Python 2.7 使用flask API从我的s3 bucket和boto3库在浏览器上下载文件

我想用我的FlaskAPI从s3 bucket下载浏览器上的文件。以前我将数据存储在服务器上，所以flask send文件对我来说非常有效，我可以下载该文件。现在，我已经切换到s3存储桶来存储我的docs send_文件，但它不起作用。 我正在使用boto3库连接s3服务器

这是代码供参考

下载文件的函数

def download_file_from_s3_bucket(KEY):
    s3_client = s3_bucket_connection()
    try:
        file_obj = open("test.pdf", "r+")
        s3_client.download_fileobj(settings.BUCKET_NAME, KEY, file_obj)
        return file_obj
    except Exception as e:
        return {"status": False, "message": e.message} 

烧瓶API：

@api.route("/return_file", methods=["GET","POST"])
@jwt_required
def return_file():
    try:
        json_data = request.get_json(force=True)
        upload_id = json_data.get('upload_id')
        upload_path,file_name = v2_business.get_upload_path(upload_id)
        file_link = upload_path

        # old way to get file from local server.
        # return send_file(file_link,file_name)
        download_file_obj = root_business.download_file_from_s3_bucket(upload_path)
        return send_file(download_file_obj, as_attachment=True, attachment_filename=file_name)
    except IOError as e:
        return jsonify({"status":  False,
                    "message": (e.__class__.__name__ + ': ' + (str(e)))})
    except Exception as e:
        return jsonify({
            "status": False,
            "message": e.message
        })