[RFC] syslog interface

[RFC] syslog interface

[Masatake YAMATO]

Hi,

 -server option added to newer emacs is very interesting.
But to write a rael server with emacs, there may be some missing
functions in emacs.

 syslog interface is one of such function. As a system administrator,
I'd like to track the event on the emacs server on which the service written 
in elisp is running via /var/log/messages.

The first question is how do you think adding syslog interface to emacs?

If it is O.k. The second question is about its implemention.  I've
found that the protocol used in syslog is still under draft stage. So
if emacs has syslog interface and the protocol is changed, we have to
modify the syslog interface code. It is not good for the maintainers.


Will Glozer wrote syslog.el(http://glozer.net/code/syslog.el).
It has both syslog daemon side code and syslog client side code.
Here my interest is the client site code. As the file name shown
it is whole written in elisp. 

I've tried Will Glozer syslog.el. The original code only supported
inet4 socket only. I've modified it to support unix socket; and 
tried to log some message. But broken message was recorded on
/var/log/messages because the syslog protcol used in syslog.el
and the protcol which syslogd was expected were not matched.
(I used rsyslog as syslogd implemention.)

At first, I should try to improve the syslog.el and take
effort it to merge emacs. But after learning the current status
of syslog protocol definition, I've changed my mind.

My idea is using syslog implemention in libc; 
it handles the protocol, and we can expect it is maintained well. If
the protocol is changed the libc maintainer will update the function.
As the result we can use/maintain syslog interfae from elisp without 
worrying about the protocol changing.

Here is sample implemention. It comes from two parts: syslog.el and a patch
for emacs. 

How to prepare

    - Apply the patch and rebuild emacs binary.
    - eval syslog.el.
    - eval (syslog 'daemon 'alert "Hello world")
    - see the tail of /var/log/messages

Regards,
Masatake YAMATO


;;; syslog.el --- syslog interface for GNU emacs

;; Copyright (C) 2010
;; Free Software Foundation, Inc.

;; Author: Masatake YAMATO <yamato@redhat.com>
;; Keywords: processes

;; This file is NOT YET part of GNU Emacs.

;; GNU Emacs 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.

;; GNU Emacs 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 GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.

;;; Commentary:

;; ...

;; TAKEN FROM sys/syslog.h of GNU Libc.
(defconst syslog-option-table
  '((pid    . #x01)
    (cons   . #x02)
    (odelay . #x04)
    (ndelay . #x08)
    (nowait . #x10)
    (perror . #x20)))

(defconst syslog-facilities-table
  (mapcar 
   (lambda (elt)
     (cons (car elt) (ash (cdr elt) 3)))
   '((kern     . 0)
     (user     . 1)
     (mail     . 2)
     (daemon   . 3)
     (auth     . 4)
     (syslog   . 5)
     (lpr      . 6)
     (news     . 7)
     (uucp     . 8)
     (cron     . 9)
     (authpriv . 10)
     (ftp      . 11)
     (local0   . 16)
     (local1   . 17)
     (local2   . 18)
     (local3   . 19)
     (local4   . 20)
     (local5   . 21)
     (local6   . 22)
     (local7   . 23))))

(defconst syslog-levels-table
  '((emerg   . 0)
    (alert   . 1)
    (crit    . 2)
    (err     . 3)
    (warning . 4)
    (notice  . 5)
    (info    . 6)
    (debug   . 7)))

(defun openlog (ident option facility)
  (let ((option (if (listp option)
		    (apply #'logior
			   (mapcar
			    (lambda (elt)
			      (cond
			       ((symbolp elt)
				(or (cdr (assq elt syslog-option-table))
				    (error "unknown element in OPTION: %S" elt)))
			       ((integerp elt) 
				elt)
			       (t
				(error 
				 "element of OPTION must be a symbol enumerated in `syslog-facilities-table' or an integer: %S" 
				 elt))))
			    option))
		  option))
	(facility (if (symbolp facility)
		      (cdr (assq facility syslog-facilities-table))
		    facility)))
    (when (fboundp 'openlog-internal)
      (openlog-internal ident option facility))))

