versioned_middleware.py

import re

version_pattern = re.compile(r"/v(?P<version>[0-9a-z\-\+\.]+)", re.IGNORECASE)


class VersionedAPIMiddleware(object):
    """
    Allows a Werkzeug/Flask application to have a versioned API.

    This middleware will extract out the API version specification in a URL
    segment and then forward the processing of the endpoint (sans version, in
    the case of the URL segment), to the application along with an
    environment variable indicating what the version requested was.

    If no appropriate version could be parsed, then `None` is set as the
    value of `API_VERSION`.

    """

    def __init__(self, app):
        self.app = app

    def __call__(self, environ, start_response):
        path = environ.get('PATH_INFO', '')

        match = version_pattern.match(path)

        if match:
            environ['API_VERSION'] = match.group(1)
            environ['PATH_INFO'] = re.sub(version_pattern, '', path, count=1)
        else:
            environ['API_VERSION'] = None

        return self.app(environ, start_response)