[#179] resolver: Refactor and document the package

Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>

resolver/dns.go

@@ -1,41 +1,35 @@
 package resolver
 
 import (
-	"fmt"
 	"net"
 
 	cid "github.com/nspcc-dev/neofs-sdk-go/container/id"
 )
 
-const (
+// DNS looks up NeoFS names using system DNS.
-	testnetDomain = ".containers.testnet.fs.neo.org"
+//
-	mainnetDomain = ".containers.fs.neo.org"
+// See also net package.
-)
+type DNS struct{}
 
-// ResolveContainerTestnet request txt record name + '.containers.testnet.fs.neo.org' to default dns server.
+// ResolveContainerName looks up for DNS TXT records for the given domain name
-func ResolveContainerTestnet(name string) (*cid.ID, error) {
+// and returns the first one which represents valid container ID in a string format.
-	return ResolveContainerDomainName(name + testnetDomain)
+// Otherwise, returns an error.
-}
+//
-
+// See also net.LookupTXT.
-// ResolveContainerMainnet request txt record name + '.containers.fs.neo.org' to default dns server.
+func (x *DNS) ResolveContainerName(name string) (*cid.ID, error) {
-func ResolveContainerMainnet(name string) (*cid.ID, error) {
+	records, err := net.LookupTXT(name)
-	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()
+	var id cid.ID
-	for _, res := range results {
+
-		if err = cnrID.Parse(res); err != nil {
+	for i := range records {
-			continue
+		err = id.Parse(records[i])
+		if err == nil {
+			return &id, nil
 		}
-		return cnrID, nil
 	}
 
-	return nil, fmt.Errorf("not found")
+	return nil, errNotFound
 }

resolver/doc.go

@@ -0,0 +1,22 @@
+/*
+Package resolver provides functionality of NeoFS name system.
+
+DNS type is designed to resolve NeoFS-related names using Domain Name System:
+	const containerName = "some-container"
+
+	var dns DNS
+
+	containerID, err := dns.ResolveContainerName(containerName)
+	// ...
+
+NNS type is designed to resolve NeoFS-related names using Neo Name Service:
+	var nns NNS
+
+	err := nns.Dial(nnsServerAddress)
+	// ...
+
+	containerID, err := nns.ResolveContainerName(containerName)
+	// ...
+
+*/
+package resolver

resolver/nns.go

@@ -1,10 +1,12 @@
 package resolver
 
 import (
+	"context"
+	"errors"
 	"fmt"
 
 	nns "github.com/nspcc-dev/neo-go/examples/nft-nd-nns"
-	"github.com/nspcc-dev/neo-go/pkg/rpc/client"
+	neoclient "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"
@@ -13,109 +15,103 @@ import (
 	cid "github.com/nspcc-dev/neofs-sdk-go/container/id"
 )
 
-type NNSResolver interface {
+// NNS looks up NeoFS names using Neo Name Service.
-	// ResolveContainerName get record for domain name+'.container' from NNS contract.
+//
-	ResolveContainerName(name string) (*cid.ID, error)
+// Instances are created with a variable declaration. Before work, the connection
+// to the NNS server MUST BE established using Dial method.
+type NNS struct {
+	nnsContract util.Uint160
+
+	// neoclient.Client interface wrapper, needed for testing
+	neoClient interface {
+		invoke(contract util.Uint160, method string, prm []smartcontract.Parameter) (*result.Invoke, error)
+	}
 }
 
-type nnsResolver struct {
+// client is a core implementation of internal NNS.neoClient which is used by NNS.Dial.
-	rpc     *client.Client
+type client neoclient.Client
-	nnsHash util.Uint160
+
+func (x *client) invoke(contract util.Uint160, method string, prm []smartcontract.Parameter) (*result.Invoke, error) {
+	return (*neoclient.Client)(x).InvokeFunction(contract, method, prm, nil)
 }
 
