HTTP Redirection
Derek Bridge
Department of Computer Science,
University College Cork
HTTP Redirection
Aims:
- to remind ourselves about HTTP status codes and header lines
- to learn how to use HTTP redirection in PHP scripts
The way we've been doing things so far
Scripts can get longer and longer as we output different things depending on the user's input, e.g.:
<?php
$users_input = $_GET['capital'];
if ($users_input == 'F')
{
// Shed-load of XHTML and PHP to output something
// if the user's input == 'F'
}
else
{
// Shed-load of XHTML and PHP to output something else
// if the user's input != 'F'
}
?>
HTTP request and successful response
Suppose the client requests www.cs.ucc.ie/mywebsite/mywebpage.html:
HTTP request and unsuccessful response
Suppose the client requests www.cs.ucc.ie/mywbsite/mywbpage.html.
Oops! Typo!
HTTP request for a page that has moved
- Suppose we re-organise and now
mywebpage.htmlis stored in a folder calledmynewwebsiteand not inmywebsite - If a client uses the old URL, we want the server to send a response which
specifies
- status code 301 (Moved Permanently) or 302 (moved temporarily)
- the new location (
mynewwebsite/mywebpage.html)
- How can we make this happen?
- For Apache web servers, one way is to add this to the
.htaccessfileRedirect 301 /mywebsite/mywebpage.html http://www.cs.ucc.ie/mynewwebsite/mywebpage.html - There are other ways!
- For Apache web servers, one way is to add this to the
- Most clients that receive this response will then issue another GET request using the new location
HTTP request for a page that has moved
Suppose the client requests the old URL,
www.cs.ucc.ie/mywebsite/mywebpage.html:
PHP's header function
- PHP's built-in
headerfunction allows us to change the status and response header lines that we send back to the client - You must use
headerbefore any of the (X)HTML is generated* - The most common use:
This will send a 302 status code and hence redirects the client to another scriptheader('Location: http://www.cs.ucc.ie/mywebsite/anotherscript.php');
(*unless PHP's output buffering is enabled, which it is not in our installation)
PHP redirection example
<?php
$users_input = $_GET['capital'];
if ($users_input == 'F')
{
header('Location: correct.html');
}
else
{
header('Location: incorrect.html');
}
?>
PHP redirection and sessions
- This is a neat way of dividing up a script into more manageable, smaller parts
- We can pass the user's data from one script to another using the session store
- We can also use redirection as another way to implement self-processing pages (not shown here)
PHP redirection and session example: capital.php
<?php
session_start();
$_SESSION['users_input'] = $_GET['capital'];
if ($_SESSION['users_input'] == 'F')
{
header('Location: correct.php');
}
else
{
header('Location: incorrect.php');
}
?>
PHP redirection and session example: incorrect.php
<?php
session_start();
?>
<?php echo '<?xml version="1.0" encoding="UTF-8"?>'; ?>
<!DOCTYPE html
PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<head>
<title>The capital of 'France'</title>
<link rel="stylesheet" type="text/css" href="formlayout.css" />
</head>
<body>
<p>
<?php
echo "No, that's not right.
{$_SESSION['users_input']} is not the capital of 'France'."
?>
</p>
</body>
</html>
cookie_checker.php
Using redirection and a single script to check whether the client accepts cookies
<?php
if ( $_GET['sent_cookie'] != 'yes' )
{
// Send the cookie...
setcookie('test_cookie', 'test_value', time() + 60);
// ...returning to this script
header('Location: cookie_checker.php?sent_cookie=yes');
}
else
{
// On your return, check whether the client sent the cookie back to you
if ( isset($_COOKIE['test_cookie']) )
{
// Do whatever you want to do in the case where the client does have cookies enable, e.g.:
echo 'You have cookies enabled!';
}
else
{
// Do whatever you want to do in the case where the client does not have cookies enabled, e.g.:
echo 'You do not have cookies enabled!';
}
}
?>