Provided by: libnet-daemon-perl_0.48-1_all 
NAME
Net::Daemon - Perl extension for portable daemons
SYNOPSIS
# 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.
}
DESCRIPTION
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.
Constructors
$server = Net::Daemon->new($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 (3)".
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 are:
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 possible.
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.
clients
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 daemon.
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 number.
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 stderr.
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 loop-timeout.
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 "--mode=threads".
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".
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)
options
Array ref of Command line options that have been passed to the server object via the
new method.
parent
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.
socket
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";
Net::Daemon->Usage();
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:
template
An option template that can be passed to Getopt::Long::GetOptions.
description
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 $options hash ref.
A typical config file might look as follows, we use the DBI::ProxyServer as an example:
# Load external modules; this is not required unless you use
# the chroot() option.
#require DBD::mysql;
#require DBD::CSV;
{
# 'chroot' => '/var/dbiproxy',
'facility' => 'daemon',
'pidfile' => '/var/dbiproxy/dbiproxy.pid',
'user' => 'nobody',
'group' => 'nobody',
'localport' => '1003',
'mode' => 'fork'
# Access control
'clients' => [
# Accept the local
{
'mask' => '^192\.168\.1\.\d+$',
'accept' => 1
},
# Accept myhost.company.com
{
'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 arguments.
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
$server->Bind();
# The following inside Bind():
if ($connection->Accept()) {
$connection->Run();
} 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 $connection
from the server object. A new thread or process is created that uses the connection object
to call your classes Accept method. This method is intended for host authorization and
should return either FALSE (refuse the client) or TRUE (accept the client).
If the client is accepted, the Run method is called which does the true work. The
connection is closed when Run returns and the corresponding thread or process exits.
Error Handling
All methods are supposed to throw Perl exceptions in case of errors.
MULTITHREADING CONSIDERATIONS
All methods are working with lexically scoped data and handle data only, the exception
being the OpenLog method which is invoked before threading starts. Thus you are safe as
long as you don't share handles between threads. I strongly recommend that your
application behaves similar. (This doesn't apply to mode 'ithreads'.)
EXAMPLE
As an example we'll write a simple calculator server. After connecting to this server you
may type expressions, one per line. The server evaluates the expressions and prints the
result. (Note this is an example, in real life we'd never implement such a security hole.
:-)
For the purpose of example we add a command line option --base that takes 'hex', 'oct' or
'dec' as values: The servers output will use the given base.
# -*- perl -*-
#
# Calculator server
#
require 5.004;
use strict;
require Net::Daemon;
package Calculator;
use vars qw($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'
};
$options;
}
# 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';
}
$self;
}
sub Run ($) {
my($self) = @_;
my($line, $sock);
$sock = $self->{'socket'};
while (1) {
if (!defined($line = $sock->getline())) {
if ($sock->error()) {
$self->Error("Client connection error %s",
$sock->error());
}
$sock->close();
return;
}
$line =~ s/\s+$//; # Remove CRLF
my($result) = eval $line;
my($rc);
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",
$sock->error());
$sock->close();
return;
}
}
}
package main;
my $server = Calculator->new({'pidfile' => 'none',
'localport' => 2000}, \@ARGV);
$server->Bind();
KNOWN PROBLEMS
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 examples:
Usage: Sys::Syslog::_PATH_LOG at ...
This problem is treated in perl bug 20000712.003. A workaround is changing line 277 of
Syslog.pm to
my $syslog = &_PATH_LOG() || croak "_PATH_LOG not found in syslog.ph";
AUTHOR AND COPYRIGHT
Net::Daemon is Copyright (C) 1998, Jochen Wiedmann
Am Eisteich 9
72555 Metzingen
Germany
Phone: +49 7123 14887
Email: joe@ispsoft.de
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.
SEE ALSO
RPC::pServer(3), Netserver::Generic(3), Net::Daemon::Log(3), Net::Daemon::Test(3)