G2207071047.go

package main

import (
    "fmt"
    "net/http"
)

func authMiddleware(f http.HandlerFunc) http.HandlerFunc {
    return func(w http.ResponseWriter, r *http.Request) {
        if token := r.Header.Get("token"); token != "fake_token" {
            _, _ = w.Write([]byte("unauthorized\n"))
            return
        }
        f(w, r)
    }
}

func loggerMiddleware(f http.HandlerFunc) http.HandlerFunc {
    return func(w http.ResponseWriter, r *http.Request) {
        fmt.Println("before")
        f(w, r)
        fmt.Println("after")
    }
}

type handler func(http.HandlerFunc) http.HandlerFunc

// Aggregate handler and middleware
func pipelineHandlers(h http.HandlerFunc, hs ...handler) http.HandlerFunc {
    for i := range hs {
        h = hs[i](h)
    }
    return h
}

func handleHello(w http.ResponseWriter, r *http.Request) {
    fmt.Println("handle hello")
    _, _ = w.Write([]byte("Hello World!\n"))
}

func main() {
    http.HandleFunc("/hello", pipelineHandlers(handleHello, loggerMiddleware, authMiddleware))
    fmt.Println(http.ListenAndServe(":8888", nil))
}