九，自寫網關(library-apigateway)

網關 library-apigateway，介面訪問的統一入口，通過 consul 獲取注冊的微服務的某一個實體，發起訪問請求，如圖：

完整代碼：

https://github.com/Justin02180218/micro-kit

包結構

目前網關的功能只是做介面轉發，所以只有一個 transport 層，

代碼實作

組態檔

server:
  port: 80
  mode: debug
  name: "apigateway"
  
consul:
  addr: "http://consul-server:8500"
  interval: "10s"
  timeout: "1s"
  client: 
    retrymax: 3
    retrytimeout: 500

修改 consul.go

func HttpClient(cfg *configs.AppConfig, name, method, path string, logger log.Logger) endpoint.Endpoint {
    consulAddr := cfg.ConsulConfig.Addr
    retryMax := cfg.ConsulConfig.Client.RetryMax
    retryTimeout := cfg.ConsulConfig.Client.RetryTimeout
    client := connectConsul(consulAddr)
    instance := consul.NewInstancer(client, logger, name, []string{name}, true)
    factory := factoryForHttp(method, path)
    endpointer := sd.NewEndpointer(instance, factory, logger)
    balancer := lb.NewRoundRobin(endpointer)
    retry := lb.Retry(retryMax, time.Millisecond*time.Duration(retryTimeout), balancer)
    return retry
}

func factoryForHttp(method, path string) sd.Factory {
    return func(instance string) (endpoint.Endpoint, io.Closer, error) {
        if !strings.HasPrefix(instance, "http") {
            instance = "http://" + instance
        }
        tgt, err := url.Parse(instance)
        if err != nil {
            return nil, nil, err
        }
        tgt.Path = path
        
        return httptransport.NewClient(
            method,
            tgt,
            utils.EncodeJSONRequest,
            utils.DecodeJSONResponse,
        ).Endpoint(), nil, nil
    }
}

transport層

在 transport 層定義 NewHttpHandler 函式，回傳 *gin.Engine，目前采用硬編碼的方式添加api介面，后續可以改成頁面配置的方式，

func NewHttpHandler(ctx context.Context, cfg *configs.AppConfig, logger log.Logger) *gin.Engine {
    r := utils.NewRouter(ctx.Value("ginMod").(string))
    e := r.Group("/api/user")
    {
        e.POST("register", func(c *gin.Context) {
            register := registers.HttpClient(cfg, "user-service", "POST", "/api/v1/register", logger)
            kithttp.NewServer(
                register,
                utils.DecodeJSONRequest,
                utils.EncodeJsonResponse,
            ).ServeHTTP(c.Writer, c.Request)
        })
        e.GET("findByID", func(c *gin.Context) {
            findByID := registers.HttpClient(cfg, "user-service", "GET", "/api/v1/findByID", logger)
            kithttp.NewServer(
                findByID,
                utils.DecodeJSONRequest,
                utils.EncodeJsonResponse,
            ).ServeHTTP(c.Writer, c.Request)
        })
        e.GET("findByEmail", func(c *gin.Context) {
            findByEmail := registers.HttpClient(cfg, "user-service", "GET", "/api/v1/findByEmail", logger)
            kithttp.NewServer(
                findByEmail,
                utils.DecodeJSONRequest,
                utils.EncodeJsonResponse,
            ).ServeHTTP(c.Writer, c.Request)
        })
        e.GET("findBooksByUserID", func(c *gin.Context) {
            findBooksByUserID := registers.HttpClient(cfg, "user-service", "GET", "/api/v1/findBooksByUserID", logger)
            kithttp.NewServer(
                findBooksByUserID,
                utils.DecodeJSONRequest,
                utils.EncodeJsonResponse,
            ).ServeHTTP(c.Writer, c.Request)
        })
    }
    e = r.Group("/api/book")
    {
        e.POST("save", func(c *gin.Context) {
            save := registers.HttpClient(cfg, "book-service", "POST", "/api/v1/save", logger)
            kithttp.NewServer(
                save,
                utils.DecodeJSONRequest,
                utils.EncodeJsonResponse,
            ).ServeHTTP(c.Writer, c.Request)
        })
        e.GET("books", func(c *gin.Context) {
            books := registers.HttpClient(cfg, "book-service", "GET", "/api/v1/books", logger)
            kithttp.NewServer(
                books,
                utils.DecodeJSONRequest,
                utils.EncodeJsonResponse,
            ).ServeHTTP(c.Writer, c.Request)
        })
        e.GET("selectBookByName", func(c *gin.Context) {
            selectBookByName := registers.HttpClient(cfg, "book-service", "GET", "/api/v1/selectBookByName", logger)
            kithttp.NewServer(
                selectBookByName,
                utils.DecodeJSONRequest,
                utils.EncodeJsonResponse,
            ).ServeHTTP(c.Writer, c.Request)
        })
        e.POST("borrowBook", func(c *gin.Context) {
            borrowBook := registers.HttpClient(cfg, "book-service", "POST", "/api/v1/borrowBook", logger)
            kithttp.NewServer(
                borrowBook,
                utils.DecodeJSONRequest,
                utils.EncodeJsonResponse,
            ).ServeHTTP(c.Writer, c.Request)
        })
    }
    return r
}

啟動服務

main.go

var confFile = flag.String("f", "apigateway.yaml", "user config file")
func main() {
    flag.Parse()
    var logger log.Logger
    {
        logger = log.NewLogfmtLogger(os.Stderr)
        logger = log.With(logger, "ts", log.DefaultTimestampUTC)
        logger = log.With(logger, "caller", log.DefaultCaller)
    }
    err := configs.Init(*confFile)
    if err != nil {
        panic(err)
    }
    ctx := context.Background()
    ctx = context.WithValue(ctx, "ginMod", configs.Conf.ServerConfig.Mode)
    r := transport.NewHttpHandler(ctx, configs.Conf, logger)
    errChan := make(chan error)
    go func() {
        errChan <- r.Run(fmt.Sprintf(":%s", strconv.Itoa(configs.Conf.ServerConfig.Port)))
    }()
    go func() {
        c := make(chan os.Signal, 1)
        signal.Notify(c, syscall.SIGINT, syscall.SIGTERM)
        errChan <- fmt.Errorf("%s", <-c)
    }()
    fmt.Println(<-errChan)
}

啟動

進入 library-apigateway 目錄，執行 go run main.go 如圖：

服務成功啟動，監聽80埠

介面測驗

在 /etc/hosts 中配置 api.library.com 域名

使用postman進行介面測驗，在這里進行了 findBooksByUserID 的介面測驗，結果如圖：

下一篇文章，我們在各個服務中加入分布式鏈路追蹤功能，

完整代碼：

https://github.com/Justin02180218/micro-kit

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