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// Copyright 2016-2018 The NATS Authors
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// A unique identifier generator that is high performance, very fast, and tries to be entropy pool friendly.
package nuid
import (
"crypto/rand"
"fmt"
"math"
"math/big"
"sync"
"time"
prand "math/rand"
)
// NUID needs to be very fast to generate and truly unique, all while being entropy pool friendly.
// We will use 12 bytes of crypto generated data (entropy draining), and 10 bytes of sequential data
// that is started at a pseudo random number and increments with a pseudo-random increment.
// Total is 22 bytes of base 62 ascii text :)
// Version of the library
const Version = "1.0.0"
const (
digits = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
base = 62
preLen = 12
seqLen = 10
maxSeq = int64(839299365868340224) // base^seqLen == 62^10
minInc = int64(33)
maxInc = int64(333)
totalLen = preLen + seqLen
)
type NUID struct {
pre []byte
seq int64
inc int64
}
type lockedNUID struct {
sync.Mutex
*NUID
}
// Global NUID
var globalNUID *lockedNUID
// Seed sequential random with crypto or math/random and current time
// and generate crypto prefix.
func init() {
r, err := rand.Int(rand.Reader, big.NewInt(math.MaxInt64))
if err != nil {
prand.Seed(time.Now().UnixNano())
} else {
prand.Seed(r.Int64())
}
globalNUID = &lockedNUID{NUID: New()}
globalNUID.RandomizePrefix()
}
// New will generate a new NUID and properly initialize the prefix, sequential start, and sequential increment.
func New() *NUID {
n := &NUID{
seq: prand.Int63n(maxSeq),
inc: minInc + prand.Int63n(maxInc-minInc),
pre: make([]byte, preLen),
}
n.RandomizePrefix()
return n
}
// Generate the next NUID string from the global locked NUID instance.
func Next() string {
globalNUID.Lock()
nuid := globalNUID.Next()
globalNUID.Unlock()
return nuid
}
// Generate the next NUID string.
func (n *NUID) Next() string {
// Increment and capture.
n.seq += n.inc
if n.seq >= maxSeq {
n.RandomizePrefix()
n.resetSequential()
}
seq := n.seq
// Copy prefix
var b [totalLen]byte
bs := b[:preLen]
copy(bs, n.pre)
// copy in the seq in base36.
for i, l := len(b), seq; i > preLen; l /= base {
i -= 1
b[i] = digits[l%base]
}
return string(b[:])
}
// Resets the sequential portion of the NUID.
func (n *NUID) resetSequential() {
n.seq = prand.Int63n(maxSeq)
n.inc = minInc + prand.Int63n(maxInc-minInc)
}
// Generate a new prefix from crypto/rand.
// This call *can* drain entropy and will be called automatically when we exhaust the sequential range.
// Will panic if it gets an error from rand.Int()
func (n *NUID) RandomizePrefix() {
var cb [preLen]byte
cbs := cb[:]
if nb, err := rand.Read(cbs); nb != preLen || err != nil {
panic(fmt.Sprintf("nuid: failed generating crypto random number: %v\n", err))
}
for i := 0; i < preLen; i++ {
n.pre[i] = digits[int(cbs[i])%base]
}
}
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