Network Programming with Perl

server2way.pl (Listing 5) and client2way.pl (Listing 6) works fine if both are ran on my pc but when I ran server2way.pl on another pc on the network (both Windows XP) I get this error on the client side:

no socket :Unknown error at client2way.pl line 14.

and this is line 14:

$sock or die "no socket :$!"; # Connect to server

I want to use this in our on going project.

Please help.

I noticed this when I converted Listings 6 (client) and 8 (server) to use EOLN delimited IO
(to better examine the behavior of concurrent stream sessions). This was initially done
because Listing 8 did not wait for new sessions after the first was closed. After the 1st
client exited accept() would return undef until another request was queued but didn't block
while waiting for the queue event. Eventually I just wrapped the outer while() in another
"while( ; sleep 2)" to give myself time to check the socket queue and match
incoming requests to accept() results. This revealed yet more oddities. Note that the
'Listen' parameter is set to SOMAXCONN (128 for my RHEL box and perl 5.8.5) for both forms
of new() socket operators. Any ideas on the following 3 oddities?

- Using IO::Socket::INET sockets -- the third concurrent session request hangs unprocessed
until one of the previous [still open] sessions exit, ie., when more than 2 open sessions
exist accept() blocks until there is only 1 open session, then processes the next waiting
request as expected.

- Using IO::Socket::UNIX sockets -- many concurrent sessions can be opened but once any of
these are closed accept() hangs until all other sessions are closed, ie., if open sessions
exist and one is closed accept() blocks until all are closed, then processes request(s) --
but not as expected, see bullet 3 below.

- Using either form of sockets -- prior to opening any sessions accept() blocks, waits for
requests to queue, and processes the first queued request as expected, but subsequent calls
to accept() return undef unless another request is queued, ie., accept() behaves as if the
O_NONBLOCK bit is being automatically set on the original socket at or after the first call.

###################################################
## The Client
###################################################

#!/usr/bin/perl -w
use strict;
use IO::Socket;
#use Carp;
#use Data::Dumper;

# Domain sockets
my $sock = new IO::Socket::UNIX( Peer => '/tmp/mysock',
Type => SOCK_STREAM ) or die $!;

## IP sockets
#my $sock = new IO::Socket::INET( PeerAddr => 'localhost', PeerPort => '7890',
# Proto => 'tcp'); $sock or die "no socket :$!";

my $buf;
while( $buf = <> ) {
chomp $buf;
print $sock "$buf\n";
print "$0 ($$): ", scalar localtime(), " sent: [$buf]\n";
$buf = scalar <$sock>;
chomp $buf;
print "$0 ($$): ", scalar localtime(), " received: [$buf]\n";
}
close $sock;

###################################################
## The server
###################################################

#!/usr/bin/perl -w
use strict;
use IO::Socket;
use POSIX qw(:sys_wait_h);
#use Carp;
#use Data::Dumper;

sub REAP {
1 until( -1 == waitpid( -1, WNOHANG ) );
$SIG{CHLD} = \&REAP;
}
$SIG{CHLD} = \&REAP;

# Domain sockets
unlink '/tmp/mysock';
my $sock = new IO::Socket::UNIX( Local => '/tmp/mysock', Type => SOCK_STREAM,
Listen => SOMAXCONN, Reuse => 1 ) or die $!;

## IP sockets
#my $sock = new IO::Socket::INET( LocalHost => 'localhost', LocalPort => 7890,
# Proto => 'tcp', Listen => SOMAXCONN, Reuse => 1) or die $!;

STDOUT->autoflush(1);

my( $new_sock, $child, $buf );
while( 1 ) {
while( $new_sock = $sock->accept() ) {
if( $child = fork ) {
close $new_sock
} elsif( defined( $child ) ) {
close $sock;
while( defined( $buf = <$new_sock> ) ) {
chomp $buf;
print "$0 ($$): ", scalar localtime(), " received: [$buf]\n";
sleep 1;
print "$0 ($$): ", scalar localtime(), " sending: [$buf]\n";
print $new_sock "$buf\n";
}
exit
} else {
die "$0 ($$): fork: $!"
}
}
sleep 2
}

###################################################
## END
###################################################

hi there,

I'm trying to execute client fork.pl on my xp machine with both client and server running on the same machine but it doesn't seem to be working. when i enter input at client, it simply accepts the input and then nothing happens.

Can anybody help me with this.

Thanks in advance,
lakshmi.

A very good example set for beginners. I am interested in knowing more about how I could use perl and start a program as server and which takes an input text from client and processes it and returns the result to client. Something using VEC and SELECT per commanda. I am woring on this code I have which uses all this. If you have any examples for that please let me know.

Thanks,

This tutorial was excelent. It was clear, concise, and informative. Although, I did have one question. What are the bennefits of using fork over thread? In most cases I know that creating a thread has most of the same bennefits of using fork but without the extra overhead. Why would one want to use fork in a web server as opposed to thread? Thanks!

Hi, i have been looking around lately for some networking related tutorials and i admit that this place is actually exactly what i was looking for.
Thanks.

PS: Beginner in perl.

a good guide to the world of the networks!

Great article, most of it worked on my FBSD server to.

Thanks alot, keep up the good work.

- Stian