transloadit/uppy · error

s3: uploadId must be provided.

Error message

s3: uploadId must be provided.

What it means

The part-upload signing endpoint POST /s3/multipart/:uploadId/:partNumber requires the route parameter uploadId to be a non-empty string. It is the AWS multipart upload ID returned when the multipart upload was created. If it's missing or empty, Companion returns HTTP 400 with this message.

Solutions

1. Store the uploadId returned from the create-multipart response and include it in the URL: POST /s3/multipart/${uploadId}/${partNumber}?key=...
2. Guard client-side: only start part uploads once uploadId is a non-empty string.
3. Re-create the multipart upload (via POST /s3/multipart) if the uploadId was lost, and abort the stale one if known.

Example fix

// before
const url = `/s3/multipart/${upload?.id}/${partNumber}` // may be /s3/multipart/undefined/1

// after
if (!upload?.id) throw new Error('missing uploadId')
const url = `/s3/multipart/${upload.id}/${partNumber}`

if (typeof uploadId !== 'string' || uploadId.length === 0) {
  throw new Error('Cannot sign part: multipart upload was not created yet')
}
const url = `/s3/multipart/${encodeURIComponent(uploadId)}/${partNumber}`

const hasUploadId = (u: unknown): u is string =>
  typeof u === 'string' && u.length > 0

try {
  const res = await signPart(...)
  if (res.status === 400) handleBadRequest(await res.json())
} catch (e) {
  // network-level errors only; 400s are handled above
}

When it happens

Trigger: Calling the sign-part endpoint with an empty uploadId path segment (POST /s3/multipart//5), or with undefined/null interpolated into the URL by a client that lost track of the uploadId after creating the multipart upload.

Common situations: Client state lost between creating the multipart upload and uploading parts (page reload, component remount), or URL construction bugs where uploadId is undefined due to a typo or async race.

Related errors

• s3: content type must be a string
• s3: the object key must be passed as a query parameter. For…
• s3: the part number must be a number between 1 and 10000.
• s3: the part numbers must be a number between 1 and 10000.
• s3: the part numbers must be passed as a comma separated…

AI-assisted analysis of transloadit/uppy@5d4dedd02a (2026-08-28). Data as JSON: /api/errors/2d2bab3df53f71d8. Report an issue: GitHub.

Appendix: source

Thrown at packages/@uppy/companion/src/server/controllers/s3.ts:327

   *
   * Expected URL parameters:
   *  - uploadId - The uploadId returned from `createMultipartUpload`.
   *  - partNumber - This part's index in the file (1-10000).
   * Expected query parameters:
   *  - key - The object key in the S3 bucket.
   * Response JSON:
   *  - url - The URL to upload to, including signed query parameters.
   */
  function signPartUpload(req: Request, res: Response, next: NextFunction) {
    const client = getS3Client(req, res)
    if (!client) return

    const uploadId = req.params['uploadId']
    const partNumber = req.params['partNumber']
    const key = req.query['key']

    if (typeof uploadId !== 'string' || uploadId.length === 0) {
      res.status(400).json({ error: 's3: uploadId must be provided.' })
      return
    }
    if (typeof key !== 'string') {
      res.status(400).json({
        error:
          's3: the object key must be passed as a query parameter. For example: "?key=abc.jpg"',
      })
      return
    }
    if (typeof partNumber !== 'string' || !parseInt(partNumber, 10)) {
      res.status(400).json({
        error: 's3: the part number must be a number between 1 and 10000.',
      })
      return
    }

    const bucket = getBucket({ bucketOrFn: config.bucket, req })

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