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/Falcon 1.2

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:

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('Bad request', msg)

You would attach this hook to an on_post responder like so:

@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:

@falcon.before(extract_project_id)
class Message(object):
    def on_post(self, req, resp):
        pass

    def on_get(self, req, resp):
        pass

Falcon middleware components can also be used to insert logic before and after requests. However, unlike hooks, middleware components are triggered globally for all requests.

falcon.before(action) [source]

Decorator to execute the given action function before the responder.

Parameters: action (callable) –

A function of the form func(req, resp, resource, params), where resource is a reference to the resource class instance associated with the request, and params is a dict of URI Template field names, if any, that will be passed into the resource responder as kwargs.

Note

Hooks may inject extra params as needed. For example:

def do_something(req, resp, resource, params):
    try:
        params['id'] = int(params['id'])
    except ValueError:
        raise falcon.HTTPBadRequest('Invalid ID',
                                    'ID was not valid.')

    params['answer'] = 42
falcon.after(action) [source]

Decorator to execute the given action function after the responder.

Parameters: action (callable) – A function of the form func(req, resp, resource), where resource is a reference to the resource class instance associated with the request

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Licensed under the Apache License, Version 2.0.
https://falcon.readthedocs.io/en/1.2.0/api/hooks.html