generate random string in go

random.go

package main

import (
	"math/rand"
	"time"
	"fmt"
)

const (
	lowercaseLetter = `abcdefghijklmnopqrstuvwxyz`
	uppercaseLetter = `ABCDEFGHIJKLMNOPQRSTUVWXYZ`
	digital         = `0123456789`
	specialSymbols  = `@-_`
)

func init() {
	rand.Seed(time.Now().UnixNano())
}

func main() {
	fmt.Println(RandString(4))
	fmt.Println(RandString(8))
	fmt.Println(RandString(16))
	fmt.Println(RandString(32))
}

// RandString 生成指定长度(length)的随机密码pwd
//  密码长度为 4~64位, 超范围返回空密码
//  密码包含以下必选项:
//  小写字母: a-z
//  大写字母: A-Z
//  印度数字: 0-9
//  特殊符号: @-_
func RandString(length int) (pwd string) {
	if length < 4 || length > 64 {
		return
	}
	// 1. 随机分配4种类型字符的数量
	assign := [...]int{1, 1, 1, 1}
	types := len(assign)
	for i := 0; i < (length - 4); i++ {
		assign[rand.Intn(types)]++
	}
	sum := 0
	for _, v := range assign {
		sum += v
	}
	if length != sum {
		return
	}
	// 2. 根据各类型字符的数量,随机填充密码
	chars := [][]byte{
		[]byte(lowercaseLetter),
		[]byte(specialSymbols),
		[]byte(uppercaseLetter),
		[]byte(digital),
	}
	pwds := make([]byte, length)
	index := 0
	for i := range pwds {
		if types > 1 {
			index = rand.Intn(types)
		} else {
			index = 0
		}
		pwds[i] = chars[index][rand.Intn(len(chars[index]))]
		if assign[index]--; assign[index] <= 0 {
			types--
			assign[index], assign[types] = assign[types], assign[index]
			chars[index], chars[types] = chars[types], chars[index]
		}
	}
	// 3. 随机打乱生成的密码序
	for i := range pwds {
		n := rand.Intn(length)
		pwds[i], pwds[n] = pwds[n], pwds[i]
	}
	pwd = string(pwds)
	return
}