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

FreeBSD Manual Pages


home | help
Net::Daemon(3)	      User Contributed Perl Documentation	Net::Daemon(3)

       Net::Daemon - Perl extension for	portable daemons

	 # Create a subclass of	Net::Daemon
	 require Net::Daemon;
	 package MyDaemon;
	 @MyDaemon::ISA	= qw(Net::Daemon);

	 sub Run ($) {
	   # This function does	the real work; it is invoked whenever a
	   # new connection is made.

       Net::Daemon is an abstract base class for implementing portable server
       applications in a very simple way. The module is	designed for Perl
       5.005 and threads, but can work with fork() and Perl 5.004.

       The Net::Daemon class offers methods for	the most common	tasks a	daemon
       needs: Starting up, logging, accepting clients, authorization,
       restricting its own environment for security and	doing the true work.
       You only	have to	override those methods that aren't appropriate for
       you, but	typically inheriting will safe you a lot of work anyways.

	 $server = Net::Daemon->new($attr, $options);

	 $connection = $server->Clone($socket);

       Two constructors	are available: The new method is called	upon startup
       and creates an object that will basically act as	an anchor over the
       complete	program. It supports command line parsing via Getopt::Long

       Arguments of new	are $attr, an hash ref of attributes (see below) and
       $options	an array ref of	options, typically command line	arguments (for
       example \@ARGV) that will be passed to Getopt::Long::GetOptions.

       The second constructor is Clone:	It is called whenever a	client
       connects. It receives the main server object as input and returns a new
       object. This new	object will be passed to the methods that finally do
       the true	work of	communicating with the client. Communication occurs
       over the	socket $socket,	Clone's	argument.

       Possible	object attributes and the corresponding	command	line arguments

       catchint	(--nocatchint)
	   On some systems, in particular Solaris, the functions accept(),
	   read() and so on are	not safe against interrupts by signals.	For
	   example, if the user	raises a USR1 signal (as typically used	to
	   reread config files), then the function returns an error EINTR.  If
	   the catchint	option is on (by default it is,	use --nocatchint to
	   turn	this off), then	the package will ignore	EINTR errors whereever

       chroot (--chroot=dir)
	   (UNIX only)	After doing a bind(), change root directory to the
	   given directory by doing a chroot().	This is	usefull	for security
	   operations, but it restricts	programming a lot. For example,	you
	   typically have to load external Perl	extensions before doing	a
	   chroot(), or	you need to create hard	links to Unix sockets. This is
	   typically done in the config	file, see the --configfile option. See
	   also	the --group and	--user options.

	   If you don't	know chroot(), think of	an FTP server where you	can
	   see a certain directory tree	only after logging in.

	   An array ref	with a list of clients.	Clients	are hash refs, the
	   attributes accept (0	for denying access and 1 for permitting) and
	   mask, a Perl	regular	expression for the clients IP number or	its
	   host	name. See "Access control" below.

       configfile (--configfile=file)
	   Net::Daemon supports	the use	of config files. These files are
	   assumed to contain a	single hash ref	that overrides the arguments
	   of the new method. However, command line arguments in turn take
	   precedence over the config file. See	the "Config File" section
	   below for details on	the config file.

       debug (--debug)
	   Turn	debugging mode on. Mainly this asserts that logging messages
	   of level "debug" are	created.

       facility	(--facility=mode)
	   (UNIX only) Facility	to use for Sys::Syslog (3). The	default	is

       group (--group=gid)
	   After doing a bind(), change	the real and effective GID to the
	   given.  This	is usefull, if you want	your server to bind to a
	   privileged port (<1024), but	don't want the server to execute as
	   root. See also the --user option.

