example go server where paths that have no extensions are directed to "/index.html"

exampleServer.go

package main

import (
	"os"
	"flag"
	"fmt"
	"log"
	"net/http"
	"path"
)

// HelpMessage is the extra information given when using flags -h or --help.
// it is prefixed to the automatically generated info by flag.PrintDefaults()
const HelpMessage = `
Example Server

USAGE:    
  exampleServer [options]

OPTIONS:
`

// Define the help messages for the OPTIONS.  These are appeneded to
// HelpMessage when flag.PrintDefaults() is called.
const (
	HelpAddress    = "Host Address and Port for HTTP connections."
	DefaultAddress = "localhost:8080"
)

var (
	addr string
)

func init() {
	flag.StringVar(&addr, "a", DefaultAddress, HelpAddress)
	flag.Usage = func() {
		fmt.Fprint(os.Stderr, HelpMessage)
		flag.PrintDefaults()
	}
}

func main() {
	flag.Parse()

	mux := http.NewServeMux()
	mux.HandleFunc("/", handleFiles)
	
	s := &http.Server{
		Addr:    (addr),
		Handler: mux,
	}

	log.Printf("Listening and Serving on %v", (addr))
	log.Fatal(s.ListenAndServe())
}

// handleFiles will serve the index page and all other files based on URL.
// This exposes all folder contents, and makes them accessible by filename.
// All incoming requests will be logged via the "logRequest" function.
func handleFiles(w http.ResponseWriter, r *http.Request) {
	logRequest(r)
	if r.Method != "GET" {
		http.Error(w, http.StatusText(405), 405)
		return
	}

	// removes trailing slash from the user input, for example of
	// this, see https://golang.org/doc/articles/wiki/#tmp_3

	target := path.Clean(r.URL.Path[1:])

	// checks for an extention.  If there is a no extention,
	// path.Ext(path) returns an empty string, see
	// https://golang.org/pkg/path/#Ext

	// path.Join will add the paths together, adding another slash
	// (/) only if it needs to.  See
	// https://golang.org/pkg/path/#Join

	if path.Ext(target) == "" {
		target = path.Join(target, "index.html")
	}

	// Check to see if the file exists or not.  404 if it does
	// not, this prevents the file directory from being displayed
	// if there is no index.html file present.
	// https://golang.org/pkg/os/#IsNotExist

	file, err := os.Stat(target)
	if os.IsNotExist(err) {
		http.Error(w, http.StatusText(404), 404)
		return
	}
	
	// At this point, if the path is still pointing to a directory,
	// then the index file does not exist.  Show a fun message.
	if file.IsDir() {
		fmt.Fprint(w, "I don't wanna show you my files!")
		return
	}

	// If there is an extention, keep it.  Most likely it will be
	// something like .js, .css, .json, or something else.  Note
	// that if http.ServeFile will automatically clear away
	// "/index.html" from the url bar in your browser. See
	// https://golang.org/pkg/net/http/#ServeFile
	log.Println("serving file:", target)
	http.ServeFile(w, r, target)
}

// logRequest prints out a useful message to the command line log,
// displaying information about the request that was just made to the server.
func logRequest(r *http.Request) {
	log.Printf("(%v) %v %v %v", r.RemoteAddr, r.Proto, r.Method, r.URL)
}