Perl not closing TCP sockets if clients are no longer connected?
- by LM
The purpose of the application is to listen for a specific UDP multicast and then to forward the data to any TCP clients connected to the server. The code works fine, but I have a problem with the sockets not closing after the TCP clients disconnects. A socketsniffer utility shows the the sockets remain open and all the UDP data continues to be forwarded to the clients. The problem I believe is with the "if ($write-connected())" block as it always return true, even if the TCP client is no longer connected. I use standard Windows Telnet to connect to the server and to see the data. When I close telnet, the TCP socket is suppose to close on the server.
Any reason why connected() show the connections as active even if they are not? Also, what alternative should I use then?
Code:
#!/usr/bin/perl
use IO::Socket::Multicast;
use IO::Socket;
use IO::Select;
my $tcp_port = "4550";
my $tcp_socket = IO::Socket::INET->new(
Listen => SOMAXCONN,
LocalAddr => '0.0.0.0',
LocalPort => $tcp_port,
Proto => 'tcp',
ReuseAddr => 1,
);
use Socket qw(IPPROTO_TCP TCP_NODELAY);
setsockopt( $tcp_socket, IPPROTO_TCP, TCP_NODELAY, 1);
use constant GROUP => '239.2.0.81';
use constant PORT => '6550';
my $udp_socket= IO::Socket::Multicast->new(Proto=>'udp',LocalPort=>PORT);
$udp_socket->mcast_add(GROUP) || die "Couldn't set group: $!\n";
my $read_select = IO::Select->new();
my $write_select = IO::Select->new();
$read_select->add($tcp_socket);
$read_select->add($udp_socket);
## Loop forever, reading data from the UDP socket and writing it to the
## TCP socket(s).
while (1) {
## No timeout specified (see docs for IO::Select). This will block until a TCP
## client connects or we have data.
my @read = $read_select->can_read();
foreach my $read (@read) {
if ($read == $tcp_socket) {
## Handle connect from TCP client. Note that UDP connections are
## stateless (no accept necessary)...
my $new_tcp = $read->accept();
$write_select->add($new_tcp);
}
elsif ($read == $udp_socket) {
## Handle data received from UDP socket...
my $recv_buffer;
$udp_socket->recv($recv_buffer, 1024, undef);
## Write the data read from UDP out to the TCP client(s). Again, no
## timeout. This will block until a TCP socket is writable.
my @write = $write_select->can_write();
foreach my $write (@write) {
## Make sure the socket is still connected before writing.
if ($write->connected()) {
$write->send($recv_buffer);
}
else {
$write_select->remove($write);
close $write;
}
}
}
}
}
