[#51] proxy: Add proxy contract

Proxy contract used by notary contract as a main tx
payment provider. `Verify` function verifies if
main tx contains multisig of 5\7 inner ring
nodes. If so, then contract pays for transaction.
This is easier than support multisig wallet with
GAS assets, because inner ring can change, therefore
multisig wallet can change periodically.

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

Makefile

@@ -9,7 +9,7 @@ all: sidechain mainnet
 sidechain: alphabet morph
 
 alphabet_sc = alphabet
-morph_sc = audit balance container neofsid netmap reputation
+morph_sc = audit balance container neofsid netmap proxy reputation
 mainnet_sc = neofs
 
 define sc_template

common/ir.go

@@ -7,7 +7,10 @@ import (
 	"github.com/nspcc-dev/neo-go/pkg/interop/storage"
 )
 
-const irListMethod = "innerRingList"
+const (
+	irListMethod    = "innerRingList"
+	multiaddrMethod = "multiaddress"
+)
 
 type IRNode struct {
 	PublicKey []byte
@@ -39,3 +42,17 @@ func InnerRingListViaStorage(ctx storage.Context, key interface{}) []IRNode {
 func InnerRingList(sc interop.Hash160) []IRNode {
 	return contract.Call(sc, irListMethod, contract.ReadOnly).([]IRNode)
 }
+
+// InnerRingMultiAddressViaStorage returns multiaddress of inner ring public
+// keys by invoking netmap contract, which scripthash stored in the contract
+// storage by the key `key`.
+func InnerRingMultiAddressViaStorage(ctx storage.Context, key interface{}) []byte {
+	sc := storage.Get(ctx, key).([]byte)
+	return InnerRingMultiAddress(sc)
+}
+
+// InnerRingMultiAddress returns multiaddress of inner ring public keys by
+// invoking netmap contract.
+func InnerRingMultiAddress(sc interop.Hash160) []byte {
+	return contract.Call(sc, multiaddrMethod, contract.ReadOnly).([]byte)
+}

proxy/config.yml

@@ -0,0 +1 @@
+name: "NeoFS Notary Proxy"

proxy/proxy_contract.go

@@ -0,0 +1,65 @@
+package proxycontract
+
+import (
+	"github.com/nspcc-dev/neo-go/pkg/interop"
+	"github.com/nspcc-dev/neo-go/pkg/interop/native/gas"
+	"github.com/nspcc-dev/neo-go/pkg/interop/native/management"
+	"github.com/nspcc-dev/neo-go/pkg/interop/runtime"
+	"github.com/nspcc-dev/neo-go/pkg/interop/storage"
+	"github.com/nspcc-dev/neofs-contract/common"
+)
+
+const (
+	version = 1
+
+	netmapContractKey = "netmapScriptHash"
+)
+
+var ctx storage.Context
+
+func init() {
+	ctx = storage.GetContext()
+}
+
+func OnNEP17Payment(from interop.Hash160, amount int, data interface{}) {
+	caller := runtime.GetCallingScriptHash()
+	if !common.BytesEqual(caller, []byte(gas.Hash)) {
+		panic("onNEP17Payment: alphabet contract accepts GAS only")
+	}
+}
+
+func Init(owner interop.Hash160, addrNetmap []byte) {
+	if !common.HasUpdateAccess(ctx) {
+		panic("only owner can reinitialize contract")
+	}
+
+	if len(addrNetmap) != 20 {
+		panic("init: incorrect length of contract script hash")
+	}
+
+	storage.Put(ctx, common.OwnerKey, owner)
+	storage.Put(ctx, netmapContractKey, addrNetmap)
+
+	runtime.Log("proxy contract initialized")
+}
+
+func Migrate(script []byte, manifest []byte) bool {
+	if !common.HasUpdateAccess(ctx) {
+		runtime.Log("only owner can update contract")
+		return false
+	}
+
+	management.Update(script, manifest)
+	runtime.Log("proxy contract updated")
+
+	return true
+}
+
+func Verify() bool {
+	sig := common.InnerRingMultiAddressViaStorage(ctx, netmapContractKey)
+	return runtime.CheckWitness(sig)
+}
+
+func Version() int {
+	return version
+}