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package uuid
import (
"crypto/md5"
"crypto/rand"
"encoding/base64"
"encoding/binary"
"fmt"
"io"
"os"
"sync/atomic"
"time"
)
const (
// UUID_LENGTH is length of a UUID
UUID_LENGTH = 16
encodeUUID = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789_."
)
var (
// _UUIDEncoding is encoding for UUID
_UUIDEncoding = base64.NewEncoding(encodeUUID).WithPadding(base64.NoPadding)
)
// GenUUID generates a new unique ObjectId.
func GenUUID() string {
var b = make([]byte, 12)
// Timestamp, 4 bytes, big endian
binary.BigEndian.PutUint32(b[:], uint32(time.Now().Unix()))
// Machine, first 3 bytes of md5(hostname)
b[4] = machineId[0]
b[5] = machineId[1]
b[6] = machineId[2]
// Pid, 2 bytes, specs don't specify endianness, but we use big endian.
pid := os.Getpid()
b[7] = byte(pid >> 8)
b[8] = byte(pid)
// Increment, 3 bytes, big endian
i := atomic.AddUint32(&objectIdCounter, 1)
b[9] = byte(i >> 16)
b[10] = byte(i >> 8)
b[11] = byte(i)
return _UUIDEncoding.EncodeToString(b)
}
func GenFixedUUID(b []byte) string {
bl := len(b)
if bl > 12 {
b = b[:12]
} else if bl < 12 {
nb := make([]byte, 12)
copy(nb[12-bl:], b)
b = nb
}
return _UUIDEncoding.EncodeToString(b)
}
// objectIdCounter is atomically incremented when generating a new ObjectId
// using NewObjectId() function. It's used as a counter part of an id.
var objectIdCounter uint32
// machineId stores machine id generated once and used in subsequent calls
// to NewObjectId function.
var machineId = readMachineId()
// readMachineId generates machine id and puts it into the machineId global
// variable. If this function fails to get the hostname, it will cause
// a runtime error.
func readMachineId() []byte {
var sum [3]byte
id := sum[:]
hostname, err1 := os.Hostname()
if err1 != nil {
_, err2 := io.ReadFull(rand.Reader, id)
if err2 != nil {
panic(fmt.Errorf("cannot get hostname: %v; %v", err1, err2))
}
return id
}
hw := md5.New()
hw.Write([]byte(hostname))
copy(id, hw.Sum(nil))
return id
}
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