如何提升图片链接替换性能？

var once sync.Once
var client *oss.Client

func initOssClient() {
    once.Do(func() {
        var err error
        client, err = oss.New(endpoint, key, secret)
        if err != nil {
            log.Fatal(err)
        }
    })
}

func Upload(url string) string {
    initOssClient()

    t1 := time.Now().Unix()
    long := 0

    obj := fmt.Sprintf("article/%d%d.png", t1, long)
    bucket, err := client.Bucket(bucketName)
    if err != nil {
        log.Fatal(err)
    }

    r, err := http.Get(url)
    if err != nil {
        log.Fatal(err)
    }
    defer r.Body.Close()

    err = bucket.PutObject(obj, r.Body)
    if err != nil {
        log.Fatal(err)
    }
    return "https://" + bucketName + "." + endpoint + "/" + obj
}

var cache = map[string]string{}

func RepImages(htmls string) string {
    var imgRE = regexp.MustCompile(`@@##@@]+\bsrc=["']([^"']+)["']`)
    imgs := imgRE.FindAllStringSubmatch(htmls, -1)
    out := make([]string, len(imgs))

    for i := range out {
        url := imgs[i][1]
        if cachedUrl, ok := cache[url]; ok {
            out[i] = imgs[i][1]
            continue
        }

        myImage := Upload(url)
        cache[url] = myImage
        resHtml := strings.Replace(resHtml, imgs[i][1], myImage, -1)
        out[i] = imgs[i][1]
    }

    return resHtml
}