Add PGPMimeWrapper.

 - PGPMimeWrapper is an adapter that provides some RFC3156 functions
   on an email.message.Message object.

1 files changed, 36 insertions, 0 deletions

diff --git a/src/mailman_pgp/pgp/mime.py b/src/mailman_pgp/pgp/mime.py
index f3b0d32..08bd111 100644
--- a/src/mailman_pgp/pgp/mime.py
+++ b/src/mailman_pgp/pgp/mime.py
@@ -1 +1,37 @@
 """"""
+from email.message import Message
+from email.utils import collapse_rfc2231_value
+
+
+class PGPMIMEWrapper:
+    def __init__(self, msg: Message):
+        self.msg = msg
+
+    def _is_mime(self):
+        is_multipart = self.msg.is_multipart()
+        payloads = len(self.msg.get_payload())
+        first_part = self.msg.get_payload(0)
+        return is_multipart and payloads == 2 and 'Version: 1' in first_part
+
+    def is_mime_signed(self):
+        """
+        Whether the whole message is MIME signed as per RFC3156 section 5.
+        :return:
+        """
+        protocol_param = collapse_rfc2231_value(self.msg.get_param('protocol'))
+        content_subtype = self.msg.get_content_subtype()
+        return self._is_mime() and \
+               content_subtype == 'signed' and \
+               protocol_param == 'application/pgp-signature'
+
+    def is_mime_encrypted(self):
+        """
+        Whether the whole message is MIME encrypted as per RFC3156 section 4.
+        :return:
+        """
+        content_subtype = self.msg.get_content_subtype()
+        protocol_param = collapse_rfc2231_value(self.msg.get_param('protocol'))
+
+        return self._is_mime() and \
+               content_subtype == 'encrypted' and \
+               protocol_param == 'application/pgp-encrypted'