This is one of my first ventures into the world of sockets....
I'm trying to through together a program that will allow multiple users to exchange information. Currently I'm picturing a server to which clients connect, but I'm not wedded to that design yet.

I've been reading through Chapter 12 of the panther book, and I'm looking at the following code: 

use IO::Socket;
use IO::Select;
$main_socket = new IO::Socket::INET (LocalHost => 'localhost',
                    LocalPort => 1200,
                    Listen    => 5,
                    Proto     => tcp,
                    Reuse     => 1);
die "Socket not created: $!\n" unless ($main_socket);
$readable_handles  = new IO::Select();
$readable_handles->add($main_socket);
while(1){
    #select() blocks until a socket is ready to be read
    ($new_readable) = IO::Select->select($readable_handles,undef,undef
+,0);
    #We now have at least one readable handle.
    foreach $sock (@$new_readable){
        if ($sock == $main_socket){
            $new_sock = $sock->accept();
            #new connection, add to list.
            #May not be readable yet.
            $readable_handles->add($new_sock);
        } else {
            #check to see if socket closed
            $buf = <$sock>;
            if($buf) {
                #Do stuff with $buf
            } else {
                #socket was closed
                $readable_handles->remove($sock);
                close($sock);
            }
        }
    }
}

[download]
My questions are:
  1. The next section in the book says that the filehandle blocks, but I don't understand this. Can someone restate it for me?
  2. While I'm expecting to trust my clients, I can see problems if one gets stuck in an infinite loop and sends me continuous data...how would I stop that? Particularly if I'm trying to read all the info the client sends before acting on it.
  3. This code has an infinite loop, which is obviously incompatible with a GUI. I'd like to make this a package that can be used by different UIs. I have an idea of how to do this (put the loop into subroutine, make it for a limited time rather than infinite, ditto with the select, and call it via a timed event in the calling program), but any advice on pitfalls to avoid would be appreciated.
  4. Because the clients will also be modules that can be GUI based, they'll probably be polling the server to check for status changes. Assuming the clients all sent a did-anything-change query once a second, would the above code allow everyone to get talked to, or would one client have priority over the others?
  5. This all sounds like its creating some significant network traffic...is this normal? I may just be nervous since I'm used to the mostly non-interactive web.

In reply to Multiple clients with IO::Sockets, IO::Select by swiftone

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