ashok.g has asked for the wisdom of the Perl Monks concerning the following question: 

#usr/bin/perl
use strict;
use warnings;
use IO::Socket;
$| = 1;
my $client;
my $socket= new IO::Socket::INET(
                                PerHost => '192.168.0.34',
                                PeerPort => '4500',
                                Proto => 'tcp',
                                );
die "Couln't open socket: $!" unless $socket;
#open ALERT, ">alerts" or die " Unable to open file alerts \n";
while(1)
{
        print "Accepting Socket....\n";
        $client = $socket->accept();
        print "Socket Accepted:$client....\n";
        my $addr = $client->peerhost();
        my $port = $client->peerport();
        print "Got Connection from \"$addr\" at port $port\n";
        while(1)
        {
                $client->recv(my $rec,1024);
                my $date = `date`;
        #       print ALERT "[ $date ] :$rec\n";
                print "[ $date ] :$rec\n";
        }
}

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When I try to run this script I'm getting this output...
Accepting Socket....
Use of uninitialized value in concatenation (.) or string at servertes
+t.pl line 18.
Socket Accepted:....
Can't call method "peerhost" on an undefined value at servertest.pl li
+ne 19.

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FYI
[root@station34 Socket]# telnet 192.168.0.34 4500
Trying 192.168.0.34...
Connected to station34 (192.168.0.34).
Escape character is '^]'.
^]
telnet> quit
Connection closed.

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Am I missing something here?

Replies are listed 'Best First'.
Re: Problem with Socket Programming Perl Script
by Anonyrnous Monk (Hermit) on Jan 24, 2011 at 09:45 UTC

    accept is for listening sockets, i.e. servers. Your constructor usage, however, looks like you want to connect to an existing service.  This is why the accept call fails and returns undef.  (If you had checked for errors, you'd have gotten "Invalid argument" in $!)

    See perlipc for examples of client-side code.

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      After modifications my script will look like
      #usr/bin/perl
use strict;
use warnings;
use IO::Socket;
$| = 1;
my $client;
my $socket= new IO::Socket::INET(
                                LocalPort => '4500',
                                Proto => 'tcp',
                                Listen => 1,
                                Reuse => 1
                                );
die "Couln't open socket: $!" unless $socket;
while(1)
{
        $client = $socket->accept() or die sprintf "ERRRR(%d)(%s)(%d)(
+%s)", $!,$!,$^E,$^E;
        print "Socket Accepted:$client....\n";
        $client->autoflush(1);
        my $addr = $client->peerhost();
        my $port = $client->peerport();
        print "Got Connection from \"$addr\" at port $port\n";
        while( <$client> )
        {
                print "$client"
        }
}

      [download]
      When I run this script I'm getting the error as
      Couln't open socket: Address already in use at servertest.pl line 14. FYR
      [root@station34 Socket]# netstat -anp | grep 4500
tcp        0      0 192.168.0.34:4500           0.0.0.0:*             
+      LISTEN      22948/nco_objserv   
tcp        0      0 192.168.0.34:32997          192.168.0.34:4500     
+      ESTABLISHED 22990/nco_p_syslog  
tcp        0      0 192.168.0.34:32996          192.168.0.34:4500     
+      ESTABLISHED 22991/nco_p_mttrapd 
tcp        0      0 192.168.0.34:4500           192.168.0.34:32997    
+      ESTABLISHED 22948/nco_objserv   
tcp        0      0 192.168.0.34:4500           192.168.0.34:32996    
+      ESTABLISHED 22948/nco_objserv   
unix  2      [ ACC ]     STREAM     LISTENING     4500   1934/gpm     
+       /dev/gpmctl

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        tcp        0      0 192.168.0.34:4500           0.0.0.0:*                   LISTEN      22948/nco_objserv

        As you've confirmed yourself, the socket/port is already in use by another process, which is why you get the "Address already in use" error.  You need to kill that process if you want to start another one listening on the same port.

        The Reuse => 1 option only means that the socket is immediately being freed for reuse when the process exists, not that you can have several processes listening on the same socket (in case that's what you thought).

        (I'm a little confused as to what exactly you're trying to do. Your first post looked like you wanted to connect to an existing service. Now it seems you want to write one yourself, but there's already nco_objserv listening on that port...(?))

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Re: Problem with Socket Programming Perl Script
by Anonymous Monk on Jan 24, 2011 at 09:46 UTC
    You're not error checking
    $client = $socket->accept()
  or die sprintf "ERRRR(%d)(%s)(%d)(%s)", $!,$!,$^E,$^E;

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