Like php://input, http_get_request_body_stream() doesn't seem to work with enctype="multipart/form-data".
(PECL pecl_http >= 0.22.0)
http_get_request_body_stream — Get request body as stream
Create a stream to read the raw request body (e.g. POST or PUT data).
This function can only be used once if the request method was another than POST.
Returns the raw request body as stream on success or NULL on failure.