fasthttp 怎么添加headers

package main

import (
    "fmt"
    "time"
    "github.com/valyala/fasthttp"

)

func main() {
    url := `http://localhost:81/page?key=123`
    req := fasthttp.AcquireRequest()
    resp := fasthttp.AcquireResponse()
    cnt := 0
    defer func() {
         fasthttp.ReleaseResponse(resp)
        fasthttp.ReleaseRequest(req)
    }()


    //req.Header.SetContentType("application/json")
    req.Header.SetMethod("POST")
    req.SetRequestURI(url)
    requestBody := []byte(`{"request":"test"}`)
    req.SetBody(requestBody)

    for {
        if cnt > 10 {
            break
        }
        if err := fasthttp.Do(req, resp); err != nil {
            fmt.Println("请求失败:", err.Error())
            return
        }
        b := resp.Body()
        fmt.Println("result:\r\n", string(b))
        time.Sleep(3 * time.Second)
        cnt += 1
    }
}

比如添加个ua怎么写？