core: fix Storage.Get to return Null when there is no value

Match C# implementation and fix state inconsistency at block 249920 of
preview2 testnet. Make our Go Storage.Get return nil and adapt
examples/tests.

docs/compiler.md

@@ -236,7 +236,11 @@ type Token struct {
 
 func (t Token) AddToCirculation(amount int) bool {
 	ctx := storage.Context()
-	inCirc := storage.Get(ctx, "in_circ").(int)
+	var inCirc int
+	val := storage.Get(ctx, "in_circ")
+	if val != nil {
+		inCirc = val.(int)
+	}
 	inCirc += amount
 	storage.Put(ctx, "in_circ", inCirc)
 	return true

examples/token-sale/token_sale.go

@@ -71,15 +71,25 @@ func NewTokenConfig() TokenConfig {
 	}
 }
 
+// getIntFromDB is a helper that checks for nil result of storage.Get and returns
+// zero as the default value.
+func getIntFromDB(ctx storage.Context, key []byte) int {
+	var res int
+	val := storage.Get(ctx, key)
+	if val != nil {
+		res = val.(int)
+	}
+	return res
+}
+
 // InCirculation return the amount of total tokens that are in circulation.
 func (t TokenConfig) InCirculation(ctx storage.Context) int {
-	amount := storage.Get(ctx, t.CirculationKey)
-	return amount.(int)
+	return getIntFromDB(ctx, t.CirculationKey)
 }
 
 // AddToCirculation sets the given amount as "in circulation" in the storage.
 func (t TokenConfig) AddToCirculation(ctx storage.Context, amount int) bool {
-	supply := storage.Get(ctx, t.CirculationKey).(int)
+	supply := getIntFromDB(ctx, t.CirculationKey)
 	supply += amount
 	storage.Put(ctx, t.CirculationKey, supply)
 	return true
@@ -88,8 +98,8 @@ func (t TokenConfig) AddToCirculation(ctx storage.Context, amount int) bool {
 // TokenSaleAvailableAmount returns the total amount of available tokens left
 // to be distributed.
 func (t TokenConfig) TokenSaleAvailableAmount(ctx storage.Context) int {
-	inCirc := storage.Get(ctx, t.CirculationKey)
-	return t.TotalSupply - inCirc.(int)
+	inCirc := getIntFromDB(ctx, t.CirculationKey)
+	return t.TotalSupply - inCirc
 }
 
 // Main smart contract entry point.
@@ -128,11 +138,11 @@ func handleOperation(op string, args []interface{}, ctx storage.Context, cfg Tok
 		return cfg.Symbol
 	}
 	if op == "totalSupply" {
-		return storage.Get(ctx, cfg.CirculationKey)
+		return getIntFromDB(ctx, cfg.CirculationKey)
 	}
 	if op == "balanceOf" {
 		if len(args) == 1 {
-			return storage.Get(ctx, args[0].([]byte))
+			return getIntFromDB(ctx, args[0].([]byte))
 		}
 	}
 	if op == "transfer" {
@@ -177,7 +187,7 @@ func transfer(cfg TokenConfig, ctx storage.Context, from, to []byte, amount int)
 	if amount <= 0 || len(to) != 20 || !runtime.CheckWitness(from) {
 		return false
 	}
-	amountFrom := storage.Get(ctx, from).(int)
+	amountFrom := getIntFromDB(ctx, from)
 	if amountFrom < amount {
 		return false
 	}
@@ -187,7 +197,7 @@ func transfer(cfg TokenConfig, ctx storage.Context, from, to []byte, amount int)
 		diff := amountFrom - amount
 		storage.Put(ctx, from, diff)
 	}
-	amountTo := storage.Get(ctx, to).(int)
+	amountTo := getIntFromDB(ctx, to)
 	totalAmountTo := amountTo + amount
 	storage.Put(ctx, to, totalAmountTo)
 	return true
@@ -201,15 +211,15 @@ func transferFrom(cfg TokenConfig, ctx storage.Context, from, to []byte, amount
 	if len(availableKey) != 40 {
 		return false
 	}
-	availableTo := storage.Get(ctx, availableKey).(int)
+	availableTo := getIntFromDB(ctx, availableKey)
 	if availableTo < amount {
 		return false
 	}
-	fromBalance := storage.Get(ctx, from).(int)
+	fromBalance := getIntFromDB(ctx, from)
 	if fromBalance < amount {
 		return false
 	}
-	toBalance := storage.Get(ctx, to).(int)
+	toBalance := getIntFromDB(ctx, to)
 	newFromBalance := fromBalance - amount
 	newToBalance := toBalance + amount
 	storage.Put(ctx, to, newToBalance)
@@ -231,7 +241,7 @@ func approve(ctx storage.Context, owner, spender []byte, amount int) bool {
 	if len(spender) != 20 {
 		return false
 	}
-	toSpend := storage.Get(ctx, owner).(int)
+	toSpend := getIntFromDB(ctx, owner)
 	if toSpend < amount {
 		return false
 	}
@@ -246,5 +256,5 @@ func approve(ctx storage.Context, owner, spender []byte, amount int) bool {
 
 func allowance(ctx storage.Context, from, to []byte) int {
 	key := append(from, to...)
-	return storage.Get(ctx, key).(int)
+	return getIntFromDB(ctx, key)
 }

examples/token/nep5/nep5.go

@@ -22,14 +22,25 @@ type Token struct {
 	CirculationKey string
 }
 
+// getIntFromDB is a helper that checks for nil result of storage.Get and returns
+// zero as the default value.
+func getIntFromDB(ctx storage.Context, key []byte) int {
+	var res int
+	val := storage.Get(ctx, key)
+	if val != nil {
+		res = val.(int)
+	}
+	return res
+}
+
 // GetSupply gets the token totalSupply value from VM storage
 func (t Token) GetSupply(ctx storage.Context) interface{} {
-	return storage.Get(ctx, t.CirculationKey)
+	return getIntFromDB(ctx, []byte(t.CirculationKey))
 }
 
