A static file server in Go

grasshopper.go

// A simple HTTP static file server.
//
//  Usage:
//     go run --root ~/Pictures --port 8001
//

package main

import (
	"errors"
	"flag"
	"fmt"
	"log"
	"net/http"
	"os"
	"regexp"
)

// Router is a http.Handler that dispatches requests to different
// handler functions.
type Router struct {
	// Root directory for serving files
	root string
}

// Override the main http method to only serve files
func (r *Router) ServeHTTP(w http.ResponseWriter, req *http.Request) {
	if !isValidPath(req.URL.Path) {
		http.NotFound(w, req)
		return
	}
	fs := http.FileServer(http.Dir(r.root))
	fs.ServeHTTP(w, req)
}

// Check if the path is something we want to serve
func isValidPath(path string) bool {
	isValid, err := regexp.Compile(`^([[:alnum:]/]+)(.png|.jpg)$`)
	if err != nil {
		log.Fatal(err)
		return false
	}
	return isValid.MatchString(path)
}

// Check if the root path specified for the server is valid
func checkRoot(root string) error {
	_, err := os.Stat(root)
	if err != nil {
		return errors.New(fmt.Sprintf("No such directory: %s", root))
	}
	return nil
}

var port = flag.String("port", ":8001", "Port on which the server will listen")
var root = flag.String("root", "/var/www/example.com/static", "Root directory from where the files will be served")

func init() {
	flag.Parse()

	log.Println("Serving from", *root, "on port", *port)
	err := checkRoot(*root)
	if err != nil {
		log.Fatal(err)
	}
}

func main() {
	err := http.ListenAndServe(*port, &Router{root: *root})
	if err != nil {
		log.Fatal(err)
	}
}