web-applications - `alice` 未调用中间件

Question

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

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")
}

Answer 1

您的中间件处理程序需要在准备就绪时调用下一个处理程序。未经测试的例子:

func S1(h http.Handler) http.Handler {
    return &H1{next: h}
}

type H1 struct{
    next http.Handler
}

func (h *H1) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
    log.Println("H1", time.Now())
    h.next.ServeHTTP(rw, req)
}

或者:

func S1(next http.Handler) http.Handler {
    return http.HandlerFunc(func(rw http.ResponseWriter, req *http.Request) {
        log.Println("H1", time.Now())
        next(rw, req)
    })
}

看http://golang.org/src/net/http/server.go?s=37638:37688#L1280中间件的另一个例子。