[manual] Use rabbitmq queue to process UserActivity.

Before this is deployed, we need to install rabbitmq and pika on the
target server (see the puppet part of this commit for how).

When this is deployed, we need to start the new user activity bot:

./manage.py process_user_activity

in the screen session on the relevant server, or user_activity logs
won't be processed (which will eventually result in all users getting
notifications about how their mirrors are out of date).

(imported from commit 44d605aca0290bef2c94fb99267e15e26b21673b)

zephyr/lib/queue.py

@@ -0,0 +1,64 @@
+#!/usr/bin/python
+from django.conf import settings
+import pika
+import simplejson
+
+# This simple queuing library doesn't expose much of the power of
+# rabbitmq/pika's queuing system; its purpose is to just provide an
+# interface for external files to put things into queues and take them
+# out from bots without having to import pika code all over our codebase.
+class SimpleQueue(object):
+    connection = None
+    channel = None
+    queues = set()
+    _inited = False
+
+    def __init__(self):
+        pass
+
+    def initialize(self):
+        # Initialize the connection
+        credentials = pika.PlainCredentials('humbug', settings.RABBITMQ_PASSWORD)
+        parameters = pika.ConnectionParameters('localhost',
+                                               credentials=credentials)
+        self.connection = pika.BlockingConnection(parameters)
+        self.channel = self.connection.channel()
+        self._inited = True
+
+    def create_queue(self, queue_name):
+        # Initialize the queues we need
+        self.channel.queue_declare(queue=queue_name, durable=True)
+        self.queues.add(queue_name)
+
+    def publish(self, queue_name, body):
+        if not self._inited:
+            self.initialize()
+        if queue_name not in self.queues:
+            self.create_queue(queue_name)
+        self.channel.basic_publish(exchange='',
+                                   routing_key=queue_name,
+                                   properties=pika.BasicProperties(delivery_mode = 2,),
+                                   body=body)
+
+    def json_publish(self, queue_name, body):
+        return self.publish(queue_name, simplejson.dumps(body))
+
+    def register_consumer(self, queue_name, callback):
+        if not self._inited:
+            self.initialize()
+        if queue_name not in self.queues:
+            self.create_queue(queue_name)
+
+        def wrapped_callback(ch, method, properties, body):
+            callback(ch, method, properties, body)
+            ch.basic_ack(delivery_tag=method.delivery_tag)
+
+        self.channel.basic_consume(wrapped_callback, queue=queue_name)
+
+    def register_json_consumer(self, queue_name, callback):
+        def wrapped_callback(ch, method, properties, body):
+            return callback(ch, method, properties, simplejson.loads(body))
+        return self.register_consumer(queue_name, wrapped_callback)
+
+    def start_consuming(self):
+        self.channel.start_consuming()