`alice` 没有调用中间件

Question

为什么这里只调用了 的ServeHTTP方法，H1而H2和 的方法H3似乎被忽略了？

alice似乎是一个不错的中间件链接，在这里我尝试将它与httprouter一起使用，但只有外部/最后一个中间件被调用：

package main

import (

    "fmt"

    "github.com/julienschmidt/httprouter"

    "github.com/justinas/alice"

    "net/http"

    "log"

    "time"

)

func main() {

    fmt.Println("started ", time.Now())

    c := alice.New(S1, S2, S3).Then(nil)

    router := httprouter.New()

    router.Handler("GET", "/app", c)

    http.ListenAndServe(":27007", router)

}

func S1(h http.Handler) http.Handler {

    var x H1

    return &x

}

func S2(h http.Handler) http.Handler {

    var x H2

    return &x

}

func S3(h http.Handler) http.Handler {

    var x H3

    return &x

}

type H1 struct{}

func (h *H1) ServeHTTP(rw http.ResponseWriter, req *http.Request) {

    log.Println("H1", time.Now())

}

type H2 struct{}

func (h *H2) ServeHTTP(rw http.ResponseWriter, req *http.Request) {

    log.Println("H2")

}

type H3 struct{}

func (h *H3) ServeHTTP(rw http.ResponseWriter, req *http.Request) {

    log.Println("H3")

}