Introducing cornice

2011-12-06T00:00:00+01:00

Wow, already my third working day at mozilla. Since Monday, I've been working with Tarek Ziadé, on a pyramid REST-ish toolkit named cornice.

Its goal is to take all the hard bits appart from you when implementing a web service, so you can focus on what's important. Cornice provides you facilities for validation of any kind.

The goal is to simplify your work, but we don't want to reinvent the wheel, so it is easily pluggable with validations frameworks, such as Collander.

Handling errors and validation

We have changed the way errors are handled. Here is how it works:

service = Service(name="service", path="/service")


def is_awesome(request):
    if not 'awesome' in request.GET:
        request.errors.add('body', 'awesome', 'You lack awesomeness!')


@service.get(validator=(is_awesome))
def get1(request):
    return {"test": "succeeded"}

All the errors collected during the validation process, or after, are collected before returning the request. If any, a error 400 is fired up, with the list of problems encoutred encoded as a nice json list (we plan to support multiple formats in the future)

As you might have seen, request.errors.add takes three parameters: location, name and description.

location is where the error arised. It can either be "body", "query", "headers" or "path". name is the name of the variable causing problem, if any, and description contains a more detailled message.

Here is an example of a malformed request:

$ # run a demo app

To describe a web service in cornice, you have to write something like this

System Message: ERROR/3 (./content/mozilla/introducing-cornice.rst, line 54)

Content block expected for the "code-block" directive; none found.

.. code-block:: python

Alexis' log

Introducing cornice

Handling errors and validation