Programming Perl, 4th Edition

setsockopt

setsockopt SOCKET, LEVEL, OPTNAME, OPTVAL

This function sets the socket option requested. The function returns undef on error. The Socket module provides the needed constants for LEVEL and OPNAME, although those for LEVEL can all be obtained from getprotobyname. LEVEL specifies which protocol layer you’re aiming the call at, or SOL_SOCKET for the socket itself at the top of all the layers. OPTVAL might either be a packed string or an integer. An integer OPTVAL is shorthand for pack("i", OPTVAL). OPTVAL may be specified as undef if you don’t want to pass an argument.

One common option to set on a socket is SO_REUSEADDR, which gets around the problem of not being able to bind to a particular address while the previous TCP connection on that port is still making up its mind to shut down. That would look like this:

use Socket;
socket(SOCK, ...) || die "Can't make socket: $!";
setsockopt(SOCK, SOL_SOCKET, SO_REUSEADDR, 1)
        || warn "Can't do setsockopt: $!\n";

Another common option is to disable Nagle’s algorithm on a socket:

use Socket qw(IPPROTO_TCP TCP_NODELAY);
setsockopt($socket, IPPROTO_TCP, TCP_NODELAY, 1);

See setsockopt(2) for other possible values.