falcon 1.3.0rc2

Quick Links

• Read the docs

• Falcon add-ons and complimentary packages

• falconry/user @ Gitter

• falconry/dev @ Gitter

How is Falcon different?

We designed Falcon to support the demanding needs of large-scale microservices and responsive app backends. Falcon complements more general Python web frameworks by providing bare-metal performance, reliability, and flexibility wherever you need it.

Fast. Same hardware, more requests. Falcon turns around requests several times faster than most other Python frameworks. For an extra speed boost, Falcon compiles itself with Cython when available, and also works well with PyPy. Considering a move to another programming language? Benchmark with Falcon + PyPy first.

Reliable. We go to great lengths to avoid introducing breaking changes, and when we do they are fully documented and only introduced (in the spirit of SemVer) with a major version increment. The code is rigorously tested with numerous inputs and we require 100% coverage at all times. Six and mimeparse are the only third-party dependencies.

Flexible. Falcon leaves a lot of decisions and implementation details to you, the API developer. This gives you a lot of freedom to customize and tune your implementation. Due to Falcon’s minimalist design, Python community members are free to independently innovate on Falcon add-ons and complimentary packages.

Debuggable. Falcon eschews magic. It’s easy to tell which inputs lead to which outputs. Unhandled exceptions are never encapsulated or masked. Potentially surprising behaviors, such as automatic request body parsing, are well-documented and disabled by default. Finally, when it comes to the framework itself, we take care to keep logic paths simple and understandable. All this makes it easier to reason about the code and to debug edge cases in large-scale deployments.

Features

• Highly-optimized, extensible code base

• Intuitive routing via URI templates and REST-inspired resource classes

• Easy access to headers and bodies through request and response classes

• DRY request processing via middleware components and hooks

• Idiomatic HTTP error responses

• Straightforward exception handling

• Snappy unit testing through WSGI helpers and mocks

• CPython 2.6-2.7, PyPy 2.7, Jython 2.7, and CPython 3.3+ support

• ~20% speed boost when Cython is available

Who’s Using Falcon?

Falcon is used around the world by a growing number of organizations, including:

• 7ideas

• Cronitor

• EMC

• Hurricane Electric

• Leadpages

• OpenStack

• Rackspace

• Shiftgig

• tempfil.es

• Opera Software

If you are using the Falcon framework for a community or commercial project, please consider adding your information to our wiki under Who’s Using Falcon?

Community

A number of Falcon add-ons, templates, and complimentary packages are available for use in your projects. We’ve listed several of these on the Falcon wiki as a starting point, but you may also wish to search PyPI for additional resources.

The Falconry community on Gitter is a great place to ask questions and share your ideas. You can find us in falconry/user. We also have a falconry/dev room for discussing the design and development of the framework itself.

Per our Code of Conduct, we expect everyone who participates in community discussions to act professionally, and lead by example in encouraging constructive discussions. Each individual in the community is responsible for creating a positive, constructive, and productive culture.

Installation

$ pip install falcon

$ pip install falcon

$ pip install ujson

$ pip install cython
$ pip install --no-binary :all: falcon

$ pip install -v --no-binary :all: falcon

$ xcode-select --install

clang: error: unknown argument: '-mno-fused-madd' [-Wunused-command-line-argument-hard-error-in-future]

$ export CFLAGS="-Qunused-arguments -Wno-unused-function"

WSGI Server

Falcon speaks WSGI, and so in order to serve a Falcon app, you will need a WSGI server. Gunicorn and uWSGI are some of the more popular ones out there, but anything that can load a WSGI app will do.

$ pip install [gunicorn|uwsgi]

Source Code

Falcon lives on GitHub, making the code easy to browse, download, fork, etc. Pull requests are always welcome! Also, please remember to star the project if it makes you happy. :)

Once you have cloned the repo or downloaded a tarball from GitHub, you can install Falcon like this:

$ cd falcon
$ pip install .

Or, if you want to edit the code, first fork the main repo, clone the fork to your desktop, and then run the following to install it using symbolic linking, so that when you change your code, the changes will be automagically available to your app without having to reinstall the package:

$ cd falcon
$ pip install -e .

You can manually test changes to the Falcon framework by switching to the directory of the cloned repo and then running pytest:

$ cd falcon
$ pip install -r requirements/tests
$ pytest tests

Or, to run the default set of tests:

$ pip install tox && tox

See also the tox.ini file for a full list of available environments.

Read the docs

The docstrings in the Falcon code base are quite extensive, and we recommend keeping a REPL running while learning the framework so that you can query the various modules and classes as you have questions.

