Perl Cookbook

Writing a TCP Server

Problem

You want to write a server that waits for clients to connect over the network to a particular port.

Solution

This recipe assumes you’re using the Internet to communicate. For TCP-like communication within a single Unix machine, see Section 17.6.

Use the standard (as of 5.004) IO::Socket::INET class:

use IO::Socket;

$server = IO::Socket::INET->new(LocalPort => $server_port,
                                Type      => SOCK_STREAM,
                                Reuse     => 1,
                                Listen    => 10 )   # or SOMAXCONN
    or die "Couldn't be a tcp server on port $server_port : $@\n";

while ($client = $server->accept()) {
    # $client is the new connection
}

close($server);

Or, craft it by hand for better control:

use Socket;

# make the socket
socket(SERVER, PF_INET, SOCK_STREAM, getprotobyname('tcp'));

# so we can restart our server quickly
setsockopt(SERVER, SOL_SOCKET, SO_REUSEADDR, 1);

# build up my socket address
$my_addr = sockaddr_in($server_port, INADDR_ANY);
bind(SERVER, $my_addr)
    or die "Couldn't bind to port $server_port : $!\n";

# establish a queue for incoming connections
listen(SERVER, SOMAXCONN)
    or die "Couldn't listen on port $server_port : $!\n";

# accept and process connections
while (accept(CLIENT, SERVER)) {
    # do something with CLIENT
}

close(SERVER);

Discussion

Setting up a server is more complicated than being a client. The optional listen function tells the operating system how many pending, unanswered connections to queue up waiting for your server. The setsockopt function used in the Solution allows you to avoid waiting two ...