package id // import "go.unistack.org/micro/v4/util/id" import ( "context" "crypto/rand" "errors" "math" "go.unistack.org/micro/v4/logger" ) // DefaultAlphabet is the alphabet used for ID characters by default var DefaultAlphabet = []rune("6789BCDFGHJKLMNPQRTWbcdfghjkmnpqrtwz") // DefaultSize is the size used for ID by default // To get uuid like collision specify 21 var DefaultSize = 16 // getMask generates bit mask used to obtain bits from the random bytes that are used to get index of random character // from the alphabet. Example: if the alphabet has 6 = (110)_2 characters it is sufficient to use mask 7 = (111)_2 func getMask(alphabetSize int) int { for i := 1; i <= 8; i++ { mask := (2 << uint(i)) - 1 if mask >= alphabetSize-1 { return mask } } return 0 } // New returns new id or error func New(opts ...Option) (string, error) { options := NewOptions(opts...) if len(options.Alphabet) == 0 || len(options.Alphabet) > 255 { return "", errors.New("alphabet must not be empty and contain no more than 255 chars") } if options.Size <= 0 { return "", errors.New("size must be positive integer") } chars := options.Alphabet mask := getMask(len(chars)) // estimate how many random bytes we will need for the ID, we might actually need more but this is tradeoff // between average case and worst case ceilArg := 1.6 * float64(mask*options.Size) / float64(len(options.Alphabet)) step := int(math.Ceil(ceilArg)) id := make([]rune, options.Size) bytes := make([]byte, step) for j := 0; ; { _, err := rand.Read(bytes) if err != nil { return "", err } for i := 0; i < step; i++ { currByte := bytes[i] & byte(mask) if currByte < byte(len(chars)) { id[j] = chars[currByte] j++ if j == options.Size { return string(id[:options.Size]), nil } } } } } // Must is the same as New but fatals on error func Must(opts ...Option) string { id, err := New(opts...) if err != nil { logger.Fatal(context.TODO(), err) } return id } // Options contains id deneration options type Options struct { Alphabet []rune Size int } // Option func signature type Option func(*Options) // Alphabet specifies alphabet to use func Alphabet(alphabet string) Option { return func(o *Options) { o.Alphabet = []rune(alphabet) } } // Size specifies id size func Size(size int) Option { return func(o *Options) { o.Size = size } } // NewOptions returns new Options struct filled by opts func NewOptions(opts ...Option) Options { options := Options{ Alphabet: DefaultAlphabet, Size: DefaultSize, } for _, o := range opts { o(&options) } return options }