Online docs are available at: https://falcon.readthedocs.io

You can build the same docs locally as follows:

$ pip install tox && tox -e docs

Once the docs have been built, you can view them by opening the following index page in your browser. On OS X it’s as simple as:

$ open docs/_build/html/index.html

Or on Linux:

$ xdg-open docs/_build/html/index.html

Getting started

Here is a simple, contrived example showing how to create a Falcon-based API.

# things.py

# Let's get this party started!
import falcon


# Falcon follows the REST architectural style, meaning (among
# other things) that you think in terms of resources and state
# transitions, which map to HTTP verbs.
class ThingsResource(object):
    def on_get(self, req, resp):
        """Handles GET requests"""
        resp.status = falcon.HTTP_200  # This is the default status
        resp.body = ('\nTwo things awe me most, the starry sky '
                     'above me and the moral law within me.\n'
                     '\n'
                     '    ~ Immanuel Kant\n\n')

# falcon.API instances are callable WSGI apps
app = falcon.API()

# Resources are represented by long-lived class instances
things = ThingsResource()

# things will handle all requests to the '/things' URL path
app.add_route('/things', things)

You can run the above example using any WSGI server, such as uWSGI or Gunicorn. For example:

$ pip install gunicorn
$ gunicorn things:app

Then, in another terminal:

$ curl localhost:8000/things

A more complex example

Here is a more involved example that demonstrates reading headers and query parameters, handling errors, and working with request and response bodies.

import json
import logging
import uuid
from wsgiref import simple_server

import falcon
import requests


class StorageEngine(object):

    def get_things(self, marker, limit):
        return [{'id': str(uuid.uuid4()), 'color': 'green'}]

    def add_thing(self, thing):
        thing['id'] = str(uuid.uuid4())
        return thing


class StorageError(Exception):

    @staticmethod
    def handle(ex, req, resp, params):
        description = ('Sorry, couldn\'t write your thing to the '
                       'database. It worked on my box.')

        raise falcon.HTTPError(falcon.HTTP_725,
                               'Database Error',
                               description)


class SinkAdapter(object):

    engines = {
        'ddg': 'https://duckduckgo.com',
        'y': 'https://search.yahoo.com/search',
    }

    def __call__(self, req, resp, engine):
        url = self.engines[engine]
        params = {'q': req.get_param('q', True)}
        result = requests.get(url, params=params)

        resp.status = str(result.status_code) + ' ' + result.reason
        resp.content_type = result.headers['content-type']
        resp.body = result.text


class AuthMiddleware(object):

    def process_request(self, req, resp):
        token = req.get_header('Authorization')
        account_id = req.get_header('Account-ID')

        challenges = ['Token type="Fernet"']

        if token is None:
            description = ('Please provide an auth token '
                           'as part of the request.')

            raise falcon.HTTPUnauthorized('Auth token required',
                                          description,
                                          challenges,
                                          href='http://docs.example.com/auth')

        if not self._token_is_valid(token, account_id):
            description = ('The provided auth token is not valid. '
                           'Please request a new token and try again.')

            raise falcon.HTTPUnauthorized('Authentication required',
                                          description,
                                          challenges,
                                          href='http://docs.example.com/auth')

    def _token_is_valid(self, token, account_id):
        return True  # Suuuuuure it's valid...


class RequireJSON(object):

    def process_request(self, req, resp):
        if not req.client_accepts_json:
            raise falcon.HTTPNotAcceptable(
                'This API only supports responses encoded as JSON.',
                href='http://docs.examples.com/api/json')

        if req.method in ('POST', 'PUT'):
            if 'application/json' not in req.content_type:
                raise falcon.HTTPUnsupportedMediaType(
                    'This API only supports requests encoded as JSON.',
                    href='http://docs.examples.com/api/json')


class JSONTranslator(object):
    # NOTE: Starting with Falcon 1.3, you can simply
    # use req.media and resp.media for this instead.

    def process_request(self, req, resp):
        # req.stream corresponds to the WSGI wsgi.input environ variable,
        # and allows you to read bytes from the request body.
        #
        # See also: PEP 3333
        if req.content_length in (None, 0):
            # Nothing to do
            return

        body = req.stream.read()
        if not body:
            raise falcon.HTTPBadRequest('Empty request body',
                                        'A valid JSON document is required.')

