.. _hooks: Hooks ===== * `Before Hooks`_ * `After Hooks`_ Falcon supports *before* and *after* hooks. You install a hook simply by applying one of the decorators below, either to an individual responder or to an entire resource. For example, consider this hook that validates a POST request for an image resource: .. code:: python def validate_image_type(req, resp, resource, params): if req.content_type not in ALLOWED_IMAGE_TYPES: msg = 'Image type not allowed. Must be PNG, JPEG, or GIF' raise falcon.HTTPBadRequest(title='Bad request', description=msg) You would attach this hook to an ``on_post`` responder like so: .. code:: python @falcon.before(validate_image_type) def on_post(self, req, resp): pass Or, suppose you had a hook that you would like to apply to *all* responders for a given resource. In that case, you would simply decorate the resource class: .. code:: python @falcon.before(extract_project_id) class Message: def on_post(self, req, resp, project_id): pass def on_get(self, req, resp, project_id): pass .. note:: When decorating an entire resource class, all method names that resemble responders, including *suffix*\ed (see also :meth:`~falcon.App.add_route`) ones, are decorated. If, for instance, a method is called ``on_get_items``, but it is not meant for handling ``GET`` requests under a route with the *suffix* ``items``, the easiest workaround for preventing the hook function from being applied to the method is renaming it not to clash with the responder pattern. Note also that you can pass additional arguments to your hook function as needed: .. code:: python def validate_image_type(req, resp, resource, params, allowed_types): if req.content_type not in allowed_types: msg = 'Image type not allowed.' raise falcon.HTTPBadRequest(title='Bad request', description=msg) @falcon.before(validate_image_type, ['image/png']) def on_post(self, req, resp): pass Falcon supports using any callable as a hook. This allows for using a class instead of a function: .. code:: python class Authorize: def __init__(self, roles): self._roles = roles def __call__(self, req, resp, resource, params): pass @falcon.before(Authorize(['admin'])) def on_post(self, req, resp): pass Falcon :ref:`middleware components ` can also be used to insert logic before and after requests. However, unlike hooks, :ref:`middleware components ` are triggered **globally** for all requests. .. Tip:: In order to pass data from a hook function to a resource function use the ``req.context`` and ``resp.context`` objects. These context objects are intended to hold request and response data specific to your app as it passes through the framework. Before Hooks ------------ .. autofunction:: falcon.before After Hooks ----------- .. autofunction:: falcon.after