Re: Message-ID's secret

["Adam Sjøgren" <asjo@koldfront.dk>]

황병희 writes:

> Really i'm Gnus' fan so i'm wondering Gnus' message-id have some secret.

Secret?

> According my view:
> gnu/linux start with "87"
> darwin start with "m2"
> windows-nt start with "86" or "83"
>
> I saw the source code in message.el but still i do not
> understand. Somebody explain about that?

This is the function you want to understand:

  (defun message-unique-id ()
    ;; Don't use microseconds from (current-time), they may be unsupported.
    ;; Instead we use this randomly inited counter.
    (setq message-unique-id-char
          (% (1+ (or message-unique-id-char
                     (random (ash 1 20))))
             ;; (current-time) returns 16-bit ints,
             ;; and 2^16*25 just fits into 4 digits i base 36.
             (* 25 25)))
    (let ((tm (current-time)))
      (concat
       (if (or (eq system-type 'ms-dos)
               ;; message-number-base36 doesn't handle bigints.
               (floatp (user-uid)))
           (let ((user (downcase (user-login-name))))
             (while (string-match "[^a-z0-9_]" user)
               (aset user (match-beginning 0) ?_))
             user)
         (message-number-base36 (user-uid) -1))
       (message-number-base36 (+ (car tm)
                                 (ash (% message-unique-id-char 25) 16)) 4)
       (message-number-base36 (+ (nth 1 tm)
                                 (ash (/ message-unique-id-char 25) 16)) 4)
       ;; Append a given name, because while the generated ID is unique
       ;; to this newsreader, other newsreaders might otherwise generate
       ;; the same ID via another algorithm.
       ".fsf")))

One way to figure out what happens is to use the M-x edebug-defun
command on the function, and then calling it. You will then be able to
step through the function, seeing every return value along the way. Here
is the manual:

 · https://www.gnu.org/software/emacs/manual/html_node/eintr/edebug.html

It is quite handy!

E.g. the "87" you see is due to your uid, from the line:

         (message-number-base36 (user-uid) -1))


  Best regards,

    Adam

-- 
 "I wish *I* was a tiger!"                                     Adam Sjøgren
 "A common lament."                                       asjo@koldfront.dk