gen.go

package main

import (
	"crypto/rand"
	"io"
)

var stdChars = []byte("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789!@#$%^&*()-_=+,.?/:;{}[]`~")

func newPassword() string {
	return randChar(8, stdChars)
}

func randChar(length int, chars []byte) string {
	newPword := make([]byte, length)
	randomData := 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, randomData); err != nil {
			panic(err)
		}
		for _, c := range randomData {
			if c >= maxrb {
				continue
			}
			newPword[i] = chars[c%clen]
			i++
			if i == length {
				return string(newPword)
			}
		}
	}
}