Learn By Example

Each demo attempts to explain some of the nuances of Brubeck.

Each example should be run from inside the demos directory after Brubeck has been installed.

This document assumes you have already read the README. If you have not, please read that and come back after.


We begin by building some knowledge of Mongrel2's internals using sqlite3 and m2reader.py.

Then there are four sets of demos. The first set contains the two demos from the README that build request handlers using classes or functions. Then we discuss how URL's are mapped to handlers. Template rendering is then shown for Jinja2, Tornado templates and Mako. This doc is then finished with an explanation of authentication over two final demos.

Kicking Mongrel2's Tires

Each of these tests can be run underneath the same Mongrel2 instance. You can bring the handlers down and back up without taking Mongrel2 down.

First, we parse the config file into a sqlite database. Configuring the database this way makes the experience of editing configs as easy as editing text, but the database is stored in a programmatically friendly way too via SQLite.

There is no need to edit the config so we can just load the config into a database using m2sh load.

$ m2sh load -config mongrel2.conf -db the.db

Now we have a sqlite database representing our config. If you have sqlite installed, open the database and take a look. You can start by typing .tables at the prompt to get a table list.

$ sqlite3 the.db 
sqlite> .tables
directory  host       mimetype   route      setting  
handler    log        proxy      server     statistic
sqlite> select * from route;

We can then turn Mongrel2 on with m2sh start.

$ m2sh start -db the.db -host localhost
... # lots of output
[INFO] (src/handler.c:285) Binding handler PUSH socket ipc:// with identity: 34f9ceee-cd52-4b7f-b197-88bf2f0ec378
[INFO] (src/handler.c:311) Binding listener SUB socket ipc:// subscribed to: 
[INFO] (src/control.c:401) Setting up control socket in at ipc://run/control

OK. Mongrel2 is now listening on port 6767 and sending messages down a ZeroMQ push socket, ipc://


Wanna see what Mongrel2 is actually saying? Turn on m2reader.py. It won't respond with a proper web request, but you can see the entire JSON message passed to Brubeck from Mongrel2.

$ ./m2reader.py 
34f9ceee-cd52-4b7f-b197-88bf2f0ec378 0 / 571:{"PATH":"/","x-forwarded-for":"","accept-language":"en-US,en;q=0.8","accept-encoding":"gzip,deflate,sdch","connection":"keep-alive","accept-charset":"ISO-8859-1,utf-8;q=0.7,*;q=0.3","accept":"text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8","user-agent":"Mozilla/5.0 (Macintosh; Intel Mac OS X 10_6_8) AppleWebKit/534.30 (KHTML, like Gecko) Chrome/12.0.742.122 Safari/534.30","host":"localhost:6767","METHOD":"GET","VERSION":"HTTP/1.1","URI":"/","PATTERN":"/"},0:,

Brubeck's job is to generate a response and send it to Mongrel2, which Mongrel2 then then forwards to our user.

The Demos

On the agenda:

Classes And Functions

As we saw in the README there are two ways of writing message handlers. demo_minimal.py implements a class that implements a get() function to answer HTTP GET. demo_noclasses.py implements a function with it's URL mapping specified with the add_route decorator.

URL Design And Handling

URL's are matched by regular expression. Sometimes parameters we need are part of the URL. Here is a quick glance at the URL's used for this demo.

urls = [(r'^/class/(\w+)$', NameHandler),
        (r'^/fun/(?P<name>\w+)$', name_handler),
        (r'^/', IndexHandler)]

In spite of being the last URL listed above, IndexHandler is the first class defined. This class responds to HTTP GET with the string 'Take five!'. That's it.

class IndexHandler(WebMessageHandler):
    def get(self):
        self.set_body('Take five!')
        return self.render()

The next class, NameHandler, defines it's get() function differently from IndexHandler. The new definition includes the parameter name. Notice that in the urls above we asign NameHandler to pattern '^/class/(\w+)$'.

Whatever matches (\w+) will be the value of the name argument below.

class NameHandler(WebMessageHandler):
    def get(self, name):
        self.set_body('Take five, %s!' % (name))
        return self.render()

The third handler defined is not a class. This handler is defined as a function. And notice that it also has a name argument tacked on.

def name_handler(application, message, name):
    return http_response('Take five, %s!' % (name), 200, 'OK', {})

We then map all three URL's to the relevant handlers and instantiate a Brubeck instance.

app = Brubeck(**config)

But hey, we'll add one more function just because we still can.

