Golang net/http middleware flow.

README.md

Golang net/http middleware flow

$ go run main.go
Called middleware03()
Called middleware02()
Called middleware01()
Called initial()

main.go

package main

import "fmt"

type Handler interface {
	ServeHTTP(writer, request string)
}

type HandlerFunc func(writer, request string)

// ServeHTTP calls f(w, r).
func (f HandlerFunc) ServeHTTP(writer, request string) {
	f(writer, request)
}

func initial() Handler {
	f := func(writer, request string) {
		fmt.Println("Called initial()")
	}

	return HandlerFunc(f)
}

func middleware01() func(Handler) Handler {
	return func(next Handler) Handler {
		f := func(writer, request string) {
			fmt.Println("Called middleware01()")
			next.ServeHTTP("", "")
		}

		return HandlerFunc(f)
	}
}

func middleware02() func(Handler) Handler {
	return func(next Handler) Handler {
		f := func(writer, request string) {
			fmt.Println("Called middleware02()")
			next.ServeHTTP("", "")
		}

		return HandlerFunc(f)
	}
}

func middleware03() func(Handler) Handler {
	return func(next Handler) Handler {
		f := func(writer, request string) {
			fmt.Println("Called middleware03()")
			next.ServeHTTP("", "")
		}

		return HandlerFunc(f)
	}
}

func execHTTP(h Handler) {
	h.ServeHTTP("", "")
}

func main() {
	h := initial()
	h = middleware01()(h)
	h = middleware02()(h)
	h = middleware03()(h)

	execHTTP(h)
}