class_docstr: !
  Integrate multiple model convertion tools, and provide convertion service for users.
  When user uploads a model to this server, convert model and upload the results to VDL Bos.
  When user downloads the model, we get the data from Bos and send it to client.
  Maybe users can download from bos directy if frontend can achieve it.
docstr: Download converted paddle model from bos.
docstr_tok: ["Download","converted","paddle","model","from","bos","."]
code: def onnx2paddle_model_download(self, request_id):
      """
      Download converted paddle model from bos.
      """
      filename = "bos://{}/onnx2paddle/{}.tar".format(
          self.bucket_name, request_id
      )
      data = None
      if self.bos_client.exists(filename):
          data = self.bos_client.read_file(filename)
      if not data:
          raise RuntimeError(
              "The requested model can not be downloaded due to not existing or convertion failed."
          )
      print(len(data))
      return data
  
imports: import base64
  import hashlib
  import json
  import os
  import shutil
  import tempfile
  import paddle
  import paddle2onnx
  from flask import request
  from x2paddle.convert import onnx2paddle
  from .xarfile import archive
  from visualdl.io.bfile import BosFileSystem
  from visualdl.server.api import gen_result
  from visualdl.server.api import result
  from visualdl.utils.dir import X2PADDLE_CACHE_PATH
label_desc: Use image node_id 3 for calling the ModelConvertApi obj's underlying member method code with example usage: obj.onnx2paddle_model_download(request_id) and returns: data