code: def check_header_validity(header):
      
      name, value = header
  
      if isinstance(value, bytes):
          pat = _CLEAN_HEADER_REGEX_BYTE
      else:
          pat = _CLEAN_HEADER_REGEX_STR
      try:
          if not pat.match(value):
              raise InvalidHeader("Invalid return character or leading space in header: %s" % name)
      except TypeError:
          raise InvalidHeader("Value for header {%s: %s} must be of type str or "
                              "bytes, not %s" % (name, value, type(value)))
docs: Verifies that header value is a string which doesn't contain
      leading whitespace or return characters. This prevents unintended
      header injection.
  
      :param header: tuple, in the format (name, value).