[SOLVED] How to use perl IO::Socket::INET with inetd

[mv]

This is a perl programming question which came up in some systemd discussion:

I have a daemon in perl which currently uses $socket = IO::Socket::INET->new(...) to create a TCP socket.

When such a daemon should be used with inetd or systemd socket activation, it should be able to use STDIN/STDOUT (or other passed filedescriptors) as a socket.

Is it possible to "transform" STDIN/STDOUT into a corresponding perl object? The intention is to replace only the above "new"-command by some code so that afterwards all of the rest of the daemon would work unchanged with inetd (so that e.g. $socket->accept(), $socket->recv(...), $socket->send(...) work afterwards with inetd by reading/writing appropriate data to STDIN/STDOUT).

[RazielFMX]

STDOUT/STDIN are default filehandles. You can use them in an OO fashion by including "use FileHandle" at the top of your code.

Then you can do things like:

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#!/usr/bin/perl -w

use strict;
use FileHandle;

#Don't buffer writes
STDOUT->autoflush(1);

#Read 256 bytes
my $buffer = '';
my $read = STDIN->sysread($buffer, 256);

I don't think you can perform socket operations on them though, but I could be wrong.

Check out this: http://www.perlmonks.org/?node_id=544341

EDIT:

I think for what you are trying to do is to have a command line switch that can be invoked by inetd to turn on inetd functionality. I would then either as a standalone PM or a nested class, do something like this:

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my $socket = ($inetdEnabled) ? InetdWrapper->new() : IO::Socket::INET->new(%args)

You then just implement what you need:

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package InetdWrapper;

use strict;
use FileHandle;

sub new {
    my $pkg = shift;
    return bless({}, $pkg);
}

sub close {
    # You might want this as a no-op, not sure
}

sub syswrite {
    my $self = shift;
    return STDOUT->syswrite(@_);
}

sub sysread {
    my $self = shift;
    return STDIN->sysread(@_);
}

You get the idea.

[mv]

The point is that I want to do socket operations on them, in particular accept() (and use the sockets obtained by that).

In German USEnet, I got now a simple receipt which I have just tested and which works:

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$socket = new IO::Socket::INET();
$socket->fdopen(0, 'r');

It is a little bit hackish, since theoretically the missing argument list of IO::Socket::INET might mean that also some other important information is not initialized, but so far it works without any issues.

[RazielFMX]

That is effectively duping the file descriptor, so it should be perfectly reasonable to use. Nifty trick.