rpc: add resolve and isAvailable NNS API to RPC client

pkg/rpc/client/native.go

@@ -3,9 +3,11 @@ package client
 // Various non-policy things from native contracts.
 
 import (
+	"errors"
 	"fmt"
 
 	"github.com/nspcc-dev/neo-go/pkg/core/native/nativenames"
+	"github.com/nspcc-dev/neo-go/pkg/core/native/nnsrecords"
 	"github.com/nspcc-dev/neo-go/pkg/core/native/noderoles"
 	"github.com/nspcc-dev/neo-go/pkg/crypto/keys"
 	"github.com/nspcc-dev/neo-go/pkg/smartcontract"
@@ -63,3 +65,54 @@ func (c *Client) GetDesignatedByRole(role noderoles.Role, index uint32) (keys.Pu
 	}
 	return topPublicKeysFromStack(result.Stack)
 }
+
+// NNSResolve invokes `resolve` method on a native NameService contract.
+func (c *Client) NNSResolve(name string, typ nnsrecords.Type) (string, error) {
+	if typ == nnsrecords.CNAME {
+		return "", errors.New("can't resolve CNAME record type")
+	}
+	rmHash, err := c.GetNativeContractHash(nativenames.NameService)
+	if err != nil {
+		return "", fmt.Errorf("failed to get native NameService hash: %w", err)
+	}
+	result, err := c.InvokeFunction(rmHash, "resolve", []smartcontract.Parameter{
+		{
+			Type:  smartcontract.StringType,
+			Value: name,
+		},
+		{
+			Type:  smartcontract.IntegerType,
+			Value: int64(typ),
+		},
+	}, nil)
+	if err != nil {
+		return "", err
+	}
+	err = getInvocationError(result)
+	if err != nil {
+		return "", fmt.Errorf("`resolve`: %w", err)
+	}
+	return topStringFromStack(result.Stack)
+}
+
+// NNSIsAvailable invokes `isAvailable` method on a native NameService contract.
+func (c *Client) NNSIsAvailable(name string) (bool, error) {
+	rmHash, err := c.GetNativeContractHash(nativenames.NameService)
+	if err != nil {
+		return false, fmt.Errorf("failed to get native NameService hash: %w", err)
+	}
+	result, err := c.InvokeFunction(rmHash, "isAvailable", []smartcontract.Parameter{
+		{
+			Type:  smartcontract.StringType,
+			Value: name,
+		},
+	}, nil)
+	if err != nil {
+		return false, err
+	}
+	err = getInvocationError(result)
+	if err != nil {
+		return false, fmt.Errorf("`isAvailable`: %w", err)
+	}
+	return topBoolFromStack(result.Stack)
+}