support setting cache size and port via cmdline flags

go/favicon.go

import (
	"errors"
	"flag"
	"fmt"
	"net/http"
	"net/url"
	"github.com/golang/groupcache/lru"
)
var port = "8080"
var port = flag.Int("p", 8080, "port [8080]")
var cacheSize = flag.Int("s", 10000, "cache size [10000]")
var faviconCache = lru.New(10000)
var faviconCache *lru.Cache
var lock sync.RWMutex
func main() {
	flag.Parse()
	faviconCache = lru.New(*cacheSize)
	http.HandleFunc("/favicon", HandleGetFavicon)
	if p := os.Getenv("PORT"); p != "" {
		port = p
		flag.Set("p", p)
	}
	fmt.Printf("listening on :%s\n", port)
	err := http.ListenAndServe(fmt.Sprintf(":%s", port), nil)
	fmt.Printf("listening on :%d\n", *port)
	err := http.ListenAndServe(fmt.Sprintf(":%d", *port), nil)
	if err != nil {
		fmt.Println("error: ", err)
		os.Exit(1)