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falcon 1.4

falcon

Media

Falcon allows for easy and customizable internet media type handling. By default Falcon only enables a single JSON handler. However, additional handlers can be configured through the falcon.RequestOptions and falcon.ResponseOptions objects specified on your falcon.API.

Note

To avoid unnecessary overhead, Falcon will only process request media the first time the media property is referenced. Once it has been referenced, it’ll use the cached result for subsequent interactions.

Usage

Zero configuration is needed if you’re creating a JSON API. Just access or set the media attribute as appropriate and let Falcon do the heavy lifting for you.

import falcon


class EchoResource(object):
    def on_post(self, req, resp):
        message = req.media.get('message')

        resp.media = {'message': message}
        resp.status = falcon.HTTP_200

Warning

Once media is called on a request, it’ll consume the request’s stream.

Validating Media

Falcon currently only provides a JSON Schema media validator; however, JSON Schema is very versatile and can be used to validate any deserialized media type that JSON also supports (i.e. dicts, lists, etc).

falcon.media.validators.jsonschema.validate(schema) [source]

Decorator for validating req.media using JSON Schema.

This decorator provides standard JSON Schema validation via the jsonschema package available from PyPI. Semantic validation via the format keyword is enabled for the default checkers implemented by jsonschema.FormatChecker.

Note

The jsonschema` package must be installed separately in order to use this decorator, as Falcon does not install it by default.

Parameters: schema (dict) – A dictionary that follows the JSON Schema specification. See json-schema.org for more information on defining a compatible dictionary.

Example

from falcon.media.validators import jsonschema

# -- snip --

@jsonschema.validate(my_post_schema)
def on_post(self, req, resp):

# -- snip --

If JSON Schema does not meet your needs, a custom validator may be implemented in a similar manner to the one above.

Content-Type Negotiation

Falcon currently only supports partial negotiation out of the box. By default, when the media attribute is used it attempts to de/serialize based on the Content-Type header value. The missing link that Falcon doesn’t provide is the connection between the falcon.Request Accept header provided by a user and the falcon.Response Content-Type header.

If you do need full negotiation, it is very easy to bridge the gap using middleware. Here is an example of how this can be done:

class NegotiationMiddleware(object):
    def process_request(self, req, resp):
        resp.content_type = req.accept

Replacing the Default Handlers

When creating your API object you can either add or completely replace all of the handlers. For example, lets say you want to write an API that sends and receives MessagePack. We can easily do this by telling our Falcon API that we want a default media-type of application/msgpack and then create a new Handlers object specifying the desired media type and a handler that can process that data.

import falcon
from falcon import media


handlers = media.Handlers({
    'application/msgpack': media.MessagePackHandler(),
})

api = falcon.API(media_type='application/msgpack')

api.req_options.media_handlers = handlers
api.resp_options.media_handlers = handlers

Alternatively, if you would like to add an additional handler such as MessagePack, this can be easily done in the following manner:

import falcon
from falcon import media


extra_handlers = {
    'application/msgpack': media.MessagePackHandler(),
}

api = falcon.API()

api.req_options.media_handlers.update(extra_handlers)
api.resp_options.media_handlers.update(extra_handlers)

Supported Handler Types

class falcon.media.JSONHandler [source]

Handler built using Python’s json module.

class falcon.media.MessagePackHandler [source]

Handler built using the msgpack module.

This handler uses msgpack.unpackb() and msgpack.packb(). The MessagePack bin type is used to distinguish between Unicode strings (str on Python 3, unicode on Python 2) and byte strings (bytes on Python 2/3, or str on Python 2).

Note

This handler requires the extra msgpack package, which must be installed in addition to falcon from PyPI:

$ pip install msgpack

Python 2.6 users will need to use the deprecated msgpack-python package instead, pinned to version 0.4.8.

Custom Handler Type

If Falcon doesn’t have an internet media type handler that supports your use case, you can easily implement your own using the abstract base class provided by Falcon:

class falcon.media.BaseHandler [source]

Abstract Base Class for an internet media type handler

serialize(obj) [source]

Serialize the media object on a falcon.Response

Parameters: obj (object) – A serializable object.
Returns: The resulting serialized bytes from the input object.
Return type: bytes
deserialize(raw) [source]

Deserialize the falcon.Request body.

Parameters: raw (bytes) – Input bytes to deserialize
Returns: A deserialized object.
Return type: object

Handlers

class falcon.media.Handlers(initial=None) [source]

A dictionary like object that manages internet media type handlers.

Media Type Constants

The falcon module provides a number of constants for common media types, including the following:

falcon.MEDIA_JSON
falcon.MEDIA_MSGPACK
falcon.MEDIA_YAML
falcon.MEDIA_XML
falcon.MEDIA_HTML
falcon.MEDIA_JS
falcon.MEDIA_TEXT
falcon.MEDIA_JPEG
falcon.MEDIA_PNG
falcon.MEDIA_GIF

© 2012–2017 by Rackspace Hosting, Inc. and other contributors
Licensed under the Apache License, Version 2.0.
https://falcon.readthedocs.io/en/1.4.1/api/media.html