bots: Add example bots for "followup" and "help".

This commit also starts to build out the infrastructure for
helping Zulip contributors to more easily author bots in
a way that sets up for running some bots on the server itself.

contrib_bots/run.py

@@ -0,0 +1,93 @@
+from __future__ import print_function
+
+import importlib
+import logging
+import optparse
+import os
+import sys
+
+our_dir = os.path.dirname(os.path.abspath(__file__))
+
+# For dev setups, we can find the API in the repo itself.
+if os.path.exists(os.path.join(our_dir, '../api/zulip')):
+    sys.path.append('../api')
+
+from zulip import Client
+
+class RestrictedClient(object):
+    def __init__(self, client):
+        # Only expose a subset of our Client's functionality
+        self.send_message = client.send_message
+
+def get_lib_module(lib_fn):
+    lib_fn = os.path.abspath(lib_fn)
+    if os.path.dirname(lib_fn) != os.path.join(our_dir, 'lib'):
+        print('Sorry, we will only import code from contrib_bots/lib.')
+        sys.exit(1)
+
+    if not lib_fn.endswith('.py'):
+        print('Please use a .py extension for library files.')
+        sys.exit(1)
+
+    sys.path.append('lib')
+    base_lib_fn = os.path.basename(os.path.splitext(lib_fn)[0])
+    module_name = 'lib.' + base_lib_fn
+    module = importlib.import_module(module_name)
+    return module
+
+def run_message_handler_for_bot(lib_module, quiet):
+    # Make sure you set up your ~/.zuliprc
+    client = Client()
+    restricted_client = RestrictedClient(client)
+
+    message_handler = lib_module.handler_class()
+
+    if not quiet:
+        print(message_handler.usage())
+
+    def handle_message(message):
+        logging.info('waiting for next message')
+        if message_handler.triage_message(message=message):
+            message_handler.handle_message(
+                message=message,
+                client=restricted_client)
+
+    logging.info('starting message handling...')
+    client.call_on_each_message(handle_message)
+
+def run():
+    usage = '''
+        python run.py <lib file>
+
+        Example: python run.py lib/followup.py
+
+        (This program loads bot-related code from the
+        library code and then runs a message loop,
+        feeding messages to the library code to handle.)
+
+        Please make sure you have a current ~/.zuliprc
+        file with the credentials you want to use for
+        this bot.
+
+        See lib/readme.md for more context.
+        '''
+
+    parser = optparse.OptionParser(usage=usage)
+    parser.add_option('--quiet', '-q',
+        action='store_true',
+        help='Turn off logging output.')
+    (options, args) = parser.parse_args()
+
+    if len(args) == 0:
+        print('You must specify a library!')
+        sys.exit(1)
+
+    lib_module = get_lib_module(lib_fn=args[0])
+
+    if not options.quiet:
+        logging.basicConfig(stream=sys.stdout, level=logging.INFO)
+
+    run_message_handler_for_bot(lib_module, quiet=options.quiet)
+
+if __name__ == '__main__':
+    run()