transloadit/uppy · warning · Error

No key returned

Error message

No key returned

What it means

The preauth route requires a non-empty string providerName path parameter. This 400 is returned when the provider segment is missing or empty in the URL.

Source

Thrown at packages/@uppy/aws-s3/src/s3-client/CompanionS3.ts:113

    if (typeof fileType !== 'string') {
      throw new TypeError(`${C.ERROR_PREFIX}fileType must be a string`)
    }

    const method = 'POST'
    const response = await this._fetch('/multipart', {
      method,
      body: JSON.stringify({ filename: keyIn, metadata, type: fileType }),
      headers: { 'content-type': 'application/json' },
      signal,
    })
    const {
      key,
      uploadId,
    }: { key?: string; uploadId?: string; bucket?: string } =
      await response.json()

    if (uploadId == null) throw new Error('No uploadId returned')
    if (key == null) throw new Error('No key returned')

    return { uploadId, key }
  }

  public override async uploadPart({
    key,
    uploadId,
    data,
    partNumber,
    onProgress,
    signal,
  }: IT.UploadPartParams) {
    const response = await this._fetch(
      `/multipart/${encodeURIComponent(uploadId)}/${encodeURIComponent(partNumber)}?${new URLSearchParams({ key })}`,
      {
        method: 'GET',
        signal,
      },

View on GitHub (pinned to 5d4dedd02a)

Solutions

1. Include the provider name in the path, e.g. /companion/url/preauth
2. Verify the provider variable is defined before building the URL
3. Check proxy path rewriting

Example fix

// before
fetch(`${companionUrl}/preauth`, ...)
// after
fetch(`${companionUrl}/${providerName}/preauth`, ...)

if (!providerName) throw new Error('provider name required for preauth URL')
await fetch(`${companionUrl}/${encodeURIComponent(providerName)}/preauth`, ...)

const isNonEmptyString = (s: unknown): s is string => typeof s === 'string' && s.length > 0

When it happens

Trigger: Calling /preauth without a provider segment, or with an empty segment (//preauth); constructing the URL from an undefined provider variable.

Common situations: Frontend builds the preauth URL from a dynamic provider value that is undefined at runtime; route mounted under a path prefix that gets stripped by a proxy.

Related errors

• Missing S3 object key for aborting upload
• No uploadId returned
• AbortError
• Missing S3 object key for resuming upload
• Missing S3 object key for uploading part

AI-assisted analysis of transloadit/uppy@5d4dedd02a (2026-08-28). Data as JSON: /api/errors/28b15ad26eb875ce. Report an issue: GitHub.