http server/client to showcase timeout

client.go

package main

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

type rt struct {
	roundTripper func(req *http.Request) (*http.Response, error)
}

func (r rt) RoundTrip(req *http.Request) (*http.Response, error) {
	return r.roundTripper(req)
}

func main() {

	c := http.Client{
		Timeout:   3 * time.Second,
		Transport:  rt{RoundTripper(http.DefaultTransport)},
	}
	resp, err := c.Get("http://127.0.0.1:9000")
	if err != nil {
		fmt.Println("err:", err)
	} else {
		body, err := ioutil.ReadAll(resp.Body)
		resp.Body.Close()
		fmt.Println(string(body), err)
	}

}
func RoundTripper(next http.RoundTripper) func(req *http.Request) (*http.Response, error) {
	return func(req *http.Request) (*http.Response, error) {
		resp, err := next.RoundTrip(req)
		if err != nil {
			return nil, fmt.Errorf("err: %w", err)
		}
		return resp, nil
	}
}

server.go

package main

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

func main() {
	router := http.NewServeMux()
	router.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		fmt.Println("HTTP Request received!")

		time.Sleep(10 * time.Second)

		fmt.Println("HTTP response sent!")
		w.WriteHeader(200)
		w.Write([]byte("OK"))
	})
	server := http.Server{
		Handler: router,
	}

	l, err := net.Listen("tcp", ":9000")
	if err != nil {
		panic(err)
	}

	if err := server.Serve(l); err != nil {
		panic(err)
	}
}