Use property wrappers to defer parsing content

lib/nntp/tiny/message.py

@@ -44,14 +44,14 @@ class MessageState(enum.Enum):
 class Message(DatabaseTable):
     __slots__ = (
         '_cache',
+        '_headers',
+        '_body',
+        '_key',
         'id',
         'newsgroup_id',
         'state',
-        'headers',
         'line',
         'content',
-        'body',
-        '_key'
     )
 
     name    = 'newsgroup_message'
@@ -71,19 +71,19 @@ class Message(DatabaseTable):
 
     def __init__(self):
         self._cache       = dict()
+        self._headers     = None
+        self._body        = None
+        self._key         = None
         self.id           = None
         self.newsgroup_id = None
         self.state        = MessageState.EMPTY
-        self.headers      = None
         self.line         = None
         self.content      = ''
-        self.body         = None
-        self._key         = None
 
     @staticmethod
     def __from_row__(row):
         message = Message()
-        message.headers      = dict()
+        message._headers     = dict()
         message.id           = row['id']
         message.newsgroup_id = row['newsgroup_id']
         message.created_on   = row['created_on']
@@ -91,7 +91,11 @@ class Message(DatabaseTable):
         message.parent_id    = row['parent_id']
         message.sender       = row['sender']
 
-        message.read(row['content'])
+        #
+        # Defer parsing the message content until a specific header not already
+        # assigned to a dedcicated property, or the message body, is required.
+        #
+        message.content = row['content']
 
         return message
 
@@ -106,6 +110,20 @@ class Message(DatabaseTable):
             self.content
         )
 
+    @property
+    def headers(self):
+        if self._headers is None:
+            self.read(self.content)
+
+        return self._headers
+
+    @property
+    def body(self):
+        if self._body is None:
+            self.read(self.content)
+
+        return self._body
+
     def header(self, key: str):
         if self.headers is None:
             self.read(self.content)
@@ -177,20 +195,20 @@ class Message(DatabaseTable):
 
         if self.state is MessageState.EMPTY:
             self.state    = MessageState.HEADER
-            self.headers = dict()
+            self._headers = dict()
 
         if self.state is MessageState.HEADER:
             if line == '\n' or line == '\r\n':
                 self.state = MessageState.BODY
             elif line[0] == ' ' or line[0] == '\t':
-                self.headers[self._key] += ' ' + decode(line.strip())
+                self._headers[self._key] += ' ' + decode(line.strip())
             else:
                 match = self.RE_HEADER.match(line)
 
                 if match:
                     self._key = match[1].lower()
 
-                    self.headers[self._key] = decode(match[2].rstrip())
+                    self._headers[self._key] = decode(match[2].rstrip())
         elif self.state is MessageState.BODY:
             if self.body is None:
                 self.body = ''