Skip site navigation (1)Skip section navigation (2)

FreeBSD Manual Pages

  
 
  

home | help 
MIMEDEFANG-NOTIFY(7)	Miscellaneous Information Manual    MIMEDEFANG-NOTIFY(7)

NAME
     mimedefang-notify - Conventions used by mimedefang-multiplexor(8) to notify
     an external program of state changes.

DESCRIPTION
     If  you  supply the -O option to mimedefang-multiplexor, then it allows ex-
     ternal programs to connect to a socket and be  notified  of  certain  state
     changes  in  the  multiplexor.  The external programs can react in whatever
     way they choose to these state changes.  The external program that  listens
     for state changes is referred to as a listener.

NOTIFICATION OVERVIEW
     From the point of view of a listener, notification works like this:

     1) The listener connects to a TCP or UNIX-domain socket.

     2)  The  listener informs mimedefang-multiplexor of the message types it is
     interested in.

     3) The listener loops, reading messages from the  socket  and  reacting  to
     them.

MESSAGES
     Each  message from the multiplexor normally consists of a single upper-case
     letter, possibly followed by a space and some arguments, and then	followed
     by a newline.

     Two  special messages are "*OK" followed by a newline, which is issued when
     a listener first connects, and "*ERR" followed by some text and a	newline,
     which is issued when an error occurs.

     The normal messages are:

     B	    This message is issued whenever a worker is killed because of a busy
	    timeout.

     F n    This  message is issued whenever the number of free workers changes.
	    The parameter n is the number of free workers.

     R	    This message is issued whenever someone has forced a filter reread.

     S n nmsg
	    This message is issued whenever worker n's status tag changes.   The
	    status  tag  is a string indicating what the worker is currently do-
	    ing; the -Z option to the multiplexor allows the Perl code to update
	    the status tag so you have a good idea what each worker is doing.

     U	    This message is issued whenever a worker has died unexpectedly.

     Y	    This message is issued whenever the number of free	workers  changes
	    from zero to non-zero.

     Z	    This  message is issued whenever the number of free workers falls to
	    zero.

EXPRESSING INTEREST
     A listener does not receive any messages until it has expressed interest in
     various message types.  To express interest, the  listener  should  send  a
     question  mark ("?") followed by the types of messages it is interested in,
     followed by a newline over the socket.  For example, a listener  interested
     in the R and F messages would send this line:

	  ?RF

     A listener interested in every possible message type should send:

	  ?*

     Once  a  listener	has  expressed	interest, it may receive messages at any
     time, and should monitor the socket for messages.

     Note that a listener always receives the special messages "*OK" and "*ERR",
     even if it has not expressed interest in them.

EXAMPLE
     The following Perl script implements a listener that, on Linux, rejects new
     SMTP connections if all workers are busy, and accepts  them  again  once  a
     worker  is  free.	 Existing SMTP connections are not shut down; the system
     merely refuses new connections if all the workers are busy.

     This script assumes that you have used the -O inet:4567 option  to  mimede-
     fang-multiplexor.

     #!/usr/bin/perl -w
     #
     # On Linux, prepare to use this script like this:
     #	   /sbin/iptables -N smtp_connect
     #	   /sbin/iptables -A INPUT --proto tcp --dport 25 --syn -j smtp_connect
     # Then run the script as root.

     use IO::Socket::INET;

     sub no_free_workers {
	 print STDERR "No free workers!\n";
	 system("/sbin/iptables -A smtp_connect -j REJECT");
     }

     sub some_free_workers {
	 print STDERR "Some free workers.\n";
	 system("/sbin/iptables -F smtp_connect");
     }

     sub main {
	 my $sock;

	 $sock = IO::Socket::INET->new(PeerAddr => '127.0.0.1',
				       PeerPort => '4567',
				       Proto => 'tcp');
	 # We are only interested in Y and Z messages
	 print $sock "?YZ\n";
	 $sock->flush();
	 while(<$sock>) {
	     if (/^Z/) {
		 no_free_workers();
	     }
	     if (/^Y/) {
		 some_free_workers();
	     }
	 }

	 # EOF from multiplexor?? Better undo firewalling
	 system("/sbin/iptables -F smtp_connect");
     }

     main();

SEE ALSO
     mimedefang.pl(8), mimedefang(8), mimedefang-multiplexor(8), mimedefang-fil-
     ter(5)

4th Berkeley Distribution	 8 February 2005	    MIMEDEFANG-NOTIFY(7)

Want to link to this manual page? Use this URL:
<https://man.freebsd.org/cgi/man.cgi?query=mimedefang-notify&sektion=7&manpath=FreeBSD+Ports+15.1.quarterly>

home | help