redis_chat_cache.py

MAX_MESSAGES = 20

# @author Kane York (@riking)
# @license BSD 2-clause

class SaveChatMessages:
    def __init__(self):
        self._redis = None
    
    def on_redis_reconnect(self, redis):
        """
        This method must be called every time the Redis connection is started or restarted.
        """
        self._redis = redis
        self._init_redis()

    def _init_redis(self):
        """
        Loads the chat message saving Lua script into the Redis cache.
        """
    
        script = """
local count
count = redis.call("LLEN", KEYS[1])
if count < %d
  redis.call("LPUSH", KEYS[1], ARGV[1])
else
  redis.call("RPOPLPUSH", KEYS[1], ARGV[1])
end
redis.call("EXPIRE", KEYS[1], 60 * 30) -- 30 minutes
""" % (MAX_MESSAGES,)
        self._script_hash = sha.new(script).hexdigest()
        self._redis.SCRIPTLOAD(script)
    
    def saveChatMessage(self, channel, message_json):
        """
        Save a single chat message to the Redis server.
        """
        self._redis.EVALSHA(self._script_hash, 1, channel, message_json)

    def getRecentChatMessages(self, channel):
        """
        Get the recent chat messages from the Redis server.
        
        Returns a list of JSON objects, from oldest to newest.
        """

        # should LRU cache this as well
        # don't forget cache invalidation in saveChatMessage()
        ary = self._redis.LRANGE(channel, 0, (MAX_MESSAGES - 1))
        ary.reverse()
        return ary