title: Let a Node.js WAMP.IO server subscribe to a clients publish in purpose to measure latency
body: <p>I know that the intended use case of a Pub/Sub pattern is to let the clients "multicast" directly to each other with the servers work transparent. But there has been a few occasions where I'd like my server to react a clients publish. Basically I'd like a <code>server.Subscribe('event:ident', callback)</code>. Before starting to implement this, I guess I'm not the first running in to this limitation. How do you folks solve it? </p>
  
  <p>In this latest case I'd like to measure the latency between two clients. So I let first client publish a message which the other client subscribe to will respond to ASAP. Obviuosly the traffic will pass through the server. So I'd like the server to also respond so I can separate the latency from the first client to the server from the latency from the server to the second client. </p>
  
  <p>Do you see any pitfalls with this approach? (Except that I'm breaking the strict PubSub pattern)</p>
  
  <p><em>Note that I'm using the <a href="https://github.com/nicokaiser/wamp.io" rel="nofollow">WAMP.IO lib</a> (implementing the WAMP-protocol). I'm <strong>not</strong> talking about Windows, Apache, PHP and MySQL server!</em></p>