PHP III¶

Super Globals¶

PHP has a concept of super globals, these are global variables that are defined for you by PHP
- There are always available in any scope, like an actual global variable
The super global variables are (all are arrays)
- $GLOBALS - all current global variables
- $_SERVER - variables about the webserver or current script
- $_GET - variables given by a GET request
- $_POST - variables given by a POST request
- $_COOKIE - HTTP cookies passed in the header
- $_FILES - variables relating to file uploads over POST
- $_ENV - Enviromental Variables
- $_REQUEST - Like $_GET, $_POST and $_COOKIE all concatenated together

<?php

function print_as_table($array) {
    print "<table><thead><tr><th>Key</th><th>Value</th></tr></thead><tbody>";
    if($array) {
      foreach(array_keys($array) as $key) {
        print "<tr><td>$key</td><td>$array[$key]</td></tr>";
      }
    } else {
      print '<tr><td colspan="2">None</td></tr>';
    }
    print "</tbody></table>";
}

?>

Available to view at https://www.csee.umbc.edu/~bwilk1/433/php_examples/web-variables.php

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="utf-8" />
    <title>Web Variables</title>
    <style>
      table { border-collapse: collapse; }
      td, th { border: 1px solid #333333; }
    </style>
  </head>
  <body>
    <h3>$_SERVER</h3>
    <?php print_as_table($_SERVER); ?>
    <h3>$_COOKIE</h3>
    <?php print_as_table($_COOKIE); ?>
    <h3>$_GET</h3>
    <?php print_as_table($_GET); ?>
    <h3>$_POST</h3>
    <?php print_as_table($_POST); ?>
    <h3>$_ENV</h3>
    <?php print_as_table($_ENV); ?>
    <h3>$GLOBALS</h3>
    <?php print_as_table($GLOBALS); ?>
  </body>
</html>

An All in one Form Page¶

Normal request to a website are done using GET
- We can use this to our advantage to create a single page that both displays and processes a form
- This is only used for simple forms

The general syntax of this type of page is

<?php if($_SERVER['REQUEST_METHOD'] == 'GET') {?>
  <form method="post">
    #HTML for Form
  </form>
<?php } else { 
  #Proecess form
}?>

Available at https://www.csee.umbc.edu/~bwilk1/433/php_examples/simple-form.php

<!DOCTYPE html>
<html lang="en">
<?php if($_SERVER['REQUEST_METHOD'] == 'GET') { ?>
    <form action="<?php echo $_SERVER['PHP_SELF']; ?>" method="post">
      <div>
        <label for="fahrenheit">Fahrenheit temperature:</label>
        <input type="text" name="fahrenheit" id="fahrenheit" />
        <input type="submit" value="Convert to Celcius" />
      </div>
    </form>
<?php } else {
      $fahrenheit = $_POST['fahrenheit'];
      $celcius = ($fahrenheit - 32) * 5 / 9;
      print "<p>$fahrenheit Fahrenheit is $celcius Celcius</p>";
    }
?>
  </body>
</html>

Multivalued Parameters¶

PHP knows how to turn certain data into arrays automatically
- The name of the input tag must end in [] for PHP to know to do this
- Useful for checkboxes or multi-select

A form sent using GET with the following HTML

<input type='checkbox' name='checks[]' value='hello'>Hello
<input type='checkbox' name='checks[]' value='hi'>Hi
<input type='checkbox' name='checks[]' value='howdy'>Howdy

Creates an array in accesssible in the following way
```
$_GET['checks']
```

Available at https://www.csee.umbc.edu/~bwilk1/433/php_examples/checkboxes.php

<!DOCTYPE html>
<?php if($_SERVER['REQUEST_METHOD'] == 'GET') { ?>
    <form action="<?php echo $_SERVER['_SELF'] ?>" method="post">
      <p>Select Languages you know</p>
      <p><input type="checkbox" name="languages[]" id="Perl" value="Perl" />
      <label for="Perl">Perl</label></p>
      <p><input type="checkbox" name="languages[]" id="JavaScript" value="JavaScript" />
      <label for="JavaScript">JavaScript</label></p>
      <p><input type="checkbox" name="languages[]" id="PHP" value="PHP" />
      <label for="PHP">PHP</label></p>
      <p><input type="checkbox" name="languages[]" id="Python" value="Python" />
      <label for="Python">Python</label></p>
      <p><input type="submit" value="Submit" /></p>
    </form>
<?php } else {
        print '<p>You know:</p>';
        $languages = $_POST['languages'];
        print_r($languages);
    }
?>
  </body>
</html>

File Uploads¶

PHP has many functions to help you safely and easily handle file uploads
Before we get a file to PHP to process, we have to set up the HTML form the correct way
```
<form enctype="multipart/form-data" action="some_url.php" method="POST">
  <input type="file" name="my_file">
</form>
```
- The encoding type must be set for PHP to handle this correctly
- File can only be sent over POST

