golang keeping additional json fields as is

json-additional-fields.go

package main

import (
	"encoding/json"
	"fmt"
)

func main() {
	str := `{"hello":{"nested":{"world":"!"}}}`
	fmt.Println("input string : ", str)

	s := struct {
		Hello map[string]interface{}
	}{}

	err := json.Unmarshal([]byte(str), &s)
	if err != nil {
		panic(err)
	}
	fmt.Println("struct : ", s)

	b, err := json.Marshal(s)
	fmt.Println("marshalled back(notice cap hello): ", string(b))

}