code: def get_host(environ):
      
      scheme = environ.get('wsgi.url_scheme')
      if 'HTTP_X_FORWARDED_HOST' in environ:
          result = environ['HTTP_X_FORWARDED_HOST']
      elif 'HTTP_HOST' in environ:
          result = environ['HTTP_HOST']
      else:
          result = environ['SERVER_NAME']
          if (scheme, str(environ['SERVER_PORT'])) not \
             in (('https', '443'), ('http', '80')):
              result += ':' + environ['SERVER_PORT']
      if result.endswith(':80') and scheme == 'http':
          result = result[:-3]
      elif result.endswith(':443') and scheme == 'https':
          result = result[:-4]
      return result
docs: Return the real host for the given WSGI environment.  This takes care
      of the `X-Forwarded-Host` header.
  
      :param environ: the WSGI environment to get the host of.