(defun syslog (facility level fmt &rest args)
  (let ((priority (logior 
		   (cond
		    ((symbolp facility)
		     (or (cdr (assq facility syslog-facilities-table))
			 (error
			  "facility must be a symbol enumerated in `syslog-facilities-table' or an integer: %S"
			  facility)))
		    ((integerp facility) 
		     facility)
		    (t
		     (error
		      "facility must be a symbol enumerated in `syslog-facilities-table' or an integer: %S"
		      facility)))
		   (cond
		    ((symbolp level)
		     (or (cdr (assq level syslog-levels-table))
			 (error
			  "level must be a symbol enumerated in `syslog-levels-table' or an integer: %S"
			  level)))
		    ((integerp level)
		     level)
		    (t
		     (error
		      "level must be a symbol enumerated in `syslog-levels-table' or an integer: %S"
		      level)))
		   ))
	(msg (apply #'format fmt args)))
    (when (fboundp 'syslog-internal)
      (syslog-internal priority msg))))

(defun closelog ()
  (when (fboundp 'closelog-internal)
    (closelog-internal)))

(provide 'syslog)
;;; syslog.el ends here




=== modified file 'configure.in'
*** configure.in	2010-05-21 16:31:45 +0000
--- configure.in	2010-05-26 00:24:43 +0000
***************
*** 3030,3035 ****
--- 3030,3037 ----
       declarations.  Define as empty for no equivalent.])
  fi
  
+ AC_CHECK_HEADERS(sys/syslog.h)
+ 
  dnl Fixme: AC_SYS_POSIX_TERMIOS should probably be used, but it's not clear
  dnl how the tty code is related to POSIX and/or other versions of termios.
  dnl The following looks like a useful start.

=== modified file 'src/emacs.c'
*** src/emacs.c	2010-05-15 21:16:20 +0000
--- src/emacs.c	2010-05-26 00:28:17 +0000
***************
*** 2476,2481 ****
--- 2476,2542 ----
    return Qt;
  }
  
+ #ifdef HAVE_SYS_SYSLOG_H
+ #include <syslog.h>
+ 
+ extern Lisp_Object Qundefined;
+ 
+ DEFUN ("openlog-internal", Fopenlog_internal, Sopenlog_internal, 3, 3, 0,
+        doc: /* See openlog(3). */)
+      (ident,
+       option,
+       facility)
+      Lisp_Object ident;
+      Lisp_Object option;
+      Lisp_Object facility;
q+ {
+   unsigned char *cident;
+   int coption;
+   int cfacility;
+ 
+ 
+   CHECK_STRING(ident);
+   CHECK_NUMBER(option);
+   CHECK_NUMBER(facility);
+ 
+   cident    = SDATA(ident);
+   coption   = XINT(option);
+   cfacility = XINT(cfacility);
+   
+   openlog(cident, coption, cfacility);
+   return Qundefined;
+ }
+ 
+ DEFUN ("syslog-internal", Fsyslog_internal, Ssyslog_internal, 2, 2, 0, 
+        doc: /* See syslog(3). */)
+      (priority,
+       log)
+        Lisp_Object priority;
+        Lisp_Object log;
+ {
+   int cpriority;
+   unsigned char *clog;
+ 
+ 
+   CHECK_NUMBER(priority);
+   CHECK_STRING(log);
+ 
+   cpriority = XINT(priority);
+   clog      = SDATA (log);
+ 
+   syslog(cpriority, "%s", clog);
+   return Qundefined;
+ }
+        
+ DEFUN ("closelog-internal", Fcloselog_internal, Scloselog_internal, 0, 0, 0,
+        doc: /* See closelog(3). */)
+      ()
+ {
+   closelog();
+   return Qundefined;
+ }
+ #endif
+ 
  void
  syms_of_emacs ()
  {
***************
*** 2493,2498 ****
--- 2554,2565 ----
    defsubr (&Sdaemonp);
    defsubr (&Sdaemon_initialized);
  
+ #ifdef HAVE_SYS_SYSLOG_H
+   defsubr (&Sopenlog_internal);
+   defsubr (&Ssyslog_internal);
+   defsubr (&Scloselog_internal);
+ #endif
+ 
    DEFVAR_LISP ("command-line-args", &Vcommand_line_args,
  	       doc: /* Args passed by shell to Emacs, as a list of strings.
  Many arguments are deleted from the list as they are processed.  */);

Re: [RFC] syslog interface

[Stefan Monnier]

>  -server option added to newer emacs is very interesting.
> But to write a rael server with emacs, there may be some missing
> functions in emacs.
>  syslog interface is one of such function. As a system administrator,
> I'd like to track the event on the emacs server on which the service written 
> in elisp is running via /var/log/messages.

