multi-stage json decoding in Go

twopass.go

package main

import (
	"encoding/json"
	"fmt"
	"strings"
)

var (
	stream = `
{
    "type": "human",
    "name": "jordan",
    "city": "new york"
}
{
    "type": "dog",
    "name": "kiba",
    "breed": "husky"
}
`

	jsonconfig = map[string]func() JSONHandler{
		"human": func() JSONHandler { return new(Human) },
		"dog":   func() JSONHandler { return new(Dog) },
	}
)

type JSONHandler interface {
	HandleJSON([]byte) error
}

type Mask struct {
	TypeName string `json:"type"`
}

type Human struct {
	Name string `json:"name"`
	City string `json:"city"`
}

func (h *Human) HandleJSON(raw []byte) error {
	if err := json.Unmarshal(raw, h); err != nil {
		return err
	}
	fmt.Println(h)
	return nil
}

type Dog struct {
	Name  string `json:"name"`
	Breed string `json:"breed"`
}

func (d *Dog) HandleJSON(raw []byte) error {
	if err := json.Unmarshal(raw, d); err != nil {
		return err
	}
	fmt.Println(d)
	return nil
}

func main() {
	e := json.NewDecoder(strings.NewReader(stream))
	for {
		var raw json.RawMessage
		if err := e.Decode(&raw); err != nil {
			break
		}
		var m Mask
		if err := json.Unmarshal(raw, &m); err != nil {
			break
		}
		if err := jsonconfig[m.TypeName]().HandleJSON([]byte(raw)); err != nil {
			break
		}
	}
}