IO::Socket echo server not echoing

[paulmlieberman]

The following code, modified from Lincoln Stein's "Network Programming
with Perl", doesn't work properly on Unix (5.6.1) or Windows systems
(5.8.6). The server receives the first message, but doesn't echo it
properly. Why?

#!/usr/bin/perl
# IOserver.pl

use strict;
use IO::Socket::INET;

use constant SIMPLE_TCP_PORT => 4001;
use constant MAX_RECV_LEN => 65536;

print "Hello, World...\n";

my $local_port = shift || SIMPLE_TCP_PORT;
my $server = IO::Socket::INET->new(Proto => 'tcp',
Type => SOCK_STREAM,
Reuse => 1,
Timeout => 60 * 60,
LocalPort => $local_port,
Listen => SOMAXCONN)
or die "Can't create server\n";

my $fromWho;
my $peeraddr;

while($fromWho = $server->accept())
{
my $hostinfo;
my $data;
$fromWho->recv($data, MAX_RECV_LEN);
if($fromWho)
{
$peeraddr = $fromWho->peeraddr();
$hostinfo = gethostbyaddr($peeraddr, AF_INET);
warn "Received from server: ", length($data), ' -> ', $data, "\n";
}
else
{
warn "IOserver: problem with recv: $!\n";
next;
}
sleep(3);
warn "Sending back to client...\n";
if (! $server->send($data, 0, $fromWho)) {
my $so_error = $server->sockopt(SO_ERROR);
die "IOserver: error $so_error sending message to $hostinfo: $!\n";
}
}
$server->close()
or warn "IOserver: close failed: $!\n";

===========================================================================

#!/usr/bin/perl
# IOclient.pl

use strict;
use IO::Socket::INET;

use constant SIMPLE_TCP_PORT => 4001;
use constant REMOTE_HOST => 'localhost';

use constant MAX_RECV_LEN => 65536;

my $remote_host = shift || REMOTE_HOST;
my $remote_port = shift || SIMPLE_TCP_PORT;
my $msg_count = 1;
my $big_chunk = 'x' x 65000;

my $client = IO::Socket::INET->new(Proto => 'tcp',
Type => SOCK_STREAM,
PeerAddr => $remote_host,
PeerPort => $remote_port)
or die "connection to remote system failed: $!\n";

while($msg_count)
{
next unless $client;

print "Enter string to echo: ";
$big_chunk = <STDIN>;
my $data = $client->sockhost() .' '. $msg_count . ' -> ' .
$big_chunk;

warn "Sending echo string to server...\n";

$client->send($data, 0)
or warn "problem with send...\n";

sleep(1);

my $fromWho = $client->recv($data, MAX_RECV_LEN, 0)
or die "Problem with recv(): $!\n";

if($fromWho)
{
my $remote_name = $client->peerhost();
warn "Received from $remote_name: ", length($data), ' => ',$data,
"\n";
}
else
{
warn "problem with recv: $!\n";
$client->close()
or warn "close failed: $!\n";
}
}
continue{
$msg_count++;
}
$client->close()
or warn "tcp_cli: close failed: $!\n";

 

[Mark Clements]

The following code, modified from Lincoln Stein's "Network Programming
with Perl", doesn't work properly on Unix (5.6.1) or Windows systems
(5.8.6). The server receives the first message, but doesn't echo it
properly. Why?

while($fromWho = $server->accept())
{
my $hostinfo;
my $data;
$fromWho->recv($data, MAX_RECV_LEN);
if($fromWho)
{
$peeraddr = $fromWho->peeraddr();
$hostinfo = gethostbyaddr($peeraddr, AF_INET);
warn "Received from server: ", length($data), ' -> ', $data, "\n";
}
else
{
warn "IOserver: problem with recv: $!\n";
next;
}
sleep(3);
warn "Sending back to client...\n";
if (! $server->send($data, 0, $fromWho)) {

You are trying to send on the listening socket, not the connected one.
try
$fromWho->send( $data, 0 )

my $fromWho = $client->recv($data, MAX_RECV_LEN, 0)
or die "Problem with recv(): $!\n";

if($fromWho)
{
my $remote_name = $client->peerhost();
warn "Received from $remote_name: ", length($data), ' => ',$data,
"\n";
}
else
{
warn "problem with recv: $!\n";
$client->close()
or warn "close failed: $!\n";
}
}

