MultipartReader process the request body as a stream example.

        var maxFileSize int64 = 10 * 1000 * 1000 //limit upload file to 10m
        if r.ContentLength > maxFileSize {
            http.Error(w, "request too large", http.StatusExpectationFailed)
            return
        }
        r.Body = http.MaxBytesReader(w, r.Body, maxFileSize)

        multipartReader, err := r.MultipartReader()
        if err != nil {
            logger.Errorln(err)
            return
        }
        var uploadfile *multipart.Part
        var token string
        for i := 0; i < 2; i++ {
            part, err := multipartReader.NextPart()
            if err == io.EOF {
                break
            }

            if part.FormName() == "token" {
                buf := new(bytes.Buffer)
                buf.ReadFrom(part)
                token = buf.String()
            } else if part.FormName() == "uploadfile" {
                uploadfile = part
            }
        }

In this time, uploadfile implement io.Reader, so we could read it as stream

    r := csv.NewReader(uploadfile)
    record, err := r.Read()
    logger.Debugln("record is ", record)
    if err == io.EOF {
        return err
    }