Example of serving templates using both the system filesystem and an in-memory fake filesystem along with custom routes

http_server_filesystem.go

package main

import (
	"log"
	"net/http"

	"github.com/spf13/afero"
)

func main() {

	//
	// v1: in memory filesystem
	//
	fs := afero.NewMemMapFs()

	file, err := fs.Create("templates/index.html")
	if err != nil {
		log.Fatal(err)
	}
	file.Write([]byte("Home: <a href='/api'>/api</a>"))
	err = file.Close()
	if err != nil {
		log.Fatal(err)
	}

	httpFs := afero.NewHttpFs(fs)
	fileserver := http.FileServer(httpFs.Dir("templates"))
	http.Handle("/", fileserver)

	//
	// v2: real filesystem
	//
	// http.Handle("/", http.FileServer(http.Dir("templates")))

	http.Handle("/api/", http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		w.Write([]byte("viewing /api"))
	}))
	http.ListenAndServe(":3000", nil)

	//
	// v3: Using httprouter
	//
	router := httprouter.New()
	router.GET("/", func(w http.ResponseWriter, r *http.Request, ps httprouter.Params) {
		fmt.Printf("GET /: %s\n", r.URL.Path)
		http.FileServer(http.Dir(("./templates"))).ServeHTTP(w, r)
	})
	router.GET("/api/", func(w http.ResponseWriter, r *http.Request, ps httprouter.Params) {
		fmt.Printf("GET /api/: %s\n", r.URL.Path)
	})
	http.ListenAndServe(":3000", router)
}

More reading: https://stackoverflow.com/questions/16742331/how-to-mock-abstract-filesystem-in-go