PHP for Web Applications

~~SLIDESHOW~~

PHP for Web Applications

Supplementary Material

Provided for Reference. This material is no longer taught on this module.

Using PHP for web applications development.

PHP for Web Applications

We conclude our review of the Basics of PHP with a discussion of its use in creating web applications.

Based on Chapter 12 of Robert W. Sebasta, Programming the World-Wide Web, 3rd Edition, Addison Wesley, 2006. and Chapter 12 of Chris Bates, Web Programming: Building Internet Applications, 3rd Edition, John Wiley, 2006.

Contents of this Lecture

PHP for web applications with examples

The Examples for PHP for Web Applications.

Learning Outcomes

At the end of this lecture you should be able to answer these questions:

How can the value of a form element be accessed by a PHP script?
What is a file variable?
What is a file pointer?
What does an fopen function return if it fails?
Explain the parameters and actions of the fread function.

Learning Outcomes (continued)

At the end of this lecture you should be able to answer these questions:

What is returned by the fwrite function?
How can a cookie be created in a PHP script?
How can a script determine whether a particular cookie exists?
How can a variable be saved in a session?

Queries and Query Strings

Parameters sent to a Web Application from a web browser take the form of a query string
The query string is either appended to the URI in a GET request as in:

   GET /webapp.cgi?query_string HTTP/1.1
   Host: some.host.com
    :

or is carried in the payload of a POST request as in:

   POST /webapp.cgi HTTP/1.1
   Host: some.host.com 
    :
   
   query_string

Processing GET rquests

Web server passes two environment variables to helper application
$REQUEST_METHOD=GET and $QUERY_STRING=query_string
The query string will be content of $QUERY_STRING (everything in resource name after query marker ?)

A Real GET request

From beer example

GET /cgi-bin/echo_params.cgi?colour=light&taste=malty HTTP/1.1
Host: localhost
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.0; en-GB; rv:1.8.1.9) Gecko/20071025 Firefox/2.0.0.9 Creative ZENcast v2.00.14
Accept: text/xml,application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5
Accept-Language: en-gb,en;q=0.5
Accept-Encoding: gzip,deflate
Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7
Keep-Alive: 300
Connection: keep-alive
Referer: http://localhost/beer_get.html

Web application is /cgi-bin/echo_params.cgi
Host is localhost
Query string is colour=light&taste=malty
Although data comes from a form (referer is http://localhost/beer_get.html), request is equivalent to and indistinguishable from URI: http://localhost/cgi-bin/echo_params.cgi?colour=light&taste=malty.

Processing POST requests

Data passed to helper application in environment variables and standard input
$REQUEST_METHOD=POST
$CONTENT_LENGTH gives size of payload
$CONTENT_TYPE is type of data: usually application/x-www-form-urlencoded
Query string is $CONTENT_LENGTH bytes read from standard input

A Real POST request

Also from beer example

POST /cgi-bin/echo_params.cgi HTTP/1.1
Host: localhost
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.0; en-GB; rv:1.8.1.9) Gecko/20071025 Firefox/2.0.0.9 Creative ZENcast v2.00.14
Accept: text/xml,application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5
Accept-Language: en-gb,en;q=0.5
Accept-Encoding: gzip,deflate
Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7
Keep-Alive: 300
Connection: keep-alive
Referer: http://localhost/beer_post.html
Content-Type: application/x-www-form-urlencoded
Content-Length: 24

colour=light&taste=malty

Web application is /cgi-bin/echo_params.cgi
Host is localhost
Content-Type is application/x-www-form-urlencoded
Content-Length is 24 bytes
Query string is colour=light&taste=malty (is ASCII 24 bytes in length)

Query String Format

A query string includes names and values of HTML form elements (widgets)
Widget values are always coded as strings
The form of a name/value pair in a query string is:

    name=value

If the form has more than one widget, their values are separated with ampersands:

    milk=2&payment=visa

URL Specification

The specification for URLs (RFC 1738, Dec. '94) limits the use of allowed characters in URLs to only a limited subset of the US-ASCII character set:

“…Only alphanumerics [0-9a-zA-Z], the special characters ”$-_.+!*'(),“ , and reserved characters used for their reserved purposes may be used unencoded within a URL.”

Any source of general text that appears in an HTML page that may be represented in a URL has to be encoded to ensure that illegal characters do not appear.
This includes widget names, and widget values.

