How to send data correct axios Error: Multipart: Boundary not found

I don't know why I receive on server [Error: Multipart: Boundary not found] and bundle.js:37628 POST http://localhost:8800/exporttocsv 500 (Internal Server Error) When I make post through

<form action="/exporttocsv" method="POST"  encType="multipart/form-data">

post works correctly, but through axios doesn't work.

Please help me fix the mistake

this my code /--client

import axios from 'axios'
var formData = new FormData()

const config = { headers: { 'Content-Type': 'multipart/form-data' } };
export const ipmortToCSV = (file) => dispatch => {

formData.append('file',file)
console.log(formData.getAll('data'))

axios.post('/exporttocsv', {
          "UploadCommand": formData
      },config)
      .then(function (response) {
        console.log(response);
      })
      .catch(function (error) {
        console.log(error);
      });

//--server

const router = require('express').Router()
var csv = require('csv-express')
const controllers = require('../../controllers/exporttocsv')
var multer  = require('multer')
var upload = multer({dest : 'exporttocsv/'})

router.get('/', (req, res) => {
      controllers.exportToCsv(req,res)
  })
router.post('/',upload.single('file'),(req,res) => { 
    //controllers.importToCsv(req,res)
})

module.exports = router

You can do this ...

Instantiate a new `FormData` instance.

const config = { headers: { 'Content-Type': 'multipart/form-data' } };
let fd = new FormData();
fd.append('file',files[0])
return axios.post("http://localhost:5000/upload", fd, config)

Using`concat` and `concat-stream`

const concat = require("concat-stream")
const fd = new FormData()

fd.append("hello", "world")
fd.append("file", fs.createReadStream(file))
fd.pipe(concat(data => {
  axios.post("/hello", data, {
    headers: fd.getHeaders()
  })
}))

Using `promise`

const promise = new Promise((resolve) => {
  const fd = new FormData();
  fd.append("hello", "world");
  fd.append("file", fs.createReadStream(binaryFile));
  fd.pipe(concat({ encoding: 'buffer' }, data => resolve({ data, headers: fd.getHeaders() })));
});
promise.then(({ data, headers }) => axios.post('/hello', data, { headers }));

I hope I've been useful! :)

References:

I was getting this problem with Axios via JavaScript because the content-type header was multipart-form-data but the boundary was missing.

Based on my research, a good way to handle it is to allow Axios to auto-detect the content type and set the headers correctly itself.

Here is an idea for how to accomplish this:

const formDataWithFiles = hasFiles ? new FormData() : undefined;

if (formDataWithFiles) {
    // axios will automatically set the content-type to multipart/form-data if the
    // data param is a FormData object
    // otherwise, it will use application/json
    // (study the Dev Tools > Network tab > XHR tab headers)
    Object.keys(modifiedFields)
        .forEach(field => formDataWithFiles.append(field, modifiedFields[field]));
}

const { data } = await axios({
    method,
    url: actionUrl,
    data: hasFiles ? formDataWithFiles : modifiedFields,
    headers: {
        ...axios.defaults.headers,
        ...headers,
    },
});

return data;

The above code is in a generic handleSubmit function that can be called from anywhere in the client-side.

Here is the function signature:

const { data } = await this.submitForm({
    actionUrl: this.actionUrl,
    method: this.method,
    modifiedFields: {
        ...this.modifiedUser,
    },
    hasFiles: true,
});

In the above code, there are two use cases. The first is the default case, where a normal payload is sent via a flat object. The second is the case when the form has files and you want multipart/form-data. In this case, we use the FormData Object as a vessel to instruct Axios to auto-detect the necessary headers and set the correct boundary.

If you do not specify the headers correctly, it is possible to receive an empty $request->all() Array in Laravel, or perhaps any server such as node.js.

The short answer to my answer is to use the FormData Object because it contains more information than a plain-old-JavaScript-object. With it, you can also access:

const formData = new FormData();

console.log('boundary:', formData._boundary);

As my annotation above hints towards, use the Dev Tools > Network tab > XHR tab to examine your request headers and make sure you have content-type application/json or application/x-www-form-urlencoded for regular form submits and multipart/form-data' if you are uploading a file.

来源：https://stackoverflow.com/questions/49579640/how-to-send-data-correct-axios-error-multipart-boundary-not-found

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