Subject: [sup-talk] [RFC] Fix parsing of encrypted messages that contain further multipart elements

From: [email-masked] (Adeodato Simó)
Date: Thu, 23 Jul 2009 19:12:58 +0200

---
Hello,

this is just a RFC, because I can't think of any elegant way to address
the issue, given the shortcomings of the RMail API. Please read the
lengthy comment in the patch, and let me know if anybody has any ideas
about this issue.

P.S.: I've created a "sup-dato" repository in Gitorious, in case that's
helpful. Should I be creating merge requests?

 lib/sup/crypto.rb |   19 ++++++++++++++++++-
 1 files changed, 18 insertions(+), 1 deletions(-)

diff --git a/lib/sup/crypto.rb b/lib/sup/crypto.rb
index 8ec277b..6ef0c0e 100644
--- a/lib/sup/crypto.rb
+++ b/lib/sup/crypto.rb
@@ -132,8 +132,25 @@ class CryptoManager
           end
         end
 
+      # This is gross. The decrypted payload could very well be a multipart
+      # element itself, as opposed to a simple payload; for example, a
+      # multipart/signed element, like Mutt does when encrypting and signing a
+      # message (instead of clearsigning it). Supposedly, decrypted_payload
+      # being a multipart element ought to work out nicely because in
+      # Message::multipart_encrypted_to_chunks() the decrypted message is run
+      # though message_to_chunks() again to get any children. However, it does
+      # not work as intended because this inner payload need not carry a
+      # MIME-Version header, yet they are fed to RMail as a top-level message,
+      # for which the MIME-Version header is required, which causes for the
+      # part not to be detected as multipart. If we detect this is happening,
+      # force the payload to be interpreted as MIME.
+      msg = RMail::Parser.read(decrypted_payload)
+      if msg.header.content_type =~ %r{^multipart/} and not msg.multipart?
+        decrypted_payload = "MIME-Version: 1.0\n" + decrypted_payload
+        msg = RMail::Parser.read(decrypted_payload)
+      end
       notice = Chunk::CryptoNotice.new :valid, "This message has been decrypted for display"
-      [RMail::Parser.read(decrypted_payload), sig, notice]
+      [msg, sig, notice]
     else
       notice = Chunk::CryptoNotice.new :invalid, "This message could not be decrypted", output.split("\n")
       [nil, nil, notice]
-- 
1.6.3.3

---

From: [email-masked] (Adeodato Simó)
Date: Thu, 23 Jul 2009 19:19:51 +0200

---
Amended patch follows, with a better wording that I had seemingly not
committed. Sorry for the noise.

 lib/sup/crypto.rb |   20 +++++++++++++++++++-
 1 files changed, 19 insertions(+), 1 deletions(-)

diff --git a/lib/sup/crypto.rb b/lib/sup/crypto.rb
index 8ec277b..acbc1d8 100644
--- a/lib/sup/crypto.rb
+++ b/lib/sup/crypto.rb
@@ -132,8 +132,26 @@ class CryptoManager
           end
         end
 
+      # This is gross. This decrypted payload could very well be a multipart
+      # element itself, as opposed to a simple payload. For example, a
+      # multipart/signed element, like those generated by Mutt when encrypting
+      # and signing a message (instead of just clearsigning the body).
+      # Supposedly, decrypted_payload being a multipart element ought to work
+      # out nicely because Message::multipart_encrypted_to_chunks() runs the
+      # decrypted message through message_to_chunks() again to get any
+      # children. However, it does not work as intended because these inner
+      # payloads need not carry a MIME-Version header, yet they are fed to
+      # RMail as a top-level message, for which the MIME-Version header is
+      # required. This causes for the part not to be detected as multipart,
+      # hence being shown as an attachment. If we detect this is happening,
+      # we force the decrypted payload to be interpreted as MIME.
+      msg = RMail::Parser.read(decrypted_payload)
+      if msg.header.content_type =~ %r{^multipart/} and not msg.multipart?
+        decrypted_payload = "MIME-Version: 1.0\n" + decrypted_payload
+        msg = RMail::Parser.read(decrypted_payload)
+      end
       notice = Chunk::CryptoNotice.new :valid, "This message has been decrypted for display"
-      [RMail::Parser.read(decrypted_payload), sig, notice]
+      [msg, sig, notice]
     else
       notice = Chunk::CryptoNotice.new :invalid, "This message could not be decrypted", output.split("\n")
       [nil, nil, notice]
-- 
1.6.3.3

---

From: [email-masked] (William Morgan)
Date: Sat, 12 Sep 2009 10:08:50 -0700

> committed. Sorry for the noise.

Not sure why I missed this. Branch crypto-mime-fix, merged into next.
Thanks!
-- 
William <wmorgan-sup at masanjin.net>