Twisted Documentation: Custom Response Codes

The previous example introduced NoResource, a Twisted Web error resource which responds with a 404 (not found) code. This example will cover the APIs that NoResource uses to do this so that you can generate your own custom response codes as desired.

First, the now-standard import preamble:

1
2
3
from twisted.web.server import Site
from twisted.web.resource import Resource
from twisted.internet import reactor

Now we'll define a new resource class that always returns a 402 (payment required) response. This is really not very different from the resources that was defined in previous examples. The fact that it has a response code other than 200 doesn't change anything else about its role. This will require using the request object, though, which none of the previous examples have done.

The Request object has shown up in a couple of places, but so far we've ignored it. It is a parameter to the getChild API as well as to render methods such as render_GET. As you might have suspected, it represents the request for which a response is to be generated. Additionally, it also represents the response being generated. In this example we're going to use its setResponseCode method to - you guessed it - set the response's status code.

1
2
3
4
class PaymentRequired(Resource):
    def render_GET(self, request):
        request.setResponseCode(402)
        return "<html><body>Please swipe your credit card.</body></html>"

Just like the other resources I've demonstrated, this one returns a string from its render_GET method to define the body of the response. All that's different is the call to setResponseCode to override the default response code, 200, with a different one.

Finally, the code to set up the site and reactor. We'll put an instance of the above defined resource at /buy:

1
2
3
4
5
root = Resource()
root.putChild("buy", PaymentRequired())
factory = Site(root)
reactor.listenTCP(8880, factory)
reactor.run()

Here's the complete example:

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
from twisted.web.server import Site
from twisted.web.resource import Resource
from twisted.internet import reactor

class PaymentRequired(Resource):
    def render_GET(self, request):
        request.setResponseCode(402)
        return "<html><body>Please swipe your credit card.</body></html>"

root = Resource()
root.putChild("buy", PaymentRequired())
factory = Site(root)
reactor.listenTCP(8880, factory)
reactor.run()

Run the server and visit http://localhost:8880/buy in your browser. It'll look pretty boring, but if you use Firefox's View Page Info right-click menu item (or your browser's equivalent), you'll be able to see that the server indeed sent back a 402 response code.