Use case

To monitor NuRaftKeeper internal status such as server info, client info, watch info, ephemeral nodes info etc. Zookeeper provides 4 letters admin tool. You can check it here.

Describe the solution you'd like

1. When startup register 4 letter word command with a <code, command_executor> map. The code is name reinterpreted int32.
2. When new connection comes, first extract the first 4 characters and check whether it is 4lw command, if yes, run the command.
3. add some methods to KeeperStorageDispatcher to collect server info.

Because the first request of a connection is hand shake request whose first 4 characters is request length and the length is fixed 44 or 45. All 4lw code is larger than 2^24 or lower than 0, so collision never happens.

In JD, we already added some 4lw commands to SvsKeeper which is a NuRaft based system likeNuRaftKeeper . If the idea is ok, I'd like to add it to NuRaftKeeper