check: set lastBlockTime in PrepareRequest handler, fix #55

It's the earliest point, if a view change happens the timer is reset (because
new view comes with a new set of transactions, potentially picking up ones
received between views).

Signed-off-by: Roman Khimov <roman@nspcc.ru>

CHANGELOG.md

@@ -9,6 +9,8 @@ New features:
 Behaviour changes:
 
 Improvements:
+ * timer adjustment for most of the consensus time, more accurate block
+   intervals (#55)
 
 Bugs fixed:
  * inappropriate log on attempt to construct Commit for anti-MEV enabled WatchOnly

check.go

@@ -5,6 +5,13 @@ import (
 )
 
 func (d *DBFT[H]) checkPrepare() {
+	if d.lastBlockIndex != d.BlockIndex || d.lastBlockView != d.ViewNumber {
+		// Notice that lastBlockTimestamp is left unchanged because
+		// this must be the value from the last header.
+		d.lastBlockTime = d.Timer.Now()
+		d.lastBlockIndex = d.BlockIndex
+		d.lastBlockView = d.ViewNumber
+	}
 	if !d.hasAllTransactions() {
 		d.Logger.Debug("check prepare: some transactions are missing", zap.Any("hashes", d.MissingTransactions))
 		return
@@ -138,8 +145,6 @@ func (d *DBFT[H]) checkCommit() {
 		d.Logger.Fatal("block processing failed", zap.Error(err))
 	}
 
-	d.lastBlockIndex = d.BlockIndex
-	d.lastBlockTime = d.Timer.Now()
 	d.blockProcessed = true
 
 	// Do not initialize consensus process immediately. It's the caller's duty to

context.go

@@ -90,6 +90,7 @@ type Context[H Hash] struct {
 	lastBlockTimestamp uint64    // ns-precision timestamp from the last header (used for the next block timestamp calculations).
 	lastBlockTime      time.Time // Wall clock time of when the last block was first seen (used for timer adjustments).
 	lastBlockIndex     uint32
+	lastBlockView      byte
 }
 
 // N returns total number of validators.