (set-keymap-parent (current-local-map) button-buffer-map)
  (set-buffer-modified-p nil)
  (setq buffer-read-only t))

(define-minor-mode sex-mode
  "Open certain files in external programs using shell execute."
  nil
  :group 'sex
  :global t
  (if sex-mode
      (progn
        (dolist (patt sex-open-alist)
          (add-to-list 'auto-mode-alist (cons patt 'sex-file-mode))
          (add-to-list 'file-name-handler-alist (cons patt 'sex-file-handler) 
t)))
    ;; Remove from the lists:
    (dolist (patt sex-open-alist)
      (setq auto-mode-alist
            (delete (cons patt 'sex-file-mode) auto-mode-alist))
      (setq file-name-handler-alist
            (delete (cons patt 'sex-file-handler)
                    file-name-handler-alist)))))

(provide 'sex-mode)
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;;; sex-mode.el ends here