File Uploads on the Server-Side¶

Back in PHP, the file is uploaded to /tmp storage by default
- This is good because /tmp as limited permissions so it is like a quarinteine zone
For each file input you have, PHP creates an array in the $_FILES super global
Import keys in that array
- $_FILES['my_file']['name'] - The original name
- $_FILES['my_file']['type'] - The MIME type as reported by the uploader, not checked, don't trust!!
- $_FILES['userfile']['tmp_name'] - The name on the server where the file was uploaded

Upload Safety¶

Allowing uploads to a server opens you up to potential exploitation
Steps you can take to reduce the risk
- Never ever ever save uploaded files to a location accessible through a URL
- Don't use the name given by the original uploader
  - Use a hash, or modify it in someway (You can keep a look up table somewhere if you need the original name too)
- Validate the contents of the file
  - You can't trust the type key, but you can trust finfo_file function (PHP 5.3+)

<!DOCTYPE html>
<html>
    if($_SERVER['REQUEST_METHOD'] == 'GET') {
?>
    <form enctype="multipart/form-data" action="<?php $_SERVER['PHP_SELF'] ?>" method="post">
      <div>
        <label for="file">JPG File:</label> 
        <input type="file" name="file" id="file"/>
        <input type="submit" value="Upload" />
      </div>
    </form>
<?php
    } else {
        // check for type - browser can lie, also check in PHP
    $finfo = finfo_open(FILEINFO_MIME_TYPE);
        if($_FILES['file']['type'] != 'image/jpeg' || finfo_file($finfo, $_FILES['file']['tmp_name']) != 'image/jpeg') {
            print '<p>File does not appear to be a JPG. ' . 
                  '<a href="' . $_SERVER['PHP_SELF'] . '">Try Again</a></p>';
        // attempt to move to location
        } else if (move_uploaded_file($_FILES['file']['tmp_name'], '/home/csee1/bwilk1/img.php')) {
            print "<p>Success - file is " . FILE . "</p>";
        // otherwise error
        } else {
            print "<p>An error occurred</p>";
        }
    }
?>
  </body>
</html>

Sending HTTP Response Headers¶

Related to processing forms, sometimes you want to someback something different than just HTML to the browser
You can do this by changing the HTTP response headers
- This must be done before any output is produced
The PHP function header is used for this purpose
- There are many different things you can send here, but a common one is to redirect to a different page
```
<?php
header("Location: http://www.umbc.edu")
?>
```

Cache Control with Headers¶

One common use of headers is to tell the browser and other network interfaces not to cache a page

This can be set inside PHP by using the following code (from PHP Manual):

<?php
 header("Cache-Control: no-cache, must-revalidate"); 
 header("Expires: Sat, 26 Jul 1997 05:00:00 GMT")
?>

Content Headers¶

The Content-Type header tells the browser how to interperate the information it is receiving
- This can be used to directly send images, pictures, pdfs, etc. and have the browser handle it correctly
```
<?php
header('Content-Type: image/jpeg');
echo file_get_contents('myimage.jpg');
?>
```

Content-Header Examples¶

Image: https://www.csee.umbc.edu/~bwilk1/433/php_examples/image.php

<?php
  header("Content-Type: image/png");
  echo file_get_contents("maryland.png");
?>

Content-Header Examples¶

PDF: https://www.csee.umbc.edu/~bwilk1/433/php_examples/pdf.php

<?php
    header('Content-Type: application/pdf');
    echo file_get_contents('https://about.umbc.edu/files/2017/09/2017-campus-map.pdf');
?>

Content-Header Examples¶

Video: https://www.csee.umbc.edu/~bwilk1/433/php_examples/video.php

<?php
    header("Content-Type: video/webm");
    echo file_get_contents("https://upload.wikimedia.org/wikipedia/commons/transcoded/2/26/Extraordinary_Adventures_of_Saturnino_Farandola_%281913%29.webm/Extraordinary_Adventures_of_Saturnino_Farandola_%281913%29.webm.360p.webm");

?>

Content-Header Examples¶

PDF: https://www.csee.umbc.edu/~bwilk1/433/php_examples/no_header.php

<?php
    echo file_get_contents('maryland.png');
?>

PHP Classes¶

Since PHP 5, there has been support for true OOP style classes
- The sytnax borrows heavily from Java strangely enough
  - But also from other scripting languages and C++

class className
{
    public/private $variableName

    public/private function functionName(){}
}

In [ ]:

class my_first_class{
    public $a_var;
    
    public function get_var(){
        return $this->a_var;
    }

}

In [ ]:

$obj = new my_first_class();
$obj->a_var = 10;
echo $obj->get_var();