        try:
            req.context['doc'] = json.loads(body.decode('utf-8'))

        except (ValueError, UnicodeDecodeError):
            raise falcon.HTTPError(falcon.HTTP_753,
                                   'Malformed JSON',
                                   'Could not decode the request body. The '
                                   'JSON was incorrect or not encoded as '
                                   'UTF-8.')

    def process_response(self, req, resp, resource):
        if 'result' not in resp.context:
            return

        resp.body = json.dumps(resp.context['result'])


def max_body(limit):

    def hook(req, resp, resource, params):
        length = req.content_length
        if length is not None and length > limit:
            msg = ('The size of the request is too large. The body must not '
                   'exceed ' + str(limit) + ' bytes in length.')

            raise falcon.HTTPRequestEntityTooLarge(
                'Request body is too large', msg)

    return hook


class ThingsResource(object):

    def __init__(self, db):
        self.db = db
        self.logger = logging.getLogger('thingsapp.' + __name__)

    def on_get(self, req, resp, user_id):
        marker = req.get_param('marker') or ''
        limit = req.get_param_as_int('limit') or 50

        try:
            result = self.db.get_things(marker, limit)
        except Exception as ex:
            self.logger.error(ex)

            description = ('Aliens have attacked our base! We will '
                           'be back as soon as we fight them off. '
                           'We appreciate your patience.')

            raise falcon.HTTPServiceUnavailable(
                'Service Outage',
                description,
                30)

        # An alternative way of doing DRY serialization would be to
        # create a custom class that inherits from falcon.Request. This
        # class could, for example, have an additional 'doc' property
        # that would serialize to JSON under the covers.
        #
        # NOTE: Starting with Falcon 1.3, you can simply
        # use resp.media for this instead.
        resp.context['result'] = result

        resp.set_header('Powered-By', 'Falcon')
        resp.status = falcon.HTTP_200

    @falcon.before(max_body(64 * 1024))
    def on_post(self, req, resp, user_id):
        try:
            # NOTE: Starting with Falcon 1.3, you can simply
            # use req.media for this instead.
            doc = req.context['doc']
        except KeyError:
            raise falcon.HTTPBadRequest(
                'Missing thing',
                'A thing must be submitted in the request body.')

        proper_thing = self.db.add_thing(doc)

        resp.status = falcon.HTTP_201
        resp.location = '/%s/things/%s' % (user_id, proper_thing['id'])


# Configure your WSGI server to load "things.app" (app is a WSGI callable)
app = falcon.API(middleware=[
    AuthMiddleware(),
    RequireJSON(),
    JSONTranslator(),
])

db = StorageEngine()
things = ThingsResource(db)
app.add_route('/{user_id}/things', things)

# If a responder ever raised an instance of StorageError, pass control to
# the given handler.
app.add_error_handler(StorageError, StorageError.handle)

# Proxy some things to another service; this example shows how you might
# send parts of an API off to a legacy system that hasn't been upgraded
# yet, or perhaps is a single cluster that all data centers have to share.
sink = SinkAdapter()
app.add_sink(sink, r'/search/(?P<engine>ddg|y)\Z')

# Useful for debugging problems in your API; works with pdb.set_trace(). You
# can also use Gunicorn to host your app. Gunicorn can be configured to
# auto-restart workers when it detects a code change, and it also works
# with pdb.
if __name__ == '__main__':
    httpd = simple_server.make_server('127.0.0.1', 8000, app)
    httpd.serve_forever()

Contributing

Kurt Griffiths (kgriffs) is the creator and current maintainer of the Falcon framework, with the generous help of a number of stylish and talented contributors.

Pull requests are always welcome. We use the GitHub issue tracker to organize our work, but you do not need to open a new issue before submitting a PR.

Before submitting a pull request, please ensure you have added/updated the appropriate tests (and that all existing tests still pass with your changes), and that your coding style follows PEP 8 and doesn’t cause pyflakes to complain.

Commit messages should be formatted using AngularJS conventions.

Comments follow Google’s style guide, with the additional requirement of prefixing inline comments using your GitHub nick and an appropriate prefix:

• TODO(riker): Damage report!

• NOTE(riker): Well, that’s certainly good to know.

• PERF(riker): Travel time to the nearest starbase?

• APPSEC(riker): In all trust, there is the possibility for betrayal.

See also: CONTRIBUTING.md

Legal

Copyright 2013-2016 by Rackspace Hosting, Inc. and other contributors as noted in the individual source files.

Falcon image courtesy of John O’Neill.

Licensed under the Apache License, Version 2.0 (the “License”); you may not use any portion of the Falcon framework except in compliance with the License. Contributors agree to license their work under the same License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an “AS IS” BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.