Merge pull request ethereum#31 from maticnetwork/abi-fix

fix abigen to create pure/view methods

accounts/abi/abi.go

@@ -114,12 +114,13 @@ func (abi ABI) UnpackIntoMap(v map[string]interface{}, name string, data []byte)
 // UnmarshalJSON implements json.Unmarshaler interface
 func (abi *ABI) UnmarshalJSON(data []byte) error {
 	var fields []struct {
-		Type      string
-		Name      string
-		Constant  bool
-		Anonymous bool
-		Inputs    []Argument
-		Outputs   []Argument
+		Type            string
+		Name            string
+		Constant        bool
+		StateMutability string
+		Anonymous       bool
+		Inputs          []Argument
+		Outputs         []Argument
 	}
 
 	if err := json.Unmarshal(data, &fields); err != nil {
@@ -142,9 +143,10 @@ func (abi *ABI) UnmarshalJSON(data []byte) error {
 				name = fmt.Sprintf("%s%d", field.Name, idx)
 				_, ok = abi.Methods[name]
 			}
+			isConst := field.Constant || field.StateMutability == "pure" || field.StateMutability == "view"
 			abi.Methods[name] = Method{
 				Name:    name,
-				Const:   field.Constant,
+				Const:   isConst,
 				Inputs:  field.Inputs,
 				Outputs: field.Outputs,
 			}