db/message: turn _email and body into cached properties

Does not really change much for now, since the email is still loaded in
the constructor, but will allow optimization later.

1 files changed, 19 insertions, 15 deletions

diff --git a/alot/db/message.py b/alot/db/message.py
index 401230ba..f2a298d7 100644
--- a/alot/db/message.py
+++ b/alot/db/message.py
@@ -6,6 +6,7 @@ import codecs
 import email
 import email.charset as charset
 import email.policy
+from functools import cached_property
 import logging
 import os
 import subprocess
@@ -383,15 +384,7 @@ class Message:
     """
     parent = None
 
-    """
-    The object providing access to the email's headers.
-    """
-    headers = None
-
-    """
-    A MimeTree object containing the body of the message.
-    """
-    body = None
+    _session_keys = None
 
     def __init__(self, dbman, thread, msg, depth):
         """
@@ -421,11 +414,7 @@ class Message:
         session_keys = []
         for name, value in msg.properties.getall('session-key', exact = True):
             session_keys.append(value)
-
-        self._email = self._load_email(session_keys)
-
-        self.body    = _MimeTree(self._email, session_keys)
-        self.headers = self.body.headers
+        self._session_keys = session_keys
 
         self._tags = set(msg.tags)
 
@@ -457,11 +446,26 @@ class Message:
             return self.id == other.id
         return NotImplemented
 
+    @cached_property
+    def body(self):
+        """
+        A MimeTree object containing the body of the message.
+        """
+        return _MimeTree(self._email, self._session_keys)
+
+    @property
+    def headers(self):
+        """
+        The object providing access to the email's headers.
+        """
+        return self.body.headers
+
     @property
     def filename(self):
         return self.filenames[0]
 
-    def _load_email(self, session_keys):
+    @cached_property
+    def _email(self):
         try:
             with open(self.filename, 'rb') as f:
                 mail = email.message_from_bytes(f.read(), policy = email.policy.SMTP)