local socket

[Punto]

Hi.

I need to leave a program on the background, and then, from time to time, 're take' control of it, to monitor it's progress.
So I was thinking of running it from a perl program, with open3(), and then open a socket to listen for commands (and print the output).

So my question is: is there any way to open a 'local' socket? All the documentation I see is about network sockets, but I only want it to be accesible from the local computer (no network)

Thanks..

[chipmunk]

If the listening process binds the socket to localhost, then it will only accept connections from the local computer.

Here's an example, using IO::Socket:

#!/usr/local/bin/perl -w

use strict;

use IO::Socket;

my $sock = IO::Socket::INET->new(Listen => 1,
                                 LocalAddr => 'localhost',
                                 LocalPort => 43546,
                                 Proto => 'tcp',
                                 Reuse => 1,
                                );

my $NL = "\015\012";

while (my $client = $sock->accept()) {
    print $client "Hello.  To close connection, type quit$NL";
    while (<$client>) {
        tr/\015\012//d;
        print "Client said $_\n";
        print $client "You said $_$NL";
        last if /^quit/i;
    }
    print "Client quit.\n";
    print $client "Bye!$NL";
    close $client;
}

Start this running, then try connecting from various computers. You'll only be able to connect from the local computer, and only when connecting specifically to 'localhost'. (Exit the server with a kill signal, e.g. Ctrl-C)

[John M. Dlugosz]

Chipmunk, that's interesting. I checked the IO::Socket::INET documentation and related pages, plus perlfunc and perlipc, but can't find a description of restricting a listener. I didn't know sockets could do that at all! Can you point to more info on that?

[chipmunk]

I don't remember where I learned about restricting sockets to specific addresses, and I can't find any really descriptive information on it. Very frustrating... :(

Here is a relevant snippet from perlipc:

       And here's a corresponding server to go along with it.
       We'll leave the address as INADDR_ANY so that the kernel
       can choose the appropriate interface on multihomed hosts.
       If you want sit on a particular interface (like the
       external side of a gateway or firewall machine), you
       should fill this in with your real address instead.

And here's something from Socket:

       INADDR_ANY
            Note: does not return a number, but a packed string.
 
            Returns the 4-byte wildcard ip address which
            specifies any of the hosts ip addresses. (A
            particular machine can have more than one ip address,
            each address corresponding to a particular network
            interface. This wildcard address allows you to bind
            to all of them simultaneously.)  Normally equivalent
            to inet_aton('0.0.0.0').

Let's say you have a machine that has two IP addresses: mymachine.example.com and foo.bar.baz.com. A server program which binds to the address mymachine.example.com will only accept connections made to mymachine.example.com. A program which binds to foo.bar.baz.com will only accept connections to foo.bar.baz.com, and a program that binds to localhost will only accept connections to localhost (which must, of course, also be from localhost).

On the other hand, a server program which binds to INADDR_ANY will accept connections made to any address that happens to resolve to the machine in question, including mymachine.example.com, foo.bar.baz.com, and localhost. That's usually what you want.

[Punto]

Hi. thanks for your reply, it's very useful.

But I was looking for one of those sockets that are like files, on the filesystem, wich would be great, because I need to set restrictions on them (after all, I'm using it to pass commands to a running program)
I think I saw mysql using them. Do you know anything about it?

Thanks..

[Anonymous Monk]

IO::Socket::UNIX