state: fix MPTRoot JSONization

Match C# implementation. It's easier to do this by changing the structure
itself.

pkg/core/state/mpt_root.go

@@ -9,10 +9,10 @@ import (
 
 // MPTRoot represents storage state root together with sign info.
 type MPTRoot struct {
-	Version byte                 `json:"version"`
-	Index   uint32               `json:"index"`
-	Root    util.Uint256         `json:"stateroot"`
-	Witness *transaction.Witness `json:"witness,omitempty"`
+	Version byte                  `json:"version"`
+	Index   uint32                `json:"index"`
+	Root    util.Uint256          `json:"roothash"`
+	Witness []transaction.Witness `json:"witnesses"`
 }
 
 // Hash returns hash of s.
@@ -39,20 +39,11 @@ func (s *MPTRoot) EncodeBinaryUnsigned(w *io.BinWriter) {
 // DecodeBinary implements io.Serializable.
 func (s *MPTRoot) DecodeBinary(r *io.BinReader) {
 	s.DecodeBinaryUnsigned(r)
-
-	var ws []transaction.Witness
-	r.ReadArray(&ws, 1)
-	if len(ws) == 1 {
-		s.Witness = &ws[0]
-	}
+	r.ReadArray(&s.Witness, 1)
 }
 
 // EncodeBinary implements io.Serializable.
 func (s *MPTRoot) EncodeBinary(w *io.BinWriter) {
 	s.EncodeBinaryUnsigned(w)
-	if s.Witness == nil {
-		w.WriteVarUint(0)
-	} else {
-		w.WriteArray([]*transaction.Witness{s.Witness})
-	}
+	w.WriteArray(s.Witness)
 }

pkg/core/state/mpt_root_test.go

@@ -17,6 +17,7 @@ func testStateRoot() *MPTRoot {
 		Version: byte(rand.Uint32()),
 		Index:   rand.Uint32(),
 		Root:    random.Uint256(),
+		Witness: []transaction.Witness{},
 	}
 }
 
@@ -25,10 +26,10 @@ func TestStateRoot_Serializable(t *testing.T) {
 	testserdes.EncodeDecodeBinary(t, r, new(MPTRoot))
 
 	t.Run("WithWitness", func(t *testing.T) {
-		r.Witness = &transaction.Witness{
+		r.Witness = []transaction.Witness{{
 			InvocationScript:   random.Bytes(10),
 			VerificationScript: random.Bytes(11),
-		}
+		}}
 		testserdes.EncodeDecodeBinary(t, r, new(MPTRoot))
 	})
 }
@@ -43,7 +44,7 @@ func TestMPTRoot_MarshalJSON(t *testing.T) {
 		js := []byte(`{
             "version": 1,
             "index": 3000000,
-            "stateroot": "0xb2fd7e368a848ef70d27cf44940a35237333ed05f1d971c9408f0eb285e0b6f3"
+            "roothash": "0xb2fd7e368a848ef70d27cf44940a35237333ed05f1d971c9408f0eb285e0b6f3"
         }`)
 
 		rs := new(MPTRoot)
@@ -51,7 +52,7 @@ func TestMPTRoot_MarshalJSON(t *testing.T) {
 
 		require.EqualValues(t, 1, rs.Version)
 		require.EqualValues(t, 3000000, rs.Index)
-		require.Nil(t, rs.Witness)
+		require.Equal(t, 0, len(rs.Witness))
 
 		u, err := util.Uint256DecodeStringLE("b2fd7e368a848ef70d27cf44940a35237333ed05f1d971c9408f0eb285e0b6f3")
 		require.NoError(t, err)

pkg/core/stateroot/module.go

@@ -132,6 +132,9 @@ func (s *Module) VerifyStateRoot(r *state.MPTRoot) error {
 	if err != nil {
 		return errors.New("can't get previous state root")
 	}
+	if len(r.Witness) != 1 {
+		return errors.New("no witness")
+	}
 	return s.verifyWitness(r)
 }
 
@@ -142,5 +145,5 @@ func (s *Module) verifyWitness(r *state.MPTRoot) error {
 	s.mtx.Lock()
 	h := s.getKeyCacheForHeight(r.Index).validatorsHash
 	s.mtx.Unlock()
-	return s.bc.VerifyWitness(h, r, r.Witness, maxVerificationGAS)
+	return s.bc.VerifyWitness(h, r, &r.Witness[0], maxVerificationGAS)
 }

pkg/core/stateroot/store.go

@@ -69,7 +69,7 @@ func (s *Module) AddStateRoot(sr *state.MPTRoot) error {
 	if err != nil {
 		return err
 	}
-	if local.Witness != nil {
+	if len(local.Witness) != 0 {
 		return nil
 	}
 	if err := s.putStateRoot(key, sr); err != nil {

pkg/core/stateroot_test.go

@@ -40,10 +40,10 @@ func testSignStateRoot(t *testing.T, r *state.MPTRoot, pubs keys.PublicKeys, acc
 
 	script, err := smartcontract.CreateMajorityMultiSigRedeemScript(pubs.Copy())
 	require.NoError(t, err)
-	r.Witness = &transaction.Witness{
+	r.Witness = []transaction.Witness{{
 		VerificationScript: script,
 		InvocationScript:   w.Bytes(),
-	}
+	}}
 	data, err := testserdes.EncodeBinary(stateroot.NewMessage(stateroot.RootT, r))
 	require.NoError(t, err)
 	return data
@@ -132,8 +132,8 @@ func TestStateRoot(t *testing.T) {
 
 	r, err = srv.GetStateRoot(updateIndex + 1)
 	require.NoError(t, err)
-	require.NotNil(t, r.Witness)
-	require.Equal(t, h, r.Witness.ScriptHash())
+	require.NotEqual(t, 0, len(r.Witness))
+	require.Equal(t, h, r.Witness[0].ScriptHash())
 }
 
 func TestStateRootInitNonZeroHeight(t *testing.T) {

pkg/services/stateroot/signature.go

@@ -81,8 +81,8 @@ func (r *incompleteRoot) finalize(stateValidators keys.PublicKeys) (*state.MPTRo
 	for i := range sigs {
 		emit.Bytes(w.BinWriter, sigs[i])
 	}
-	r.root.Witness = &transaction.Witness{
+	r.root.Witness = []transaction.Witness{{
 		InvocationScript: w.Bytes(),
-	}
+	}}
 	return r.root, true
 }