334 lines
7.2 KiB
Go
334 lines
7.2 KiB
Go
package main
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import (
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"encoding/binary"
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"errors"
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"fmt"
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"io"
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"log"
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"math/rand"
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"slices"
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"time"
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"github.com/oklog/ulid"
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)
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// ULID spec is mirrored here:
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// https://git.wisellama.rocks/Mirrors/ulid-spec
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func main() {
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t := time.Date(2024, 02, 16, 14, 02, 15, 17, time.UTC)
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t = time.Unix(0, 0)
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ms := uint64(t.UnixMilli())
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msBytes, err := GetMSBytes(t)
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if err != nil {
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log.Fatal(err)
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}
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log.Printf("%X%X%X%X%X%X", msBytes[0], msBytes[1], msBytes[2], msBytes[3], msBytes[4], msBytes[5])
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seed := int64(0)
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entropy := rand.New(rand.NewSource(seed))
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u, err := ulid.New(ms, entropy)
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if err != nil {
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log.Fatal(err)
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}
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ub, _ := u.MarshalBinary()
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log.Printf("%X", ub)
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log.Printf("%v", u.String())
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log.Printf("%016X", u.Time())
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log.Printf("%016X", ms)
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entropy = rand.New(rand.NewSource(seed))
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ulidBytes, err := NewULID(t, entropy)
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if err != nil {
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log.Fatal(err)
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}
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log.Printf("%X", ulidBytes)
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ulidString := CrockfordEncode(ulidBytes)
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log.Printf("ULID string: %v", ulidString)
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}
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// NewULIDString create a new ULID and returns its encoded string.
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// See NewULID for more details.
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func NewULIDString(t time.Time, entropy io.Reader) (string, error) {
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bytes, err := NewULID(t, entropy)
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if err != nil {
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return "", err
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}
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s := CrockfordEncode(bytes)
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return s, nil
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}
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// NewULID creates a new ULID.
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//
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// A ULID is a 128-bit (16-byte) value similar to a UUID (and
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// compatible with UUIDs because of this). The first 48-bits (6 bytes)
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// are based on a timestamp. The remaining 80-bits (10 bytes) are
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// random. I'm not implementing the monotonicity part of the ULID spec
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// because I don't need it. Any ULIDs created during the same
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// millisecond will just receive random values with no ordering
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// guarantee.
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func NewULID(t time.Time, entropy io.Reader) ([]byte, error) {
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if entropy == nil {
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return nil, errors.New("entropy was nil")
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}
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randomBytes := make([]byte, 10)
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_, err := entropy.Read(randomBytes)
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if err != nil {
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return nil, fmt.Errorf("failed to read bytes from entropy source: %w", err)
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}
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msBytes, err := GetMSBytes(t)
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if err != nil {
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return nil, err
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}
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if len(msBytes) != 6 {
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return nil, errors.New("timestamp bytes are wrong")
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}
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if len(randomBytes) != 10 {
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return nil, errors.New("random bytes are wrong")
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}
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ulidBytes := make([]byte, 0, 16)
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for _, b := range msBytes {
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ulidBytes = append(ulidBytes, b)
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}
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for _, b := range randomBytes {
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ulidBytes = append(ulidBytes, b)
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}
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return ulidBytes, nil
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}
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// GetMSBytes returns the given Unix time in milliseconds as a 6-byte
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// array. It truncates the 64-bit Unix epoch time down to 48-bits (6
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// bytes) and returns that 6 byte array. According to the ULID spec,
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// 48-bits is enough room that we won't run out of space until 10889
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// AD.
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func GetMSBytes(t time.Time) ([]byte, error) {
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ms := uint64(t.UnixMilli())
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// Put the 64-bit int into a byte array
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bytes := make([]byte, 8)
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binary.BigEndian.PutUint64(bytes, ms)
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if bytes[0] != 0 || bytes[1] != 0 {
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return nil, errors.New("time overflow")
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}
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// Chop off the first 2 bytes (16 bits) to get the 6 byte (48-bit)
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// output.
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return bytes[2:], nil
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}
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var (
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// crockfordEncodeMap takes binary values and converts them to
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// characters in Crockford base32.
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crockfordEncodeMap = map[uint8]rune{
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0: '0',
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1: '1',
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2: '2',
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3: '3',
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4: '4',
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5: '5',
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6: '6',
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7: '7',
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8: '8',
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9: '9',
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10: 'A',
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11: 'B',
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12: 'C',
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13: 'D',
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14: 'E',
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15: 'F',
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16: 'G',
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17: 'H',
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18: 'J',
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19: 'K',
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20: 'M',
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21: 'N',
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22: 'P',
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23: 'Q',
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24: 'R',
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25: 'S',
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26: 'T',
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27: 'V',
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28: 'W',
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29: 'X',
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30: 'Y',
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31: 'Z',
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}
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// crockfordDecodeMap takes characters and converts them to binary
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// values based on Crockford base32.
