[#42] Add ResolveContractHash method

Signed-off-by: Pavel Pogodaev <p.pogodaev@yadro.com>

ns/nns.go

@@ -10,6 +10,7 @@ import (
 	"git.frostfs.info/TrueCloudLab/frostfs-sdk-go/container"
 	cid "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/container/id"
 	"github.com/nspcc-dev/neo-go/pkg/core/state"
+	"github.com/nspcc-dev/neo-go/pkg/encoding/address"
 	"github.com/nspcc-dev/neo-go/pkg/neorpc/result"
 	"github.com/nspcc-dev/neo-go/pkg/rpcclient"
 	"github.com/nspcc-dev/neo-go/pkg/rpcclient/invoker"
@@ -116,3 +117,46 @@ func (n *NNS) ResolveContainerDomain(domain container.Domain) (cid.ID, error) {
 
 	return cid.ID{}, errNotFound
 }
+
+// ResolveContractHash looks up for NNS TXT records for the given container domain
+// by calling `resolve` method of NNS contract. Returns the first record which represents
+// valid contract hash 20 bytes long unsigned integer. Otherwise, returns an error.
+//
+// ResolveContractHash MUST NOT be called before successful Dial.
+//
+// See also https://docs.neo.org/docs/en-us/reference/nns.html.
+func (n *NNS) ResolveContractHash(domain container.Domain) (util.Uint160, error) {
+	item, err := unwrap.Item(n.invoker.Call(n.nnsContract, "resolve",
+		domain.Name()+"."+domain.Zone(), int64(nns.TXT),
+	))
+	if err != nil {
+		return util.Uint160{}, fmt.Errorf("contract invocation: %w", err)
+	}
+
+	if _, ok := item.(stackitem.Null); !ok {
+		arr, ok := item.Value().([]stackitem.Item)
+		if !ok {
+			// unexpected for types from stackitem package
+			return util.Uint160{}, errors.New("invalid cast to stack item slice")
+		}
+
+		for i := range arr {
+			recordValue, err := arr[i].TryBytes()
+			if err != nil {
+				return util.Uint160{}, fmt.Errorf("convert array item to byte slice: %w", err)
+			}
+
+			strRecordValue := string(recordValue)
+			scriptHash, err := address.StringToUint160(strRecordValue)
+			if err == nil {
+				return scriptHash, nil
+			}
+			scriptHash, err = util.Uint160DecodeStringLE(strRecordValue)
+			if err == nil {
+				return scriptHash, nil
+			}
+		}
+	}
+
+	return util.Uint160{}, errNotFound
+}

ns/nns_test.go

@@ -154,3 +154,86 @@ func TestNNS_ResolveContainerDomain(t *testing.T) {
 		require.Equal(t, id, res)
 	})
 }
+
+func TestNNS_ResolveContractHash(t *testing.T) {
+	var testContainerDomain container.Domain
+	testContainerDomain.SetName("some_container")
+
+	var nnsContract util.Uint160
+
+	rand.Read(nnsContract[:])
+
+	testC := &testNeoClient{
+		t:                t,
+		expectedContract: nnsContract,
+	}
+
+	n := NNS{
+		nnsContract: nnsContract,
+		invoker:     testC,
+	}
+
+	t.Run("invocation failure", func(t *testing.T) {
+		err1 := errors.New("invoke err")
+		testC.err = err1
+
+		_, err2 := n.ResolveContractHash(testContainerDomain)
+		require.ErrorIs(t, err2, err1)
+	})
+
+	testC.err = nil
+
+	t.Run("fault exception", func(t *testing.T) {
+		_, err := n.ResolveContractHash(testContainerDomain)
+		require.Error(t, err)
+	})
+
+	testC.res.State = vmstate.Halt.String()
+
+	t.Run("empty stack", func(t *testing.T) {
+		_, err := n.ResolveContractHash(testContainerDomain)
+		require.Error(t, err)
+	})
+
+	testC.res.Stack = make([]stackitem.Item, 1)
+
+	t.Run("non-array last stack item", func(t *testing.T) {
+		testC.res.Stack[0] = stackitem.NewBigInteger(big.NewInt(11))
+
+		_, err := n.ResolveContractHash(testContainerDomain)
+		require.Error(t, err)
+	})
+
+	t.Run("null array", func(t *testing.T) {
+		testC.res.Stack[0] = stackitem.Null{}
+
+		_, err := n.ResolveContractHash(testContainerDomain)
+		require.ErrorIs(t, err, errNotFound)
+	})
+
+	t.Run("array stack item with non-slice value", func(t *testing.T) {
+		testC.res.Stack[0] = brokenArrayStackItem{}
+
+		_, err := n.ResolveContractHash(testContainerDomain)
+		require.Error(t, err)
+	})
+
+	arr := make([]stackitem.Item, 2)
+	testC.res.Stack[0] = stackitem.NewArray(arr)
+
+	t.Run("non-bytes array element", func(t *testing.T) {
+		arr[0] = stackitem.NewArray(nil)
+
+		_, err := n.ResolveContractHash(testContainerDomain)
+		require.Error(t, err)
+	})
+
+	arr[0] = stackitem.NewByteArray([]byte("some byte array 1"))
+
+	t.Run("non-container array elements", func(t *testing.T) {
+		arr[1] = stackitem.NewByteArray([]byte("some byte array 2"))
+
+		_, err := n.ResolveContractHash(testContainerDomain)
+		require.Error(t, err)
+	})
+}