old_contents: import webapp2
  import ipaddr
  
  class Default(webapp2.RequestHandler):
      def get(self):
          self.response.headers['Content-Type'] = 'text/plain'
          self.response.write(self.request.remote_addr)
  
  class CheckIPVersion(webapp2.RequestHandler):
      def get(self, ip_version):
          self.response.headers['Content-Type'] = 'text/plain'
          ip=ipaddr.IPAddress(self.request.remote_addr, version=ip_version)
  
          if ip_version == '4':
              self.response.write(isinstance(ip,ipaddr.IPv4Address))
          elif ip_version == '6':
              self.response.write(isinstance(ip,ipaddr.IPv6Address))
  
  class RedirectToHTTPS(webapp2.RequestHandler):
      def get(self, str):
          self.redirect("https://minivi-ip-echo.appspot.com/")
  
  class LetsEncryptHandler(webapp2.RequestHandler):
      def get(self, challenge):
          self.response.headers['Content-Type'] = 'text/plain'
          responses = {
                      'rldLVXbWmljTa0Vnf-jcgTX0cYBN7javEvFk008Awpk': 'rldLVXbWmljTa0Vnf-jcgTX0cYBN7javEvFk008Awpk.-6tKHL8U8EMsqcdR-VVBfXLMb2iqPOysH0Y2xWlkJ7E',
                  }
          self.response.write(responses.get(challenge, ''))
  
  application = webapp2.WSGIApplication([
      ('/', Default),
      (r'/isipv(4|6)', CheckIPVersion),
      (r'/(secure|tls|https)', RedirectToHTTPS),
      ('/.well-known/acme-challenge/([\w-]+)', LetsEncryptHandler),
  ])
  
new_contents: import webapp2
  import ipaddr
  
  class Default(webapp2.RequestHandler):
      def get(self):
          self.response.headers['Content-Type'] = 'text/plain'
          self.response.write(self.request.remote_addr)
  
  class CheckIPVersion(webapp2.RequestHandler):
      def get(self, ip_version):
          self.response.headers['Content-Type'] = 'text/plain'
          ip=ipaddr.IPAddress(self.request.remote_addr, version=ip_version)
  
          if ip_version == '4':
              self.response.write(isinstance(ip,ipaddr.IPv4Address))
          elif ip_version == '6':
              self.response.write(isinstance(ip,ipaddr.IPv6Address))
  
  class RedirectToHTTPS(webapp2.RequestHandler):
      def get(self, str):
          self.redirect("https://minivi-ip-echo.appspot.com/")
  
  class LetsEncryptHandler(webapp2.RequestHandler):
      def get(self, challenge):
          self.response.headers['Content-Type'] = 'text/plain'
          responses = {
              'rldLVXbWmljTa0Vnf-jcgTX0cYBN7javEvFk008Awpk': 'rldLVXbWmljTa0Vnf-jcgTX0cYBN7javEvFk008Awpk.-6tKHL8U8EMsqcdR-VVBfXLMb2iqPOysH0Y2xWlkJ7E',
              'u2sosNZKagrUOFrweofVuEBu--njhnrEjBy81kvYqnI': 'u2sosNZKagrUOFrweofVuEBu--njhnrEjBy81kvYqnI.aATglod0Ki8gH8iAIPXUShPu6jEMA_z3QPVXaMn7RjY',
                  }
          self.response.write(responses.get(challenge, ''))
  
  application = webapp2.WSGIApplication([
      ('/', Default),
      (r'/isipv(4|6)', CheckIPVersion),
      (r'/(secure|tls|https)', RedirectToHTTPS),
      ('/.well-known/acme-challenge/([\w-]+)', LetsEncryptHandler),
  ])
  
subject: modify challenge-response for letsencrypt