multipart/form-data requests of multiple files on the same parameter are not returned

[erunion]

With the following code that sends multiple files to https://httpbin.org/anything only one of them is returned in the payload.

const form = new FormData();

const files = [
  new File(
    [
      'data:image/png;name=owlbert.png;base64,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',
    ],
    'owlbert.png',
    { type: 'image/png' }
  ),
  new File(
    [
      'data:image/png;name=owlbert-shrub.png;base64,iVBORw0KGgoAAAANSUhEUgAAABAAAAAQCAYAAAAf8/9hAAACNUlEQVR4AWJkIA2wCQHqJgcouZ0ADv+SmayR28PibPOP2jafzdp6Lh/v2bVt2+1zbdvtbtbMpGfmvmD8jStc9uB3v75gdNmqtJqsa6qCDEBPRVH7XpKk1P9yHLZv3mG6keV9BIsWGqNuvNaiy+YoARFIXFXwf6Frjz/X9oS4LNRkty4QH/0MSnnWDHORHV3pJsiozRk0zWW/9MEi0A9ffqOhf5RRDW6SGLT/ZXcT8C1hWvao8iF1c4ecKx5eejW1bii1y1asW14P5XsUNkogmvVQg2aPLOnrqss9qE81OYlAucRrN/LrqlBSWYufv34jq7gKseA7MCr0IOhffForGsTWDBJnqE2/B0H+hKRRG3DtxEGk6QBZQ9UFClMSnTJe/cCVI5uQJJpx+8AyOBUPPv+JIpJjgJqCZzKT0AGdAgT/1OLtSzsKI2/gspnxvGExZYFADcoSsqM10SADF4jC4TCCUDN8nih+eoIgPAdGeajBNxyMH20JwsPNMwSicUjBCAwmAZ6GkCmA7I+qCxTGRHSkVzZiCRmKAsRkuVmWiENrt6gL5Di7iw4oogFSINIkCTU09hNAP64CREPUBbzAx9ABrc2I3w2NeY5DMByHu8AGY3YyeoKIuSmBWCD6OuqLPJXe/Dpvkb3FuoDbdENKuBVJ4nxZJpKgWoUXCMcYUwBwDfR8FxZPN4wfWK2Zunq7tGLmZMOc7x7ZUn/RuDmrX0H/4FffQ2teylCecuWmDNsTnainfwFPuNZTR3MemwAAAABJRU5ErkJggg==',
    ],
    'owlbert-shrub.png',
    { type: 'image/png' }
  )
];

for (const file of files) {
  form.append('files', file, file.name);
}

fetch('https://httpbin.org/anything', {
  method: 'post',
  body: form,
})
  .then(res => res.json())
  .then(console.log);

{
  "args": {},
  "data": "",
  "files": {
    "files": "data:image/png;name=owlbert.png;base64,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"
  },
  "form": {},
  "headers": {
    "Accept": "*/*",
    "Accept-Encoding": "gzip, deflate, br",
    "Accept-Language": "en-US,en;q=0.9",
    "Content-Length": "1784",
    "Content-Type": "multipart/form-data; boundary=----WebKitFormBoundarywCjQuPHebN5OoDBI",
    "Host": "httpbin.org",
    "Origin": "http://httpbin.org",
    "Referer": "http://httpbin.org/",
    "Sec-Ch-Ua": "\".Not/A)Brand\";v=\"99\", \"Google Chrome\";v=\"103\", \"Chromium\";v=\"103\"",
    "Sec-Ch-Ua-Mobile": "?0",
    "Sec-Ch-Ua-Platform": "\"macOS\"",
    "Sec-Fetch-Dest": "empty",
    "Sec-Fetch-Mode": "cors",
    "Sec-Fetch-Site": "cross-site",
    "User-Agent": "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/103.0.0.0 Safari/537.36",
    "X-Amzn-Trace-Id": "REDACTED"
  },
  "json": null,
  "method": "POST",
  "origin": "REDACTED",
  "url": "https://httpbin.org/anything"
}

However, both files are actually being delivered but only owlbert.png was returned:

In order to rule out that this was an HTTPBin issue I spun up a small Express server to test this out with multer and the multiple files are returned:

const express = require('express')
const multer = require('multer')
const upload = multer({ dest: 'uploads/' })

const app = express()

app.post('/', upload.array('files', 12), function (req, res, next) {
  console.log(req.files)
})

const port = 3000;

app.listen(port);
console.log(`Express app started on port ${port}`);

And the logged out data from sending the same POST request to http://localhost:3000/:

[
  {
    fieldname: 'files',
    originalname: 'owlbert.png',
    encoding: '7bit',
    mimetype: 'image/png',
    destination: 'uploads/',
    filename: '4c9a0a2c4360b21d9da215270d4ce7a5',
    path: 'uploads/4c9a0a2c4360b21d9da215270d4ce7a5',
    size: 575
  },
  {
    fieldname: 'files',
    originalname: 'owlbert-shrub.png',
    encoding: '7bit',
    mimetype: 'image/png',
    destination: 'uploads/',
    filename: '5456576fa1b1f17b517b15085d618327',
    path: 'uploads/5456576fa1b1f17b517b15085d618327',
    size: 877
  }
]

I also thought that maybe it was because I was sending the payload as files instead of files[], but making a request with that returned similar results:

{
  "args": {},
  "data": "",
  "files": {
    "files[]": "data:image/png;name=owlbert.png;base64,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"
  },
  "form": {},
  "headers": {
    "Accept": "*/*",
    "Accept-Encoding": "gzip, deflate, br",
    "Accept-Language": "en-US,en;q=0.9",
    "Content-Length": "1788",
    "Content-Type": "multipart/form-data; boundary=----WebKitFormBoundaryB0dcYW2WEwUoiUgo",
    "Host": "httpbin.org",
    "Origin": "http://httpbin.org",
    "Referer": "http://httpbin.org/",
    "Sec-Ch-Ua": "\".Not/A)Brand\";v=\"99\", \"Google Chrome\";v=\"103\", \"Chromium\";v=\"103\"",
    "Sec-Ch-Ua-Mobile": "?0",
    "Sec-Ch-Ua-Platform": "\"macOS\"",
    "Sec-Fetch-Dest": "empty",
    "Sec-Fetch-Mode": "cors",
    "Sec-Fetch-Site": "cross-site",
    "User-Agent": "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/103.0.0.0 Safari/537.36",
    "X-Amzn-Trace-Id": "REDACTED"
  },
  "json": null,
  "method": "POST",
  "origin": "REDACTED",
  "url": "https://httpbin.org/anything"
}