Flask Ensure Domain (redirect) Middleware

readme.md

The middleware helps ensure a site domain. Useful when the main domain change and we want to keep links and user attending the new domain.

There are a few settings via environment variables, state bellow.

• FLASK_ENV (required) has to be production otherwise will not apply redirection;
• SITE_DOMAIN (required) the principal domain to redirect to;
• PRODUCTION_DOMAINS (optional) to list your available domains (comma separated). When supplied will only redirect from those domains. Useful for pre-production domains.

app.py

import flask
import middleware

app = flask.create_app(os.path.dirname(__file__))
app.wsgi_app = middleware.EnsureDomainMiddleWare(app.wsgi_app)

middleware.py

import os
from flask import redirect

class EnsureDomainMiddleWare(object):
  '''Simple WSGI middleware'''
  def __init__(self, app):
    self.app = app
  
  def __call__(self, environ, start_response):
    if self.is_production(environ):
      # ensure required site domain
      site_domain = os.environ.get('SITE_DOMAIN')
      if site_domain and site_domain != environ['HTTP_HOST']:
        redirected_uri = '//%s%s?domain=%s' % (site_domain, environ.get('REQUEST_URI', environ.get('PATH_INFO', '')), environ.get('HTTP_HOST'))
        response = redirect(redirected_uri, code=301)
        return response(environ, start_response)

    return self.app(environ, start_response)

  def is_production(self, environ):
      production_env = os.environ.get('FLASK_ENV') == 'production'
      production_domain = True
      domains = os.environ.get('PRODUCTION_DOMAINS', "").split(',')
      if len(domains):
        production_domain = environ.get('HTTP_HOST') in domains
      return production_env and production_domain