lazy loading of message body

Currently `Message.mime_part` is set in `Message.__init__`. As a result,
when `Thread.get_authors` calls `Thread.get_messages`, the  message
contents are read from disk. Here, I defined `Message.get_mime_part` and
`Message.set_mime_part`, and the mime part is no longer set during init.
As a result, the mime part is only loaded on the first call of
`Message.get_mime_part`. As `Message.get_author` doesn't need the mime
part, this fixes the slowness issue.

alot/buffers/thread.py

@@ -57,7 +57,7 @@ def get_info(self):
         info['thread_tags'] = self.translated_tags_str()
         info['intersection_tags'] = self.translated_tags_str(intersection=True)
         info['mimetype'] = (
-            self.get_selected_message().mime_part.get_content_type())
+            self.get_selected_message().get_mime_part().get_content_type())
         return info
 
     def get_selected_thread(self):

alot/commands/thread.py

@@ -595,7 +595,7 @@ def matches(msgt):
                 if self.mimepart == 'toggle':
                     message = mt.get_message()
                     mimetype = {'plain': 'html', 'html': 'plain'}[
-                        message.mime_part.get_content_subtype()]
+                        message.get_mime_part().get_content_subtype()]
                     mimepart = get_body_part(message.get_email(), mimetype)
                 elif self.mimepart is True:
                     mimepart = ui.get_deep_focus().mimepart

alot/db/message.py

@@ -46,6 +46,7 @@ def __init__(self, dbman, msg, thread=None):
         self._filename = msg.get_filename()
         self._email = None  # will be read upon first use
         self._attachments = None  # will be read upon first use
+        self._mime_part = None  # will be read upon first use
         self._mime_tree = None  # will be read upon first use
         self._tags = set(msg.get_tags())
 
@@ -68,8 +69,6 @@ def __init__(self, dbman, msg, thread=None):
         else:
             self._from = '"Unknown" <>'
 
-        self.mime_part = get_body_part(self.get_email())
-
     def __str__(self):
         """prettyprint the message"""
         aname, aaddress = self.get_author()
@@ -275,9 +274,17 @@ def _is_attachment(part, ct_override=None):
 
         return False
 
+    def get_mime_part(self):
+        if not self._mime_part:
+            self._mime_part = get_body_part(self.get_email())
+        return self._mime_part
+
+    def set_mime_part(self, mime_part):
+        self._mime_part = mime_part
+
     def get_body_text(self):
         """ returns bodystring extracted from this mail """
-        return extract_body_part(self.mime_part)
+        return extract_body_part(self.get_mime_part())
 
     def matches(self, querystring):
         """tests if this messages is in the resultset for `querystring`"""

alot/widgets/thread.py

@@ -361,7 +361,7 @@ def _text_tree_to_widget_tree(self, tree):
 
     def set_mimepart(self, mimepart):
         """ Set message widget mime part and invalidate body tree."""
-        self.get_message().mime_part = mimepart
+        self.get_message().set_mime_part(mimepart)
         self._bodytree = None