This is the last set of notes developed in class during the July 08 lecture/lab.

Today is Wednesday. One intensive summer session ends today. 

Tomorrow is Thursday. There is no class whatsoever. 

But we have office hours 9-10 and 11-5pm. 

The new summer sessions starts on Friday with lecture. Java. 

So tomorrow we work out midterm grades for A202/A598 as well as final grades for one A290/A590. 

(Grades will be final only on July 28 though). 

Here's the first program that we developed: 

<?
  $d1 = "N/A"; 
  $d2 = "N/A"; 
  $d3 = "N/A"; 

  if ($message) {
    if ($action == "Deposit") {
      $balance += $amount;       
    } else {
      $d1 = rand(1, 6);       
      $d2 = rand(1, 6);       
      $d3 = rand(1, 6);       
      if ($d1 == $d2 && $d2 == $d3) {
        $balance += 2 * $bet; 
      } else {
        if ($d1 == $d2 || $d2 == $d3 || $d1 == $d3) {
          $balance += $bet; 
        } else {
          $balance -= $bet; 
        } 
      } 
    }
  } else {
    $balance = 0; 
    $message = "Welcome"; 
  }   

 ?>

<form>
  <table border cellpadding=2> 
    <tr> <td> <?=$d1?> <td> <?=$d2?> <td> <?=$d3?> 
  </table> <p>    

  Current balance: <?=$balance?> <p> 
  Add money: <input type=text name=amount> and press <input type=submit name=action value=Deposit> <p> 
  Bet: <input type=text name=bet> and press <input type=submit name=action value=Spin> 

  <input type=hidden name=message value="<?=$message?>"> 
  <input type=hidden name=balance value="<?=$balance?>"> 

</form> 

The second one is very straightforward: 

<? session_start(); 

  $d1 = "N/A"; 
  $d2 = "N/A"; 
  $d3 = "N/A"; 

  if ($message) {
    if ($action == "Deposit") {
      $balance += $amount;       
    } else {
      $d1 = rand(1, 6);       
      $d2 = rand(1, 6);       
      $d3 = rand(1, 6);       
      if ($d1 == $d2 && $d2 == $d3) {
        $balance += 2 * $bet; 
      } else {
        if ($d1 == $d2 || $d2 == $d3 || $d1 == $d3) {
          $balance += $bet; 
        } else {
          $balance -= $bet; 
        } 
      } 
    }
  } else {
    session_register("message"); 
    session_register("balance"); 
    $balance = 0; 
    $message = "Welcome"; 
  }   

 ?>

<form>
  <table border cellpadding=2> 
    <tr> <td> <?=$d1?> <td> <?=$d2?> <td> <?=$d3?> 
  </table> <p>    

  Current balance: <?=$balance?> <p> 
  Add money: <input type=text name=amount> and press <input type=submit name=action value=Deposit> <p> 
  Bet: <input type=text name=bet> and press <input type=submit name=action value=Spin> 

</form> 

Now we convert to Perl/CGI:

#!/usr/bin/perl

use CGI;

$q = new CGI; 

print $q->header, $q->start_html; 

$message = $q->param('message'); 
$balance = $q->param('balance'); 

$amount  = $q->param('amount'); 
$bet  = $q->param('bet'); 
$action  = $q->param('action'); 

$d1 = "N/A"; 
$d2 = "N/A"; 
$d3 = "N/A"; 

if ($message) {
  if ($action eq "Deposit") {
    $balance += $amount;       
  } else {
    $d1 = int(rand(6) + 1);       
    $d2 = int(rand(6) + 1);       
    $d3 = int(rand(6) + 1);       
    if ($d1 == $d2 && $d2 == $d3) {
      $balance += 2 * $bet; 
    } else {
      if ($d1 == $d2 || $d2 == $d3 || $d1 == $d3) {
        $balance += $bet; 
      } else {
        $balance -= $bet; 
      } 
    } 
  }
} else {
  $balance = 0; 
  $message = "Welcome"; 
}   

print qq{
<form>
  <table border cellpadding=2> 
    <tr> <td> $d1 <td> $d2 <td> $d3 
  </table> <p>    

  Current balance: $balance <p> 
  Add money: <input type=text name=amount> and press <input type=submit name=action value=Deposit> <p> 
  Bet: <input type=text name=bet> and press <input type=submit name=action value=Spin> 

  <input type=hidden name=message value="$message"> 
  <input type=hidden name=balance value="$balance"> 

</form> 
}; 

Now we need to convert to server-side state with Perl/CGI: 

The first thing that I need to do is create a table to hold the state.

create table last (
    session_id char(8) primary key,     
    message    varchar(240),
    balance    int,     
    modified   timestamp
);

Then I change the client-side state program to this (based on ch. 11): 

#!/usr/bin/perl

use CGI;
use DBI;

use Digest::MD5 qw(md5 md5_hex md5_base64);

$DB       = "dbi:mysql:homeworkThree:silo.cs.indiana.edu:port=44089";
$username = "lbird"; 
$password = "sp00n";
$DB_TABLE = "last";

