@vercel/blob: uploading empty file throws `BlobError: Vercel Blob: Missing [x]-content-length header.`

[arthurfiorette]

Some files, like .gitkeep or blank test files that we do not have control over, must be uploaded. Instead of successfully uploading, a BlobError: Vercel Blob: Missing [x]-content-length header. is thrown in these cases.

[vvo]

Hey @arthurfiorette, we'll fix this soon, sorry about that

[movila]

We're also facing same issue. Is there any updates on this?

[matingathani]

I tracked down the root cause and opened a fix in #1036.

The problem is in api.ts — x-content-length is only sent when onUploadProgress is set or the VERCEL_BLOB_USE_X_CONTENT_LENGTH env var is present. For a 0-byte file in production without progress tracking, neither condition is true, so the header is never sent and the API rejects the request.

The fix makes all bodies with a deterministic size (Blob, File, Buffer, string) always send x-content-length — including when that size is 0. Streams are kept as-is since their size can't be known upfront.

Happy to adjust anything if there's a reason the header was intentionally scoped to those conditions!

[vvo]

Uploading empty files is now working 👍