Today we want to learn how to write our Homework One in PHP. 

We have PHP, we installed it yesterday. 

If you create 

   pico ~/apache/htdocs/four.php

Put this in the file: 

<? phpinfo() ?>

Then save and exit. Call the file from

http://silo.cs.indiana.edu:44xxx/four.php

All your PHP scripts need to be placed in htdocs with extension .php

A PHP script is essentially an HTML file that can (but doesn't have to) have code in it. 

So if you create a file five.php: 

<form>
  What's your name: <input type="text" name="userName">
  <input type="submit" name="proceed" value="Proceed">
</form>

Access it from 

http://silo.cs.indiana.edu:44xxx/five.php

Now change it to: 

<form>
  Welcome to silo: <? echo date('l jS \of F Y h:i:s A'); ?> <p>       

  What's your name: <input type="text" name="userName">
  <input type="submit" name="proceed" value="Proceed"> 
</form>

Then call it again to see it reporting the time. 

To post the code set up a symbolic link: 

   ln -s five.php five.phps

Then see the source code on-line: 

http://silo.cs.indiana.edu:44xxx/five.phps

When a form containing a field named "something" sends 
data to a PHP script the PHP script automatically does
all the parsing and the data binding that took us so much
in Python and Perl and places the value of the field in a
variable with the same name ($something) in the script:

To prove this change five.php: 

<form>
  Welcome <? echo $something; ?>  <p>
  
  Welcome to silo where the time is: <? echo date('l jS \of F Y h:i:s A'); ?> <p>
  
  What's your name: <input type="text" name="something">
  <input type="submit" name="proceed" value="Proceed">
</form>

Then access it: 

http://silo.cs.indiana.edu:44xxx/five.php

Then in the form type a name, push submit, verify the name is reported. 

Now we go back to

#!/usr/bin/python

import cgi, random

input = cgi.FieldStorage()
print "Content-type: text/html\n\n"

(message, n1, n2, m1, m2, answer) = ("", "", "", "", "", "") 

if input.has_key("message"): message = input["message"].value
if input.has_key("n1"): n1 = input["n1"].value
if input.has_key("n2"): n2 = input["n2"].value
if input.has_key("m1"): m1 = input["m1"].value
if input.has_key("m2"): m2= input["m2"].value
if input.has_key("answer"): answer = input["answer"].value

if message: 
  if int(answer) == int(n1) + int(n2): 
    m1 = str(int(m1) + 1)    
  m2 = str(int(m2) + 1)    
  message = "The score is " + m1 + " out of " + m2 + " currently"
  n1 = random.randrange(-50, 50)
  n2 = random.randrange(-50, 50)
else:
  message = "Welcome"
  n1 = random.randrange(-50, 50)
  n2 = random.randrange(-50, 50)
  m1 = 0
  m2 = 0

print """
<form>
  %s <p>  

  What is %s + %s ? Answer: <input type=text name=answer size=4> <p>

  Press <input type="submit" value="Proceed"> to submit your answer. 

  <input type="hidden" name="n1" value="%s"> 
  <input type="hidden" name="n2" value="%s"> 
  <input type="hidden" name="m1" value="%s"> 
  <input type="hidden" name="m2" value="%s"> 
  <input type="hidden" name="message" value="%s"> 
  
</form> 
""" % (message, n1, n2, n1, n2, m1, m2, message) 

Place this program somewhere make sure it works. 

We know what it does, how could we write it in PHP? 

Here's the conversion: 

<?
if ($message) {  
  if ($answer == $n1 + $n2) { 
    $m1 = $m1 + 1;   
  } 
  $m2 = $m2 + 1; 
  $message = "The score is " . $m1 . " out of " . $m2 . " currently";
  $n1 = rand(-50, 50); 
  $n2 = rand(-50, 50); 
} else { 
  $message = "Welcome";
  $n1 = rand(-50, 50);
  $n2 = rand(-50, 50);
  $m1 = 0;
  $m2 = 0;
}
?> 

<form>
  <?=$message?> <p>  

  What is <?=$n1?> + <?=$n2?> ? 
  Answer: <input type=text name=answer size=4> <p>

  Press <input type="submit" value="Proceed"> to submit your answer. 

  <input type="hidden" name="n1" value="<?=$n1?>"> 
  <input type="hidden" name="n2" value="<?=$n2?>"> 
  <input type="hidden" name="m1" value="<?=$m1?>"> 
  <input type="hidden" name="m2" value="<?=$m2?>"> 
  <input type="hidden" name="message" value="<?=$message?>"> 
  
</form> 

This is still five.php so access it or the source code as before. 

