zulip_bots: Make StateHandler optional.

This has the convenient side-effect of making
the bot_handler.storage attribute read-only.

zulip_bots/zulip_bots/bots/incrementor/incrementor.py

@@ -2,6 +2,11 @@
 
 
 class IncrementorHandler(object):
+    META = {
+        'name': 'Incrementor',
+        'description': 'Example bot to test the update_message() function.',
+        'uses_storage': True,
+    }
 
     def usage(self):
         return '''

zulip_bots/zulip_bots/bots/tictactoe/tictactoe.py

@@ -267,6 +267,11 @@ class ticTacToeHandler(object):
     tic-tac-toe bot! Make sure your message starts with
     "@mention-bot".
     '''
+    META = {
+        'name': 'TicTacToe',
+        'description': 'Lets you play Tic-tac-toe against a computer.',
+        'uses_storage': True,
+    }
 
     def usage(self):
         return '''

zulip_bots/zulip_bots/bots/virtual_fs/virtual_fs.py

@@ -4,6 +4,12 @@ import re
 import os
 
 class VirtualFsHandler(object):
+    META = {
+        'name': 'VirtualFs',
+        'description': 'Provides a simple, permanent file system to store and retrieve strings.',
+        'uses_storage': True,
+    }
+
     def usage(self):
         return get_help()
 

zulip_bots/zulip_bots/lib.py

@@ -92,14 +92,15 @@ class StateHandler(object):
                 raise StateHandlerError("Error updating state: {}".format(str(response)))
 
 class ExternalBotHandler(object):
-    def __init__(self, client, root_dir):
+    def __init__(self, client, root_dir, bot_details={}):
-        # type: (Client, str) -> None
+        # type: (Client, str, Dict[str, Any]) -> None
         # Only expose a subset of our Client's functionality
         user_profile = client.get_profile()
         self._rate_limit = RateLimit(20, 5)
         self._client = client
         self._root_dir = root_dir
-        self.storage = StateHandler(client)
+        self.bot_details = bot_details
+        self._storage = StateHandler(client) if self.bot_details.get('uses_storage', False) else None
         try:
             self.user_id = user_profile['user_id']
             self.full_name = user_profile['full_name']
@@ -109,6 +110,20 @@ class ExternalBotHandler(object):
                           ' up the zuliprc file correctly.')
             sys.exit(1)
 
+    @property
+    def storage(self):
+        # type: () -> StateHandler
+        if not self._storage:
+            raise AttributeError("""Bot tried to access storage, but has not enabled
+storage access. To enable storage access, add
+    META = {
+        'uses_storage': True,
+    }
+to your bot handler class. Check out the incrementor
+bot for an example on how to do this.
+""")
+        return self._storage
+
     def send_message(self, message):
         # type: (Dict[str, Any]) -> Dict[str, Any]
         if self._rate_limit.is_legal():
@@ -194,21 +209,20 @@ def run_message_handler_for_bot(lib_module, quiet, config_file, bot_name):
     # inherit from a common prototype specifying the handle_message
     # function.
     #
-    # Make sure you set up your ~/.zuliprc
-    client = Client(config_file=config_file, client="Zulip{}Bot".format(bot_name.capitalize()))
-    bot_dir = os.path.dirname(lib_module.__file__)
-    restricted_client = ExternalBotHandler(client, bot_dir)
-
-    message_handler = lib_module.handler_class()
-    if hasattr(message_handler, 'initialize'):
-        message_handler.initialize(bot_handler=restricted_client)
-
     # Set default bot_details, then override from class, if provided
     bot_details = {
         'name': bot_name.capitalize(),
         'description': "",
     }
     bot_details.update(getattr(lib_module.handler_class, 'META', {}))
+    # Make sure you set up your ~/.zuliprc
+    client = Client(config_file=config_file, client="Zulip{}Bot".format(bot_name.capitalize()))
+    bot_dir = os.path.dirname(lib_module.__file__)
+    restricted_client = ExternalBotHandler(client, bot_dir, bot_details)
+
+    message_handler = lib_module.handler_class()
+    if hasattr(message_handler, 'initialize'):
+        message_handler.initialize(bot_handler=restricted_client)
 
     if not quiet:
         print("Running {} Bot:".format(bot_details['name']))