Per the GridFS specification:

Aborting an upload

Drivers SHOULD provide a mechanism to abort an upload. When using open_upload_stream, the returned Stream SHOULD have an Abort method. When using upload_from_stream, the upload will be aborted if the source stream raises an error.

When an upload is aborted any chunks already uploaded MUST be deleted. Note that this differs from the case where an attempt to insert a chunk fails, in which case drivers immediately report the failure without attempting to delete any chunks already uploaded.

Abort MUST raise an error if it is unable to succesfully abort the upload (for example, if an error occurs while deleting any chunks already uploaded). However, if the upload is being aborted because the source stream provided to upload_from_stream raised an error then the original error should be re-raised.

Abort MUST also close the Stream, or at least place it in an aborted state, so any further attempts to write additional content to the Stream after Abort has been called fail immediately.

PHP's StreamWrapper has no API for aborting an upload; however, we should still follow the abort process if uploading a file encounters an error.