// generates a random MAC.
func genMAC() (mac [6]byte) {
rand.Read(mac[:])
mac[0] |= 0x01 // multicast
return
}
// New returns a unique 32-byte url-safe string.
func New() string {
var (
timeNow = time.Now()
timeNowUnix = timeNow.Unix()
timestamp = unix100nano(timeNow)
sequence uint32
saltShouldUpdate = false
saltSequence uint32
)
gMutex.Lock() // Lock
switch {
case timestamp > gLastTimestamp:
sequence = gSequenceStart
gLastTimestamp = timestamp
gLastSequence = sequence
case timestamp == gLastTimestamp:
sequence = (gLastSequence + 1) & sequenceMask
if sequence == gSequenceStart {
timestamp = tillNext100nano(timestamp)
gLastTimestamp = timestamp
}
gLastSequence = sequence
default:
gSequenceStart = rand.Uint32() & sequenceMask // NOTE
sequence = gSequenceStart
gLastTimestamp = timestamp
gLastSequence = sequence
}
if timeNowUnix >= gSaltLastUpdateTimestamp+saltUpdateInterval {
saltShouldUpdate = true
gSaltLastUpdateTimestamp = timeNowUnix
}
gSaltSequence++
saltSequence = gSaltSequence
gMutex.Unlock() // Unlock
// 56bits unix100ns + 12bits pid + 12bits sequence + 48bits node + 64bits hashsum
var idx [24]byte
// time_low
idx[0] = byte(timestamp >> 24)
idx[1] = byte(timestamp >> 16)
idx[2] = byte(timestamp >> 8)
idx[3] = byte(timestamp)
// time_mid
idx[4] = byte(timestamp >> 40)
idx[5] = byte(timestamp >> 32)
// time_hi_and_pid_low
idx[6] = byte(timestamp >> 48)
idx[7] = byte(pid)
// clk_seq_hi_pid
idx[8] = byte(sequence>>8) & 0x0f
idx[8] |= byte(pid>>8) << 4
// clk_seq_low
idx[9] = byte(sequence)
// node
copy(idx[10:], node)
// hashsum
if saltShouldUpdate {
rand.Read(gSalt)
copy(idx[16:], gSalt)
} else {
var src [8 + 4 + saltLen]byte // 8+4+43==55
src[0] = byte(timestamp >> 56)
src[1] = byte(timestamp >> 48)
src[2] = byte(timestamp >> 40)
src[3] = byte(timestamp >> 32)
src[4] = byte(timestamp >> 24)
src[5] = byte(timestamp >> 16)
src[6] = byte(timestamp >> 8)
src[7] = byte(timestamp)
src[8] = byte(saltSequence >> 24)
src[9] = byte(saltSequence >> 16)
src[10] = byte(saltSequence >> 8)
src[11] = byte(saltSequence)
copy(src[12:], gSalt)
hashsum := sha1.Sum(src[:])
copy(idx[16:], hashsum[:])
}
id := make([]byte, 32)
base64.URLEncoding.Encode(id, idx[:])
return string(id)
}
