http-handler-middleware.go

package main

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

// handlerFuncs sayHello for http://localhost:4000/hello url
func sayHello(w http.ResponseWriter, r *http.Request) {
	reply := "Hello, nice day isn't it :)"
	// print to console
	log.Println("reply =>", reply)
	// write to our response (data received by Browser)
	fmt.Fprint(w, reply)
}

// handleFuncs homePage func executed when url will be http://localhost:4000
func homePage(w http.ResponseWriter, r *http.Request) {
	reply := "This is Awesome Home Page"
	// print to console
	log.Println("reply =>", reply)
	// write to our response (data received by Browser)
	fmt.Fprint(w, reply)
}

// this will add loggin before and after some h which is handlerFunc executed
func logReq(h http.HandlerFunc) http.HandlerFunc {
	// wrap h argument which is HandlerFunc and add functionality to it
	// we should return http.HandlerFunc so the signature
	return func(w http.ResponseWriter, r *http.Request) {
		// this is logger decorator
		log.Println("log => something before request")
		// call and execute func passed as argument
		h(w, r)
		// do something after execution of h func
		log.Println("log => after request")
	}
}

// this will add measuring execution time of handlerFunc passed as h argument
func measureExecTime(h http.HandlerFunc) http.HandlerFunc {
	// wrap handlerFunc to add some functionality
	return func(w http.ResponseWriter, r *http.Request) {
		// for measuring time we need start time and stop time
		// to get duration of action
		start := time.Now()
		// call h which is HandlerFunc
		h(w, r)
		// print to console execution duration with time.Since(Start))
		log.Println("handler execution time =>", time.Since(start))
	}
}

func main() {
	// register url and handlerFunc called for "/" url
	http.HandleFunc("/", homePage)
	// register url and handlerFunc for "/hello" url
	// with measuring execution time and loggin features
	http.HandleFunc("/hello", measureExecTime(logReq(sayHello)))
	// write that server starting in console
	fmt.Println("Starting Server ...")
	// start server and check for errors, maybe port is busy and it could
	// not start
	err := http.ListenAndServe("localhost:4000", nil)
	// fatal (stop program) on errors
	if err != nil {
		// fatal and log error
		log.Fatal("Server could not started", err)
	}

}

http-hanlder-common-middleware.go

package main

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

// handlerFuncs sayHello for http://localhost:4000/hello url
func sayHello(w http.ResponseWriter, r *http.Request) {
	reply := "Hello, nice day isn't it :)"
	// print to console
	log.Println("reply =>", reply)
	// write to our response (data received by Browser)
	fmt.Fprint(w, reply)
}

// handleFuncs homePage func executed when url will be http://localhost:4000
func homePage(w http.ResponseWriter, r *http.Request) {
	reply := "This is Awesome Home Page"
	// print to console
	log.Println("reply =>", reply)
	// write to our response (data received by Browser)
	fmt.Fprint(w, reply)
}

// this will add loggin before and after some h which is handlerFunc executed
func logReq(h http.HandlerFunc) http.HandlerFunc {
	// wrap h argument which is HandlerFunc and add functionality to it
	// we should return http.HandlerFunc so the signature
	return func(w http.ResponseWriter, r *http.Request) {
		// this is logger decorator
		log.Println("log => something before request")
		// call and execute func passed as argument
		h(w, r)
		// do something after execution of h func
		log.Println("log => after request")
	}
}

// this will add measuring execution time of handlerFunc passed as h argument
func measureExecTime(h http.HandlerFunc) http.HandlerFunc {
	// wrap handlerFunc to add some functionality
	return func(w http.ResponseWriter, r *http.Request) {
		// for measuring time we need start time and stop time
		// to get duration of action
		start := time.Now()
		// call h which is HandlerFunc
		h(w, r)
		// print to console execution duration with time.Since(Start))
		log.Println("handler execution time =>", time.Since(start))
	}
}

// common middleware for request, you can stack them
func commonAction(h http.HandlerFunc) http.HandlerFunc {
	return measureExecTime(logReq(h))
}

func main() {
	// register url and handlerFunc called for "/" url
	http.HandleFunc("/", commonAction(homePage))
	// register url and handlerFunc for "/hello" url
	// with measuring execution time and loggin features
	http.HandleFunc("/hello", commonAction(sayHello))
	// write that server starting in console
	fmt.Println("Starting Server ...")
	// start server and check for errors, maybe port is busy and it could
	// not start
	err := http.ListenAndServe("localhost:4000", nil)
	// fatal (stop program) on errors
	if err != nil {
		// fatal and log error
		log.Fatal("Server could not started", err)
	}

}