Is MsgPropose/MsgReadIndex silently ignored when the node role is candidate?

[tisonkun]

Application read and write generally go into MsgPropose or MsgReadIndex. While I don't have ideas on how to sort out inbound messages, I notice that MsgPropose/MsgReadIndex will be silently ignored when the node role is in candidate.

Even I can store the node role and update on Ready, I step messages in batch and handle Ready at the end. So it's possible that node role switch to candidate intermediately.

Shall I force handle Ready and check node role before step MsgPropose/MsgReadIndex? Or is there other best practice to properly handle application issues read and write (MsgPropose/MsgReadIndex)?

cc @BusyJay

[BusyJay]

TiKV will check pending entries and pending read index count to detect if a request is accepted. Though it's more appropriate to return an error instead.