[ Golang ] Rest Api 스펙이 틀릴때 (타입이 틀릴때) Json decode(Unmarshal) 하기

외부 혹은 내부 Rest API 를 사용할때 문서에 적혀있는 스펙과 다른 타입을 반환할때가 종종있다.

이럴때 그냥 그대로 json decode (unmarshal) 를 하게될경우 err 가 발생하는것을 확인할수 있다.

따라서 아래와 같이 예방할수있다.

package example_wrong_type_api_spec

import (
	"encoding/json"
	"strconv"
	"strings"
	"time"
)

type ProductResponseSpec struct {
	Name      string    `json:"name"`
	Price     int       `json:"price"`
	CreatedAt time.Time `json:"created_at"`
}

type ProductResponseSpecProtect struct {
	Name      string   `json:"name"`
	Price     SafeInt  `json:"price"`
	CreatedAt SafeTime `json:"created_at"`
}

type SafeTime struct {
	time.Time
}
type SafeInt struct {
	Value int
}

func (m *SafeInt) UnmarshalJSON(data []byte) error {
	strData := string(data)
	if strData == "null" || strData == `""` {
		return nil
	}
	n, err := strconv.Atoi(strings.ReplaceAll(strData, "\"", ""))
	*m = SafeInt{n}
	return err
}

func (m *SafeTime) UnmarshalJSON(data []byte) error {
	if string(data) == "null" || string(data) == `""` {
		return nil
	}
	tt, err := time.Parse(`"`+time.RFC3339+`"`, string(data))
	*m = SafeTime{tt}
	return err
}

type HttpClient interface {
	Request() string
}
type HttpResponse struct {
	StatusCode int
	Url        string
	Body       string
}

type ProductProxyAPI struct {
	h HttpClient
}

func NewProductProxyAPI(h HttpClient) ProductProxyAPI {
	return ProductProxyAPI{h: h}
}

func (p ProductProxyAPI) Search() (ProductResponseSpec, error) {
	response := p.h.Request()
	spec := ProductResponseSpec{}
	if err := json.Unmarshal([]byte(response), &spec); err != nil {
		return ProductResponseSpec{}, err
	}
	return spec, nil
}

func (p ProductProxyAPI) SafeSearch() (ProductResponseSpecProtect, error) {
	response := p.h.Request()
	spec := ProductResponseSpecProtect{}
	if err := json.Unmarshal([]byte(response), &spec); err != nil {
		return ProductResponseSpecProtect{}, err
	}
	return spec, nil
}



package example_wrong_type_api_spec_test

import (
	"github.com/golang/mock/gomock"
	"github.com/hoyeonUM/golang-example/example_wrong_type_api_spec"
	mock_example_wrong_type_api_spec "github.com/hoyeonUM/golang-example/example_wrong_type_api_spec/mock"
	"github.com/stretchr/testify/assert"
	"testing"
	"time"
)

var response = `
{
	"name" : "test product",
	"price" : "",
	"created_at" : ""
}
`

func TestAPI(t *testing.T) {
	t.Run(`given wrong type response when use non safe struct json unmarshal then return error`, func(t *testing.T) {
		ctrl := gomock.NewController(t)
		defer ctrl.Finish()
		m := mock_example_wrong_type_api_spec.NewMockHttpClient(ctrl)
		m.EXPECT().Request().Return(response).Times(1)
		api := example_wrong_type_api_spec.NewProductProxyAPI(m)
		_, err := api.Search()
		assert.Error(t, err)
	})

	t.Run(`given wrong type response when use safe struct json unmarshal then return struct and nil`, func(t *testing.T) {
		ctrl := gomock.NewController(t)
		defer ctrl.Finish()
		m := mock_example_wrong_type_api_spec.NewMockHttpClient(ctrl)
		m.EXPECT().Request().Return(response).Times(1)
		api := example_wrong_type_api_spec.NewProductProxyAPI(m)
		result, err := api.SafeSearch()
		assert.Nil(t, err)
		assert.Equal(t, "test product", result.Name)
		assert.Equal(t, 0, result.Price.Value)
		assert.Equal(t, time.Time{}.Format(time.RFC3339), result.CreatedAt.Format(time.RFC3339))
	})
}