Update: I started WWW::Slides from the base of this script.

Hi all,

I came up with an idea that I'd like to share with you, hoping for some feedback/suggestions. I did not find any reference to the tecnique I'm going to show, but it's probable that I didn't search well, so any pointer is appreciated as well.

Basically, it's a sistem to make presentations online. No, it's not "yet another text-to-html-slides" system - you have to prepare your html slides before. This is a system to present these slides online, with many listeners around the web and the presenter that controls the display of the different slides for each of them.

Strictly speaking this is not a Perl issue, but I realised it in Perl, of course :). Here comes the skeleton script: 

#!/usr/bin/perl 
use strict;
use warnings;
use IO::Socket;
use IO::Select;
use Socket qw( sockaddr_in inet_ntoa );

# Socket to receive commands
my $controllers_listener = IO::Socket::INET->new(
   Proto     => 'udp',
   LocalPort => 50605,
   ReuseAddr => 1,
) or die "new socket: $!";

# Socket for listening to incoming connections
my $clients_listener = IO::Socket::INET->new(
   Proto     => 'tcp',
   LocalPort => 50605,
   ReuseAddr => 1,
   Listen    => 3,
) or die "new socket: $!";
my %clients;

# Use select to coordinate requests
my $sel = IO::Select->new($controllers_listener, $clients_listener);

my @slides = load_slides();

$|++;
my $slide = 0;    # Tracks current slide
my %shown_marker_for; # Tracks slides sent to different clients

my %callback_for = ( # Available commands
   'first' => sub {
      goto_slide(0);
   },
   'last' => sub {
      goto_slide($#slides);
   },
   'next' => sub {
      goto_slide($slide + 1);
   },
   previous => sub {
      goto_slide($slide - 1);
   },
   show => sub {
      my $slide = shift;
      goto_slide($slide - 1) if $slide;
   },
);

# Main loop
while (my @ready = $sel->can_read()) {
 FILEHANDLE:
   for my $fh (@ready) {
      if ($fh == $clients_listener) { # add new client
         my ($socket, $peer) = $clients_listener->accept();
         exhaust_input($socket); # ignore input data
         $clients{$socket} = [$socket, $peer];
         $sel->add($socket);
         activity($peer, 'client entered');

         # Send the current slide
         print_header($socket);
         print_slide($socket, $slide);
      } ## end if ($fh == $clients_listener)
      elsif (exists $clients{$fh}) {    # close connection
         activity($clients{$fh}[1], 'client exited');
         $sel->remove($fh);
         $fh->close();
         delete $clients{$fh};
      }
      else { # Command received, via UDP
         # Command from controller
         my $peer = $fh->recv(my $command_string, 1500)
            or next FILEHANDLE;
         next FILEHANDLE unless $command_string;
         for my $command_line (split /\n+/, $command_string) {
            next unless $command_line =~ /\S/;
            my ($command, @args) = split /\s+/, $command_line;
            activity($peer, "trying command '$command_line'");
            $callback_for{$command}->(@args)
               if exists $callback_for{$command};
         }
      } ## end else [ if ($fh == $controllers_listener)
   } ## end for my $fh (@ready)
} ## end while (@ready = $sel->can_read...

# Log on STDOUT about what's happening
sub activity {
   my ($peer, $msg) = @_;
   my ($port, $iaddr) = sockaddr_in($peer);
   my $addr = inet_ntoa($iaddr);
   print {*STDOUT} "$addr:$port - $msg\n";
   return;
}

# Send header to the client
sub print_header {
   my ($socket) = @_;
   print {$socket} "HTTP/1.1 200 OK\r\n";
   print {$socket} "Content-type: text/html\r\n\r\n";
   print {$socket} "<html><head></head><body>\n";
} ## end sub print_header

sub hide_slide {
   my ($socket, $slide) = @_;
   print {$socket} "<style>#slide$slide { display: none }</style>\n";
}

sub print_slide {
   my ($socket, $slide) = @_;

   if ($shown_marker_for{$socket}{$slide}) { # just resume
      print {$socket} "<style>#slide$slide { display: block }</style>\
+n";
   }
   else {
      print {$socket} qq(
        <div id="slide$slide">
            $slides[$slide]
         </div>
      );
   }
   $shown_marker_for{$socket}{$slide} = 1;
} ## end sub print_slide

# Transition function, for each client hides the previous
# and shows the new
sub goto_slide {
   my ($new_slide) = @_;
   return unless $new_slide =~ /\A\d+\z/mxs;
   return unless $new_slide < @slides;
   my $old_slide = $slide;

   print {*STDOUT} "going to $new_slide from $old_slide\n";
   for my $client (values %clients) {
      hide_slide($client->[0], $old_slide);
      print_slide($client->[0], $new_slide);
   }
   $slide = $new_slide;
   return;
} ## end sub goto_slide

# Eliminate input data coming from clients
sub exhaust_input {
   my ($socket) = @_;
   my $sel = IO::Select->new($socket);
   while ($sel->can_read(0)) {
      $socket->sysread(my $input, 1500);
      return 0 unless length $input;
   }
   return 1; # for many reasons...
} ## end sub exhaust_input

# Dummy function, loads test slides after __END__
sub load_slides {
   local $/ = "\n----------\n";
   chomp(@slides = <DATA>);
   return @slides;
}

__END__
<h1>This is slide 1</h1>
Here you can find the contents for slide #1. You can insert images:
<p>
<img src="http://www.polettix.it/cgi-bin/wiki.pl/download/PerlFlowers.
+png"
     alt="Perl flowers" title="Perl flowers">
<p>as well as other elements:
<ul>
<li>a</li>
<li>simple</li>
<li>list</li>
</ul>

----------

<h1>This is slide 2</h1>
The contents are completely different here.
<hr>
<p>
<img src="http://www.polettix.it/cgi-bin/wiki.pl/download/Soffietto-so
+luzione.png"
     alt="solution" title="solution">


----------

<h1>This is slide 3</h1>
The contents are completely different here, with respect to the other
two pages.
<hr>
<p>
<img src="http://www.polettix.it/cgi-bin/wiki.pl/download/Casa.png"
     alt="solution" title="solution">
<p>I live here!

[download]
Update: some bug fixes.

Usage:

Each slide is enclosed in a div with id "slideN", where N is the number of the slide (from 0). Each time a new slide is visited, the previuos one is hidden setting the display style of the div to "none". The script keeps track of already-sent slides, that can be re-visited with a simple style change (back to "display: block").

It's far from a good shape, of course. It has bugs (e.g. it does not handle client browser stops very well) and has a design that can be surely improved. For example, should it be implemented as a CGI? Comments and suggestions are welcome!!!

Flavio
perl -ple'$_=reverse' <<<ti.xittelop@oivalf

Don't fool yourself.

In reply to RFC: Web Presentations by polettix

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and:  <code> code here </code>
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