[nspcc-dev#266] nns: return empty Array from getRecords instead of Null

And adjust method usages along the way.

container/container_contract.go

@@ -295,8 +295,8 @@ func checkNiceNameAvailable(nnsContractAddr interop.Hash160, domain string) bool
 	}
 
 	res := contract.Call(nnsContractAddr, "getRecords",
-		contract.ReadStates|contract.AllowCall, domain, 16 /* TXT */)
-	if res != nil {
+		contract.ReadStates|contract.AllowCall, domain, 16 /* TXT */).([]string)
+	if len(res) > 0 {
 		panic("name is already taken")
 	}
 
@@ -351,8 +351,8 @@ func Delete(containerID []byte, signature interop.Signature, token []byte) {
 		// by other means (expiration, manual), thus leading to failing `deleteRecord`
 		// and inability to delete a container. We should also check if we own the record in case.
 		nnsContractAddr := storage.Get(ctx, nnsContractKey).(interop.Hash160)
-		res := contract.Call(nnsContractAddr, "getRecords", contract.ReadStates|contract.AllowCall, domain, 16 /* TXT */)
-		if res != nil && std.Base58Encode(containerID) == string(res.([]interface{})[0].(string)) {
+		res := contract.Call(nnsContractAddr, "getRecords", contract.ReadStates|contract.AllowCall, domain, 16 /* TXT */).([]string)
+		if len(res) > 0 && std.Base58Encode(containerID) == res[0] {
 			contract.Call(nnsContractAddr, "deleteRecords", contract.All, domain, 16 /* TXT */)
 		}
 	}

nns/nns_contract.go

@@ -542,11 +542,11 @@ func putNameStateWithKey(ctx storage.Context, tokenKey []byte, ns NameState) {
 	storage.Put(ctx, nameKey, nsBytes)
 }
 
-// getRecordsByType returns domain record.
+// getRecordsByType returns domain record. It returns empty array if no records found.
 func getRecordsByType(ctx storage.Context, tokenId []byte, name string, typ RecordType) []string {
 	recordsKey := getRecordsKeyByType(tokenId, name, typ)
 
-	var result []string
+	result := []string{}
 	records := storage.Find(ctx, recordsKey, storage.ValuesOnly|storage.DeserializeValues)
 	for iterator.Next(records) {
 		r := iterator.Value(records).(RecordState)

tests/nns_test.go

@@ -251,6 +251,23 @@ func TestNNSGetAllRecords(t *testing.T) {
 	require.False(t, iter.Next())
 }
 
+func TestNNSGetRecords(t *testing.T) {
+	c := newNNSInvoker(t, true)
+
+	refresh, retry, expire, ttl := int64(101), int64(102), int64(103), int64(104)
+	c.Invoke(t, true, "register",
+		"testdomain.com", c.CommitteeHash,
+		"[email protected]", refresh, retry, expire, ttl)
+
+	txtData := "first TXT record"
+	c.Invoke(t, stackitem.Null{}, "addRecord", "testdomain.com", int64(nns.TXT), txtData)
+	c.Invoke(t, stackitem.Null{}, "addRecord", "testdomain.com", int64(nns.A), "1.2.3.4")
+
+	c.Invoke(t, stackitem.NewArray([]stackitem.Item{stackitem.Make(txtData)}), "getRecords", "testdomain.com", int64(nns.TXT))
+	// Check empty result.
+	c.Invoke(t, stackitem.NewArray([]stackitem.Item{}), "getRecords", "testdomain.com", int64(nns.AAAA))
+}
+
 func TestExpiration(t *testing.T) {
 	c := newNNSInvoker(t, true)