URL Encoding

Performed automatically by Browser on form submission
Each special character is encoded as a percent sign and a two-character hexadecimal number (the ASCII code for the character)
Some browsers code spaces as plus signs, rather than as %20
You should URL encode any text that will be sent to the browser in a form widget, or in the action, src, href, etc.

For more more information on URL encoding see ¹⁾

URL Encoding – Examples

URL encode general text (e.g. from file input or results of a previous form submission)

  <?php
    echo '<a href="mycgi?foo=', urlencode($userinput), '">';
  ?>

URL encode user input, then convert results into valid HTML (e.g. & → &)

  <?php
    $query_string = 'foo=' . urlencode($foo) . '&bar=' . urlencode($bar);
    echo '<a href="mycgi?' . htmlentities($query_string) . '">';
  ?>

PHP and Query Data

PHP takes care of extracting the query parameters for you
It maps the HTTP request fields into PHP variables
It extracts the query string from the HTTP request, extracts the name/value pairs and places them into an array.
Array $_GET will contain data for GET method and $_POST will contain data passed by the POST method
- value subscripts are the widget names
This is transparent and it does not matter whether GET or POST method is used to transmit the form data

Query parameters

If the query string has colour=light&taste=malty
$_POST[“colour”] will return “light” and $_POST[“taste”] will return “malty”
Query matching will also turn check box group colour=red&colour=blue to an array so that $_POST[“colour”] returns the right thing.

Form Handling

Simple in PHP
Forms could be handled by the same document that creates the form, but that may be confusing
Better to separate “view” from data handling

Example – Popcorn Sales

The Form Page (just HTML) : popcorn3.html ( popcorn3.html @ localhost )

<html>

  <form action = "popcorn3.php"
  method = "post">
    <h2> Welcome to Millennium Gymnastics Booster Club Popcorn
    Sales </h2>
    <table>
      <!-- Text widgets for the customer's name and address -->
      <tr>
        <td> Buyer's Name: </td>
        <td>
        <input type = "text" name = "name"
        size = "30" required placeholder="Your name"/>
        </td>
      </tr>
      <tr>
        <td> Street Address: </td>
        <td>
        <input type = "text" name = "street"
        size = "30" required placeholder = "Street"/>
        </td>
      </tr>
      <tr>
        <td> City, State, Zip: </td>
        <td>
        <input type = "text" name = "city"
        size = "30" required placeholder="City, State, Zip"/>
        </td>
      </tr>
    </table>
    <p />
    <table border = "border">
      <!-- First, the column headings -->
      <tr>
        <th> Product </th>
        <th> Price </th>
        <th> Quantity </th>
      </tr>
      <!-- Now, the table data entries -->
      <tr>
        <td> Unpopped Popcorn (1 lb.) </td>
        <td> $3.00 </td>
        <td align = "center">
        <input type = "number" name = "unpop"
        size = "3" min="0" pattern="\d+" />
        </td>
      </tr>
      <tr>
        <td> Caramel Popcorn (2 lb. canister) </td>
        <td> $3.50 </td>
        <td align = "center">
        <input type = "number" name = "caramel"
        size = "3" min="0" pattern="\d+" />
        </td>
      </tr>
      <tr>
        <td> Caramel Nut Popcorn (2 lb. canister) </td>
        <td> $4.50 </td>
        <td align = "center">
        <input type = "number" name = "caramelnut"
        size = "3" min="0" pattern="\d+" />
        </td>
      </tr>
      <tr>
        <td> Toffey Nut Popcorn (2 lb. canister) </td>
        <td> $5.00 </td>
        <td align = "center">
        <input type = "number" name = "toffeynut"
        size = "3" min="0" pattern="\d" />
        </td>
      </tr>
    </table>
    <p />
    <!-- The radio buttons for the payment method -->
    <h3> Payment Method </h3>
    <p>
      <input type = "radio" name = "payment" value = "visa"
      checked = "checked" />
      Visa
      <br />
      <input type = "radio" name = "payment" value = "mc" />
      Master Card
      <br />
      <input type = "radio" name = "payment"
      value = "discover" />
      Discover
      <br />
      <input type = "radio" name = "payment" value = "check" />
      Check
      <br />
      <br />
      <!-- The submit and reset buttons -->
      <input type = "submit" value = "Submit Order" />
      <input type = "reset" value = "Clear Order Form" />
    </p>
  </form>

