net::daemon(3)

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.
}

WARNING

THIS IS ALPHA SOFTWARE. It is *only* 'Alpha' because the
interface (API) is not finalised. The Alpha status does
not reflect code quality or stability.

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 any
ways.

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 com
mand 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 direc
tory 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 --con
figfile 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 log
ging 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-time
out" 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 for get to look at the catchint option!); It is recommended to use the loop-child option in con junction 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=threads".; If threads are not available, but you have a working
fork(), then the server will behave similar by creat
ing 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 use
ful if you have neither threads nor fork(), for exam
ple on the Macintosh. For debugging purposes you can
force this mode with "--mode=single".; When running in mode single, you can still handle mul
tiple 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 pro
cesses 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 con
nect_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. Sock
ets 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 immedi
ately.
Note that most of these attributes (facility, mode, local
addr, 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(), "0;; 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 con tain Perl source that returns a hash ref of options. These options override the "new" args and will in turn be over written 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.+$',
'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 con trol scheme. By default access is open for anyone. How ever, if you create an attribute $self->{'clients'}, typi cally in the config file, then access control is disabled by default. For any connection the client list is pro cessed: 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 accept
ing 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.

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->{'op

tions'}->{'base'}) {
$self->{'base'} = $self->{'op

tions'}->{'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;

}
$line =~ s/; # Remove CRLF
my($result) = eval $line;
my($rc);
if ($self->{'base'} eq 'hex') {

$rc = printf $sock ("%x0, $result);

} elsif ($self->{'base'} eq 'oct') {

$rc = printf $sock ("%o0, $result);

} else {

$rc = printf $sock ("%d0, $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
You may distribute this package under the terms of ei
ther the GNU General Public License or the Artistic License, as spec
ified in the Perl README file.

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