How can I create a TCP server daemon process in Perl? - perl

Question

I wish to create a TCP server daemon process in Perl.
Which is the best framework/module for it?.
Is there anything that comes bundled with Perl?
Edit: Something that has start | stop | restart options would be great.
Edit: It has to be a Multi threaded server.

Answer 1

Well - it's better if you could state what this daemon is supposed to do. As there are specialized frameworks/libraries for various tasks.
For simplest daemon that does nothing, just exists, you can easily do this:
#!/usr/bin/perl
use strict;
use warnings;
use Carp;
use POSIX qw( setsid );
daemonize();
do_your_daemon_stuff();
exit;
sub daemonize {
chdir '/' or croak "Can't chdir to /: $!";
open STDIN, '/dev/null' or croak "Can't read /dev/null: $!";
open STDOUT, '>/dev/null' or croak "Can't write to /dev/null: $!";
defined(my $pid = fork) or croak "Can't fork: $!";
exit if $pid;
setsid or croak "Can't start a new session: $!";
open STDERR, '>&STDOUT' or croak "Can't dup stdout: $!";
}
sub daemonize() was liften from perldoc perlipc (with minor change).
That's all - the code now properly daemonizes, and can do anything you want.
I just read your edit, that you want TCP server.
OK. Here is simplistic code:
#!/usr/bin/perl
use strict;
use warnings;
use Carp;
use POSIX qw( setsid );
use IO::Socket;
my $server_port = get_server_port();
daemonize();
handle_connections( $server_port );
exit;
sub daemonize {
chdir '/' or croak "Can't chdir to /: $!";
open STDIN, '/dev/null' or croak "Can't read /dev/null: $!";
open STDOUT, '>/dev/null' or croak "Can't write to /dev/null: $!";
defined(my $pid = fork) or croak "Can't fork: $!";
exit if $pid;
setsid or croak "Can't start a new session: $!";
open STDERR, '>&STDOUT' or croak "Can't dup stdout: $!";
}
sub get_server_port {
my $server = IO::Socket::INET->new(
'Proto' => 'tcp',
'LocalPort' => 31236,
'Listen' => SOMAXCONN,
'Reuse' => 1,
);
die "can't setup server" unless $server;
return $server;
}
sub handle_connections {
my $port = shift;
my $handled = 0;
while ( my $client = $port->accept() ) {
$handled++;
print $client "Hi, you're client #$handled\n";
chomp ( my $input = <$client> );
my $output = reverse $input;
print $client $output, "\n";
print $client "Bye, bye.\n";
close $client;
}
return;
}
Just remember that this is blocking tcp server, so it will be able to handle 1 connection at the time. If you want more than 1 - it becomes more complex, and you have to ask yourself if you prefer multithreading (or multi-processing), or you prefer single-process, event based server.

Answer 2

You do not actually want to write multithreaded perl. Perl threads are broken - they do not work properly (in my opinion).
Creating a new perl thread clones the entire interpreter including all the data currently in scope - therefore is basically WORSE than creating a new process (which of course, would use copy-on-write) and less useful.
So you definitely don't want it multithreaded.

Answer 3

If possible, I would consider looking at something like AnyEvent as an alternative to a pure threaded approach.

Answer 4

I've never had occasion to try it myself, but I believe POE is highly regarded for that sort of thing.
Here are some examples of TCP servers written with POE.

Answer 5

A quick search reveals quite a few possibilities. Daemon::Generic seems to be straightforward to use.
In addition, there are many server modules for various protocols. In fact, HTTP::Daemon has been a core module for a while now.

Answer 6

"Something that has start | stop | restart options would be great"
There are modules on CPAN which will provide this. E.g., I can see Daemon::Generic which claims to be a framework to provide start/stop/reload for a daemon.
/I3az/