uuid.go

package uuid

import (
  "crypto/rand"
  "fmt"
  "math/big"
)

const base62alphabet = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"

// Creates a hexadecimal UUID.
func NewUuid() string {
  b := make([]byte, 16)
  rand.Read(b)
  return fmt.Sprintf("%x", b)
}

// Creates a base-62 UUID.
func NewUuid62() string {
  return ConvertUp(NewUuid(), base62alphabet)
}

// ConvertUp converts a hexadecimal UUID string to a base alphabet greater than
// 16. It is used here to compress a 32 character UUID down to 23 URL friendly
// characters.
func ConvertUp(oldNumber string, baseAlphabet string) string {
  n := big.NewInt(0)
  n.SetString(oldNumber, 16)

  base := big.NewInt(int64(len(baseAlphabet)))

  newNumber := make([]byte, 23) //converted size of max base-62 uuid
  i := len(newNumber)

  for n.Int64() != 0 {
    i--
    _, r := n.DivMod(n, base, big.NewInt(0))
    newNumber[i] = baseAlphabet[r.Int64()]
  }
  return string(newNumber[i:])
}