rpc: fix wrong script marshalling in getcontractstate RPC server

problem: `script` field of result.ContractState is marshalled as []byte

solution: add marshaller for result.ContractState

pkg/rpc/response/result/contract_state.go

@@ -1,6 +1,9 @@
 package result
 
 import (
+	"encoding/hex"
+	"encoding/json"
+
 	"github.com/nspcc-dev/neo-go/pkg/core/state"
 	"github.com/nspcc-dev/neo-go/pkg/smartcontract"
 	"github.com/nspcc-dev/neo-go/pkg/util"
@@ -29,6 +32,21 @@ type Properties struct {
 	IsPayable        bool `json:"is_payable"`
 }
 
+// contractState is an auxilliary struct for proper Script marshaling.
+type contractState struct {
+	Version     byte                      `json:"version"`
+	ScriptHash  util.Uint160              `json:"hash"`
+	Script      string                    `json:"script"`
+	ParamList   []smartcontract.ParamType `json:"parameters"`
+	ReturnType  smartcontract.ParamType   `json:"returntype"`
+	Name        string                    `json:"name"`
+	CodeVersion string                    `json:"code_version"`
+	Author      string                    `json:"author"`
+	Email       string                    `json:"email"`
+	Description string                    `json:"description"`
+	Properties  Properties                `json:"properties"`
+}
+
 // NewContractState creates a new Contract wrapper.
 func NewContractState(c *state.Contract) ContractState {
 	properties := Properties{
@@ -51,3 +69,56 @@ func NewContractState(c *state.Contract) ContractState {
 		Description: c.Description,
 	}
 }
+
+// MarshalJSON implements json.Marshaler interface.
+func (c ContractState) MarshalJSON() ([]byte, error) {
+	s := &contractState{
+		Version:     c.Version,
+		ScriptHash:  c.ScriptHash,
+		Script:      hex.EncodeToString(c.Script),
+		ParamList:   c.ParamList,
+		ReturnType:  c.ReturnType,
+		Name:        c.Name,
+		CodeVersion: c.CodeVersion,
+		Author:      c.Author,
+		Email:       c.Email,
+		Description: c.Description,
+		Properties: Properties{
+			HasStorage:       c.Properties.HasStorage,
+			HasDynamicInvoke: c.Properties.HasDynamicInvoke,
+			IsPayable:        c.Properties.IsPayable,
+		},
+	}
+	return json.Marshal(s)
+}
+
+// UnmarshalJSON implements json.Unmarshaler interface.
+func (c *ContractState) UnmarshalJSON(data []byte) error {
+	s := new(contractState)
+	if err := json.Unmarshal(data, s); err != nil {
+		return err
+	}
+
+	script, err := hex.DecodeString(s.Script)
+	if err != nil {
+		return err
+	}
+
+	c.Version = s.Version
+	c.ScriptHash = s.ScriptHash
+	c.Script = script
+	c.ParamList = s.ParamList
+	c.ReturnType = s.ReturnType
+	c.Name = s.Name
+	c.CodeVersion = s.CodeVersion
+	c.Author = s.Author
+	c.Email = s.Email
+	c.Description = s.Description
+	c.Properties = Properties{
+		HasStorage:       s.Properties.HasStorage,
+		HasDynamicInvoke: s.Properties.HasDynamicInvoke,
+		IsPayable:        s.Properties.IsPayable,
+	}
+
+	return nil
+}