扩展HTTP处理程序

Question

我的Go Web应用程序中有一个相当快捷的错误处理程序，它会引发HTTP错误，记录响应的重要部分并提供错误模板。我想删除在处理程序中多次编写类似代码的重复：

err := doSomething()
if err != nil {
    serverError(w, r, err, code)
}

我已经阅读了Error Handling and Go文章，其中定义了一个自定义HTTP处理程序类型，该类型将返回这样的错误类型/结构（甚至返回int，err）：

type appHandler func(http.ResponseWriter, *http.Request) *appError

type appError struct {
        code int
        Err error
}

// Ensures appHandler satisfies the http.Handler interface
func (fn appHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
    if err := fn(w, r); err != nil {
        switch err.Code {

        case http.StatusNotFound:
            http.NotFound(w, r)

        case http.StatusInternalServerError:
            http.Error(w, "message", http.StatusInternalServerError)

        default:
            http.Error(w, "message", err.Code)

        }
    }
}

但是我不确定如何保留现有的中间件功能/包装，使我可以像这样链接中间件：r.HandleFunc("/route", use(myHandler, middleware1, middleware2))where use和我的中间件看起来像这样：

func use(h http.HandlerFunc, middleware ...func(http.HandlerFunc) http.HandlerFunc) http.HandlerFunc {
    for _, m := range middleware {
        h = m(h)
    }

    return h
}

 func AntiCSRF(h http.HandlerFunc) http.HandlerFunc {
        return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
                // do something
                // h.ServeHTTP(w,r)
            }
     }

据我所知，它会像下面这样（不起作用）。我说错了cannot use m(h) (type http.Handler) as type appHandler in assignment: need type assertion。我如何解决这个问题，同时又保持中间件本身“不变”？

您可以在此处找到一个（简化的）游乐场示例：http :
//play.golang.org/p/Cmmo-wK2Af

r.Handle("/route", use(myHandler, middleware.NoCache)) // Contrived example!

func use(h myHandlerType?, middleware ...func(http.Handler) http.Handler) http.Handler {
    for _, m := range middleware {
        h = m(h)
    }

    return h
}

func myHandler(w http.ResponseWriter, r *http.Request) *appError {

    // Extremely contrived example
    name := "Matt"
    _, err := fmt.Fprintf(w, "Hi %s", name)
    if err != nil {
        return &appError{500, err}
    }

    return nil
}

func contrivedMiddleware(h http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {

        w.Header().Set("Cache-Control", "max-age=0, private, must-revalidate")
        w.Header().Set("X-Accel-Expires", "0")

        h.ServeHTTP(w, r)
    })
}

我缺少什么，还有更好的方法吗？

Answer 1

感谢＃go-nuts上的“
cronos”帮助，我设法解决了这一问题。

该解决方案允许我使用自定义处理程序类型，链中间件，并避免重复包装处理程序（即appHandler（myHandler），中间件…）：

type appHandler func(http.ResponseWriter, *http.Request) *appError

type appError struct {
    Code  int
    Error error
}

func (fn appHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
    if e := fn(w, r); e != nil {

        switch e.Code {

        case http.StatusNotFound:
            notFound(w, r)
        case http.StatusInternalServerError:
            serverError(w, r, e.Error, e.Code)
        default:
            serverError(w, r, e.Error, e.Code)
        }
    }
}

func use(h appHandler, middleware ...func(http.Handler) http.Handler) http.Handler {
    var res http.Handler = h
    for _, m := range middleware {
        res = m(res)
    }

    return res
}

func someMiddleware(h http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {

        w.Header().Set("Cache-Control", "max-age=0, private, must-revalidate")
        w.Header().Set("X-Accel-Expires", "0")
        h.ServeHTTP(w, r)
    })
}

func myHandler(w http.ResponseWriter, r *http.Request) *appError {

    err := doSomething()
    if err != nil {
        return &appError{500, err}
    }

    // render your template, etc.
    return nil
}

路线如下所示： r.Handle("/route", use(myHandler, someMiddleware))

您显然可以进行修改appHandler以返回所需的内容，并向其添加其他字段appError等等。如果要将路由器应用于所有路由，则中间件也可以包装路由器-即http.Handle("/", someMiddleware(r))