go-urlencode

func urlencode(s string) (result string){
  for _, c := range(s) {
    if c <= 0x7f { // single byte 
      result += fmt.Sprintf("%%%X", c)
    } else if c > 0x1fffff {// quaternary byte
      result += fmt.Sprintf("%%%X%%%X%%%X%%%X",
        0xf0 + ((c & 0x1c0000) >> 18),
        0x80 + ((c & 0x3f000) >> 12),
        0x80 + ((c & 0xfc0) >> 6),
        0x80 + (c & 0x3f),
      )
    } else if c > 0x7ff { // triple byte
      result += fmt.Sprintf("%%%X%%%X%%%X",
        0xe0 + ((c & 0xf000) >> 12),
        0x80 + ((c & 0xfc0) >> 6),
        0x80 + (c & 0x3f),
      )
    } else { // double byte
      result += fmt.Sprintf("%%%X%%%X",
        0xc0 + ((c & 0x7c0) >> 6),
        0x80 + (c & 0x3f),
      )
    }
  }

  return result
}