code: def _op_msg_no_header(flags, command, identifier, docs, check_keys, opts):
      
      # Encode the command document in payload 0 without checking keys.
      encoded = _dict_to_bson(command, False, opts)
      flags_type = _pack_op_msg_flags_type(flags, 0)
      total_size = len(encoded)
      max_doc_size = 0
      if identifier:
          type_one = _pack_byte(1)
          cstring = _make_c_string(identifier)
          encoded_docs = [_dict_to_bson(doc, check_keys, opts) for doc in docs]
          size = len(cstring) + sum(len(doc) for doc in encoded_docs) + 4
          encoded_size = _pack_int(size)
          total_size += size
          max_doc_size = max(len(doc) for doc in encoded_docs)
          data = ([flags_type, encoded, type_one, encoded_size, cstring] +
                  encoded_docs)
      else:
          data = [flags_type, encoded]
      return b''.join(data), total_size, max_doc_size
docs: Get a OP_MSG message.
  
      Note: this method handles multiple documents in a type one payload but
      it does not perform batch splitting and the total message size is
      only checked *after* generating the entire message.