code: def host(environ):  # pragma: no cover
      
  
      url = environ['wsgi.url_scheme'] + '://'
  
      if environ.get('HTTP_HOST'):
          url += environ['HTTP_HOST']
      else:
          url += environ['SERVER_NAME']
  
          if environ['wsgi.url_scheme'] == 'https':
              if environ['SERVER_PORT'] != '443':
                  url += ':' + environ['SERVER_PORT']
          else:
              if environ['SERVER_PORT'] != '80':
                  url += ':' + environ['SERVER_PORT']
  
      return url + quote(environ.get('SCRIPT_NAME', ''))
docs: Reconstruct host from environment. A modified version
      of http://www.python.org/dev/peps/pep-0333/#url-reconstruction