go - 如何在Golang中将值从处理程序传递到中间件？

Question

我试图将一些值从处理程序传递到中间件，但是它不起作用
处理程序

func (s *Server) handler(w http.ResponseWriter, r *http.Request) {

    //code
    v := map[string]string{
        "created_by":   CreatedBy,
        "name": Name,
    }
    context.WithValue(r.Context(), "result", v)
    api.Send(w, http.StatusOK, value)
}

中间件

func activity(next http.Handler) http.Handler {

    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        next.ServeHTTP(w, r)
        result := getParams(r.Context())
        fmt.Println("result", result)

    })
}


func getParams(ctx context.Context) map[string]string {
    if ctx == nil {
        return nil
    }

    result, ok := ctx.Value("result").(map[string]string)
    if ok {
        return result
    }

    return nil
}

从上下文接收值之后，它显示为空的map。是将处理程序中的某些值传递给中间件的任何其他方法。

Answer 1

在这种情况下，您必须使用新的上下文创建copy的http.Request

v := map[string]string{
    "created_by":   CreatedBy,
    "name": Name,
}
rcopy := r.WithContext(context.WithValue(r.Context(), "result", v))

然后，您必须通过所有处理程序( http.Request)“发送” firstHandler -> activity -> lastHandler

func main() {
    //firstHandler ➡️ activity ➡️ lastHandler`
    http.Handle("/", firstHandler(activity(lastHandler())))
    http.ListenAndServe(":80", nil)
}


func firstHandler(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        v := map[string]string{
            "created_by": CreatedBy,
            "name":       Name,
        }
        rcopy := r.WithContext(context.WithValue(r.Context(), "result", v))
        next.ServeHTTP(w, rcopy)
    })
}

func activity(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        result := getParams(r.Context())
        fmt.Println("activity result", result)
        next.ServeHTTP(w, r)
    })
}

func lastHandler() http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        result := getParams(r.Context())
        fmt.Println("last result", result)
    })
}