Posting formdata may result in request header 'Content-Length': 'NaN' being set

[thhermansen]

Describe the bug

Passing a FormData object to Axios client may result in request header 'Content-Length': 'NaN' being set.

To Reproduce

Given the following code:

// client is an Axios instance
const pdf = await client.get(pdfUrl, { responseType: 'stream' });

const form = new FormData();
form.append('file', pdf.data, { filename, contentType: 'application/pdf' });

const res = await client.post(urlToUploadService, form);

We get the following request header added:

    headers: AxiosHeaders {
      Accept: 'application/json, text/plain, */*',
      'Content-Type': 'multipart/form-data; boundary=--------------------------852062351748726458865935',
      'User-Agent': 'axios/1.3.2',
      'Content-Length': 'NaN',
      'Accept-Encoding': 'gzip, compress, deflate, br'
    },

I believe 'Content-Length': 'NaN', is not something we want :) I'm pretty sure the header was not added with Axios version 1.2.6.

---

I believe this is related code:

axios/lib/adapters/http.js

Lines 266 to 267 in 0b44929

	const knownLength = await util.promisify(data.getLength).call(data);
	headers.setContentLength(knownLength);

If we log form's getLength:

  form.getLength((err, length) => {
    console.log(err, length);
  }),

We'll get a hint of what is going on:

null NaN

Axios Version

1.3.2

Adapter Version

No response

Browser

No response

Browser Version

No response

Node.js Version

v18.14.0

OS

macos 13.2

Additional Library Versions

No response

Additional context/Screenshots

• I believe fix(formdata): add hotfix to use the asynchronous API to compute the content-length header value; #5521 is relevant as it tried to fix some related issue(?).
• Not 100% sure if this is a https://github.com/form-data/form-data issue or an Axios issue, but given it previously worked I though I would register it here.

[DigitalBrainJS]

Thanks for the report! I can't reproduce the error, but we'll add an isFinite check on our side, just in case. Apparently, there are some unhandled cases under which the method returns NaN instead of calling its callback with an error.

[thhermansen]

Thank you! :)