From: a@example.com
Subject: [PATCH] asdf
Message-ID: <patch@example.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit
Content-Type: multipart/mixed; boundary="b"

--b
Content-Type: text/plain

hi, see attached
--b
Content-Type: text/plain
Content-Disposition: inline; filename="foo&.patch"

--- a/file
+++ b/file
@@ -49, 7 +49,34 @@

--b--