git.sr.ht/~pingoo/stdx@v0.0.0-20240218134121-094174641f6e/uuid/v4.go (about)

     1  // Copyright 2016 Google Inc.  All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package uuid
     6  
     7  import "io"
     8  
     9  // New creates a new random UUID or panics.  New is equivalent to
    10  // the expression
    11  //
    12  //	uuid.Must(uuid.NewRandom())
    13  func NewV4() UUID {
    14  	return Must(newRandom())
    15  }
    16  
    17  // NewRandom returns a Random (Version 4) UUID.
    18  //
    19  // The strength of the UUIDs is based on the strength of the crypto/rand
    20  // package.
    21  //
    22  // Uses the randomness pool if it was enabled with EnableRandPool.
    23  //
    24  // A note about uniqueness derived from the UUID Wikipedia entry:
    25  //
    26  //	Randomly generated UUIDs have 122 random bits.  One's annual risk of being
    27  //	hit by a meteorite is estimated to be one chance in 17 billion, that
    28  //	means the probability is about 0.00000000006 (6 × 10−11),
    29  //	equivalent to the odds of creating a few tens of trillions of UUIDs in a
    30  //	year and having one duplicate.
    31  func newRandom() (UUID, error) {
    32  	if !poolEnabled {
    33  		return NewRandomFromReader(rander)
    34  	}
    35  	return newRandomFromPool()
    36  }
    37  
    38  // NewRandomFromReader returns a UUID based on bytes read from a given io.Reader.
    39  func NewRandomFromReader(r io.Reader) (UUID, error) {
    40  	var uuid UUID
    41  	_, err := io.ReadFull(r, uuid[:])
    42  	if err != nil {
    43  		return Nil, err
    44  	}
    45  	uuid[6] = (uuid[6] & 0x0f) | 0x40 // Version 4
    46  	uuid[8] = (uuid[8] & 0x3f) | 0x80 // Variant is 10
    47  	return uuid, nil
    48  }
    49  
    50  func newRandomFromPool() (UUID, error) {
    51  	var uuid UUID
    52  	poolMu.Lock()
    53  	if poolPos == randPoolSize {
    54  		_, err := io.ReadFull(rander, pool[:])
    55  		if err != nil {
    56  			poolMu.Unlock()
    57  			return Nil, err
    58  		}
    59  		poolPos = 0
    60  	}
    61  	copy(uuid[:], pool[poolPos:(poolPos+16)])
    62  	poolPos += 16
    63  	poolMu.Unlock()
    64  
    65  	uuid[6] = (uuid[6] & 0x0f) | 0x40 // Version 4
    66  	uuid[8] = (uuid[8] & 0x3f) | 0x80 // Variant is 10
    67  	return uuid, nil
    68  }