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crockfordDecodeMap = map[rune]uint8{
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'0': 0,
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'O': 0,
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'o': 0,
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'1': 1,
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'I': 1,
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'i': 1,
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'L': 1,
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'l': 1,
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'2': 2,
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'3': 3,
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'4': 4,
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'5': 5,
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'6': 6,
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'7': 7,
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'8': 8,
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'9': 9,
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'A': 10,
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'a': 10,
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'B': 11,
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'b': 11,
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'C': 12,
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'c': 12,
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'D': 13,
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'd': 13,
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'E': 14,
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'e': 14,
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'F': 15,
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'f': 15,
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'G': 16,
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'g': 16,
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'H': 17,
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'h': 17,
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'J': 18,
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'j': 18,
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'K': 19,
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'k': 19,
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'M': 20,
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'm': 20,
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'N': 21,
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'n': 21,
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'P': 22,
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'p': 22,
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'Q': 23,
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'q': 23,
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'R': 24,
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'r': 24,
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'S': 25,
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's': 25,
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'T': 26,
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't': 26,
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'V': 27,
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'v': 27,
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'W': 28,
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'w': 28,
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'X': 29,
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'x': 29,
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'Y': 30,
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'y': 30,
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'Z': 31,
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'z': 31,
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}
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)
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// CrockfordEncode takes a byte array and encodes it into a character
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// string according to Crockford's base 32 encoding. Every 5-bits
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// corresponds to a character. This specific implementation uses Big
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// Endian byte order to fit the ULID spec ("network byte ordering")
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//
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// https://www.crockford.com/base32.html
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// https://git.wisellama.rocks/Mirrors/ulid-spec
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func CrockfordEncode(bytes []byte) string {
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// Crockford is a base 32 encoding.
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// 2^5 = 32, so every 5 bits will give us a character.
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//
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// Each byte is 8 bits, so we'll have to smoosh bytes together to
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// get values divisible by 5. Any remainder will be padded with
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// zeros.
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//
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// For ULIDs, we have 128 bits which doesn't evenly divide by 5.
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// Technically we'll be encoding 130 bits of information
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// (divisible by 5), but the timestamp will should always start
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// with some zero padding.
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//
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// According to the spec, this is why the maximum ULID value is
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// `7ZZZZZZZZZZZZZZZZZZZZZZZZZ` instead of all Z's.
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// The largest supported timestamp is 2^48 - 1.
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if len(bytes) == 0 {
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return ""
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}
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// Split our byte array up into 5-bit sections and determine how
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// much of a remainder we have.
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splitSize := len(bytes) * 8 / 5
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remainder := len(bytes) * 8 % 5
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// Then determine how many uint8's we need to represent these
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// bits.
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numInts := splitSize
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if remainder > 0 {
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numInts += 1
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}
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intList := make([]uint8, 0, numInts)
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// Go right to left across the bits grabbing each 5-bit chunk
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byteIndex := len(bytes) - 1
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bitsRemaining := 8
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bitsNeeded := 5
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currentByte := uint8(bytes[byteIndex])
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for byteIndex >= 0 {
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mask := uint8(0b11111)
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// We have all the bits we need
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if bitsRemaining > bitsNeeded {
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// Just grab what we need and shift down
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bitsRemaining -= 5
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newInt := currentByte & mask
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currentByte = currentByte >> 5
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intList = append(intList, newInt)
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} else {
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// Take our remaining bits and them fill in the rest from the next byte
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bitsNeeded -= bitsRemaining
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oldB := currentByte
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byteIndex--
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// Grab the next byte and shift it upwards
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tempB := byte(0)
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if byteIndex >= 0 {
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tempB = uint8(bytes[byteIndex])
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}
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tempB = tempB << bitsRemaining
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// Merge its bits with our remaining bits.
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merged := tempB | oldB
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newInt := merged & mask
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intList = append(intList, newInt)
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// Finally grab the next byte and shift it downwards to
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// discard the bits we already used.
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if byteIndex >= 0 {
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currentByte = uint8(bytes[byteIndex])
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currentByte = currentByte >> bitsNeeded
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}
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// Update our tracking values
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bitsRemaining = 8 - bitsNeeded
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bitsNeeded = 5
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}
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}
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slices.Reverse(intList)
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// Encode those ints into strings 5-bits at a time.
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output := make([]rune, 0, len(intList))
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for _, i := range intList {
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lookup := i & 0b11111
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output = append(output, crockfordEncodeMap[lookup])
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}
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return string(output)
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}
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