Finally: 

a) make sure you have ~/apache/phpsessions 
if not: create it with mkdir ~/apache/phpsessions

b) make sure that ~/apache/conf/php.ini at line 892 (or so) has

session.save_path = "/u/username/apache/phpsessions"

where username is your username (for me: dgerman) 

Once we restart the server we will be able to use sessions. 

Let's modify this program to keep state on the server side. 

So go to ~/apache/htdocs and copy five.php into six.php then open it. 

I will convert this program to keep state on the server side. 

1. Where will the state be? 

In the folder ~/apache/phpsessions

Take a look at it now, it's empty. 

2. Why? 

Because php.ini says so. 

Restart the server to make sure it knows. 

~/apache/bin/apachectl restart 

3. Make the following three changes in the program:

   a) place session_start(); at the top of your code

Please call my script at

   http://silo.cs.indiana.edu:44063/six.php

We see that sessions get created. My script now keeps track of
you all. Like this: 

-bash-3.2$ ls
sess_10cea6b3e4d6066abca2dcdc3ac0b429
sess_2695dcf75cf5ab7ef4083f00c41c369c
sess_359914280060b4a9f11ff91cc69c9868
sess_430fc84ac2b60320400279c7e0d5cdd9
sess_5c11774e7809d5fb05094feedd77a437
sess_7c9978e49515ad55e51c0042f8a92603
sess_9e645098cc2ca367993ce304ba7aaf5e
sess_ac190843d67979c9a8c58c958db7cfef
sess_e3d1ff7de275be7332be63ebd8379708
-bash-3.2$

   b) in the initialization part of your script/template
register your state variables with the session (please do
not register input variables or output variables, just the
session variables). Like so: 

} else {
  session_register("message");
  session_register("n1");     
  session_register("n2");     
  session_register("m1");     
  session_register("m2");     
  $message = "Welcome";
  $n1 = rand(-50, 50);
  $n2 = rand(-50, 50);
  $m1 = 0;
  $m2 = 0;
}

   c) now remove the hidden fields from your output 

You're done: 

<? session_start(); 
if ($message) {  
  if ($answer == $n1 + $n2) { 
    $m1 = $m1 + 1;   
  } 
  $m2 = $m2 + 1; 
  $message = "The score is " . $m1 . " out of " . $m2 . " currently";
  $n1 = rand(-50, 50); 
  $n2 = rand(-50, 50); 
} else { 
  session_register("message"); 
  session_register("n1"); 
  session_register("n2"); 
  session_register("m1"); 
  session_register("m2"); 
  $message = "Welcome";
  $n1 = rand(-50, 50);
  $n2 = rand(-50, 50);
  $m1 = 0;
  $m2 = 0;
}
?> 

<form>
  <?=$message?> <p>  

  What is <?=$n1?> + <?=$n2?> ? 
  Answer: <input type=text name=answer size=4> <p>

  Press <input type="submit" value="Proceed"> to submit your answer. 

</form> 

I removed all the sessions and I called again. 

Here's how the session evolved: 

-bash-3.2$ more sess_9e645098cc2ca367993ce304ba7aaf5e 
message|s:7:"Welcome";n1|i:10;n2|i:17;m1|i:0;m2|i:0;

-bash-3.2$ more sess_9e645098cc2ca367993ce304ba7aaf5e 
message|s:33:"The score is 1 out of 1 currently";n1|i:-3;n2|i:-14;m1|i:
1;m2|i:1;

-bash-3.2$ more sess_9e645098cc2ca367993ce304ba7aaf5e 
message|s:33:"The score is 1 out of 2 currently";n1|i:14;n2|i:-11;m1|i:
1;m2|i:2;

-bash-3.2$

Final question for today: do these two programs that we developed

http://silo.cs.indiana.edu:44063/five.php

http://silo.cs.indiana.edu:44063/six.php

today (one keeps state in hidden fields on the client side and the
other one invents and distributes ids and stores state in files in
phpsessions with the name the ids generated) work the same or are
they different at all? 

Some answers: 

a) different are the urls when we work with them

http://silo.cs.indiana.edu:44063/five.php?answer=5&n1=-7&n2=12&m1=0&m2=0&message=Welcome

http://silo.cs.indiana.edu:44063/six.php?answer=34

b) same is the result, they both correctly grade our answers

c) they are different (really different!) in how they handle refresh/reload. 

Possible issues: if you don't put <? session_start() at the 
very top of your file you might prevent the session id to be
sent as a header and as a result you might get error messages
like this: 

Warning: session_start() [function.session-start]: Cannot send session cache limiter - headers already sent (output started at /nfs/nfs1/home/dgerman/apache/htdocs/six.php:4) in /nfs/nfs1/home/dgerman/apache/htdocs/six.php on line 4

Monday we will discuss how we can make a script that keeps state
on the server side immune to accidental reloads. Think about it and
let me know how we might approach it.