Commits on Apr 14, 2023

1. raft: fix out-of-order terms …

   This commit adds a couple invariant checks which were silently ignored and
   resulted in incorrectly setup tests passing, and incorrect messages exchanged.
   
   Property 1: for a MsgApp message m, m.Entries[i].Term >= m.LogTerm. Or, more
   generally, m.Entries is a slice of contiguous entries with a non-decreasing
   Term, and m.Index+1 == m.Entries[0].Index && m.LogTerm <= m.Entries[0].Term.
   
   This property was broken in a few tests. The root cause was that leader appends
   out-of-order entries to its own log when it becomeLeader(). This was a result
   of incorrectly set up tests: they restored to a snapshot at (index=11,term=11),
   but became leader at an earlier term 1. Then it was sending the following,
   obviously incorrect, MsgApp: {Index=11,LogTerm=11,Entries={{Index=12,Term=1}}.
   
   The fix in tests is either going through a follower state at the correct term,
   by calling becomeFollower(term, ...), or initializing from a correct HardState
   in storage.
   
   Property 2: For a MsgSnap message m, m.Term >= m.Snapshot.Metadata.Term,
   because the leader doesn't know of any higher term than its own, and hence
   can't send a message with such an inversion.
   
   This was broken in TestRestoreFromSnapMsg, and is now fixed.
   
   Signed-off-by: Pavel Kalinnikov <[email protected]>

   

   pav-kv committed Apr 14, 2023
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