@classmethod<EOL><INDENT>def _encode_message_header(cls, client_id, correlation_id, request_key,<EOL>version=<NUM_LIT:0>):<DEDENT>
return struct.pack('<STR_LIT>' % len(client_id),<EOL>request_key,          <EOL>version,              <EOL>correlation_id,       <EOL>len(client_id),       <EOL>client_id)            <EOL>
Encode the common request envelope