Middleware (Basic)

This example will show how to create basic logging middleware in Go.

A middleware simply takes a http.HandlerFunc as one of its parameters, wraps it and returns a new http.HandlerFunc for the server to call.

  1. // basic-middleware.go
  2. package main
  4. import (
  5.     "fmt"
  6.     "log"
  7.     "net/http"
  8. )
  10. func logging(f http.HandlerFunc) http.HandlerFunc {
  11.     return func(w http.ResponseWriter, r *http.Request) {
  12.         log.Println(r.URL.Path)
  13.         f(w, r)
  14.     }
  15. }
  17. func foo(w http.ResponseWriter, r *http.Request) {
  18.     fmt.Fprintln(w, "foo")
  19. }
  21. func bar(w http.ResponseWriter, r *http.Request) {
  22.     fmt.Fprintln(w, "bar")
  23. }
  25. func main() {
  26.     http.HandleFunc("/foo", logging(foo))
  27.     http.HandleFunc("/bar", logging(bar))
  29.     http.ListenAndServe(":8080", nil)
  30. }
  1. $ go run basic-middleware.go
  2. 2017/02/10 23:59:34 /foo
  3. 2017/02/10 23:59:35 /bar
  4. 2017/02/10 23:59:36 /foo?bar
  6. $ curl -s http://localhost:8080/foo
  7. $ curl -s http://localhost:8080/bar
  8. $ curl -s http://localhost:8080/foo?bar