	   GID's can be	passed as group	names or numeric values.

       localaddr (--localaddr=ip)
	   By default a	daemon is listening to any IP number that a machine
	   has.	This attribute allows to restrict the server to	the given IP

       localpath (--localpath=path)
	   If you want to restrict your	server to local	services only, you'll
	   prefer using	Unix sockets, if available. In that case you can use
	   this	option for setting the path of the Unix	socket being created.
	   This	option implies --proto=unix.

       localport (--localport=port)
	   This	attribute sets the port	on which the daemon is listening. It
	   must	be given somehow, as there's no	default.

       logfile (--logfile=file)
	   By default logging messages will be written to the syslog (Unix) or
	   to the event	log (Windows NT). On other operating systems you need
	   to specify a	log file. The special value "STDERR" forces logging to

       loop-child (--loop-child)
	   This	option forces creation of a new	child for loops. (See the
	   loop-timeout	option.) By default the	loops are serialized.

       loop-timeout (--loop-timeout=secs)
	   Some	servers	need to	take an	action from time to time. For example
	   the Net::Daemon::Spooler attempts to	empty its spooling queue every
	   5 minutes. If this option is	set to a positive value	(zero being
	   the default), then the server will call its Loop method every
	   "loop-timeout" seconds.

	   Don't trust too much	on the precision of the	interval: It depends
	   on a	number of factors, in particular the execution time of the
	   Loop() method. The loop is implemented by using the select
	   function. If	you need an exact interval, you	should better try to
	   use the alarm() function and	a signal handler. (And don't forget to
	   look	at the catchint	option!)

	   It is recommended to	use the	loop-child option in conjunction with

       mode (--mode=modename)
	   The Net::Daemon server can run in three different modes, depending
	   on the environment.

	   If you are running Perl 5.005 and did compile it for	threads, then
	   the server will create a new	thread for each	connection. The	thread
	   will	execute	the server's Run() method and then terminate. This
	   mode	is the default,	you can	force it with "--mode=ithreads"	or

	   If threads are not available, but you have a	working	fork(),	then
	   the server will behave similar by creating a	new process for	each
	   connection.	This mode will be used automatically in	the absence of
	   threads or if you use the "--mode=fork" option.

	   Finally there's a single-connection mode: If	the server has
	   accepted a connection, he will enter	the Run() method. No other
	   connections are accepted until the Run() method returns. This
	   operation mode is useful if you have	neither	threads	nor fork(),
	   for example on the Macintosh.  For debugging	purposes you can force
	   this	mode with "--mode=single".

	   When	running	in mode	single,	you can	still handle multiple clients
	   at a	time by	preforking multiple child processes. The number	of
	   childs is configured	with the option	"--childs".

	   Use this parameter to let Net::Daemon run in	prefork	mode, which
	   means it forks the number of	childs processes you give with this
	   parameter, and all child handle connections concurrently. The
	   difference to fork mode is, that the	child processes	continue to
	   run after a connection has terminated and are able to accept	a new
	   connection.	This is	useful for caching inside the childs process
	   (e.g.  DBI::ProxyServer connect_cached attribute)

	   Array ref of	Command	line options that have been passed to the
	   server object via the new method.

	   When	creating an object with	Clone the original object becomes the
	   parent of the new object. Objects created with new usually don't
	   have	a parent, thus this attribute is not set.

       pidfile (--pidfile=file)
	   (UNIX only) If this option is present, a PID	file will be created
	   at the given	location.

       proto (--proto=proto)
	   The transport layer to use, by default tcp or unix for a Unix
	   socket. It is not yet possible to combine both.

	   The socket that is connected	to the client; passed as $client
	   argument to the Clone method. If the	server object was created with
	   new,	this attribute can be undef, as	long as	the Bind method	isn't
	   called.  Sockets are	assumed	to be IO::Socket objects.

       user (--user=uid)
	   After doing a bind(), change	the real and effective UID to the
	   given.  This	is usefull, if you want	your server to bind to a
	   privileged port (<1024), but	don't want the server to execute as
	   root. See also the --group and the --chroot options.

