TypeError: Failed to parse body as FormData with Axios

[kettanaito]

Bug Description

When performing a POST request with FormData and Axios, Undici fails to parse the request body.

Reproducible By

import axios from 'axios'
import { http } from 'msw'
import { setupServer } from 'msw/node'

const server = setupServer(
  http.post('*/upload', async ({ request }) => {
    // This is a regular Request instance constructed using Undici.
    const data = await request.formData()
    return Response.json(data)
  })
)
server.listen()

const request = axios.create({
  baseURL: 'https://example.com/upload',
  onUploadProgress() {},
})

const formData = new FormData()
const file = new Blob(['Hello', 'world'], { type: 'text/plain' })
formData.set('file', file, 'doc.txt')

const response = await request.post('https://example.com/upload', formData).catch(error => {
  throw error.response.data
})

This throws the following error:

{
  name: 'TypeError',
  message: 'Failed to parse body as FormData.',
  stack: 'TypeError: Failed to parse body as FormData.\n' +
    '    at node:internal/deps/undici/undici:5415:27\n' +
    '    at successSteps (node:internal/deps/undici/undici:5459:27)\n' +
    '    at fullyReadBody (node:internal/deps/undici/undici:4378:9)\n' +
    '    at process.processTicksAndRejections (node:internal/process/task_queues:95:5)\n' +
    '    at async consumeBody (node:internal/deps/undici/undici:5468:7)\n' +
    '    at async file:///mswjs/msw/repro.mjs:8:18\n' +
    '    at async file:///mswjs/msw/lib/core/handlers/RequestHandler.mjs:121:24\n' +
    '    at async HttpHandler.run (file:///mswjs/msw/lib/core/handlers/RequestHandler.mjs:107:28)\n' +
    '    at async executeHandlers (file:///mswjs/msw/lib/core/utils/executeHandlers.mjs:10:14)\n' +
    '    at async until (file:///mswjs/msw/node_modules/.pnpm/@open-draft+until@2.1.0/node_modules/@open-draft/until/lib/index.mjs:4:18)'
}

Node.js v22.3.0

I have a strong reason to believe something has changed in Undici between Node.js v21 and v22, which is causing this parsing issue. This same scenario is passing with the same dependencies using Node.js v18-v20.

Expected Behavior

Undici parses the FormData body sent from Axios.

Logs & Screenshots

Here's the FormData body read as text. This looks okay to me.

--axios-1.6.8-boundary-3Jx5-4T27f9Yo6Ul865QObiBm
Content-Disposition: form-data; name="file"; filename="doc.txt"
Content-Type: text/plain

Helloworld
--axios-1.6.8-boundary-3Jx5-4T27f9Yo6Ul865QObiBm--

Environment

• Node v22.3.0
• Axios v1.6.8 (the behavior is the same on the latest Axios version v1.7.7)

[kettanaito]

Can it be that Undici became strict to who constructs the FormData? The headers of the data clearly feature some Axiom boundary. Can that be the thing that upsets Undici? Does it only accept FormData instances created by itself?

[KhafraDev]

Could you provide an example that doesn't use axios or msw? I'd need the exact body (including \r\n's) and the content-type header to assess.

[kettanaito]

@KhafraDev, that doesn't seem to be possible. I can omit MSW since it has nothing to do with this scenario, but the issue is specific to Axios. If you feel raising it with Axios is a better approach, I will do so. If nothing rings a bell by looking at the payload above, then I suppose the FormData payload is okay.

I can share the request body as buffer, which should preserve the newlines and other characters. Would that help?

[KhafraDev]

I need the raw body and the content-type header.

[KhafraDev]

I found a repro without dependencies. Will have a fix soon.

const response = new Response([
  '--axios-1.7.7-boundary-bPgZ9x77LfApGVUN839vui4V7\r\n' +
  'Content-Disposition: form-data; name="file"; filename="doc.txt"\r\n' +
  'Content-Type: text/plain\r\n' +
  '\r\n' +
  'Helloworld\r\n' +
  '--axios-1.7.7-boundary-bPgZ9x77LfApGVUN839vui4V7--\r\n' +
  '\r\n',
].join(''), {
  headers: {
    'content-type': 'multipart/form-data; boundary=axios-1.7.7-boundary-bPgZ9x77LfApGVUN839vui4V7'
  }
})

await response.formData()

[kettanaito]

Thank you for fixing this, @KhafraDev! Amazing job, as always.

[539hex]

Hi, in which version of node is this fixed ? @KhafraDev i am using node 23.3.0 and got the same issue

[SilvanBauser]

This popped up again as of last week in Node 22 & 23.

[busy-dog]

Bug Description

When performing a POST request with FormData and Axios, Undici fails to parse the request body.

Reproducible By

import axios from 'axios'
import { http } from 'msw'
import { setupServer } from 'msw/node'

const server = setupServer(
http.post('*/upload', async ({ request }) => {
// This is a regular Request instance constructed using Undici.
const data = await request.formData()
return Response.json(data)
})
)
server.listen()

const request = axios.create({
baseURL: 'https://example.com/upload',
onUploadProgress() {},
})

const formData = new FormData()
const file = new Blob(['Hello', 'world'], { type: 'text/plain' })
formData.set('file', file, 'doc.txt')

const response = await request.post('https://example.com/upload', formData).catch(error => {
throw error.response.data
})
This throws the following error:

{
  name: 'TypeError',
  message: 'Failed to parse body as FormData.',
  stack: 'TypeError: Failed to parse body as FormData.\n' +
    '    at node:internal/deps/undici/undici:5415:27\n' +
    '    at successSteps (node:internal/deps/undici/undici:5459:27)\n' +
    '    at fullyReadBody (node:internal/deps/undici/undici:4378:9)\n' +
    '    at process.processTicksAndRejections (node:internal/process/task_queues:95:5)\n' +
    '    at async consumeBody (node:internal/deps/undici/undici:5468:7)\n' +
    '    at async file:///mswjs/msw/repro.mjs:8:18\n' +
    '    at async file:///mswjs/msw/lib/core/handlers/RequestHandler.mjs:121:24\n' +
    '    at async HttpHandler.run (file:///mswjs/msw/lib/core/handlers/RequestHandler.mjs:107:28)\n' +
    '    at async executeHandlers (file:///mswjs/msw/lib/core/utils/executeHandlers.mjs:10:14)\n' +
    '    at async until (file:///mswjs/msw/node_modules/.pnpm/@open-draft+until@2.1.0/node_modules/@open-draft/until/lib/index.mjs:4:18)'
}

Node.js v22.3.0

I have a strong reason to believe something has changed in Undici between Node.js v21 and v22, which is causing this parsing issue. This same scenario is passing with the same dependencies using Node.js v18-v20.

Expected Behavior

Undici parses the FormData body sent from Axios.

Logs & Screenshots

Here's the FormData body read as text. This looks okay to me.

--axios-1.6.8-boundary-3Jx5-4T27f9Yo6Ul865QObiBm
Content-Disposition: form-data; name="file"; filename="doc.txt"
Content-Type: text/plain

Helloworld
--axios-1.6.8-boundary-3Jx5-4T27f9Yo6Ul865QObiBm--

Environment

• Node v22.3.0
• Axios v1.6.8 (the behavior is the same on the latest Axios version v1.7.7)

reopen this issue plz