rpc: allow to marshal Iterators for invoke* results

pkg/config/config.go

@@ -7,6 +7,7 @@ import (
 
 	"github.com/nspcc-dev/neo-go/pkg/config/netmode"
 	"github.com/nspcc-dev/neo-go/pkg/core/native/nativenames"
+	"github.com/nspcc-dev/neo-go/pkg/rpc"
 	"gopkg.in/yaml.v2"
 )
 
@@ -49,6 +50,9 @@ func LoadFile(configPath string) (Config, error) {
 		ApplicationConfiguration: ApplicationConfiguration{
 			PingInterval: 30,
 			PingTimeout:  90,
+			RPC: rpc.Config{
+				MaxIteratorResultItems: 100,
+			},
 		},
 	}
 

pkg/rpc/response/result/invoke.go

@@ -2,8 +2,10 @@ package result
 
 import (
 	"encoding/json"
+	"fmt"
 
 	"github.com/nspcc-dev/neo-go/pkg/core/transaction"
+	"github.com/nspcc-dev/neo-go/pkg/vm"
 	"github.com/nspcc-dev/neo-go/pkg/vm/stackitem"
 )
 
@@ -16,6 +18,19 @@ type Invoke struct {
 	Stack                  []stackitem.Item
 	FaultException         string
 	Transaction            *transaction.Transaction
+	maxIteratorResultItems int
+}
+
+// NewInvoke returns new Invoke structure with the given fields set.
+func NewInvoke(vm *vm.VM, script []byte, faultException string, maxIteratorResultItems int) *Invoke {
+	return &Invoke{
+		State:                  vm.State().String(),
+		GasConsumed:            vm.GasConsumed(),
+		Script:                 script,
+		Stack:                  vm.Estack().ToArray(),
+		FaultException:         faultException,
+		maxIteratorResultItems: maxIteratorResultItems,
+	}
 }
 
 type invokeAux struct {
@@ -27,16 +42,52 @@ type invokeAux struct {
 	Transaction    []byte          `json:"tx,omitempty"`
 }
 
+type iteratorAux struct {
+	Type      string            `json:"type"`
+	Value     []json.RawMessage `json:"iterator"`
+	Truncated bool              `json:"truncated"`
+}
+
+// Iterator represents deserialized VM iterator values with truncated flag.
+type Iterator struct {
+	Values    []stackitem.Item
+	Truncated bool
+}
+
 // MarshalJSON implements json.Marshaler.
 func (r Invoke) MarshalJSON() ([]byte, error) {
 	var st json.RawMessage
 	arr := make([]json.RawMessage, len(r.Stack))
 	for i := range arr {
-		data, err := stackitem.ToJSONWithTypes(r.Stack[i])
+		var (
+			data []byte
+			err  error
+		)
+		if (r.Stack[i].Type() == stackitem.InteropT) && vm.IsIterator(r.Stack[i]) {
+			iteratorValues, truncated := vm.IteratorValues(r.Stack[i], r.maxIteratorResultItems)
+			value := make([]json.RawMessage, len(iteratorValues))
+			for j := range iteratorValues {
+				value[j], err = stackitem.ToJSONWithTypes(iteratorValues[j])
 				if err != nil {
 					st = []byte(`"error: recursive reference"`)
 					break
 				}
+			}
+			data, err = json.Marshal(iteratorAux{
+				Type:      stackitem.InteropT.String(),
+				Value:     value,
+				Truncated: truncated,
+			})
+			if err != nil {
+				return nil, fmt.Errorf("failed to marshal iterator: %w", err)
+			}
+		} else {
+			data, err = stackitem.ToJSONWithTypes(r.Stack[i])
+			if err != nil {
+				st = []byte(`"error: recursive reference"`)
+				break
+			}
+		}
 		arr[i] = data
 	}
 
@@ -76,6 +127,26 @@ func (r *Invoke) UnmarshalJSON(data []byte) error {
 			if err != nil {
 				break
 			}
+			if st[i].Type() == stackitem.InteropT {
+				iteratorAux := new(iteratorAux)
+				if json.Unmarshal(arr[i], iteratorAux) == nil {
+					iteratorValues := make([]stackitem.Item, len(iteratorAux.Value))
+					for j := range iteratorValues {
+						iteratorValues[j], err = stackitem.FromJSONWithTypes(iteratorAux.Value[j])
+						if err != nil {
+							err = fmt.Errorf("failed to unmarshal iterator values: %w", err)
+							break
+						}
+					}
+
+					// it's impossible to restore initial iterator type; also iterator is almost
+					// useless outside of the VM, thus let's replace it with a special structure.
+					st[i] = stackitem.NewInterop(Iterator{
+						Values:    iteratorValues,
+						Truncated: iteratorAux.Truncated,
+					})
+				}
+			}
 		}
 		if err == nil {
 			r.Stack = st

pkg/rpc/rpc_config.go

@@ -13,6 +13,7 @@ type (
 		// MaxGasInvoke is a maximum amount of gas which
 		// can be spent during RPC call.
 		MaxGasInvoke           fixedn.Fixed8 `yaml:"MaxGasInvoke"`
+		MaxIteratorResultItems int           `yaml:"MaxIteratorResultItems"`
 		Port                   uint16        `yaml:"Port"`
 		TLSConfig              TLSConfig     `yaml:"TLSConfig"`
 	}

pkg/rpc/server/server.go

@@ -1320,14 +1320,7 @@ func (s *Server) runScriptInVM(t trigger.Type, script []byte, contractScriptHash
 	if err != nil {
 		faultException = err.Error()
 	}
-	result := &result.Invoke{
-		State:          vm.State().String(),
-		GasConsumed:    vm.GasConsumed(),
-		Script:         script,
-		Stack:          vm.Estack().ToArray(),
-		FaultException: faultException,
-	}
-	return result, nil
+	return result.NewInvoke(vm, script, faultException, s.config.MaxIteratorResultItems), nil
 }
 
 // submitBlock broadcasts a raw block over the NEO network.

pkg/vm/interop.go

@@ -71,6 +71,12 @@ func init() {
 	})
 }
 
+// IsIterator returns whether stackitem implements iterator interface.
+func IsIterator(item stackitem.Item) bool {
+	_, ok := item.Value().(iterator)
+	return ok
+}
+
 // IteratorNext handles syscall System.Enumerator.Next.
 func IteratorNext(v *VM) error {
 	iop := v.Estack().Pop().Interop()
@@ -89,6 +95,18 @@ func IteratorValue(v *VM) error {
 	return nil
 }
 
+// IteratorValues returns an array of up to `max` iterator values. The second
+// return parameter denotes whether iterator is truncated.
+func IteratorValues(item stackitem.Item, max int) ([]stackitem.Item, bool) {
+	var result []stackitem.Item
+	arr := item.Value().(iterator)
+	for arr.Next() && max > 0 {
+		result = append(result, arr.Value())
+		max--
+	}
+	return result, arr.Next()
+}
+
 // NewIterator creates new iterator from the provided stack item.
 func NewIterator(item stackitem.Item) (stackitem.Item, error) {
 	switch t := item.(type) {