	   UID's can be	passed as group	names or numeric values.

       version (--version)
	   Supresses startup of	the server; instead the	version	string will be
	   printed and the program exits immediately.

       Note that most of these attributes (facility, mode, localaddr,
       localport, pidfile, version) are	meaningfull only at startup. If	you
       set them	later, they will be simply ignored. As almost all attributes
       have appropriate	defaults, you will typically use the localport
       attribute only.

   Command Line	Parsing
	 my $optionsAvailable =	Net::Daemon->Options();

	 print Net::Daemon->Version(), "\n";


       The Options method returns a hash ref of	possible command line options.
       The keys	are option names, the values are again hash refs with the
       following keys:

	   An option template that can be passed to Getopt::Long::GetOptions.

	   A description of this option, as used in Usage

       The Usage method	prints a list of all possible options and returns.  It
       uses the	Version	method for printing program name and version.

   Config File
       If the config file option is set	in the command line options or in the
       in the "new" args, then the method

	 $server->ReadConfigFile($file,	$options, $args)

       is invoked. By default the config file is expected to contain Perl
       source that returns a hash ref of options. These	options	override the
       "new" args and will in turn be overwritten by the command line options,
       as present in the $options hash ref.

       A typical config	file might look	as follows, we use the
       DBI::ProxyServer	as an example:

	   # Load external modules; this is not	required unless	you use
	   # the chroot() option.
	   #require DBD::mysql;
	   #require DBD::CSV;

	       # 'chroot' => '/var/dbiproxy',
	       'facility' => 'daemon',
	       'pidfile' => '/var/dbiproxy/',
	       'user' => 'nobody',
	       'group' => 'nobody',
	       'localport' => '1003',
	       'mode' => 'fork'

	       # Access	control
	       'clients' => [
		   # Accept the	local
		       'mask' => '^192\.168\.1\.\d+$',
		       'accept'	=> 1
		   # Accept
		       'mask' => '^myhost\.company\.com$',
		       'accept'	=> 1
		   # Deny everything else
		       'mask' => '.*',
		       'accept'	=> 0

   Access control
       The Net::Daemon package supports	a host based access control scheme. By
       default access is open for anyone. However, if you create an attribute
       $self->{'clients'}, typically in	the config file, then access control
       is disabled by default. For any connection the client list is
       processed: The clients attribute	is an array ref	to a list of hash
       refs. Any of the	hash refs may contain arbitrary	attributes, including
       the following:

       mask    A Perl regular expression that has to match the clients IP
	       number or its host name.	The list is processed from the left to
	       the right, whenever a 'mask' attribute matches, then the
	       related hash ref	is choosen as client and processing the	client
	       list stops.

       accept  This may	be set to true or false	(default when omitting the
	       attribute), the former means accepting the client.

   Event logging
	 $server->Log($level, $format, @args);
	 $server->Debug($format, @args);
	 $server->Error($format, @args);
	 $server->Fatal($format, @args);

       The Log method is an interface to Sys::Syslog (3) or Win32::EventLog
       (3). It's arguments are $level, a syslog	level like debug, notice or
       err, a format string in the style of printf and the format strings

       The Debug and Error methods are shorthands for calling Log with a level
       of debug	and err, respectively. The Fatal method	is like	Error, except
       it additionally throws the given	message	as exception.

       See Net::Daemon::Log(3) for details.

   Flow	of control
	 # The following inside	Bind():
	 if ($connection->Accept()) {
	 } else	{
	     $connection->Log('err', 'Connection refused');

       The Bind	method is called by the	application when the server should
       start. Typically	this can be done right after creating the server
       object $server. Bind usually never returns, except in case of errors.

       When a client connects, the server uses Clone to	derive a connection
       object $connection from the server object. A new	thread or process is
       created that uses the connection	object to call your classes Accept
       method. This method is intended for host	authorization and should
       return either FALSE (refuse the client) or TRUE (accept the client).

