Start external process and communicate with it as soon as send messages

Question

I use gnus configured to read mails from the davmail IMAP server. This one is used to read mails from outlook and translate them according to the IMAP protocol.

When I start gnus, I configured emacs to autostart the davmail server, with following function :

(defun davmail/start ()
  "Run davmail externally for gnus."
  (interactive)
  (if (buffer-live-p "*davmail*")
      (kill-buffer "*davmail*"))
  (let ((default-directory davmail-directory))
    (start-process "davmail" "*davmail*" local-java-path "-jar" davmail-jar davmail-properties)))

The trouble is that davmail often asks to accept the outlook server certificate, which blocks gnus. To overcome this issue, I implemented this function :

(defun davmail/accept_certificate ()
  "Accept certificate."
  (interactive)
  (if (get-process "davmail")
      (process-send-string "davmail" "o\n")
    (message "No running davmail process")))

which retrieves the emacs davmail process and send to it the "o" (accept) string.

It works but it remains a little painful. I would like to trigger this function whenever the davmail process asks for certificate acceptation. Usually, it is a line containing "accept certificate (o/n) ?"

This way, I would not have to do it manually each time it occurs. But i am rather new to emacs/lisp and implementing this overpasses my skills. Could you give me some pieces of advices ?

I am aware that it is not really an emacs related issue, I could as well ask to the davmail developers to implement some kind of auto accept certificate option. But it is a good opportunity for me to improve my emacs skills.

Regards

Answer 1

You can do this by switching to using make-process and specifying a :filter function that checks for the expected output. Something like this:

(defvar davmail-output nil)
(defun davmail/start ()
  "Run davmail externally for gnus."
  (interactive)
  (setq davmail-output nil)
  (let ((default-directory davmail-directory))
    (make-process :name "davmail"
                  :buffer nil
                  :command (list local-java-path "-jar" davmail-jar davmail-properties)
                  :filter (lambda (proc string)
                            (setq davmail-output (concat davmail-output string))
                            (when (string-match "accept certificate" davmail-output)
                              (davmail/accept-certificate))))))