</html>

<!DOCTYPE html>
<!-- popcorn3.html - This describes the popcorn sales form -->
<html lang="en">
  <head>
    <meta charset="utf-8" />
    <title> Popcorn Sales - for PHP handling </title>
  </head>
  <body>
    <form action = "popcorn3.php"
    method = "post">
      <h2> Welcome to Millennium Gymnastics Booster Club Popcorn
      Sales </h2>
      <table>
        <!-- Text widgets for the customer's name and address -->
        <tr>
          <td> Buyer's Name: </td>
          <td>
          <input type = "text" name = "name"
          size = "30" required placeholder="Your name"/>
          </td>
        </tr>
        <tr>
          <td> Street Address: </td>
          <td>
          <input type = "text" name = "street"
          size = "30" required placeholder = "Street"/>
          </td>
        </tr>
        <tr>
          <td> City, State, Zip: </td>
          <td>
          <input type = "text" name = "city"
          size = "30" required placeholder="City, State, Zip"/>
          </td>
        </tr>
      </table>
      <p />
      <table border = "border">
        <!-- First, the column headings -->
        <tr>
          <th> Product </th>
          <th> Price </th>
          <th> Quantity </th>
        </tr>
        <!-- Now, the table data entries -->
        <tr>
          <td> Unpopped Popcorn (1 lb.) </td>
          <td> $3.00 </td>
          <td align = "center">
          <input type = "number" name = "unpop"
          size = "3" min="0" pattern="\d+" />
          </td>
        </tr>
        <tr>
          <td> Caramel Popcorn (2 lb. canister) </td>
          <td> $3.50 </td>
          <td align = "center">
          <input type = "number" name = "caramel"
          size = "3" min="0" pattern="\d+" />
          </td>
        </tr>
        <tr>
          <td> Caramel Nut Popcorn (2 lb. canister) </td>
          <td> $4.50 </td>
          <td align = "center">
          <input type = "number" name = "caramelnut"
          size = "3" min="0" pattern="\d+" />
          </td>
        </tr>
        <tr>
          <td> Toffey Nut Popcorn (2 lb. canister) </td>
          <td> $5.00 </td>
          <td align = "center">
          <input type = "number" name = "toffeynut"
          size = "3" min="0" pattern="\d" />
          </td>
        </tr>
      </table>
      <p />
      <!-- The radio buttons for the payment method -->
      <h3> Payment Method </h3>
      <p>
        <input type = "radio" name = "payment" value = "visa"
        checked = "checked" />
        Visa
        <br />
        <input type = "radio" name = "payment" value = "mc" />
        Master Card
        <br />
        <input type = "radio" name = "payment"
        value = "discover" />
        Discover
        <br />
        <input type = "radio" name = "payment" value = "check" />
        Check
        <br />
        <br />
        <!-- The submit and reset buttons -->
        <input type = "submit" value = "Submit Order" />
        <input type = "reset" value = "Clear Order Form" />
      </p>
    </form>
  </body>
</html>

