woodpecker/vendor/github.com/dchest/uniuri/uniuri.go
2016-04-19 18:47:58 -07:00

71 lines
2 KiB
Go

// Package uniuri generates random strings good for use in URIs to identify
// unique objects.
//
// Example usage:
//
// s := uniuri.New() // s is now "apHCJBl7L1OmC57n"
//
// A standard string created by New() is 16 bytes in length and consists of
// Latin upper and lowercase letters, and numbers (from the set of 62 allowed
// characters), which means that it has ~95 bits of entropy. To get more
// entropy, you can use NewLen(UUIDLen), which returns 20-byte string, giving
// ~119 bits of entropy, or any other desired length.
//
// Functions read from crypto/rand random source, and panic if they fail to
// read from it.
package uniuri
import (
"crypto/rand"
"io"
)
const (
// Standard length of uniuri string to achive ~95 bits of entropy.
StdLen = 16
// Length of uniurl string to achive ~119 bits of entropy, closest
// to what can be losslessly converted to UUIDv4 (122 bits).
UUIDLen = 20
)
// Standard characters allowed in uniuri string.
var StdChars = []byte("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789")
// New returns a new random string of the standard length, consisting of
// standard characters.
func New() string {
return NewLenChars(StdLen, StdChars)
}
// 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 {
b := make([]byte, length)
r := make([]byte, length+(length/4)) // storage for random bytes.
clen := byte(len(chars))
maxrb := byte(256 - (256 % len(chars)))
i := 0
for {
if _, err := io.ReadFull(rand.Reader, r); err != nil {
panic("error reading from random source: " + err.Error())
}
for _, c := range r {
if c >= maxrb {
// Skip this number to avoid modulo bias.
continue
}
b[i] = chars[c%clen]
i++
if i == length {
return string(b)
}
}
}
panic("unreachable")
}