Golangで超小規模のAPIを実装する際にフレームワークを使うべきかどうかを考える

{
  code: 2000,
  message: "OK"
}

$ DB_USERNAME=username DB_PASSWORD=password go run sample-go-api.go

func main() {
	http.HandleFunc("/request", makeHandler(requestHandler))
	http.HandleFunc("/person", makeHandler(personHandler))
	http.ListenAndServe(":8080", nil)
}

func makeHandler(fn func(http.ResponseWriter, *http.Request, appEnvironment)) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		fn(w, r, getAppEnvironment())
	}
}

// 環境変数の定義
type appEnvironment struct {
	username string
	password string
}

func getAppEnvironment() appEnvironment {
	if len(os.Getenv("DB_USERNAME")) == 0 || len(os.Getenv("DB_PASSWORD")) == 0 {
		panic("appEnvironment not setting.")
	}

	return appEnvironment{
		username: os.Getenv("DB_USERNAME"),
		password: os.Getenv("DB_PASSWORD"),
	}
}

func createResponsJson(a *apiRequestResponse) []byte {
	json, err := json.Marshal(*a)
	if err != nil {
		panic("json can not marshal.")
	}
	return json
}

func requestHandler(w http.ResponseWriter, r *http.Request, env appEnvironment) {
	// headerセット
	w.Header().Set("Content-Type", "application/json; charset=utf-8")

	// methodバリデーション
	if r.Method != http.MethodGet {
		w.WriteHeader(http.StatusMethodNotAllowed)
		w.Write(createResponsJson(&apiRequestResponse{Code: 2001, Message: "Method not allowed."}))
		return
	}

	// クエリパラメータ取得&バリデーションチェック
	paramKey := r.URL.Query().Get("key")
	if len(paramKey) == 0 {
		w.WriteHeader(http.StatusBadRequest)
		w.Write(createResponsJson(&apiRequestResponse{Code: 2002, Message: "key paramater not found."}))
		return
	}

	// HTTPリクエストを行い結果をログに出力
	resp, _ := http.Get("http://httpbin.org/get?key=" + paramKey)
	if resp == nil {
		w.WriteHeader(http.StatusInternalServerError)
		w.Write(createResponsJson(&apiRequestResponse{Code: 2003, Message: "HTTP Request failed."}))
		return
	}
	defer resp.Body.Close()
	byteArray, _ := ioutil.ReadAll(resp.Body)
	fmt.Printf("log: %s", byteArray)

	// レスポンスデータの生成
	w.Write(createResponsJson(&apiRequestResponse{Code: 2000, Message: "OK"}))
}

func personHandler(w http.ResponseWriter, r *http.Request, env appEnvironment) {
	// headerセット
	w.Header().Set("Content-Type", "application/json; charset=utf-8")

	// methodバリデーション
	if r.Method != http.MethodGet {
		w.WriteHeader(http.StatusMethodNotAllowed)
		w.Write(createResponsJson(&apiRequestResponse{Code: 2001, Message: "Method not allowed."}))
		return
	}

	// クエリパラメータ取得&バリデーションチェック
	paramUser := r.URL.Query().Get("user")
	if len(paramUser) == 0 {
		w.WriteHeader(http.StatusBadRequest)
		w.Write(createResponsJson(&apiRequestResponse{Code: 2002, Message: "user paramater not found."}))
		return
	}

	// DBからデータを取得して結果をログに出力
	db, err := sql.Open("mysql", "root:"+env.password+"@/"+env.username)
	if err != nil {
		panic(err.Error())
	}
	defer db.Close()
	rows, err := db.Query("SELECT * FROM person")
	if err != nil {
		panic(err.Error())
	}
	defer rows.Close()
	for rows.Next() {
		var person person
		err := rows.Scan(&person.id, &person.name)
		if err != nil {
			panic(err.Error())
		}
		fmt.Println(person.id, person.name)
	}
	err = rows.Err()
	if err != nil {
		panic(err.Error())
	}

	// レスポンスデータの生成
	w.Write(createResponsJson(&apiRequestResponse{Code: 2000, Message: "OK"}))
}

$ DB_USERNAME=username DB_PASSWORD=password go run sample-go-echo-api.go

func main() {
	e := echo.New()
	e.GET("/request", makeHandler(requestHandler))
	e.GET("/person", makeHandler(personHandler))
	e.HTTPErrorHandler = customHTTPErrorHandler
	e.Logger.Fatal(e.Start(":8080"))
}

func makeHandler(fn func(c echo.Context, env appEnvironment) error) echo.HandlerFunc {
	return func(c echo.Context) error {
		return fn(c, getAppEnvironment())
	}
}

func requestHandler(c echo.Context, env appEnvironment) error {
	// クエリパラメータ取得&バリデーションチェック
	paramKey := c.QueryParam("key")
	if len(paramKey) == 0 {
		return c.JSON(http.StatusOK, apiRequestResponse{Code: 2002, Message: "key paramater not found."})
	}

	// HTTPリクエストを行い結果をログに出力
	resp, _ := http.Get("http://httpbin.org/get?key=" + paramKey)
	if resp == nil {
		return c.JSON(http.StatusOK, apiRequestResponse{Code: 2003, Message: "HTTP Request failed."})
	}
	defer resp.Body.Close()
	byteArray, _ := ioutil.ReadAll(resp.Body)
	fmt.Printf("log: %s", byteArray)

	return c.JSON(http.StatusOK, apiRequestResponse{Code: 2000, Message: "OK"})
}

func customHTTPErrorHandler(err error, c echo.Context) {
	code := http.StatusInternalServerError
	if he, ok := err.(*echo.HTTPError); ok {
		code = he.Code
	}

	if code == http.StatusMethodNotAllowed {
		// 405エラーの場合にレスポンスをカスタマイズする
		c.JSON(code, apiRequestResponse{Code: 2001, Message: "Method not allowed."})
	} else {
		// 405以外のエラーが発生した場合は以下の内容でレスポンスする
		c.JSON(code, apiRequestResponse{Code: 5000, Message: "Internal server error."})
	}
}

func personHandler(c echo.Context, env appEnvironment) error {
	// クエリパラメータ取得&バリデーションチェック
	paramUser := c.QueryParam("user")
	if len(paramUser) == 0 {
		return c.JSON(http.StatusOK, apiRequestResponse{Code: 2002, Message: "user paramater not found."})
	}

	// DBからデータを取得して結果をログに出力
	db, err := sql.Open("mysql", "root:"+env.password+"@/"+env.username)
	if err != nil {
		panic(err.Error())
	}
	defer db.Close()
	rows, err := db.Query("SELECT * FROM person")
	if err != nil {
		panic(err.Error())
	}
	defer rows.Close()
	for rows.Next() {
		var person person
		err := rows.Scan(&person.id, &person.name)
		if err != nil {
			panic(err.Error())
		}
		fmt.Println(person.id, person.name)
	}
	err = rows.Err()
	if err != nil {
		panic(err.Error())
	}

	return c.JSON(http.StatusOK, apiRequestResponse{Code: 2000, Message: "OK"})
}