Add 0x prefix when converting to string

(cherry picked from commit bd04917)

Author: sobolev-igor

accounts/abi/unpack.go

@@ -18,7 +18,6 @@ package abi
 
 import (
 	"encoding/binary"
-	"encoding/hex"
 	"errors"
 	"fmt"
 	"math"
@@ -416,25 +415,25 @@ func toString(index int, t Type, output []byte) (interface{}, error) {
 		}
 		return strconv.FormatBool(b), nil
 	case AddressTy:
-		return hex.EncodeToString(common.BytesToAddress(returnOutput).Bytes()), nil
+		return common.Bytes2HexWithPrefix(common.BytesToAddress(returnOutput).Bytes()), nil
 	case HashTy:
-		return hex.EncodeToString(common.BytesToHash(returnOutput).Bytes()), nil
+		return common.Bytes2HexWithPrefix(common.BytesToHash(returnOutput).Bytes()), nil
 	case BytesTy:
-		return hex.EncodeToString(output[begin : begin+length]), nil
+		return common.Bytes2HexWithPrefix(output[begin : begin+length]), nil
 	case FixedBytesTy:
 		var b interface{}
 		b, err = ReadFixedBytes(t, returnOutput)
 		if err != nil {
 			return nil, fmt.Errorf("abi: cannot convert value as fixed bytes array: %v", returnOutput)
 		}
-		return hex.EncodeToString(b.([]byte)), nil
+		return common.Bytes2HexWithPrefix(b.([]byte)), nil
 	case FunctionTy:
 		var f interface{}
 		f, err = ReadFixedBytes(t, returnOutput)
 		if err != nil {
 			return nil, fmt.Errorf("abi: cannot convert value as function: %v", returnOutput)
 		}
-		return hex.EncodeToString(f.([]byte)), nil
+		return common.Bytes2HexWithPrefix(f.([]byte)), nil
 	default:
 		return nil, fmt.Errorf("abi: unknown type %v", t.T)
 	}

common/bytes.go

@@ -75,6 +75,11 @@ func Bytes2Hex(d []byte) string {
 	return hex.EncodeToString(d)
 }
 
+// Bytes2Hex returns the hexadecimal encoding of d.
+func Bytes2HexWithPrefix(d []byte) string {
+	return "0x" + Bytes2Hex(d)
+}
+
 // Hex2Bytes returns the bytes represented by the hexadecimal string str.
 func Hex2Bytes(str string) []byte {
 	h, _ := hex.DecodeString(str)