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 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 the section on "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 the section on
"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 the
section on "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 the section on "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=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 the section on "Sys::Syslog
(3)" or the section on "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 the Net::Daemon::Log(3) manpage 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->{'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:
[email protected]
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
the RPC::pServer(3) manpage, the Netserver::Generic(3) manpage,
the Net::Daemon::Log(3) manpage, the Net::Daemon::Test(3)
manpage
