Golangのnet/httpを利用したサンプルAPI

sample-go-api.go

package main

import (
	"database/sql"
	"encoding/json"
	"fmt"
	"io/ioutil"
	"net/http"
	"os"

	_ "github.com/go-sql-driver/mysql"
)

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

// レスポンスJsonの定義
type apiRequestResponse struct {
	Code    int    `json:"code"`
	Message string `json:"message"`
}

// DBのフィールド
type person struct {
	id   int
	name string
}

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

// handlerに共通の変数を渡すため、3つの引数をもつfunctionを引数にとり、func(ResponseWriter, *Request)を返す
func makeHandler(fn func(http.ResponseWriter, *http.Request, appEnvironment)) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		fn(w, r, getAppEnvironment())
	}
}

// APIを叩いてレスポンスを返す
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"}))
}

// DBを叩いてレスポンスを返す
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"}))
}

// 都度Marshalしてエラーチェックするのは面倒なので
func createResponsJson(a *apiRequestResponse) []byte {
	json, err := json.Marshal(*a)
	if err != nil {
		panic("json can not marshal.")
	}
	return json
}

// 環境変数を取得
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"),
	}
}