       If the client is	accepted, the Run method is called which does the true
       work. The connection is closed when Run returns and the corresponding
       thread or process exits.

   Error Handling
       All methods are supposed	to throw Perl exceptions in case of errors.

       All methods are working with lexically scoped data and handle data
       only, the exception being the OpenLog method which is invoked before
       threading starts. Thus you are safe as long as you don't	share handles
       between threads.	I strongly recommend that your application behaves
       similar.	(This doesn't apply to mode 'ithreads'.)

       As an example we'll write a simple calculator server. After connecting
       to this server you may type expressions,	one per	line. The server
       evaluates the expressions and prints the	result.	(Note this is an
       example,	in real	life we'd never	implement such a security hole.	:-)

       For the purpose of example we add a command line	option --base that
       takes 'hex', 'oct' or 'dec' as values: The servers output will use the
       given base.

	 # -*- perl -*-
	 # Calculator server
	 require 5.004;
	 use strict;

	 require Net::Daemon;

	 package Calculator;

	 use vars qw($VERSION @ISA);
	 $VERSION = '0.01';
	 @ISA =	qw(Net::Daemon); # to inherit from Net::Daemon

	 sub Version ($) { 'Calculator Example Server, 0.01'; }

	 # Add a command line option "--base"
	 sub Options ($) {
	     my($self) = @_;
	     my($options) = $self->SUPER::Options();
	     $options->{'base'}	= { 'template' => 'base=s',
				    'description' => '--base		      '
					   . 'dec (default), hex or oct'

	 # Treat command line option in	the constructor
	 sub new ($$;$)	{
	     my($class,	$attr, $args) =	@_;
	     my($self) = $class->SUPER::new($attr, $args);
	     if	($self->{'parent'}) {
		 # Called via Clone()
		 $self->{'base'} = $self->{'parent'}->{'base'};
	     } else {
		 # Initial call
		 if ($self->{'options'}	 &&  $self->{'options'}->{'base'}) {
		     $self->{'base'} = $self->{'options'}->{'base'}
	     if	(!$self->{'base'}) {
		 $self->{'base'} = 'dec';

	 sub Run ($) {
	     my($self) = @_;
	     my($line, $sock);
	     $sock = $self->{'socket'};
	     while (1) {
		 if (!defined($line = $sock->getline())) {
		     if	($sock->error()) {
			 $self->Error("Client connection error %s",
		 $line =~ s/\s+$//; # Remove CRLF
		 my($result) = eval $line;
		 if ($self->{'base'} eq	'hex') {
		     $rc = printf $sock	("%x\n", $result);
		 } elsif ($self->{'base'} eq 'oct') {
		     $rc = printf $sock	("%o\n", $result);
		 } else	{
		     $rc = printf $sock	("%d\n", $result);
		 if (!$rc) {
		     $self->Error("Client connection error %s",

	 package main;

	 my $server = Calculator->new({'pidfile' => 'none',
				       'localport' => 2000}, \@ARGV);

       Most, or	even any, known	problems are related to	the Sys::Syslog	module
       which is	by default used	for logging events under Unix. I'll quote some

       Usage: Sys::Syslog::_PATH_LOG at	...
	   This	problem	is treated in perl bug 20000712.003. A workaround is
	   changing line 277 of to

	     my	$syslog	= &_PATH_LOG() || croak	"_PATH_LOG not found in";

	 Net::Daemon is	Copyright (C) 1998, Jochen Wiedmann
					    Am Eisteich	9
					    72555 Metzingen

					    Phone: +49 7123 14887

	 All rights reserved.

	 You may distribute this package under the terms of either the GNU
	 General Public	License	or the Artistic	License, as specified in the
	 Perl README file.

       RPC::pServer(3),	Netserver::Generic(3), Net::Daemon::Log(3),

perl v5.24.1			  2011-03-09			Net::Daemon(3)


Want to link to this manual page? Use this URL:

home | help