uuid.go

Documentation: github.com/aws/smithy-go/rand

     1  package rand
     2  
     3  import (
     4  	"encoding/hex"
     5  	"io"
     6  )
     7  
     8  const dash byte = '-'
     9  
    10  // UUIDIdempotencyToken provides a utility to get idempotency tokens in the
    11  // UUID format.
    12  type UUIDIdempotencyToken struct {
    13  	uuid *UUID
    14  }
    15  
    16  // NewUUIDIdempotencyToken returns a idempotency token provider returning
    17  // tokens in the UUID random format using the reader provided.
    18  func NewUUIDIdempotencyToken(r io.Reader) *UUIDIdempotencyToken {
    19  	return &UUIDIdempotencyToken{uuid: NewUUID(r)}
    20  }
    21  
    22  // GetIdempotencyToken returns a random UUID value for Idempotency token.
    23  func (u UUIDIdempotencyToken) GetIdempotencyToken() (string, error) {
    24  	return u.uuid.GetUUID()
    25  }
    26  
    27  // UUID provides computing random UUID version 4 values from a random source
    28  // reader.
    29  type UUID struct {
    30  	randSrc io.Reader
    31  }
    32  
    33  // NewUUID returns an initialized UUID value that can be used to retrieve
    34  // random UUID version 4 values.
    35  func NewUUID(r io.Reader) *UUID {
    36  	return &UUID{randSrc: r}
    37  }
    38  
    39  // GetUUID returns a random UUID version 4 string representation sourced from the random reader the
    40  // UUID was created with. Returns an error if unable to compute the UUID.
    41  func (r *UUID) GetUUID() (string, error) {
    42  	var b [16]byte
    43  	if _, err := io.ReadFull(r.randSrc, b[:]); err != nil {
    44  		return "", err
    45  	}
    46  	r.makeUUIDv4(b[:])
    47  	return format(b), nil
    48  }
    49  
    50  // GetBytes returns a byte slice containing a random UUID version 4 sourced from the random reader the
    51  // UUID was created with. Returns an error if unable to compute the UUID.
    52  func (r *UUID) GetBytes() (u []byte, err error) {
    53  	u = make([]byte, 16)
    54  	if _, err = io.ReadFull(r.randSrc, u); err != nil {
    55  		return u, err
    56  	}
    57  	r.makeUUIDv4(u)
    58  	return u, nil
    59  }
    60  
    61  func (r *UUID) makeUUIDv4(u []byte) {
    62  	// 13th character is "4"
    63  	u[6] = (u[6] & 0x0f) | 0x40 // Version 4
    64  	// 17th character is "8", "9", "a", or "b"
    65  	u[8] = (u[8] & 0x3f) | 0x80 // Variant most significant bits are 10x where x can be either 1 or 0
    66  }
    67  
    68  // Format returns the canonical text representation of a UUID.
    69  // This implementation is optimized to not use fmt.
    70  // Example: 82e42f16-b6cc-4d5b-95f5-d403c4befd3d
    71  func format(u [16]byte) string {
    72  	// https://en.wikipedia.org/wiki/Universally_unique_identifier#Version_4_.28random.29
    73  
    74  	var scratch [36]byte
    75  
    76  	hex.Encode(scratch[:8], u[0:4])
    77  	scratch[8] = dash
    78  	hex.Encode(scratch[9:13], u[4:6])
    79  	scratch[13] = dash
    80  	hex.Encode(scratch[14:18], u[6:8])
    81  	scratch[18] = dash
    82  	hex.Encode(scratch[19:23], u[8:10])
    83  	scratch[23] = dash
    84  	hex.Encode(scratch[24:], u[10:])
    85  
    86  	return string(scratch[:])
    87  }
    88
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