[#11] Add dns, nns resolver

Signed-off-by: Denis Kirillov <denis@nspcc.ru>

resolver/dns.go

@@ -0,0 +1,41 @@
+package resolver
+
+import (
+	"fmt"
+	"net"
+
+	cid "github.com/nspcc-dev/neofs-sdk-go/container/id"
+)
+
+const (
+	testnetDomain = ".containers.testnet.fs.neo.org"
+	mainnetDomain = ".containers.fs.neo.org"
+)
+
+// ResolveContainerTestnet request txt record name + '.containers.testnet.fs.neo.org' to default dns server.
+func ResolveContainerTestnet(name string) (*cid.ID, error) {
+	return ResolveContainerDomainName(name + testnetDomain)
+}
+
+// ResolveContainerMainnet request txt record name + '.containers.fs.neo.org' to default dns server.
+func ResolveContainerMainnet(name string) (*cid.ID, error) {
+	return ResolveContainerDomainName(name + mainnetDomain)
+}
+
+// ResolveContainerDomainName trys to resolve container domain name to container ID using system dns server.
+func ResolveContainerDomainName(domain string) (*cid.ID, error) {
+	results, err := net.LookupTXT(domain)
+	if err != nil {
+		return nil, err
+	}
+
+	cnrID := cid.New()
+	for _, res := range results {
+		if err = cnrID.Parse(res); err != nil {
+			continue
+		}
+		return cnrID, nil
+	}
+
+	return nil, fmt.Errorf("not found")
+}

resolver/nns.go

@@ -0,0 +1,130 @@
+package resolver
+
+import (
+	"context"
+	"fmt"
+
+	nns "github.com/nspcc-dev/neo-go/examples/nft-nd-nns"
+	"github.com/nspcc-dev/neo-go/pkg/rpc/client"
+	"github.com/nspcc-dev/neo-go/pkg/rpc/response/result"
+	"github.com/nspcc-dev/neo-go/pkg/smartcontract"
+	"github.com/nspcc-dev/neo-go/pkg/util"
+	"github.com/nspcc-dev/neo-go/pkg/vm"
+	"github.com/nspcc-dev/neo-go/pkg/vm/stackitem"
+	cid "github.com/nspcc-dev/neofs-sdk-go/container/id"
+)
+
+type NNSResolver interface {
+	// ResolveContainerName get record for domain name+'.container' from NNS contract.
+	ResolveContainerName(name string) (*cid.ID, error)
+}
+
+type nnsResolver struct {
+	rpc     *client.Client
+	nnsHash util.Uint160
+}
+
+const (
+	resolve         = "resolve"
+	containerDomain = ".container"
+)
+
+// NewNNSResolver creates resolver that can get records from NNS contract.
+func NewNNSResolver(ctx context.Context, address string) (NNSResolver, error) {
+	rpc, err := client.New(ctx, address, client.Options{})
+	if err != nil {
+		return nil, err
+	}
+	if err = rpc.Init(); err != nil {
+		return nil, err
+	}
+
+	nnsContract, err := rpc.GetContractStateByID(1)
+	if err != nil {
+		return nil, err
+	}
+
+	return &nnsResolver{
+		rpc:     rpc,
+		nnsHash: nnsContract.Hash,
+	}, nil
+}
+
+func (n *nnsResolver) ResolveContainerName(name string) (*cid.ID, error) {
+	res, err := n.rpc.InvokeFunction(n.nnsHash, resolve, []smartcontract.Parameter{
+		{
+			Type:  smartcontract.StringType,
+			Value: name + containerDomain,
+		},
+		{
+			Type:  smartcontract.IntegerType,
+			Value: int64(nns.TXT),
+		},
+	}, nil)
+	if err != nil {
+		return nil, err
+	}
+	if err = getInvocationError(res); err != nil {
+		return nil, err
+	}
+
+	arr, err := getArrString(res.Stack)
+	if err != nil {
+		return nil, err
+	}
+
+	cnrID := cid.New()
+	for _, rec := range arr {
+		if err = cnrID.Parse(rec); err != nil {
+			continue
+		}
+		return cnrID, nil
+	}
+
+	return nil, fmt.Errorf("not found")
+}
+
+func getArrString(st []stackitem.Item) ([]string, error) {
+	array, err := getArray(st)
+	if err != nil {
+		return nil, err
+	}
+
+	res := make([]string, len(array))
+	for i, item := range array {
+		bs, err := item.TryBytes()
+		if err != nil {
+			return nil, err
+		}
+		res[i] = string(bs)
+	}
+
+	return res, nil
+}
+
+func getArray(st []stackitem.Item) ([]stackitem.Item, error) {
+	index := len(st) - 1 // top stack element is last in the array
+	arr, err := st[index].Convert(stackitem.ArrayT)
+	if err != nil {
+		return nil, err
+	}
+	if _, ok := arr.(stackitem.Null); ok {
+		return nil, nil
+	}
+
+	iterator, ok := arr.Value().([]stackitem.Item)
+	if !ok {
+		return nil, fmt.Errorf("bad conversion")
+	}
+	return iterator, nil
+}
+
+func getInvocationError(result *result.Invoke) error {
+	if result.State != vm.HaltState.String() {
+		return fmt.Errorf("invocation failed: %s", result.FaultException)
+	}
+	if len(result.Stack) == 0 {
+		return fmt.Errorf("result stack is empty")
+	}
+	return nil
+}