middleware/request_id.go
func init() {
	hostname, err := os.Hostname()
	if hostname == "" || err != nil {
		hostname = "localhost"
	}
	var buf [12]byte
	var b64 string
	for len(b64) < 10 {
		rand.Read(buf[:])
		b64 = base64.StdEncoding.EncodeToString(buf[:])
		b64 = strings.NewReplacer("+", "", "/", "").Replace(b64)
	}

	prefix = fmt.Sprintf("%s/%s", hostname, b64[0:10])
}
func init() {
	hostname, err := os.Hostname()
	if hostname == "" || err != nil {
		hostname = "localhost"
	}
	var buf [12]byte
	var b64 string
	for len(b64) < 10 {
		rand.Read(buf[:])
		b64 = base64.StdEncoding.EncodeToString(buf[:])
		b64 = strings.NewReplacer("+", "", "/", "").Replace(b64)
	}

	prefix = fmt.Sprintf("%s/%s", hostname, b64[0:10])
}
// A quick note on the statistics here: we're trying to calculate the chance that
// two randomly generated base62 prefixes will collide. We use the formula from
// http://en.wikipedia.org/wiki/Birthday_problem
//
// P[m, n] \approx 1 - e^{-m^2/2n}
//
// We ballpark an upper bound for $m$ by imagining (for whatever reason) a server
// that restarts every second over 10 years, for $m = 86400 * 365 * 10 = 315360000$
//
// For a $k$ character base-62 identifier, we have $n(k) = 62^k$
//
// Plugging this in, we find $P[m, n(10)] \approx 5.75%$, which is good enough for
// our purposes, and is surely more than anyone would ever need in practice -- a
// process that is rebooted a handful of times a day for a hundred years has less
// than a millionth of a percent chance of generating two colliding IDs.