def METHOD_NAME(request, visa_id, attach_slug):
    visa = get_object_or_404(Visa, pk=visa_id)
    attachment = get_object_or_404(visa.attachments.all(), slug=attach_slug)
    filename = attachment.contents.name.rsplit('/')[-1]
    resp = StreamingHttpResponse(attachment.contents.chunks(), content_type=attachment.mediatype)
    resp['Content-Disposition'] = 'attachment; filename="' + filename + '"'
    resp['Content-Length'] = attachment.contents.size
    return resp