Assign Message-ID, validate message before adding

lib/nntp/tiny/session.py

@@ -721,6 +721,13 @@ class Session():
         if len(newsgroups) == 0:
             return False
 
+        message.message_id_assign()
+
+        if not message.validate():
+            return self.respond(ResponseCode.NNTP_POST_FAILED)
+
+        self.db.add(message)
+
         for newsgroup in newsgroups:
             sql = """
                 insert into newsgroup_message (