Turbogears comes with a handy flash() function that can be used to set a plaintext status or feedback message that will be displayed on the next web page shown to the user. For instance:
from turbogears import controllers, expose, flash class Root(controllers.RootController): @expose(template="foo.templates.welcome") def index(self): flash('Your application is now running') return dict()
The message passed to the flash() function is stored in a cookie, so this does not work if cookies are not enabled in the browser. Also, by default, HTML in flash() messages is rendered literally (see below for how you can change this).
By default, the flash() messages is rendered as a div block with with the CSS class name flash, but you can change this easily in your master.kid template.
If you want to use XHTML tags or entities in your flash messages, you need to modify your master.kid template to use Kid’s XML() function for displaying the message, i.e. replace:
in the master.kid template with:
Caution: Be careful with the trick using the XML() function described in the page linked here. This opens up the possibility of introducing Cross-Site-Scripting vulnerabilities, if you include things in your flash messages that were entered by a user, for example the name of a wiki page or similar without escaping them properly.
Consider the following scenario:
User A creates a new wiki page with the title:
User B views that page and deletes it (assuming there is a delete function)
You controller does:
turbogears.flash("Page '%s' deleted." % page.title)
and shows the next page
User B will load the page that contains:
<div class="flash">Page '<script>alert("Vulnerable!");</script>' deleted.</div>
Without the use of the XML() function page.title would get properly escaped and no harm is done. You could, of course, escape page.title seperately and everything would be fine, but it’s easy to forget. Granted, you should always escape input from users when redisplaying it later, but Kid makes it easy to forget this, because it normally does not let you insert literal HTML code unescaped.