core: provide monotonically increasing ID for contracts

ID is a contract identifier which doesn't change during migration.
It is also used as a part of storage context instead of contract hash.

pkg/core/dao/dao.go

@@ -31,6 +31,7 @@ type DAO interface {
 	GetHeaderHashes() ([]util.Uint256, error)
 	GetNEP5Balances(acc util.Uint160) (*state.NEP5Balances, error)
 	GetNEP5TransferLog(acc util.Uint160, index uint32) (*state.NEP5TransferLog, error)
+	GetNextContractID() (int32, error)
 	GetStorageItem(scripthash util.Uint160, key []byte) *state.StorageItem
 	GetStorageItems(hash util.Uint160) (map[string]*state.StorageItem, error)
 	GetStorageItemsWithPrefix(hash util.Uint160, prefix []byte) (map[string]*state.StorageItem, error)
@@ -45,6 +46,7 @@ type DAO interface {
 	PutCurrentHeader(hashAndIndex []byte) error
 	PutNEP5Balances(acc util.Uint160, bs *state.NEP5Balances) error
 	PutNEP5TransferLog(acc util.Uint160, index uint32, lg *state.NEP5TransferLog) error
+	PutNextContractID(id int32) error
 	PutStorageItem(scripthash util.Uint160, key []byte, si *state.StorageItem) error
 	PutVersion(v string) error
 	StoreAsBlock(block *block.Block) error
@@ -169,6 +171,27 @@ func (dao *Simple) DeleteContractState(hash util.Uint160) error {
 	return dao.Store.Delete(key)
 }
 
+// GetNextContractID returns id for the next contract and increases stored id.
+func (dao *Simple) GetNextContractID() (int32, error) {
+	key := storage.SYSContractID.Bytes()
+	data, err := dao.Store.Get(key)
+	if err != nil {
+		if err == storage.ErrKeyNotFound {
+			err = nil
+		}
+		return 0, err
+	}
+	return int32(binary.LittleEndian.Uint32(data)), nil
+}
+
+// PutNextContractID sets next contract id to id.
+func (dao *Simple) PutNextContractID(id int32) error {
+	key := storage.SYSContractID.Bytes()
+	data := make([]byte, 4)
+	binary.LittleEndian.PutUint32(data, uint32(id))
+	return dao.Store.Put(key, data)
+}
+
 // -- end contracts.
 
 // -- start nep5 balances.

pkg/core/dao/dao_test.go

@@ -82,6 +82,17 @@ func TestDeleteContractState(t *testing.T) {
 	require.Nil(t, gotContractState)
 }
 
+func TestSimple_GetNextContractID(t *testing.T) {
+	dao := NewSimple(storage.NewMemoryStore())
+	id, err := dao.GetNextContractID()
+	require.NoError(t, err)
+	require.EqualValues(t, 0, id)
+	require.NoError(t, dao.PutNextContractID(10))
+	id, err = dao.GetNextContractID()
+	require.NoError(t, err)
+	require.EqualValues(t, 10, id)
+}
+
 func TestPutGetAppExecResult(t *testing.T) {
 	dao := NewSimple(storage.NewMemoryStore())
 	hash := random.Uint256()

pkg/core/interop_neo.go

@@ -98,7 +98,16 @@ func contractCreate(ic *interop.Context, v *vm.VM) error {
 	contract, err := ic.DAO.GetContractState(newcontract.ScriptHash())
 	if contract != nil {
 		return errors.New("contract already exists")
-	} else if err := ic.DAO.PutContractState(newcontract); err != nil {
+	}
+	id, err := ic.DAO.GetNextContractID()
+	if err != nil {
+		return err
+	}
+	newcontract.ID = id
+	if err := ic.DAO.PutNextContractID(id); err != nil {
+		return err
+	}
+	if err := ic.DAO.PutContractState(newcontract); err != nil {
 		return err
 	}
 	v.Estack().PushVal(stackitem.NewInterop(newcontract))

pkg/core/storage/store.go

@@ -18,6 +18,7 @@ const (
 	IXHeaderHashList KeyPrefix = 0x80
 	SYSCurrentBlock  KeyPrefix = 0xc0
 	SYSCurrentHeader KeyPrefix = 0xc1
+	SYSContractID    KeyPrefix = 0xc2
 	SYSVersion       KeyPrefix = 0xf0
 )