99 lines
2.1 KiB
Go
99 lines
2.1 KiB
Go
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package utils
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import (
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"crypto/rand"
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"fmt"
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"math"
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)
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const (
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defaultAlphabet = "_-0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ" // len=64
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defaultSize = 21
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defaultMaskSize = 5
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)
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// Generator function
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type Generator func([]byte) (int, error)
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// BytesGenerator is the default bytes generator
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var BytesGenerator Generator = rand.Read
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func initMasks(params ...int) []uint {
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var size int
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if len(params) == 0 {
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size = defaultMaskSize
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} else {
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size = params[0]
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}
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masks := make([]uint, size)
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for i := 0; i < size; i++ {
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shift := 3 + i
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masks[i] = (2 << uint(shift)) - 1
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}
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return masks
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}
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func getMask(alphabet string, masks []uint) int {
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for i := 0; i < len(masks); i++ {
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curr := int(masks[i])
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if curr >= len(alphabet)-1 {
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return curr
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}
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}
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return 0
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}
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// GenerateUID is a low-level function to change alphabet and ID size.
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func GenerateUID(alphabet string, size int) (string, error) {
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if len(alphabet) == 0 || len(alphabet) > 255 {
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return "", fmt.Errorf("alphabet must not empty and contain no more than 255 chars. Current len is %d", len(alphabet))
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}
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if size <= 0 {
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return "", fmt.Errorf("size must be positive integer")
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}
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masks := initMasks(size)
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mask := getMask(alphabet, masks)
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ceilArg := 1.6 * float64(mask*size) / float64(len(alphabet))
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step := int(math.Ceil(ceilArg))
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id := make([]byte, size)
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bytes := make([]byte, step)
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for j := 0; ; {
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_, err := BytesGenerator(bytes)
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if err != nil {
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return "", err
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}
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for i := 0; i < step; i++ {
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currByte := bytes[i] & byte(mask)
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if currByte < byte(len(alphabet)) {
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id[j] = alphabet[currByte]
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j++
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if j == size {
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return string(id[:size]), nil
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}
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}
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}
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}
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}
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// NewUID generates secure URL-friendly unique ID.
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func NewUID(param ...int) (string, error) {
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var size int
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if len(param) == 0 {
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size = defaultSize
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} else {
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size = param[0]
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}
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bytes := make([]byte, size)
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_, err := BytesGenerator(bytes)
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if err != nil {
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return "", err
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}
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id := make([]byte, size)
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for i := 0; i < size; i++ {
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id[i] = defaultAlphabet[bytes[i]&63]
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}
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return string(id[:size]), nil
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}
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