Example – Popcorn Sales Receipt

The results page – HTML with embedded PHP: popcorn3.php

<!DOCTYPE html>
<!-- popcorn3.php - Processes the form described in
popcorn3.html
-->
<html lang="en">
  <head>
    <meta charset="utf-8" />
    <title> Process the popcorn3.html form </title>
  </head>
  <body>
    <?php
// Get form data values
$unpop=$_POST["unpop"];
$caramel=$_POST["caramel"];
$caramelnut=$_POST["caramelnut"];
$toffeynut=$_POST["toffeynut"];
$name=$_POST["name"];
$street=$_POST["street"];
$city=$_POST["city"];
$payment=$_POST["payment"];
// If any of the quantities are blank, set them to zero
if($unpop=="")
$unpop=0;
if($caramel=="")
$caramel=0;
if($caramelnut=="")
$caramelnut=0;
if($toffeynut=="")
$toffeynut=0;
// Compute the item costs and total cost
$unpop_cost=3.0*$unpop;
$caramel_cost=3.5*$caramel;
$caramelnut_cost=4.5*$caramelnut;
$toffeynut_cost=5.0*$toffeynut;
$total_price=$unpop_cost+$caramel_cost+$caramelnut_cost+$toffeynut_cost;
$total_items=$unpop+$caramel+$caramelnut+$toffeynut;
// Return the results to the browser in a table
    ?>
    <h4> Customer: </h4>
    <?php
print("$name <br /> $street <br /> $city <br />");
    ?>
    <p />
    <p />
    <table border = "border">
      <caption>
        Order Information
      </caption>
      <tr>
        <th> Product </th>
        <th> Unit Price </th>
        <th> Quantity Ordered </th>
        <th> Item Cost </th>
      </tr>
      <tr align = "center">
        <td> Unpopped Popcorn </td>
        <td> $3.00 </td>
        <td><?php print("$unpop");?></td>
        <td><?php printf("$ %4.2f",$unpop_cost);?></td>
      </tr>
      <tr align = "center">
        <td> Caramel Popcorn </td>
        <td> $3.50 </td>
        <td><?php print("$caramel");?></td>
        <td><?php printf("$ %4.2f",$caramel_cost);?></td>
      </tr>
      <tr align = "center">
        <td> Caramel Nut Popcorn </td>
        <td> $4.50 </td>
        <td><?php print("$caramelnut");?></td>
        <td><?php printf("$ %4.2f",$caramelnut_cost);?></td>
      </tr>
      <tr align = "center">
        <td> Toffey Nut Popcorn </td>
        <td> $5.00 </td>
        <td><?php print("$toffeynut");?></td>
        <td><?php printf("$ %4.2f",$toffeynut_cost);?></td>
      </tr>
    </table>
    <p />
    <p />
    <?php
print("You ordered $total_items popcorn items <br />");
printf("Your total bill is: $ %5.2f <br />",$total_price);
print("Your chosen method of payment is: $payment <br />");
    ?>
  </body>
</html>

Output

<html>

      <h4> Customer: </h4>
   <br />  <br />  <br />    <p /> <p />

    <caption> Order Information </caption>
    <tr>
      <th> Product </th>
      <th> Unit Price </th>
      <th> Quantity Ordered </th>
      <th> Item Cost </th>
    </tr>
    <tr align = "center">
      <td> Unpopped Popcorn </td>
      <td> $3.00 </td>
      <td> 0 </td>
      <td> $ 0.00        </td>
    </tr>
    <tr align = "center">
      <td> Caramel Popcorn </td>
      <td> $3.50 </td>
      <td> 0 </td>
      <td> $ 0.00        </td>
      </tr>
    <tr align = "center">
      <td> Caramel Nut Popcorn </td>
      <td> $4.50 </td>
      <td> 0 </td>
      <td> $ 0.00        </td>
    </tr>
    <tr align = "center">
      <td> Toffey Nut Popcorn </td>
      <td> $5.00 </td>
      <td> 0 </td>
      <td> $ 0.00        </td>
    </tr>
  </table>
  <p /> <p />

  You ordered 0 popcorn items <br />Your total bill is: $  0.00 <br />Your chosen method of payment is:  <br />

</html>

Files

PHP can:
- Deal with any files on the server
- Deal with any files on the Internet, using either HTTP or FTP
Instead of filehandles, PHP associates a variable with a file, called the file variable (for program reference)
A file has a file pointer (where to read or write)

Opening a File

Command to open a file and assign to a file variable:

  $fptr = fopen(filename, use_indicator)

File use indicators

Indicator	Purpose
`r`	read only, from the beginning
`r+`	read and write, from the beginning
`w`	write only, from the beginning (also creates the file, if necessary)
`w+`	read and write, from the beginning (also creates the file, if necessary)
`a`	write only, at the end, if it exists (creates the file, if necessary)
`a+`	read and write, read at the beginning, write at the end

File opening and closing

Because fopen could fail, use it with die:

  $file_var = fopen("testdata.dat", "r") or
    die ("Error - testdata.dat cannot be opened");

Use file_exists(filename) to determine whether file exists before trying to open it
Use fclose(file_var) to close a file

File use cases

Read all or part of the file into a string variable
Read the lines of the file into an array
Read one line from the file
Read one character at a time

Read all or part of the file into a string variable

  $str = fread(file_var, number_of_bytes)

To read the whole file, use filesize(file_name) as the second parameter

Read the lines of the file into an array

  $file_lines = file(file_name)

Need not open or close the file

Read one line from the file

  $line = fgets(file_var, number_of_bytes)

Reads characters until eoln, eof, or number_of_bytes characters have been read

Read one character at a time

  $ch = fgetc(file_var)

