Marshal of json.RawMessage

Please find the code here http://play.golang.org/p/zdQ14ItNBZ

I am keeping JSON data as RawMessage, but cannot decode it out. I need the containing struct to be Marshalled and Unmarshalled, but I would expect still be able to get the JSON field.

code:

package main

import (
	"encoding/json"
	"fmt"
)

type Data struct {
	Name string
	Id   int
	Json json.RawMessage
}
type Data2 struct {
	Name string
	Id   int
}


func main() {

	tmp := Data2{"World", 2}

	b, err := json.Marshal(tmp)
	if err != nil {
		fmt.Println("Error %s", err.Error())
	}
	fmt.Println("b %s", string(b))

	test := Data{"Hello", 1, b}
	b2, err := json.Marshal(test)
	if err != nil {
		fmt.Println("Error %s", err.Error())
	}

	fmt.Println("b2 %s", string(b2))

	var d Data
	err = json.Unmarshal(b2, &d)
	if err != nil {
		fmt.Println("Error %s", err.Error())
	}
	fmt.Println("d.Json %s", string(d.Json))
	
	var tmp2 Data2
	err = json.Unmarshal(d.Json, &tmp2)
	if err != nil {
		fmt.Println("Error %s", err.Error())
	}
	fmt.Println("Data2 %+v", tmp2)

}

out:

b %s {"Name":"World","Id":2}
b2 %s {"Name":"Hello","Id":1,"Json":"eyJOYW1lIjoiV29ybGQiLCJJZCI6Mn0="}
d.Json %s "eyJOYW1lIjoiV29ybGQiLCJJZCI6Mn0="
Error %s json: cannot unmarshal string into Go value of type main.Data2
Data2 %+v { 0}

the methods on json.RawMessage all take a pointer receiver, which is why you're not able to utilize any of them; you don't have a pointer.

This "works" in the sense that it executes, but this is likely not the strategy that you want: http://play.golang.org/p/jYvh8nHata

basically you need this:

type Data struct {
    Name string
    Id   int
    Json *json.RawMessage
}

and then propagate that change through the rest of your program. What... what are you actually trying to do?

jorellis answer is correct for versions of Go before 1.8.

Go 1.8 and newer will correctly handle marshalling of both a pointer and non-pointer json.RawMessage.

Fixing commit: https://github.com/golang/go/commit/1625da24106b610f89ff7a67a11581df95f8e234