How to verify file type for multipart/form data upload in vertx? - vert.x

Question

I have a multipart/form with file upload in my Vert.x web application.
The issue I am running into is that I can only seem to validate the type of the uploaded file after having the request go through Vertx's BodyHandler.
Now I can validate the type after it went through, but the BodyHandler has already uploaded the file at this point in time. On a similair issue it was stated that you should check the content-type with your own handler before the BodyHandler, but this always returns an empty formAttributes.
I've tried creating my own handler:
public void handle(RoutingContext context) {
context.request().setExpectMultipart(true);
MultiMap attributes = context.request().formAttributes();
System.out.println(attributes);
context.next();
}
But attributes is always empty, so I can't verify the content-type of the file uploaded.
After it passes through the BodyHandler into my other handler it works fine:
MultiMap attributes = context.request().formAttributes();
Set<FileUpload> uploads = context.fileUploads();
for (FileUpload file : uploads
) {
System.out.println(file.contentType());
// This returns image/jpeg
}
context.response().end();
But as I stated above, the file is already uploaded when it has passed through the BodyHandler.
Here is the code for the handlers:
router.post("/api/someendpoint").handler(new FileTypeHandler());
router.post("/api/someendpoint").handler(BodyHandler.create()
.setUploadsDirectory("static/images")
.setBodyLimit(MB * 1));
router.post("/api/someendpoint").handler(new EndPointHandler());
How can I verify the type of a file being uploaded before it passes through the BodyHandler, so that I can reject any other file upload except an image?