Introduce `StartRound` function to the backend (#95)

* Introduce StartRound function to the backend

* Add error to the StartRound signature

* Remove sequence aborting

core/backend.go

@@ -62,6 +62,9 @@ type Backend interface {
 	Verifier
 	ValidatorBackend
 
+	// StartRound notifies the backend implementation whenever new round is about to start
+	StartRound(view *proto.View) error
+
 	// BuildProposal builds a new proposal for the given view (height and round)
 	BuildProposal(view *proto.View) []byte
 

core/ibft.go

@@ -323,6 +323,10 @@ func (i *IBFT) RunSequence(ctx context.Context, h uint64) {
 	for {
 		view := i.state.getView()
 
+		if err := i.backend.StartRound(view); err != nil {
+			i.log.Error("failed to handle start round callback on backend", "round", view.Round, "err", err)
+		}
+
 		i.log.Info("round started", "round", view.Round)
 
 		currentRound := view.Round

core/mock_test.go

@@ -64,6 +64,7 @@ type buildRoundChangeMessageDelegate func(
 type insertProposalDelegate func(*proto.Proposal, []*messages.CommittedSeal)
 type idDelegate func() []byte
 type getVotingPowerDelegate func(uint64) (map[string]*big.Int, error)
+type startRoundDelegate func(*proto.View) error
 
 var _ Backend = &mockBackend{}
 
@@ -83,6 +84,7 @@ type mockBackend struct {
 	insertProposalFn          insertProposalDelegate
 	idFn                      idDelegate
 	getVotingPowerFn          getVotingPowerDelegate
+	startRoundFn              startRoundDelegate
 }
 
 func (m mockBackend) ID() []byte {
@@ -202,6 +204,14 @@ func (m mockBackend) GetVotingPowers(height uint64) (map[string]*big.Int, error)
 	return map[string]*big.Int{}, nil
 }
 
+func (m mockBackend) StartRound(view *proto.View) error {
+	if m.startRoundFn != nil {
+		return m.startRoundFn(view)
+	}
+
+	return nil
+}
+
 // Define delegation methods
 type multicastFnDelegate func(*proto.Message)