生成预签名下载链接

func (p *S3Demo) generateUrl() {
    bucket := "<your-bucket-name>"
    key := "<your-key-name>"
    expire := <expire-time> // e.g. 5*time.Minute
    req, _ := p.svc.GetObjectRequest(&s3.GetObjectInput{
        Bucket: &bucket,
        Key:    &key,
    })
    urlStr, err := req.Presign(expire)
    if err != nil {
        fmt.Println("err, ", err)
        return
    }
    fmt.Println("success, ", urlStr)
}