A very simple url shortener

shortener.go

package main

import (
	"bufio"
	"bytes"
	"crypto/sha1"
	"flag"
	"fmt"
	"io/ioutil"
	"net/http"
	"os"
	"path"
	"path/filepath"
)

var cacheDir = flag.String("d", ".", "directory to store files")
var addr = flag.String("a", ":8080", "listen address")

func filePath(p string) string {
	cleaned := path.Clean("/" + p)
	sum := sha1.Sum([]byte(cleaned))
	h := fmt.Sprintf("%x", sum[:])
	parent := filepath.Join(*cacheDir, h[0:3])
	os.Mkdir(parent, 0777)
	return filepath.Join("/", h[0:3], h[3:])
}

func unShorten(w http.ResponseWriter, r *http.Request) {
	if r.Method != "GET" {
		http.Error(w, "Accepts only GET", http.StatusMethodNotAllowed)
		return
	}
	pos := filepath.Join(*cacheDir, path.Clean(r.URL.Path))
	buf, err := ioutil.ReadFile(pos)
	if err != nil {
		http.Error(w, "Not Found", http.StatusNotFound)
		return
	}
	http.Redirect(w, r, string(buf), http.StatusFound)
}

func shorten(w http.ResponseWriter, r *http.Request) {
	if r.Method != "POST" {
		http.Error(w, "Accepts only POST", http.StatusMethodNotAllowed)
		return
	}

	var buf bytes.Buffer
	defer r.Body.Close()
	scanner := bufio.NewScanner(r.Body)
	for scanner.Scan() {
		line := scanner.Text()
		p := filePath(line)
		fmt.Fprintf(&buf, "%s %s\n", line, p)
		if err := ioutil.WriteFile(filepath.Join(*cacheDir, p), []byte(line), os.ModePerm); err != nil {
			http.Error(w, "Internal Error", http.StatusInternalServerError)
			return
		}
	}
	if err := scanner.Err(); err != nil {
		http.Error(w, "Error Reading input", http.StatusBadRequest)
		return
	}

	w.Write(buf.Bytes())
}

func main() {
	flag.Parse()

	http.HandleFunc("/", unShorten)
	http.HandleFunc("/shorten", shorten)
	http.ListenAndServe(*addr, nil)
}