JSON Encoding in Go: Dealing with Sensitive Fields

json_sensitive_fields.go

//
// Golang example: Handling sensitive struct fields when JSON encoding.
// 
// Blog Post: http://blakecaldwell.net/blog/2015/1/20/json-encoding-in-go-dealing-with-sensitive-fields.html
//
// Try this in the Go Playground: https://play.golang.org/p/Du5ztx6zjC
//
// Author
// ------
//
// Blake Caldwell
// http://blakecaldwell.net
// http://twitter.com/blakecaldwell
//
// Script Output
// -------------
//
// Person: {
//     "FirstName": "Arthur",
//     "LastName": "Dent",
//     "AuthToken": "green-ones"
// }
// SafePerson: {
//     "FirstName": "Arthur",
//     "LastName": "Dent"
// }
// PrettySafePerson - AuthToken has value: {
//     "FirstName": "Arthur",
//     "LastName": "Dent",
//     "AuthToken": "green-ones"
// }
// PrettySafePerson - AuthToken is empty: {
//     "FirstName": "Arthur",
//     "LastName": "Dent"
// }
// PublicPerson: {
//     "FirstName": "Arthur",
//     "LastName": "Dent"
// }
// PublicPerson with AuthToken: {
//     "FirstName": "Arthur",
//     "LastName": "Dent",
//     "AuthToken": "green-ones"
// }
//
package main

import (
	"encoding/json"
	"fmt"
)

// Person struct that includes all fields in JSON
type Person struct {
	FirstName string
	LastName  string
	AuthToken string
}

// SafePerson omits AuthToken in JSON
type SafePerson struct {
	FirstName string
	LastName  string
	AuthToken string `json:"-"`
}

// PrettySafePerson omits AuthToken if it doesn't have a value
type PrettySafePerson struct {
	FirstName string
	LastName  string
	AuthToken string `json:",omitempty"`
}

// PublicPerson decorates a Person, hiding AuthToken by default
type PublicPerson struct {
	*Person
	AuthToken string `json:",omitempty"`
}

// IncludeAuthToken unhides the Person's AuthToken
func (p *PublicPerson) IncludeAuthToken() {
	p.AuthToken = p.Person.AuthToken
}

func main() {
	// Print JSON for a Person, which shows all fields
	person := Person{
		FirstName: "Arthur",
		LastName:  "Dent",
		AuthToken: "green-ones",
	}
	printJSON("Person", person)

	// Print JSON for a SafePerson, which hides AuthToken because it's always omitted
	safePerson := SafePerson{
		FirstName: "Arthur",
		LastName:  "Dent",
		AuthToken: "green-ones",
	}
	printJSON("SafePerson", safePerson)

	// Print JSON for PrettySafePerson, which hides AuthToken if it's empty
	prettySafePerson := PrettySafePerson{
		FirstName: "Arthur",
		LastName:  "Dent",
		AuthToken: "green-ones",
	}
	printJSON("PrettySafePerson - AuthToken has value", prettySafePerson)
	prettySafePerson.AuthToken = ""
	printJSON("PrettySafePerson - AuthToken is empty", prettySafePerson)

	// Print JSON for PublicPerson, which decorates Person, hiding AuthToken by overriding it
	pe := PublicPerson{
		Person: &person,
	}
	printJSON("PublicPerson", pe)

	// Print JSON for the same PublicPerson after including AuthToken
	pe.IncludeAuthToken()
	printJSON("PublicPerson with AuthToken", pe)
}

func printJSON(name string, thing interface{}) {
	jsonBytes, err := json.MarshalIndent(thing, "", "    ")
	if err != nil {
		fmt.Printf("ERROR: %s\n", err)
		return
	}
	fmt.Printf("%s: %s\n", name, string(jsonBytes))
}