+@never_cache
+def embargo_link(request, key, format_, slug):
+    book = get_object_or_404(Book, slug=slug)
+    if format_ not in Book.formats:
+        raise Http404
+    if key != book.preview_key:
+        raise Http404
+    media_file = book.get_media(format_)
+    if not book.preview:
+        return HttpResponseRedirect(media_file.url)
+    return HttpResponse(media_file, content_type=constants.EBOOK_CONTENT_TYPES[format_])
+
+