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

I am trying to get the following segment of code to work - the code sends a message between processes then waits (at least in my mind) for a response from the process to which it just sent: 
                if($name eq $match)
        {
            print "Second found match: $name\n";
            print "Second sending \"$name\" to Third\n";
            
            print $t_socket "$match\n";
        
            while(<$t_socket>)
            {
                #print "Second has accepted socket to Third...\n";
                
                my $name = $_;
                chomp($name);
                
                my $t_host = gethostbyaddr($t_socket->peeraddr, AF_INE
+T);
                my $t_port = $t_socket->peerport;
                
                print "Received from [$f_host $f_port]: $name\n";     
            }
        }

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however for some reason I can never enter the while(<$t_socket>){...} loop...

I was told not to use $t_socket->accept() since I have already opened the socket, is this correct?

why can I not listen on this $t_socket after I have sent to it?

I am including my entire code below: 

use IO::Socket;
use strict;
use warnings;

our $F_PORT = shift or die "Please specify First port number\n";
our $T_PORT = shift or die "Please specify Third port number\n";

#our $file = shift or die "Please specify input file\n";;

my $f_socket = IO::Socket::INET->new('LocalPort' => $F_PORT,
                       'Proto' => 'tcp',
                       'Listen' => 2)
    or die "Second: Can't create socket to First($!)\n";
   
my $t_socket = IO::Socket::INET->new( 'PeerAddr' => "localhost",
                    'PeerPort' => $T_PORT,
                       'Proto' => 'tcp')
    or die "Second: Can't create socket to Third($!)\n";

my $match = "brenna";
    
print "Second listening\n";
while(my $first = $f_socket->accept()) 
{
    #setup acknowledgement
    print "Second: Accepted connection from First..\n";
    my $f_host = gethostbyaddr($first->peeraddr, AF_INET);
    my $f_port = $first->peerport;
    
    while (<$first>) 
    {
        my $name = $_;
        chomp($name);
        
        #send acknowledgement message to First
        print "Received from [$f_host $f_port]: $name\n";
        #print $f_socket "$.: $name\n";
        
        if($name eq $match)
        {
            print "Second found match: $name\n";
            print "Second sending \"$name\" to Third\n";
            
            print $t_socket "$match\n";
        
            while(<$t_socket>)
            {
                #print "Second has accepted socket to Third...\n";
                
                my $name = $_;
                chomp($name);
                
                my $t_host = gethostbyaddr($t_socket->peeraddr, AF_INE
+T);
                my $t_port = $t_socket->peerport;
                
                print "Received from [$f_host $f_port]: $name\n";     
            }
        }                    
    }
}
die "Second: Can't accept socket from First($!)\n";

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Any advice would be much appreciated!

Thanks!

Replies are listed 'Best First'.
Re: Read/Write Socket question (Bidirectional my ass...)
by castaway (Parson) on Jul 04, 2005 at 10:26 UTC
    What sort of data do you get back from the $T_PORT process? Reading with <$t_socket> will only work if the data you are expecting contains newlines. (the angle brackets are a call to readline), if you have no newlines, then try using recv instead.

    Have you tried testing with telnet? ie connect with telnet to localhost $T_PORT, type in the data you are trying to send with your script, and see what it answers?

    C.

[reply]
[d/l]
      Do I need to setup a UDP connection specifically to use recv? To do this do I only need to specify 'Proto'=>'udp' when opening the socket?

      I am attempt to read a string back through the <$t_socket> -it is a name that I need to find a eq match for - the link below has a better description of my project:

      http://www.perlmonks.org/?node_id=472004

      Essentially I am trying to match input given to me by a First process, if I match this input in the Second process I send it to the Third process to see if I have yet another match. However if the First/Second match is not confirmed by the Third process, then I need to respond to the Second to find another match.

      Sending the data from First, to Second, to Third works fine.

      My problem comes in being able to establish a connection "downstream" (Third, to Second, to First) using the same set of sockets that I originally used to send data "upstream". In short, I cannot seem to pick up a response from Third to Second, and then from Second to First.

      The code for my Third process is appended below - as you can see I am adding a newline at the end of the string before I send it back to the Second process - but for some reason the while(<$t_socket>){...} loop never executes - either it is indefinitely waiting on the <$t_socket> or it is skipping the loop altogether. 

      
use IO::Socket;
use strict;
use warnings;

my $PORT = shift or die "Please specify First port number\n";

#my $file = shift or die "Please specify input file\n";

my $socket = IO::Socket::INET->new('LocalPort' => $PORT,
                       'Proto' => 'tcp',
                       'Listen' => 2)
    or die "Third: Can't create socket to Second($!)\n";

my $match = "brenna";
    
print "Third listening\n";
while (my $second = $socket->accept) 
{
    #setup acknowledgement message to Second
    my $host = gethostbyaddr($second->peeraddr, AF_INET);
    my $port = $second->peerport;
    
    while (<$second>) 
    {
        my $name = $_;
        chomp($name);
        
        print "[$host $port] $name\n";
        #print $socket "$.: $name\n";

        if($name eq $match)
        {    
            print "Third sending \"$name\" to Second\n";
            print $socket "$name\n";
            #close $second or die "Can't close ($!)\n";
        }
    }
}
die "Third: Can't accept receive socket from Second($!)\n";

      [download]
      Any help/advice you can offer to help me figure this out would be much appreciated!
[reply]
[d/l]
        No you don't, or I wouldnt have suggested using it. recv works with a socket, no matter how it is connected.

        Does $name in fact equal $match? ie is the third one actually answering at all? Please try testing it using telnet, or give the data that you are using.

        C.

[reply]

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