PHP in Action

Redirects are useful in web programming, especially when implementing the Post-Redrect-Get pattern. But there is a problem with redirects: there is no simple way to send a message to the user across the redirect. When processing a GET request, you can display whatever messages you want. The most simplistic way is to echo them directly; or if just slightly more sophisticated, set it in the template that's about to become the web page. When processing a POST request that is to be followed by a redirect, you can't do that. The response (redirect) sent back to the browser does not have any text or HTML content. In practice, it just contains the URL of the page you're redirecting to. If you try echoing the message, it will cause the redirect to fail because you sent content before the header that signals redirect.

So how to get the message displayed? The simplest way to do it would be to include it in the URL:

header('Location: http://www.example.com/index.php?message='.urlencode($message));
 

It's possible, but your URLs can get very long and you might find it silly:

http://www.example.com/index.php?message=This+is+a+message+to+demonstrate+how+long+a+URL+can+get+when+you+put+long+strings+into+it

The more common choice is to keep the message in session and make sure it's removed from session after it's been displayed. That's what flash messages do. In military terminology, a flash message is defined as:

A category of precedence reserved for initial enemy contact messages or operational combat messages of extreme urgency.

I don't like a name that could be confused with Adobe Flash, so when I implemented my version of this, I looked up "flash" in the thesaurus and decided to call them flares instead.

Here are a couple of examples I've picked up.

$flashMessenger = $this->_helper->FlashMessenger;
$flashMessenger->setNamespace('actionErrors');
$flashMessenger->addMessage($message);
 

CakePHP (from http://labs.iamkoa.net/2008/01/13/session-based-flash-messages-look-better-cakephp/):

$this->Session->setFlash('Your post has been saved.');
$this->redirect('/news/index');
 

In my own work, I've done it in a slightly different way by letting the redirect object hande the flash/flare and returning the redirect object from the action method, somewhat like this:

return Redirect::toAction('settings')->addFlare('Settings changed');
 

I don't necessarily claim that it's better than the others, but it makes sense to have alternatives.

This article was originally posted with an incorrect timestamp, and has been updated to the current time as of June 2.

I keep saying that sort of thing, too. I also say it raises your IQ. But when I attended a presentation by Uncle Bob (Robert C. Martin) last summer, I was mildly shocked to see that he described TDD as tedious (but a requirement for professionalism). I confronted him politely about it, emphasizing that above all I find TDD relaxing. Why? Because bugs bug me. I get stressed when I have to search for a bug and even more so when it takes much longer than expected (I'm sure that never happens to you). With TDD, bugs are always small and easy to locate.

Uncle Bob seemed to agree with me as far as his own experience was concerned, but he believed that many developers found the non-TDD process exciting rather than stressful.

Sounds weird to me. But I know from long experience that sometimes people are different from me in ways that make reality seem stranger than fiction.

• Main
• Archives

• More beautiful code
• Beautiful code
• Refactoring is design
• Get links with XPath
• Many test methods versus custom assertions
• Type hints are more useful for scalars than objects
• Performance optimism
• Testing a Zend Framework action controller with View Helpers
• Flash messages
• The psychology of test-driven development

• Application design [15]
• Testing [11]
• PHP [22]
• Refactoring [2]
• Ruby [3]
• Smidig2008 [1]
• Java [1]
• General [0]
• Frameworks [2]
• CSS [0]
• JavaScript/Ajax [0]
• Me [4]
• Vim [1]
• Humor [0]

• RSS 0.90
• RSS 1.0
• RSS 2.0
• Atom