 // BalanceOf gets the token balance of a specific address
 func (t Token) BalanceOf(ctx storage.Context, hodler []byte) interface{} {
-	return storage.Get(ctx, hodler)
+	return getIntFromDB(ctx, hodler)
 }
 
 // Transfer token from one user to another
@@ -48,7 +59,7 @@ func (t Token) Transfer(ctx storage.Context, from []byte, to []byte, amount int)
 		storage.Put(ctx, from, diff)
 	}
 
-	amountTo := storage.Get(ctx, to).(int)
+	amountTo := getIntFromDB(ctx, to)
 	totalAmountTo := amountTo + amount
 	storage.Put(ctx, to, totalAmountTo)
 	runtime.Notify("transfer", from, to, amount)
@@ -61,7 +72,7 @@ func (t Token) CanTransfer(ctx storage.Context, from []byte, to []byte, amount i
 		return -1
 	}
 
-	amountFrom := storage.Get(ctx, from).(int)
+	amountFrom := getIntFromDB(ctx, from)
 	if amountFrom < amount {
 		return -1
 	}
@@ -98,8 +109,8 @@ func (t Token) Mint(ctx storage.Context, to []byte) bool {
 	if !IsUsableAddress(t.Owner) {
 		return false
 	}
-	minted := storage.Get(ctx, []byte("minted")).(bool)
-	if minted {
+	minted := storage.Get(ctx, []byte("minted"))
+	if minted != nil && minted.(bool) == true {
 		return false
 	}
 

pkg/core/interop_system.go

@@ -289,7 +289,7 @@ func storageGet(ic *interop.Context, v *vm.VM) error {
 	if si != nil && si.Value != nil {
 		v.Estack().PushVal(si.Value)
 	} else {
-		v.Estack().PushVal([]byte{})
+		v.Estack().PushVal(stackitem.Null{})
 	}
 	return nil
 }

pkg/interop/storage/storage.go

@@ -38,9 +38,9 @@ func GetReadOnlyContext() Context { return Context{} }
 func Put(ctx Context, key interface{}, value interface{}) {}
 
 // Get retrieves value stored for the given key using given Context. See Put
-// documentation on possible key and value types. This function uses
-// `System.Storage.Get` syscall.
-func Get(ctx Context, key interface{}) interface{} { return 0 }
+// documentation on possible key and value types. If the value is not present in
+// the database it returns nil. This function uses `System.Storage.Get` syscall.
+func Get(ctx Context, key interface{}) interface{} { return nil }
 
 // Delete removes key-value pair from storage by the given key using given
 // Context. See Put documentation on possible key types. This function uses

pkg/rpc/server/server_test.go

@@ -50,8 +50,8 @@ type rpcTestCase struct {
 	check  func(t *testing.T, e *executor, result interface{})
 }
 
-const testContractHash = "e65ff7b3a02d207b584a5c27057d4e9862ef01da"
-const deploymentTxHash = "b0428600383ec7f7b06734978a24dbe81edc87b781f58c0614f122c735d8cf6a"
+const testContractHash = "10e262ef80c76bdecca287a2c047841fc02c3129"
+const deploymentTxHash = "ad8b149c799d4b2337162b0ad23e0ba8845cddb9cfca8a45587ee207015d2a7c"
 
 var rpcTestCases = map[string][]rpcTestCase{
 	"getapplicationlog": {

pkg/rpc/server/testdata/test_contract.go

@@ -32,7 +32,11 @@ func Main(operation string, args []interface{}) interface{} {
 			runtime.Log("invalid address")
 			return false
 		}
-		amount := storage.Get(ctx, addr).(int)
+		var amount int
+		val := storage.Get(ctx, addr)
+		if val != nil {
+			amount = val.(int)
+		}
 		runtime.Notify("balanceOf", addr, amount)
 		return amount
 	case "transfer":
@@ -53,7 +57,11 @@ func Main(operation string, args []interface{}) interface{} {
 			return false
 		}
 
-		fromBalance := storage.Get(ctx, from).(int)
+		var fromBalance int
+		val := storage.Get(ctx, from)
+		if val != nil {
+			fromBalance = val.(int)
+		}
 		if fromBalance < amount {
 			runtime.Log("insufficient funds")
 			return false
@@ -61,7 +69,11 @@ func Main(operation string, args []interface{}) interface{} {
 		fromBalance -= amount
 		storage.Put(ctx, from, fromBalance)
 
-		toBalance := storage.Get(ctx, to).(int)
+		var toBalance int
+		val = storage.Get(ctx, to)
+		if val != nil {
+			toBalance = val.(int)
+		}
 		toBalance += amount
 		storage.Put(ctx, to, toBalance)