How to check if connection was aborted in node.js server

Question

I'm making some long polling with node.js.
Basically, node.js server accepts request from the user and then checks for some updates. If there're no updates, it will check them after the timeout.
But what if user has closed his tab, or went to another page? In my case, the script continues working.
Is there a way in node.js to check or detect or to catch an event when user has aborted his request (closed the connection)?

Answer 1

You need to use req.on('close', function(err) { ... }); instead of req.connection.on('close', function(err) { ... });

There is a very important distinction. req.on() adds a listener to this request while req.connection.on(), you add a listener to the (keep-alive) connection between the client and the server. If you use req.connection.on(), every time the client re-uses a connection, you add one more listener to the same connection. When the connection is finally aborted, all listeners are fired.

Function scoping typically keeps you safe from this screwing up your server logic, but it's a dangerous thing nevertheless. Fortunately at least NodeJS 0.10.26 is smart enough to warn the user of this:

(node) warning: possible EventEmitter memory leak detected. 11 listeners added. Use emitter.setMaxListeners() to increase limit.
Trace: 
  at Socket.EventEmitter.addListener (events.js:160:15)
  at Socket.Readable.on (_stream_readable.js:689:33)
  ...