Fix negative ETA caused by rollback in vm.SetState (#3036)

snow/engine/snowman/bootstrap/bootstrapper.go

@@ -150,6 +150,14 @@ func (b *Bootstrapper) Clear(context.Context) error {
 }
 
 func (b *Bootstrapper) Start(ctx context.Context, startReqID uint32) error {
+	b.Ctx.State.Set(snow.EngineState{
+		Type:  p2p.EngineType_ENGINE_TYPE_SNOWMAN,
+		State: snow.Bootstrapping,
+	})
+	if err := b.VM.SetState(ctx, snow.Bootstrapping); err != nil {
+		return fmt.Errorf("failed to notify VM that bootstrapping has started: %w", err)
+	}
+
 	lastAccepted, err := b.getLastAccepted(ctx)
 	if err != nil {
 		return err
@@ -161,14 +169,6 @@ func (b *Bootstrapper) Start(ctx context.Context, startReqID uint32) error {
 		zap.Uint64("lastAcceptedHeight", lastAcceptedHeight),
 	)
 
-	b.Ctx.State.Set(snow.EngineState{
-		Type:  p2p.EngineType_ENGINE_TYPE_SNOWMAN,
-		State: snow.Bootstrapping,
-	})
-	if err := b.VM.SetState(ctx, snow.Bootstrapping); err != nil {
-		return fmt.Errorf("failed to notify VM that bootstrapping has started: %w", err)
-	}
-
 	// Set the starting height
 	b.startingHeight = lastAcceptedHeight
 	b.requestID = startReqID

snow/engine/snowman/bootstrap/bootstrapper_test.go

@@ -742,6 +742,37 @@ func TestBootstrapperReceiveStaleAncestorsMessage(t *testing.T) {
 	require.Equal(snow.Bootstrapping, config.Ctx.State.Get().State)
 }
 
+func TestBootstrapperRollbackOnSetState(t *testing.T) {
+	require := require.New(t)
+
+	config, _, _, vm := newConfig(t)
+
+	blks := snowmantest.BuildChain(2)
+	initializeVMWithBlockchain(vm, blks)
+
+	blks[1].StatusV = choices.Accepted
+
+	bs, err := New(
+		config,
+		func(context.Context, uint32) error {
+			config.Ctx.State.Set(snow.EngineState{
+				Type:  p2ppb.EngineType_ENGINE_TYPE_SNOWMAN,
+				State: snow.NormalOp,
+			})
+			return nil
+		},
+	)
+	require.NoError(err)
+
+	vm.SetStateF = func(context.Context, snow.State) error {
+		blks[1].StatusV = choices.Processing
+		return nil
+	}
+
+	require.NoError(bs.Start(context.Background(), 0))
+	require.Equal(blks[0].HeightV, bs.startingHeight)
+}
+
 func initializeVMWithBlockchain(vm *block.TestVM, blocks []*snowmantest.Block) {
 	vm.CantSetState = false
 	vm.LastAcceptedF = func(context.Context) (ids.ID, error) {