You need to look at the return value of recv:

recv SOCKET,SCALAR,LENGTH,FLAGS
Receives a message on a socket. Attempts to receive
LENGTH characters of data into variable SCALAR from
the specified SOCKET filehandle. SCALAR will be
grown or shrunk to the length actually read. Takes
the same flags as the system call of the same name.
Returns the address of the sender if SOCKET's
protocol supports this; returns an empty string
otherwise. If there's an error, returns the
undefined value. This call is actually implemented
in terms of recvfrom(2) system call. See "UDP

ie the error condition is undef, so your check should be


if(defined $fromWho){

With these modifications:

bob 606 $ perl testechoclient.pl
Enter string to echo: sdfg
Sending echo string to server...
Received at server: 20 -> 127.0.0.1 1 -> sdfg

Sending back to client...
Received from 127.0.0.1: 20 => 127.0.0.1 1 -> sdfg


regards,

Mark

 

[paulmlieberman]

OK! With those changes, it now works for the first iteration: the
client sends, the server echos. But when the client tries to send a
second string, it fails.

Here's my modified code.

- Paul

#!/usr/bin/perl
# IOserver.pl

use strict;
use IO::Socket::INET;

use constant SIMPLE_TCP_PORT => 4001;
use constant MAX_RECV_LEN => 65536;

print "Hello, World...\n";

my $local_port = shift || SIMPLE_TCP_PORT;
my $server = IO::Socket::INET->new(Proto => 'tcp',
Type => SOCK_STREAM,
Reuse => 1,
Timeout => 60 * 60,
LocalPort => $local_port,
Listen => SOMAXCONN)
or die "Can't create server\n";

my $fromWho;
my $peeraddr;

while($fromWho = $server->accept())
{
my $hostinfo;
my $data;
$fromWho->recv($data, MAX_RECV_LEN);
if(defined $fromWho)
{
$peeraddr = $fromWho->peeraddr();
$hostinfo = gethostbyaddr($peeraddr, AF_INET);
warn "Received from server: ", length($data), ' -> ', $data, "\n";
}
else
{
warn "IOserver: problem with recv: $!\n";
next;
}
sleep(3);
warn "Sending back to client...\n";
if (! $fromWho->send($data, 0)) {
my $so_error = $fromWho->sockopt(SO_ERROR);
die "IOserver: error $so_error sending message to $hostinfo: $!\n";
}
close($fromWho)
or warn "IOserver: close failed: $!\n";
warn "Waiting for another connection!\n";
}
=================================================================
#!/usr/bin/perl
# IOclient.pl

use strict;
use IO::Socket::INET;

use constant SIMPLE_TCP_PORT => 4001;
use constant REMOTE_HOST => 'localhost';

use constant MAX_RECV_LEN => 65536;

my $remote_host = shift || REMOTE_HOST;
my $remote_port = shift || SIMPLE_TCP_PORT;
my $msg_count = 1;
my $big_chunk = 'x' x 65000;

my $client = IO::Socket::INET->new(Proto => 'tcp',
Type => SOCK_STREAM,
PeerAddr => $remote_host,
PeerPort => $remote_port)
or die "connection to remote system failed: $!\n";

while($msg_count)
{
next unless $client;

print "Enter string to echo: ";
$big_chunk = <STDIN>;
my $data = $client->sockhost() .' '. $msg_count . ' -> ' .
$big_chunk;

warn "Sending echo string to server...\n";

$client->send($data, 0)
or warn "problem with send...\n";

sleep(1);

my $fromWho = $client->recv($data, MAX_RECV_LEN, 0)
or die "Problem with recv(): $!\n";

if(defined $fromWho)
{
my $remote_name = $client->peerhost();
warn "Received from $remote_name: ", length($data), ' => ',$data,
"\n";
}
else
{
warn "problem with recv: $!\n";
$client->close()
or warn "close failed: $!\n";
}
}
continue{
$msg_count++;
}
$client->close()
or warn "IOclient: close failed: $!\n";