golang json failback

json_decode_failback.go

package main

import (
	"encoding/json"
	"strings"
)

type Data struct {
	Build struct {
		Name string `json:"name"`
	} `json:"build"`
}

func (d *Data) UnmarshalJSON(data []byte) error {
	type oldData struct {
		Build string `json:"build"`
	}
	o := oldData{}

	if err := json.Unmarshal(data, &o); err == nil {
		return nil
	}

	type typeAlias *Data
	return json.Unmarshal(data, typeAlias(d))
}

func main() {
	for _, test := range []struct {
		raw      string
		expected string
	}{
		{
			raw:      `{"build": "invalid data"}`,
			expected: "",
		},
		{
			raw:      `{"build": {"name": "hello"}}`,
			expected: "hello",
		},
	} {
		d := &Data{}
		if err := json.NewDecoder(strings.NewReader(test.raw)).Decode(d); err != nil {
			panic(err)
		}

		if test.expected != d.Build.Name {
			panic("Not equals")
		}
	}
}