core: allow to add several headers with StateRootInHeader on

Problem: with StateRootInHeader setting on only one header of height N+1
can be added to the chain of height N, because we need local stateroot
to verify headers (which is calculated for the last stored block N).
Thus, adding chunk of headers starting from the current chain's heigh
is impossible and (*Blockchain).AddHeaders doesn't have much sense.

Solution: verify header.PrevStateRoot only for header N+1. Rest of the
headers should be added without PrevStateRoot verification.

pkg/core/blockchain.go

@@ -782,6 +782,15 @@ func (bc *Blockchain) storeBlock(block *block.Block, txpool *mempool.Pool) error
 		// because changes applied are the ones from HALTed transactions.
 		return fmt.Errorf("error while trying to apply MPT changes: %w", err)
 	}
+	if bc.config.StateRootInHeader && bc.HeaderHeight() > sr.Index {
+		h, err := bc.GetHeader(bc.GetHeaderHash(int(sr.Index) + 1))
+		if err != nil {
+			return fmt.Errorf("failed to get next header: %w", err)
+		}
+		if h.PrevStateRoot != sr.Root {
+			return fmt.Errorf("local stateroot and next header's PrevStateRoot mismatch: %s vs %s", sr.Root.StringBE(), h.PrevStateRoot.StringBE())
+		}
+	}
 
 	if bc.config.SaveStorageBatch {
 		bc.lastBatch = cache.DAO.GetBatch()
@@ -1430,9 +1439,11 @@ var (
 
 func (bc *Blockchain) verifyHeader(currHeader, prevHeader *block.Header) error {
 	if bc.config.StateRootInHeader {
-		if sr := bc.stateRoot.CurrentLocalStateRoot(); currHeader.PrevStateRoot != sr {
-			return fmt.Errorf("%w: %s != %s",
-				ErrHdrInvalidStateRoot, currHeader.PrevStateRoot.StringLE(), sr.StringLE())
+		if bc.stateRoot.CurrentLocalHeight() == prevHeader.Index {
+			if sr := bc.stateRoot.CurrentLocalStateRoot(); currHeader.PrevStateRoot != sr {
+				return fmt.Errorf("%w: %s != %s",
+					ErrHdrInvalidStateRoot, currHeader.PrevStateRoot.StringLE(), sr.StringLE())
+			}
 		}
 	}
 	if prevHeader.Hash() != currHeader.PrevHash {

pkg/core/blockchain_test.go

@@ -158,6 +158,28 @@ func TestAddBlockStateRoot(t *testing.T) {
 	require.NoError(t, bc.AddBlock(b))
 }
 
+func TestAddHeadersStateRoot(t *testing.T) {
+	bc := newTestChainWithCustomCfg(t, func(c *config.Config) {
+		c.ProtocolConfiguration.StateRootInHeader = true
+	})
+
+	r := bc.stateRoot.CurrentLocalStateRoot()
+	h1 := bc.newBlock().Header
+
+	// invalid stateroot
+	h1.PrevStateRoot[0] ^= 0xFF
+	require.True(t, errors.Is(bc.AddHeaders(&h1), ErrHdrInvalidStateRoot))
+
+	// valid stateroot
+	h1.PrevStateRoot = r
+	require.NoError(t, bc.AddHeaders(&h1))
+
+	// unable to verify stateroot (stateroot is computed for block #0 only => can
+	// verify stateroot of header #1 only) => just store the header
+	h2 := newBlockWithState(bc.config, 2, h1.Hash(), nil).Header
+	require.NoError(t, bc.AddHeaders(&h2))
+}
+
 func TestAddBadBlock(t *testing.T) {
 	bc := newTestChain(t)
 	// It has ValidUntilBlock == 0, which is wrong

pkg/core/stateroot/module.go

@@ -70,6 +70,11 @@ func (s *Module) CurrentLocalStateRoot() util.Uint256 {
 	return s.currentLocal.Load().(util.Uint256)
 }
 
+// CurrentLocalHeight returns height of the local state root.
+func (s *Module) CurrentLocalHeight() uint32 {
+	return s.localHeight.Load()
+}
+
 // CurrentValidatedHeight returns current state root validated height.
 func (s *Module) CurrentValidatedHeight() uint32 {
 	return s.validatedHeight.Load()