create an indexless dir filesystem instead of http.Dir for http.FileServer

example.go

package main

import "net/http"

func main() {
  mux := http.NewServeMux()
  // add a "/files" route from the "./static" directory, http://localhost:8080/files/{file}
  mux.Handle("/files/", http.StripPrefix("/files/", http.FileServer(utils.NewIndexlessDir("./static"))))
  http.ListenAndServe(":8080", mux)
}

indexless_dir.go

package utils

import (
	"net/http"
	"strings"
)

type indexlessFileSystem struct {
	fs http.FileSystem
}

// NewIndexlessDir will create an indexless http.FileSystem in the specified path
func NewIndexlessDir(path string) http.FileSystem {
	return &indexlessFileSystem{http.Dir(path)}
}

// Open a file path or any dir path which has index.html
func (ulfs indexlessFileSystem) Open(name string) (http.File, error) {
	file, err := ulfs.fs.Open(name)
	if err != nil {
		return nil, err
	}
	info, err := file.Stat()
	if err != nil {
		return nil, err
	}
	if info.IsDir() {
		index := strings.TrimSuffix(name, "/") + "/index.html"
		if _, err := ulfs.fs.Open(index); err != nil {
			return nil, err
		}
	}
	return file, nil
}