-const (
+// Dial connects to the address of the NNS server. If fails, the instance
-	resolve         = "resolve"
+// SHOULD NOT be used.
-	containerDomain = ".container"
+func (n *NNS) Dial(address string) error {
-)
+	cli, err := neoclient.New(context.Background(), address, neoclient.Options{})
-
-// NewNNSResolver creates resolver that can get records from NNS contract.
-func NewNNSResolver(rpc *client.Client) (NNSResolver, error) {
-	nnsContract, err := rpc.GetContractStateByID(1)
 	if err != nil {
-		return nil, err
+		return fmt.Errorf("create neo client: %w", err)
 	}
 
-	return &nnsResolver{
+	if err = cli.Init(); err != nil {
-		rpc:     rpc,
+		return fmt.Errorf("initialize neo client: %w", err)
-		nnsHash: nnsContract.Hash,
+	}
-	}, nil
+
+	nnsContract, err := cli.GetContractStateByID(1)
+	if err != nil {
+		return fmt.Errorf("get NNS contract state: %w", err)
+	}
+
+	n.neoClient = (*client)(cli)
+	n.nnsContract = nnsContract.Hash
+
+	return nil
 }
 
-func (n *nnsResolver) ResolveContainerName(name string) (*cid.ID, error) {
+// ResolveContainerName looks up for NNS TXT records for the given container name
-	res, err := n.rpc.InvokeFunction(n.nnsHash, resolve, []smartcontract.Parameter{
+// by calling `resolve` method of NNS contract. Returns the first record which represents
+// valid container ID in a string format. Otherwise, returns an error.
+//
+// ResolveContainerName MUST NOT be called before successful Dial.
+//
+// See also https://docs.neo.org/docs/en-us/reference/nns.html.
+func (n *NNS) ResolveContainerName(name string) (*cid.ID, error) {
+	res, err := n.neoClient.invoke(n.nnsContract, "resolve", []smartcontract.Parameter{
 		{
 			Type:  smartcontract.StringType,
-			Value: name + containerDomain,
+			Value: name + ".container",
 		},
 		{
 			Type:  smartcontract.IntegerType,
 			Value: int64(nns.TXT),
 		},
-	}, nil)
+	})
 	if err != nil {
-		return nil, err
+		return nil, fmt.Errorf("invoke NNS contract: %w", err)
-	}
-	if err = getInvocationError(res); err != nil {
-		return nil, err
 	}
 
-	arr, err := getArrString(res.Stack)
+	if res.State != vm.HaltState.String() {
+		return nil, fmt.Errorf("NNS contract fault exception: %s", res.FaultException)
+	} else if len(res.Stack) == 0 {
+		return nil, errors.New("empty stack in invocation result")
+	}
+
+	itemArr, err := res.Stack[len(res.Stack)-1].Convert(stackitem.ArrayT) // top stack element is last in the array
 	if err != nil {
-		return nil, err
+		return nil, fmt.Errorf("convert stack item to %s", stackitem.ArrayT)
 	}
 
-	cnrID := cid.New()
+	if _, ok := itemArr.(stackitem.Null); !ok {
-	for _, rec := range arr {
+		arr, ok := itemArr.Value().([]stackitem.Item)
-		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")
+			// unexpected for types from stackitem package
+			return nil, errors.New("invalid cast to stack item slice")
 		}
-	return iterator, nil
-}
 
-func getInvocationError(result *result.Invoke) error {
+		var id cid.ID
-	if result.State != vm.HaltState.String() {
+
-		return fmt.Errorf("invocation failed: %s", result.FaultException)
+		for i := range arr {
+			bs, err := arr[i].TryBytes()
+			if err != nil {
+				return nil, fmt.Errorf("convert array item to byte slice: %w", err)
 			}
-	if len(result.Stack) == 0 {
+
-		return fmt.Errorf("result stack is empty")
+			err = id.Parse(string(bs))
+			if err == nil {
+				return &id, nil
 			}
-	return nil
+		}
+	}
+
+	return nil, errNotFound
 }

