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package rand
import (
"encoding/hex"
"io"
)
const dash byte = '-'
// UUIDIdempotencyToken provides a utility to get idempotency tokens in the
// UUID format.
type UUIDIdempotencyToken struct {
uuid *UUID
}
// NewUUIDIdempotencyToken returns a idempotency token provider returning
// tokens in the UUID random format using the reader provided.
func NewUUIDIdempotencyToken(r io.Reader) *UUIDIdempotencyToken {
return &UUIDIdempotencyToken{uuid: NewUUID(r)}
}
// GetIdempotencyToken returns a random UUID value for Idempotency token.
func (u UUIDIdempotencyToken) GetIdempotencyToken() (string, error) {
return u.uuid.GetUUID()
}
// UUID provides computing random UUID version 4 values from a random source
// reader.
type UUID struct {
randSrc io.Reader
}
// NewUUID returns an initialized UUID value that can be used to retrieve
// random UUID version 4 values.
func NewUUID(r io.Reader) *UUID {
return &UUID{randSrc: r}
}
// GetUUID returns a random UUID version 4 string representation sourced from the random reader the
// UUID was created with. Returns an error if unable to compute the UUID.
func (r *UUID) GetUUID() (string, error) {
var b [16]byte
if _, err := io.ReadFull(r.randSrc, b[:]); err != nil {
return "", err
}
r.makeUUIDv4(b[:])
return format(b), nil
}
// GetBytes returns a byte slice containing a random UUID version 4 sourced from the random reader the
// UUID was created with. Returns an error if unable to compute the UUID.
func (r *UUID) GetBytes() (u []byte, err error) {
u = make([]byte, 16)
if _, err = io.ReadFull(r.randSrc, u); err != nil {
return u, err
}
r.makeUUIDv4(u)
return u, nil
}
func (r *UUID) makeUUIDv4(u []byte) {
// 13th character is "4"
u[6] = (u[6] & 0x0f) | 0x40 // Version 4
// 17th character is "8", "9", "a", or "b"
u[8] = (u[8] & 0x3f) | 0x80 // Variant most significant bits are 10x where x can be either 1 or 0
}
// Format returns the canonical text representation of a UUID.
// This implementation is optimized to not use fmt.
// Example: 82e42f16-b6cc-4d5b-95f5-d403c4befd3d
func format(u [16]byte) string {
// https://en.wikipedia.org/wiki/Universally_unique_identifier#Version_4_.28random.29
var scratch [36]byte
hex.Encode(scratch[:8], u[0:4])
scratch[8] = dash
hex.Encode(scratch[9:13], u[4:6])
scratch[13] = dash
hex.Encode(scratch[14:18], u[6:8])
scratch[18] = dash
hex.Encode(scratch[19:23], u[8:10])
scratch[23] = dash
hex.Encode(scratch[24:], u[10:])
return string(scratch[:])
}
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