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Copy pathstring.go
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61 lines (57 loc) · 1.59 KB
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// Package randstring generates random strings.
//
// Example usage:
//
// s := randstring.NewLen(4) // s is now "apHC"
//
// A standard string created by NewLen consists of Latin upper and
// lowercase letters, and numbers (from the set of 62 allowed
// characters).
//
// Functions read from crypto/rand random source, and panic if they fail to
// read from it.
//
// This package is adapted (simplified) from Dmitry Chestnykh's uniuri
// package.
package randstring
import "crypto/rand"
// stdChars is a set of standard characters allowed in the string.
var stdChars = []byte("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789")
// NewLen returns a new random string of the provided length,
// consisting of standard characters.
func NewLen(length int) string {
return NewLenChars(length, stdChars)
}
// NewLenChars returns a new random string of the provided length,
// consisting of the provided byte slice of allowed characters
// (maximum 256).
func NewLenChars(length int, chars []byte) string {
if length == 0 {
return ""
}
clen := len(chars)
if clen < 2 || clen > 256 {
panic("randstring: wrong charset length for NewLenChars")
}
maxrb := 255 - (256 % clen)
b := make([]byte, length)
r := make([]byte, length+(length/4)) // storage for random bytes.
i := 0
for {
if _, err := rand.Read(r); err != nil {
panic("randstring: error reading random bytes: " + err.Error())
}
for _, rb := range r {
c := int(rb)
if c > maxrb {
// Skip this number to avoid modulo bias.
continue
}
b[i] = chars[c%clen]
i++
if i == length {
return string(b)
}
}
}
}