resolver/nns_test.go

@@ -0,0 +1,157 @@
+package resolver
+
+import (
+	"errors"
+	"fmt"
+	"math/big"
+	"math/rand"
+	"strings"
+	"testing"
+
+	nns "github.com/nspcc-dev/neo-go/examples/nft-nd-nns"
+	"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"
+	cidtest "github.com/nspcc-dev/neofs-sdk-go/container/id/test"
+	"github.com/stretchr/testify/require"
+)
+
+// testNeoClient represents test Neo client which checks invocation arguments
+// and returns predefined result.
+type testNeoClient struct {
+	t *testing.T
+
+	expectedContract util.Uint160
+
+	res result.Invoke
+
+	err error
+}
+
+func (x *testNeoClient) invoke(contract util.Uint160, method string, prm []smartcontract.Parameter) (*result.Invoke, error) {
+	require.Equal(x.t, x.expectedContract, contract)
+	require.Equal(x.t, "resolve", method)
+	require.Len(x.t, prm, 2)
+	require.Equal(x.t, smartcontract.StringType, prm[0].Type)
+	require.Equal(x.t, smartcontract.IntegerType, prm[1].Type)
+	require.EqualValues(x.t, nns.TXT, prm[1].Value)
+
+	val, ok := prm[0].Value.(string)
+	require.True(x.t, ok)
+	require.True(x.t, strings.HasSuffix(val, ".container"))
+	require.NotEmpty(x.t, strings.TrimSuffix(val, ".container"))
+
+	return &x.res, x.err
+}
+
+// implements test stackitem.Item which is obviously incorrect:
+// it returns itself on Convert(stackitem.ArrayT), but returns integer from Value.
+type brokenArrayStackItem struct {
+	stackitem.Item
+}
+
+func (x brokenArrayStackItem) Value() interface{} {
+	return 1
+}
+
+func (x brokenArrayStackItem) Convert(t stackitem.Type) (stackitem.Item, error) {
+	if t != stackitem.ArrayT {
+		panic(fmt.Sprintf("unexpected stack item type %s", t))
+	}
+
+	return x, nil
+}
+
+func TestNNS_ResolveContainerName(t *testing.T) {
+	const testContainerName = "some_container"
+
+	var nnsContract util.Uint160
+
+	rand.Read(nnsContract[:])
+
+	testC := &testNeoClient{
+		t:                t,
+		expectedContract: nnsContract,
+	}
+
+	n := NNS{
+		nnsContract: nnsContract,
+		neoClient:   testC,
+	}
+
+	t.Run("invocation failure", func(t *testing.T) {
+		testC.err = errors.New("invoke err")
+
+		_, err := n.ResolveContainerName(testContainerName)
+		require.Error(t, err)
+	})
+
+	testC.err = nil
+
+	t.Run("fault exception", func(t *testing.T) {
+		_, err := n.ResolveContainerName(testContainerName)
+		require.Error(t, err)
+	})
+
+	testC.res.State = vm.HaltState.String()
+
+	t.Run("empty stack", func(t *testing.T) {
+		_, err := n.ResolveContainerName(testContainerName)
+		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.ResolveContainerName(testContainerName)
+		require.Error(t, err)
+	})
+
+	t.Run("null array", func(t *testing.T) {
+		testC.res.Stack[0] = stackitem.Null{}
+
+		_, err := n.ResolveContainerName(testContainerName)
+		require.Error(t, err)
+	})
+
+	t.Run("array stack item with non-slice value", func(t *testing.T) {
+		testC.res.Stack[0] = brokenArrayStackItem{}
+
+		_, err := n.ResolveContainerName(testContainerName)
+		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.ResolveContainerName(testContainerName)
+		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.ResolveContainerName(testContainerName)
+		require.Error(t, err)
+	})
+
+	t.Run("with container array element", func(t *testing.T) {
+		id := cidtest.ID()
+
+		arr[1] = stackitem.NewByteArray([]byte(id.String()))
+
+		res, err := n.ResolveContainerName(testContainerName)
+		require.NoError(t, err)
+
+		require.Equal(t, id, res)
+	})
+}

resolver/util.go

@@ -0,0 +1,5 @@
+package resolver
+
+import "errors"
+
+var errNotFound = errors.New("record not found")