--AaB03x
Content-Disposition: form-data; name="foo"

bar
--AaB03x
Content-Disposition: form-data; name="files"
Content-Type: multipart/mixed, boundary=BbC04y

--BbC04y
Content-Disposition: attachment; filename="file.txt"
Content-Type: text/plain

contents
--BbC04y
Content-Disposition: attachment; filename="flowers.jpg"
Content-Type: image/jpeg
Content-Transfer-Encoding: binary

contents
--BbC04y--
--AaB03x--