The add_route decorator is now available to us on the Brubeck instance (app). Wrap any function with this decorator to assign it to a URL pattern and HTTP method. Passing parameters in URL's works fine here too.

@app.add_route('^/deco/(?P<name>\w+)$', method='GET')
def new_name_handler(application, message, name):
    return http_response('Take five, %s!' % (name), 200, 'OK', {})

Then we turn it on by calling run() and all four URL's can answer requests. Try this one: http://localhost:6767/class/james. Or this one: http://localhost:6767/fun/james. Or this one: http://localhost:6767/deco/james.

The only URL left is the boring one: http://localhost:6767/.

Template Rendering

Template rendering is adequately covered as part of the README for now.


Authentication comes in many forms. The first example will cover the basic system for authenticating requests. The second demo will combine cookies, templates and a hard coded user to demonstrate a full login system.

Auth Over POST

To place authentication restrictions on any function you can use the @authenticated decorator. The purpose of this decorator is tell the web server to fail with errors sent via the relevant protocol. When using a WebMessageHandler errors will be sent as HTTP level errors. We will discuss another decorator @web_authenticated in the next section.

Here is what using it looks like.

def post(self):

For the purpose of the demonstration I hardcode a User instance with the username 'jd' and the password 'foo'. Brubeck comes with a User and UserProfile model but we only use the User model here.

demo_user = User.create_user('jd', 'foo')

All get_current_user does is check the request arguments for a username and password and validate them. Brubeck makes the authenticated user available for you as self.current_user.

Let's try it using it curl.

$ curl -d "username=jd&password=foo" localhost:6767/brubeck
jd logged in successfully!

Now let's see it fail. We will tell curl to fail silently, meaning it won't print out any returned HTML, so we can see the 401 error Brubeck returns.

$ curl -f -d "username=jd&password=bar" localhost:6767/brubeck
curl: (22) The requested URL returned error: 401

Someone could build the first draft of an API using this example. All errors would be passed via HTTP.

Authenticated Website

This example is considerably more involved. Let's look at the URL's before we dig in.

handler_tuples = [
    (r'^/login', LoginHandler),
    (r'^/logout', LogoutHandler),
    (r'^/', LandingHandler),

We can probably guess that LoginHandler logs a user in and LogoutHandler logs a user out. But what happens if we visit http://localhost:6767/ before logging in?


Try visiting http://localhost:6767 and you'll be redirected to http://localhost:6767/login. This happens because we wrapped LoginHandler's get() method with the @web_authenticated decorator.

class LandingHandler(CustomAuthMixin, Jinja2Rendering):
    def get(self):

Failures to pass authentication are redirected to the application's login_url, as specified in Brubeck's config.

config = {
    'login_url': '/login',

If you need to redirect a user to the login url at any point in your code, you could write the following.

return self.redirect(self.application.login_url)

The implementation of LoginHandler is straight forward. The get() method renders the login template with fields for a username and password. The implementation of post() has the @web_authenticated decorator on it, meaning it expects auth credentials to be provided. If the credentials pass post() then calls self.redirect('/') to send a logged-in user to the landing page.

Authentication Tracking

A cookie was set the first time @web_authenticated was called because we provided the correct username and password. This doesn't happen automatically. It happened because of these two lines in get_current_user.

self.set_cookie('username', username) # DEMO: Don't actually put a
self.set_cookie('password', password) # password in a cookie...

Notice the comment suggesting you shouldn't actually store a password in the cookie. This is done to keep the demo focused. Secure cookies will be covered soon..

Authenticated Browsing

Now that we're logged in, LandingHandler let's us call get() and it renders landing.html. It simply says hello and offers a logout button.

Clicking logout sends us to http://localhost:6767/logout and LogoutHandler calls self.delete_cookies(). We are no longer authenticated so it sends us the login screen when it's finished.

Secure Cookies

Brubeck also supports secure cookies. This is what it looks like to use them.

Setting one:

self.set_cookie('user_id', username,

Reading one:

user_id = self.get_cookie('user_id',

The List Surf project features secure cookies in it's authentication system.