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random.go
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random.go
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package gokits
import (
"crypto/rand"
"io"
)
var chars = []byte("0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz")
func RandomString(length int) string {
b := randomBytesMod(length, byte(len(chars)))
for i, c := range b {
b[i] = chars[c]
}
return string(b)
}
func randomBytesMod(length int, mod byte) (b []byte) {
if length == 0 {
return nil
}
if mod == 0 {
panic("captcha: bad mod argument for randomBytesMod")
}
maxrb := 255 - byte(256%int(mod))
b = make([]byte, length)
i := 0
for {
r := randomBytes(length + (length / 4))
for _, c := range r {
if c > maxrb {
// Skip this number to avoid modulo bias.
continue
}
b[i] = c % mod
i++
if i == length {
return
}
}
}
}
func randomBytes(length int) (b []byte) {
b = make([]byte, length)
if _, err := io.ReadFull(rand.Reader, b); err != nil {
panic("captcha: error reading random source: " + err.Error())
}
return
}