Special Functions¶

The following functions are called automatically in special contexts, and are all preceeded by two underscores
- __construct (The object constructor)
- __destruct (What is called when garbage collection is performed)
- __toString (Used in print or echo)

In [ ]:

class Person{
    private $name;
    private $age;
    
    function __construct($name = "Jane Doe", $age = 30){
        $this->name = $name;
        $this->age = $age;
    }
    
    function __toString(){
        return $this->name . " is ". $this->age;
    }
}

In [ ]:

$p1 = new Person();
echo $p1;

$p2 = new Person("Timmy");
echo $p2;

$p3 = new Person("Harry", 45);
echo $p3;

Inheritance¶

PHP permits only single inheritance, through use of the extends keyword
- Have access to public and protected methods and members
- To refer to parent method or member, used parent keyword
- Use the :: operator to access a method staticlly

In [ ]:

class Employee extends Person{
    private $workplace;
    
    function __construct($workplace = "UMBC"){
        parent::_construct();
        $this->workplace = $workplace;
    }
    
     function __construct($name="Joe Student", $age=19, $workplace = "UMBC"){
        parent::_construct($name,$age);
        $this->workplace = $workplace;
    }
    
    
    function __toString(){
        return parent::__toString . " and works at " . $this->workplace;
    }
}

Object Example¶

Implement an object to represent a shopper (in an online store)

Object Practice¶

Implement an object to represent a student

Interfaces¶

Because PHP doesn't allow multiple inheritance (just like Java), they allow intrefaces (just like Java) that can be "implemented" (just like Java)

The syntax for creating an interface is

interface name{
  public function name(); #Note there is no definition
}

Static and Constant¶

Any method or member can be made static by adding the keyword static after the access modifier
- A static method/member must be refered to using ::
  - If you are inside the class defintion use self::
A member can also be made constant by using the const keyword
- These are static by default
- They can only be made private in PHP 7.1+

In [ ]:

class my_static{
    private static $counter = 0;
    const UPDATE_BY = 1;
    
    function increment(){
        self::$counter += self::UPDATE_BY;
        return self::$counter;
    }
}

In [ ]:

$ms1 = new my_static();
echo $ms1->increment();

In [ ]:

$ms2 = new my_static();
echo $ms2->increment();

Sessions¶

It many web applications it is useful to keep track of a user as the progress around your site
PHP does this through a concept known as sessions, which requires cookies on the front end to use
- The PHP server sends a cookie to the browser with a unique session id
- Everytime it sees a particular session ID in a cookie, it populates $_SESSION with the appropriate values
To use sessions, call the session_start() function in your PHP code

Available at https://www.csee.umbc.edu/~bwilk1/433/php_examples/session-store.php

<?php
    session_start();
?>
<!DOCTYPE html>
<html lang="en">
<?php if($_SERVER['REQUEST_METHOD'] == 'GET') { ?>
    <form action="<?php $_SERVER['PHP_SELF'] ?>" method="post">
      <div>
        <label for="name">Name:</label>
        <input type="text" name="name" id="name" />
        <input type="submit" value="Submit" />
      </div>
    </form>
<?php } else {
        $_SESSION['name'] = $_POST['name'];
        $name = $_POST['name'];
        print "<p>Hello, $name</p>";
    }
?>
  </body>
</html>

Available at https://www.csee.umbc.edu/~bwilk1/433/php_examples/session-recall.php

<?php session_start(); ?>
<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="utf-8" />
    <title>Recall Things from Session</title>
  </head>
  <body>
    <p>Hello, <?php echo $_SESSION['name'] ?></p>
  </body>
</html>

JSON¶

JSON support was added to base PHP in PHP 5.2.0
The two functions we care about are
- json_encode() - Turns PHP object into JSON
- json_decode() - Smartly produces an array/object/etc.

In [ ]:

$an_array = array(1,2,3,5,6);
echo json_encode($an_array);

In [ ]:

$an_object->date = "November 21, 2017";
$an_object->time = "12:??";
echo json_encode($an_object);

In [ ]:

$an_assoc_array = array('a' => 20, 'b' => 30);
echo json_encode($an_assoc_array);

In [ ]:

$p1 = new Person();
echo json_encode($p1);

In [ ]:

echo print_r(json_decode("[1,2,3,4,5]"),true);

In [ ]:

echo print_r(json_decode('{"name":"John Watson","dob":"November 10th 1860","birthplace":"London"}')
,true);

JSON and PHP Object Comparison¶

When going from PHP to JSON
- A PHP Object is always a JSON object
- A PHP array is an JSON object when it is associative
- A PHP array is a JSON array when it has no keys other than continuous integers
When going from JSON to PHP
- A JSON object is always a generic PHP object of type Object
- A JSON array is always a simple indexed array