title: netty-socketio: client did not complete upgrade - closing transport
body: <p>I have a socket server running with netty-socketio and a web app that connects to it using socket.io-client JS library.</p>
  
  <p>The problem is that I'm losing a few connections (not all, let's say 20%). </p>
  
  <p>For the lost connections: right after the connection is made by the client, the server logs <code>client did not complete upgrade - closing transport</code> and disconnects the client.</p>
  
  <p>This happens on my production server (using nginx as proxy) and also on my local environment (connecting directly to the netty-socketio server). It's pretty much random and I cant identify a pattern on it. For example, if I continuously keep refreshing the client app on the browser (with a 5 seconds interval), at some point this error will happen, and for the subsequent tries it will work normal again (until it happens another time).</p>
  
  <p>This is the error on the netty-socketio lib: <a href="https://github.com/mrniko/netty-socketio/blob/master/src/main/java/com/corundumstudio/socketio/transport/WebSocketTransport.java#L196" rel="nofollow">https://github.com/mrniko/netty-socketio/blob/master/src/main/java/com/corundumstudio/socketio/transport/WebSocketTransport.java#L196</a>
  but I could not figure out why it happens randomly (some times at the first try)</p>
  
  <p>Any thoughts on this are really appreciated.</p>
  
  <p>Thanks</p>