Bug in the get_node method

Hi @dcramer.

After this pull request, I found a bug. These are the steps to reproduce the bug:

1- Start at least 2 redis servers.

2- Run some application that uses nydus.db.create_cluster method to handle the redis cluster. In my case, I started a simple flask application.

hosts = {
    0 : {'host':'localhost', 'port':6290},
    1 : {'host':'localhost', 'port':6291}
}

create_cluster({
    'backend': 'nydus.db.backends.redis.Redis',
    'router': 'nydus.db.routers.keyvalue.ConsistentHashingRouter',
    'hosts': hosts
})

3- Restart the redis server.

After doing it, the mark_connection_up method from nydus.db.routers.keyvalue.ConsistentHashingRouter is called twice, one for each server that went up.

In the first call, the condition I added in this pull request returns None as expected, because ketama nodes are empty (the servers were down).

What happens:

mark_connection_up called with db_num parameter as 0 (host key)
check if the node isn't in the up nodes list (the if condition of this pull request)

self._hash.get_node(node_key) is None: #returns None, so add the node
    self._hash.add_node(node_key)

The result of self._hash.get_node(node_key) is None, so, add node_key redis://localhost:6290/0 ConsistentHashingRouter._hash.nodes is now set(['redis://localhost:6290/0'])

In the second call, the condition returns the first node added instead of returning None, as expected. I think it's a bug from get_node method.

# node_key is `redis://localhost:6291/0`
self._hash.get_node(node_key) is None: # returns redis://localhost:6290/0
    self._hash.add_node(node_key)

Isn't None, so, don't add the node

Is there a bug with get_node method? If no, please, revert this pull request.

If you need more information about this bug, let me know.

Thanks in advance.

disqus / nydus

Bug in the get_node method #28