UDP Client and Server in one

[mhirschb]

Hello Monks,

I should write a thin and easy emulation of a networked device which is controlled by simple UDP commands. The device listens to UDP port 7070 and if a request arrives, it immediately responses with some status data.

I solved this easily with

use IO::Socket;
my $PORTNO = 7090;
$sock = IO::Socket::INET->new(LocalPort => $PORTNO, Proto => 'udp')
while ($sock->recv($request, $MAXLEN)) {
    $response=parseRequest($request);
    $sock->send($response);
}

My problem is, that this box should also send time-triggered status notifications every five seconds. Additionaly, these "five seconds" and the content of the status notifications are modified by the incoming request.

Currently, I have no clear idea, how the solution might look like. Any hint?

Thanks for your time!

[NetWallah]

Here is one way to do it:

* Make your "recv" non-blocking, with a 5-second timeout
* Write to your socket with content based on the most recent successful recv


You will likely run into trouble implementing this - once you have some code, post back here, and we can help.

[tybalt89]

#!/usr/bin/perl

# http://perlmonks.org/?node_id=1183721

use strict;
use warnings;
use IO::Socket;
use IO::Select;
use Time::HiRes 'time';

@ARGV and $ARGV[0] eq 'tester' and do_test_routine();

my $from;
my $PORTNO = 7090;
my $timerinterval = 5;
my $timedresponse = "default timed response\n";
my $MAXLEN = 512;

my $sock = IO::Socket::INET->new(LocalPort => $PORTNO, Proto => 'udp')
  or die $@;
my $sel = IO::Select->new($sock);
my $nexttimer = time + $timerinterval;

for(;;)
  {
  my $timeout = $nexttimer - time;
  if( $timeout <= 0 )
    {
    warn "timed out @{[int time - $^T]}\n";
    if( defined $from ) #send time-triggered status
      {
      $sock->send($timedresponse, 0, $from);
      }
    $nexttimer = $timerinterval + time;
    }
  else
    {
    for my $fh ( $sel->can_read($timeout) )
      {
      $from = $fh->recv(my $request, $MAXLEN);
      my $response = parseRequest($request);
      $fh->send($response, 0, $from);
      }
    }
  }

sub parseRequest
  {
  warn "got @_";
  return "canned response\n";
  }

sub do_test_routine # for testing purposes only
  {
  my $sock = IO::Socket::INET->new(LocalPort => 7091, Proto => 'udp',
    PeerPort => 7090, PeerHost => 'localhost',
    ) or die $@;
  $sock->send("a test message\n");
  for(;;)
    {
    $sock->recv(my $buf, 512);
    warn "tester got: $buf";
    }
  }

semi-tested :)

[thanos1983]

Hello mhirschb,

I just wanted to add something here regarding your title of your question.

You are writting UDP Client and Server in one. From my point of view if I understand correctly you think that Server is receiving your messages and client is replying back.

If this is the case it would be nice to read a similar question What is the difference between udp client and server?.

Answer given by sundialsvc4 from the question:

“The difference between a client and a server” has nothing to do with “UDP.” Rather, it has to do with the role that each program plays, in relation to one another. A “server” is any computer program that is primarily designed to talk to other computer programs, rather than to people. “Servers” often work by listening on network connections ... TCP/IP or UDP ... but some internal-only servers use other techniques such as named pipes. Many commercial servers support multiple modes of communication. Within CPAN, you will find substantial building-blocks for constructing server programs. If you look hard enough before “just diving in,” you’ll find that a great deal of your work has been done for you. The code is, by and large, very high-performance, reliable, and well tested.

I hope this clears things a bit, as NetWallah said start implementing your solution and repost and we will be more than happy to assist you with your solution.