Not sure what's the purpose here: the emacs-server is normally expected
to be run by users, not as a system process (it's not expected to be
shared by all users of the system), whereas syslog is normally used only
for messages coming from system processes rather than from
user processes.

Can you give some additional info about what use case you're
thinking of?


        Stefan


PS: the "return Qundefined" is wrong, because Qundefined is a special
value that Elisp code should never see.  Return Qnil instead.

Re: [RFC] syslog interface

[Eli Zaretskii]

> Date: Thu, 27 May 2010 14:18:47 +0900 (JST)
> From: Masatake YAMATO <yamato@redhat.com>
> 
> My idea is using syslog implemention in libc; 
> it handles the protocol, and we can expect it is maintained well. If
> the protocol is changed the libc maintainer will update the function.
> As the result we can use/maintain syslog interfae from elisp without 
> worrying about the protocol changing.
> 
> Here is sample implemention. It comes from two parts: syslog.el and a patch
> for emacs. 

IMHO, this syslog.el is too specific to the single platform on which
it was coded.  It should be more portable: not to expose highly
system-dependent constants, for example.  All this unportable stuff
should be inside the primitive, because the primitive will have to be
implemented for every platform that has its own syslog facility and
API.

See proced.el for an example of another similar facility, and the
primitives it uses.

Re: [RFC] syslog interface

[Masatake YAMATO]

Thank you for comment.

>>  -server option added to newer emacs is very interesting.
>> But to write a rael server with emacs, there may be some missing
>> functions in emacs.
>>  syslog interface is one of such function. As a system administrator,
>> I'd like to track the event on the emacs server on which the service written 
>> in elisp is running via /var/log/messages.
> 
> Not sure what's the purpose here: the emacs-server is normally expected
> to be run by users, not as a system process (it's not expected to be
> shared by all users of the system), whereas syslog is normally used only
> for messages coming from system processes rather than from
> user processes.
> 
> Can you give some additional info about what use case you're
> thinking of?
> 

My use case is `font-lock' server.
Here is a prototype:

     http://srpmix.org/api/browse.cgi?path=sources/e/emacs/23.2-3.fc14/pre-build/emacs-23.2/ChangeLog&display=font-lock

ChangeLog file is taken from emacs-23.2-3. When the file is requested
from web client, web server at srpmix.org asks emacs-server to convert
the file to a file in html format via emacsclient. It may be possible to 
do the same thing with emacs --batch but to handle multiple clients 
quickly I'd like to implemnt it with emacs-server. Because of disk size
limitation I don't like to use pre-convert technique; converting all
files into html format. What I'll deal is source code files of 2TB. 

How about this one if you think just font-locking a file is not so interesting?

     http://srpmix.org/api/browse.cgi?path=sources/e/emacs/23.2-3.fc14/pre-build/emacs-23.2&display=font-lock

This is something like dired. I'd like to integrate other goodies in
emacs to the output web page: etags, imenu, vc, etc. 

>         Stefan
> 
> 
> PS: the "return Qundefined" is wrong, because Qundefined is a special
> value that Elisp code should never see.  Return Qnil instead.
> 

Thanks.

Masatake YAMATO

Re: [RFC] syslog interface

[Masatake YAMATO]

>> Date: Thu, 27 May 2010 14:18:47 +0900 (JST)
>> From: Masatake YAMATO <yamato@redhat.com>
>> 
>> My idea is using syslog implemention in libc; 
>> it handles the protocol, and we can expect it is maintained well. If
>> the protocol is changed the libc maintainer will update the function.
>> As the result we can use/maintain syslog interfae from elisp without 
>> worrying about the protocol changing.
>> 
>> Here is sample implemention. It comes from two parts: syslog.el and a patch
>> for emacs. 
> 
> IMHO, this syslog.el is too specific to the single platform on which
> it was coded.  It should be more portable: not to expose highly
> system-dependent constants, for example.  All this unportable stuff
> should be inside the primitive, because the primitive will have to be
> implemented for every platform that has its own syslog facility and
> API.
> 
> See proced.el for an example of another similar facility, and the
> primitives it uses.
> 

Thank you for advice. I'll look at proced.el.

Masatake YAMATO