Golang net/http HandlerFunc demo

main.go

package main

import (
	"fmt"
	"io/ioutil"
	"net/http"
	"time"
)

func sayHelloHandlerFunc(w http.ResponseWriter, r *http.Request) {
	w.Write([]byte("Hello, World!"))
}

func protectThis(db map[string]string, f http.HandlerFunc) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		username, password, found := r.BasicAuth()
		if !found {
			w.Write([]byte("Access denied!"))
			return
		}

		// check db
		matchPW, found := db[username]
		if !found {
			w.Write([]byte("Access denied!"))
			return
		}

		if matchPW != password {
			w.Write([]byte("Access denied!"))
			return
		}

		// proceed to protected resource
		f(w, r)
	}
}

func main() {
	mainHandler := http.NewServeMux()
	// unprotected
	mainHandler.HandleFunc("/free", sayHelloHandlerFunc)
	// protected resource
	// dummy userdb
	db := map[string]string{
		"doctor": "who",
	}
	mainHandler.HandleFunc("/protected", protectThis(db, sayHelloHandlerFunc))
	go func() {
		if err := http.ListenAndServe(":8080", mainHandler); err != nil {
			panic(err)
		}
	}()
	fmt.Println("Started web server")
	// give the server sometime to start
	time.Sleep(time.Millisecond)

	// test starts here
	// request for /free
	req, err := http.NewRequest("GET", "http://127.0.0.1:8080/free", nil)
	if err != nil {
		panic(err)
	}
	req.Close = true

	fmt.Println("Calling /free")
	lookup(req)

	// request for /protected
	req, err = http.NewRequest("GET", "http://127.0.0.1:8080/protected", nil)
	if err != nil {
		panic(err)
	}
	req.Close = true

	fmt.Println("Calling /protected without auth")
	lookup(req)

	fmt.Println("Calling /protected with wrong credential")
	req.SetBasicAuth("foo", "bar")
	lookup(req)

	fmt.Println("Calling /protected with correct credential")
	req.SetBasicAuth("doctor", "who")
	lookup(req)
}

// since this is a test, all errors will result in panic
func lookup(r *http.Request) {
	resp, err := http.DefaultClient.Do(r)
	if err != nil {
		panic(err)
	}
	defer resp.Body.Close()

	b, err := ioutil.ReadAll(resp.Body)
	if err != nil {
		panic(err)
	}
	fmt.Printf("Received response,\n%s\n===\n", b)
}

output.txt

Started web server
Calling /free
Received response,
Hello, World!
===
Calling /protected without auth
Received response,
Access denied!
===
Calling /protected with wrong credential
Received response,
Access denied!
===
Calling /protected with correct credential
Received response,
Hello, World!
===