evalphobia/hierogolyph

package hierogolyph

import "crypto/rand"

const (
    letters       = "!\"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|}~"
    letterSize    = len(letters)
    letterIdxMask = 0x7F // 127
)

// getRandomString gets random strings which has given length.
// The characters are used from `letters`.
func getRandomString(length int) (string, error) {
    buf := make([]byte, length)
    if _, err := rand.Read(buf); err != nil {
        return "", err
    }

    for i := 0; i < length; {
        idx := int(buf[i] & letterIdxMask)
        if idx < letterSize {
            buf[i] = letters[idx]
            i++
        } else {
            if _, err := rand.Read(buf[i : i+1]); err != nil {
                return "", err
            }
        }
    }
    return string(buf), nil
}

// getRandomBytes gets random bytes which has given length.
func getRandomBytes(length int) ([]byte, error) {
    buf := make([]byte, length)
    _, err := rand.Read(buf)
    return buf, err
}