$SECRET    = "something secret"; 
$EXPIRE    = 30 * 60 * 60 * 24; # one month 
$MAX_TRIES = 10; 
$ID_LENGTH =  8;

$q = new CGI;

# Open the database --------------------------------------------------------
$DBH = DBI->connect($DB, $username, $password, {PrintError => 0}) || die "Couldn't open database: ", $DBI::errstr;

# get the current session ID, or make one ----------------------------------
my ($session_id, $note) = &get_session_id();

# start the page -----------------------------------------------------------
print $q->header,
      $q->start_html(-title => 'Last Lab',
                     -bgcolor => 'lightgrey');

my $state = &get_state($session_id);

$message   = $state->{'message'}; # state variables
$balance   = $state->{'balance'}; 

$amount  = $q->param('amount'); # input 
$bet  = $q->param('bet'); 
$action  = $q->param('action'); 

$d1 = "N/A"; 
$d2 = "N/A"; 
$d3 = "N/A"; 

if ($message) {
  if ($action eq "Deposit") {
    $balance += $amount;       
  } else {
    $d1 = int(rand(6) + 1);       
    $d2 = int(rand(6) + 1);       
    $d3 = int(rand(6) + 1);       
    if ($d1 == $d2 && $d2 == $d3) {
      $balance += 2 * $bet; 
    } else {
      if ($d1 == $d2 || $d2 == $d3 || $d1 == $d3) {
        $balance += $bet; 
      } else {
        $balance -= $bet; 
      } 
    } 
  }
} else {
  $balance = 0; 
  $message = "Welcome"; 
}   

$state->{'message'} = $message; 
$state->{'balance'} = $balance; 

&save_state($state, $session_id);

print qq{
<form>
  <table border cellpadding=2> 
    <tr> <td> $d1 <td> $d2 <td> $d3 
  </table> <p>    

  Current balance: $balance <p> 
  Add money: <input type=text name=amount> and press <input type=submit name=action value=Deposit> <p> 
  Bet: <input type=text name=bet> and press <input type=submit name=action value=Spin> 

  <input type=hidden name=message value="$message"> 
  <input type=hidden name=balance value="$balance"> 

</form> 
}, $q->end_html;

# get the state from the database ------------------------------get_state---
sub get_state {
  my $id = shift;  
  my $query = 
      "SELECT * FROM $DB_TABLE WHERE session_id = '$id'"; 
  my $sth = $DBH->prepare($query) || die "Prepare: ", $DBH->errstr;
  $sth->execute || die "Execute: ", $sth->errstr; 
  my $state = $sth->fetchrow_hashref; 
  $sth->finish; 
  return $state; 
}

# retrieve the session ID from the path info. if it's -----get_session_id---
# not already there, add it to the path info (more or less) with a redirect 
sub get_session_id {

  my (@result); 
  &expire_old_sessions(); 
  my ($id) = $q->path_info() =~ m:^/([a-h0-9]{$ID_LENGTH}):o;
  return @result if $id and @result = &check_id($id); 
  
  # if we get here, there's not already an ID in the path info 
  my $session_id = &generate_id(); 
  die "Couldn't make a new session id" unless $session_id; 
  print $q->redirect($q->script_name() . "/$session_id"); 
  exit 0; 
}

# find a new unique ID and insert it into the database -------generate_id---
sub generate_id {
  # create a new session id 
  my $tries = 0; 
  my $id = &hash($SECRET . rand()); 

  while ($tries++ < $MAX_TRIES) {
    last if $DBH->do("INSERT INTO $DB_TABLE (session_id) VALUES ('$id')"); 
    $id = &hash($id); 
  }

  return undef if $tries >= $MAX_TRIES; # we failed 
  return $id; 
}

# check to see that an old ID is valid --------------------------check_id---
sub check_id {

  my $id = shift; 

  return ($id, '') 

    if $DBH->do("SELECT 1 FROM $DB_TABLE WHERE session_id = '$id'") > 0; 

  return ($id, 'The record of your game may have expired. Restarting.')

    if $DBH->do("INSERT INTO $DB_TABLE (session_id) VALUES ('$id')"); 

  return (); 

}

# generate a hash value ---------------------------------------------hash---
sub hash {
  my $value = shift; 
  return substr(md5_hex($value), 0, $ID_LENGTH); 
}

sub expire_old_sessions { # --------------------------expire_old_sessions---
  $DBH->do(<<END); 
DELETE FROM $DB_TABLE
  WHERE (unix_timestamp() - unix_timestamp(modified)) > $EXPIRE
END
}

# save the state in the database ------------------------------save_state---
sub save_state {
  my ($state, $id) = @_; 
  my $sth = $DBH->prepare(<<END) || die "prepare: ", $DBH->errstr;
UPDATE $DB_TABLE
  SET message=?,balance=?
  WHERE session_id='$id'
END
  $sth->execute(@{$state}{qw(message balance)})
    || die "execute: ", $DBH->errstr;
  $sth->finish; 
} 

So you see that if you have to emulate the class extension mechanism by hand you have to do a lot of extra work. 
--