http://qs321.pair.com?node_id=440034

DrManhattan has asked for the wisdom of the Perl Monks concerning the following question:

This is perhaps more of a general networking question than an Perl question, but I'm writing a multiplexed server using IO::Socket::INET, and I notice that some of the sockets I get back from accept() have no peer host. Here's the framework:
#!/usr/bin/perl # Pragma use strict; use Carp qw(cluck); use IO::Socket; use IO::Select; # Default port(s) on which to listen our @PORTS = qw(1234 1235 1236); # Setup IO::Select objects to manage the sockets. our $LISTENERS = IO::Select->new() or die "IO::Select"; our $CLIENTS = IO::Select->new() or die "IO::Select"; # Open our listening ports foreach my $port (@PORTS) { my $listen_socket = IO::Socket::INET->new( LocalPort => $port, Listen => 20, Proto => 'tcp', Reuse => 1 ); die "Bind failed for port $port: $@" unless $listen_socket; $LISTENERS->add($listen_socket); } print "Waiting for connections\n"; while (1) { # Look for incoming connections my @ready = $LISTENERS->can_read(1); foreach my $socket (@ready) { my $connect = $socket->accept(); if ($connect) { if (!$connect->peerhost()) { cluck("NULL PEERHOST: " . join(" : ", $connect->sockhost(), $connect->sockport(), $connect->peerhost(), $connect->peerport(), $! )); close($connect); next; } print "Connection from ", $connect->peerhost(), " on port ", $connect->sockport(), "\n"; $CLIENTS->add($connect); } } @ready = $CLIENTS->can_read(1); foreach my $socket (@ready) { my $input; my $bytes = sysread($socket, $input, 1024); if ($bytes) { print "Read from client: $input"; } else { print "Disconnect from ", $socket->peerhost(), " on port ", $socket->sockport(), "\n"; $CLIENTS->remove($socket); close($socket); } } }

The question I have is related to that cluck(). Sometimes accept() returns an IO::Socket object, but it has no peerhost. The script output looks like this:

NULL PEERHOST: X.X.X.X : 1234 :  :  : Transport endpoint is not connected at ./foo.pl line 45
What causes that?

-Matt