fix: follow redirects when fetching uploaded files for MIME type detection (#16708)

paulpopus · web-flow · commit ac46214b6d09 · 2026-05-29T14:44:28.000-04:00
## Summary

- When using S3 (or any storage adapter) with `signedDownloads` enabled,
the `staticHandler` returns a `302` redirect to a pre-signed URL.
Payload's `addDataAndFileToRequest` utility calls this handler
internally to fetch back the just-uploaded file for MIME type detection,
but Node.js `fetch` does not automatically follow redirects on a
`Response` object returned from an internal handler call — resulting in
an empty `ArrayBuffer` and a `DataView.getUint16()` bounds error.
- The existing guard in the S3 `staticHandler` (`if (signedDownloads &amp;&amp;
!clientUploadContext)`) was meant to skip the redirect for internal
upload processing, but fires anyway when `clientUploadContext` is
`undefined` (i.e. when no upload context is configured for the
collection).
- Added redirect-following between receiving the handler response and
consuming its body: if the response is a 3xx redirect,
`addDataAndFileToRequest` now follows the `Location` header to retrieve
the actual file bytes before processing.
diff --git a/packages/payload/src/utilities/addDataAndFileToRequest.ts b/packages/payload/src/utilities/addDataAndFileToRequest.ts
@@ -102,6 +102,13 @@ export const addDataAndFileToRequest: AddDataAndFileToRequest = async (req) => {
           throw new APIError('Expected response from the upload handler.')
         }
 
+        if (response.status >= 300 && response.status < 400) {
+          const redirectUrl = response.headers.get('Location')
+          if (redirectUrl) {
+            response = await fetch(redirectUrl)
+          }
+        }
+
         req.file = {
           name: filename,
           clientUploadContext,
