[#74] neofs: Pay withdraw fee to processing contract

Processing contracts pays for cheque that transfer
assets back to the user, so user should transfer
some fee to this contract.

Withdraw fee defined in NeoFS global configuration.

Signed-off-by: Alex Vanin <alexey@nspcc.ru>

neofs/neofs_contract.go

@@ -53,12 +53,15 @@ type (
 
 const (
 	candidateFeeConfigKey = "InnerRingCandidateFee"
+	withdrawFeeConfigKey  = "WithdrawFee"
 
 	version = 3
 
 	alphabetKey   = "alphabet"
 	candidatesKey = "candidates"
 
+	processingContractKey = "processingScriptHash"
+
 	publicKeySize = 33
 
 	maxBalanceAmount = 9000 // Max integer of Fixed12 in JSON bound (2**53-1)
@@ -72,7 +75,7 @@ var (
 )
 
 // Init set up initial alphabet node keys.
-func Init(owner interop.PublicKey, args []interop.PublicKey) bool {
+func Init(owner, addrProc interop.Hash160, args []interop.PublicKey) bool {
 	ctx := storage.GetContext()
 
 	if !common.HasUpdateAccess(ctx) {
@@ -85,6 +88,10 @@ func Init(owner interop.PublicKey, args []interop.PublicKey) bool {
 		panic("neofs: at least one alphabet key must be provided")
 	}
 
+	if len(addrProc) != 20 {
+		panic("neofs: incorrect length of contract script hash")
+	}
+
 	for i := 0; i < len(args); i++ {
 		pub := args[i]
 		if len(pub) != publicKeySize {
@@ -98,6 +105,7 @@ func Init(owner interop.PublicKey, args []interop.PublicKey) bool {
 	common.SetSerialized(ctx, candidatesKey, []common.IRNode{})
 
 	storage.Put(ctx, common.OwnerKey, owner)
+	storage.Put(ctx, processingContractKey, addrProc)
 
 	runtime.Log("neofs: contract initialized")
 
@@ -246,7 +254,7 @@ func Deposit(from interop.Hash160, amount int, rcv interop.Hash160) bool {
 }
 
 // Withdraw initialize gas asset withdraw from NeoFS balance.
-func Withdraw(user []byte, amount int) bool {
+func Withdraw(user interop.Hash160, amount int) bool {
 	if !runtime.CheckWitness(user) {
 		panic("withdraw: you should be the owner of the wallet")
 	}
@@ -259,9 +267,20 @@ func Withdraw(user []byte, amount int) bool {
 		panic("withdraw: out of max amount limit")
 	}
 
-	amount = amount * 100000000
+	// transfer fee to proxy contract to pay cheque invocation
+	ctx := storage.GetContext()
+	fee := getConfig(ctx, withdrawFeeConfigKey).(int)
+	processingAddr := storage.Get(ctx, processingContractKey).(interop.Hash160)
 
+	transferred := gas.Transfer(user, processingAddr, fee, []byte{})
+	if !transferred {
+		panic("withdraw: failed to transfer withdraw fee, aborting")
+	}
+
+	// notify alphabet nodes
+	amount = amount * 100000000
 	tx := runtime.GetScriptContainer()
+
 	runtime.Notify("Withdraw", user, amount, tx.Hash)
 
 	return true