Control reading lines or characters with eof detection using feof (TRUE for eof; FALSE otherwise):

  while( ! feof($file_var) ) {
    $ch = fgetc($file_var);
  }

Writing to files

To write to a file use:

  $bytes_written = fwrite(file_var, string)

fwrite returns the number of bytes it wrote
Files can be locked (to avoid interference from concurrent accesses) with flock²⁾

Storing Information about Client State

A session is the time span during which a browser interacts with a particular server
The HTTP protocol is stateless
But, there are several reasons why it is useful for the server to relate a request to a session
- Shopping carts for many different simultaneous customers
- Customer profiling for advertising
- Customized interfaces for specific clients
Approaches to storing client information:
- Store it on the server – often too much to store!
- Store it on the client machine – this works

Session Tracking with Cookies

A cookie is a small object of information consisting of a name and a textual value
Cookies are created by some software system on the server
Every HTTP communication between the browser and the server includes information in its header about the message
At the time a cookie is created, it is given a lifetime
Every time the browser sends a request to the server that created the cookie, while the cookie is still alive, the cookie is included
A browser can be set to reject all cookies

Baking Cookies

Create a cookie with setcookie:

  setcookie(cookie_name, cookie_value, lifetime)

e.g.:

  setcookie("voted", "true", time() + 86400);

Cookies must be created before any other HTML is created by the script

<note> Lifetime is measured in seconds. The value 86400 is 24 hours. The PHP function time() returns the number of seconds since the “UNIX epoch date” [Midnight GMT, 1st January 1970]. Thus the use of time() + 86400 creates a cookie that expires 24 hours from the time it was set. </note>

Consuming Cookies

Cookies are obtained in a script the same way form values are obtained, using the $_COOKIES array

Session Tracking

For session tracking, PHP creates and maintains a session tracking id
Create the id with a call to session_start with no parameters
Subsequent calls to session_start retrieves any session variables that were previously registered in the session

Session Tracking

To create a session variable, use the global array $_SESSION

Session Tracking: Example

To count number of pages visited in a web site, put the following code in all documents:

  <?php session_start(); // must be called before any HTML is output 
  ?>
  :
  <?php
     if (!IsSet($_SESSION['page_number']))
        $_SESSION['page_number'] = 1;
     print("You have now visited " . $_SESSION['page_number'] . " pages <br />");
     $_SESSION['page_number']++;
  ?>

Summary of this Lecture

PHP for web applications with examples

The Examples for PHP for Web Applications.

Learning Outcomes

At the end of this lecture you should be able to answer these questions:

How can the value of a form element be accessed by a PHP script?
What is a file variable?
What is a file pointer?
What does an fopen function return if it fails?
Explain the parameters and actions of the fread function.

Learning Outcomes (continued)

At the end of this lecture you should be able to answer these questions:

What is returned by the fwrite function?
How can a cookie be created in a PHP script?
How can a script determine whether a particular cookie exists?
How can a variable be saved in a session?

Homework Exercise

Write, test, and debug (if necessary) a PHP script for the following function. Write functions and the code to test them.

Parameter: A file variable of a file of text, where the words are separated by spaces or colons. Return value: The word that appears most often in the file.

There are more exercises here and in the second coursework.

What's Next?

Database Access through the Web

Previous Lecture | home | Next Lecture

¹⁾

Brian Wilson, URL Encoding (or: 'What are the “%20” codes in URLs?'), Index DOT Html, URL: http://www.blooberry.com/indexdot/html/topics/urlencoding.htm

²⁾

PHP Manual Page: Flock

Table of Contents

PHP for Web Applications

PHP for Web Applications

Contents of this Lecture

Learning Outcomes

Learning Outcomes (continued)

Queries and Query Strings

Processing GET rquests

A Real GET request

Processing POST requests

A Real POST request

Query String Format

URL Specification

URL Encoding

URL Encoding – Examples

PHP and Query Data

Query parameters

Form Handling

Example – Popcorn Sales

Example – Popcorn Sales Receipt

Files

Opening a File

File use indicators

File opening and closing

File use cases

Read all or part of the file into a string variable

Read the lines of the file into an array

Read one line from the file

Read one character at a time

Writing to files

Storing Information about Client State

Session Tracking with Cookies

Baking Cookies

Consuming Cookies

Session Tracking

Session Tracking

Session Tracking: Example

Summary of this Lecture

Learning Outcomes

Learning Outcomes (continued)

Homework Exercise

What's Next?