NodeJS后端调用Python文件上传API报错：Expected UploadFile, received <class 'str'>

应用架构 #

• 前端：React Admin框架接收文件，将图片编码为Base64格式后发送至后端API
• 后端：基于NestJS开发，接收前端传来的Base64图片
• 核心问题：后端需要将图片转发至外部Python API完成上传，但多次尝试均失败

已尝试的方案及错误结果 #

方案1：将Base64转为Buffer后直接发送 #

import axios from 'axios';
import FormData from 'form-data';

export async function upload(
  fileBase64: string,
  filename: string
): Promise<any> {

  const buffer = Buffer.from(fileBase64, 'base64')
  const extension = fileBase64.substring(fileBase64.indexOf('/') + 1, fileBase64.indexOf(";;base64"))
  const cleanBase64 = fileBase64.replace(/^data:image\/png;base64,/, '')
  const cleanImageBuffer = Buffer.from(cleanBase64, 'base64')

  const formData = new FormData();
  // 也尝试过传入cleanImageBuffer，结果一致
  formData.append('file', buffer);
  formData.append('fileName', filename + '.' + extension);
  formData.append('namespace', 'test');
  
  return await axios
    .post('external_api_url', JSON.stringify(formData), {
      headers: {
        Authorization: `Bearer token`,
        ContentType: 'multipart/form-data'
      }
    })
    .then((response) => {
      console.log('response = ' + JSON.stringify(response))
    })

错误结果：

{
    "status": "error",
    "error": {
        "code": "bad_request",
        "message": "file Expected UploadFile, received: <class 'str'>"
    }
}

方案2：保存Base64到本地磁盘，通过文件流发送 #

import fs from 'fs';
import axios from 'axios';
import FormData from 'form-data';

export async function upload (
  fileBase64: string,
  filename: string
): Promise<any> {

  const extension = fileBase64.substring(fileBase64.indexOf('/') + 1, fileBase64.indexOf(";;base64"))
  const cleanBase64 = fileBase64.replace(/^data:image\/png;base64,/, '')

  const TMP_UPLOAD_PATH = '/tmp'

  if (!fs.existsSync(TMP_UPLOAD_PATH)) {
    fs.mkdirSync(TMP_UPLOAD_PATH);
  }

  fs.writeFile(TMP_UPLOAD_PATH + '/' + filename + '.' + extension, cleanBase64, 'base64', function(err) {
    console.log(err);
  })

  const fileStream = fs.createReadStream(TMP_UPLOAD_PATH + '/' + filename + '.' + extension)

  const formData = new FormData();
  formData.append('file', fileStream, filename + '.' + extension);
  formData.append('fileName', filename + '.' + extension);
  formData.append('namespace', 'test');

  return await axios
    .post('external_api_url', formData, {
      headers: {
        Authorization: `Bearer token`,
        ContentType: 'multipart/form-data'
      }
    })
    .then((response) => {
      console.log('response = ' + JSON.stringify(response))
    })
}

错误结果：

{
    "status": "error",
    "error": {
        "code": "bad_request",
        "message": "file Expected UploadFile, received: <class 'str'>"
    }
}

其他尝试 #

• 使用node-fetch的fetch方法发送，得到相同错误
• 升级axios至最新版本1.1.3，问题依旧

期望的最优方案 #

无需将Base64图片保存到本地磁盘，直接转为Buffer后发送至外部Python API

可用的Python示例代码（验证过可正常运行） #

import requests

url = "http://127.0.0.1:8000/external_api"

payload={'namespace': 'test'}
files=[
  ('file',('lbl-pic.png',open('/local/path/lbl-pic.png','rb'),'image/png'))
]
headers = {
  'Authorization': 'Bearer token'
}

response = requests.request("POST", url, headers=headers, data=payload, files=files)

print(response.text)

内容的提问来源于stack exchange，提问作者aaa