Example of using a middleware with [httprouter](https://github.com/julienschmidt/httprouter)

httprouter-middleware-example.go

package main

import (
	"fmt"
	"github.com/julienschmidt/httprouter"
	"log"
	"net/http"
)

// The type of our middleware consists of the original handler we want to wrap and a message
type Middleware struct {
	next http.Handler
	message string
}

// Make a constructor for our middleware type since its fields are not exported (in lowercase)
func NewMiddleware(next http.Handler, message string) *Middleware {
	return &Middleware{next: next, message: message}
}

// Our middleware handler
func (m *Middleware) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	// We can modify the request here; for simplicity, we will just log a message
	log.Printf("msg: %s, Method: %s, URI: %s\n", m.message, r.Method, r.RequestURI)
	m.next.ServeHTTP(w, r)
	// We can modify the response here
}

// Our handle function
func Index(w http.ResponseWriter, r *http.Request, _ httprouter.Params) {
	fmt.Fprint(w, "Welcome!\n")
}
func main() {
	router := httprouter.New()
	router.GET("/", Index)
	m := NewMiddleware(router, "I'm a middleware")
	log.Fatal(http.ListenAndServe(":3000", m))
}