Sometimes receive "Not leader" response from leader in OnStartingFollowing()

[atellwu]

Describe the bug

• Problem:
  • OnStartingFollowing(): When you add Node to leader, you receive a response from leader that returns "Not leader" (our own implementation).
• Reason
  • In the internal process of jraft, node becomes leader - > sends leader heartbeat to all nodes - > other nodes become follower (asynchronous callback onStarting Following) - > leader receives all follower ACK (asynchronous callback onLeaderStart).
  • So visit leader in onStarting Following, and leader will report "Not leader" because it has not yet executed onLeaderStart (because our code sets leaderTerm in onLeaderStart).
• Restoration plan
  • Do not judge leader based on leaderTerm, but directly on Node.isLeader().
• Interim plan
  • In the short term, you can sleep in on StartingFollowing() for a few seconds (for example, 3s) and then visit the leader.