Any way to know if a client connection was dropped/closed?

[asiby]

Hi guys

Nice library. Thanks for this. I am wondering if someone can help me with the following this issue.

I am trying to know when a client connection was dropped. But I can't find any way to do it with this java-express. It is based on what's done in Expressjs. So to help you better understand what I'm trying to achieve, please check the following code that can be used as a GET event handler in Expressjs ... I borrowed it from https://alligator.io/nodejs/server-sent-events-build-realtime-app/#sse-express-backend

function eventsHandler(req, res, next) {
  // Mandatory headers and http status to keep connection open
  const headers = {
    'Content-Type': 'text/event-stream',
    'Connection': 'keep-alive',
    'Cache-Control': 'no-cache'
  };
  res.writeHead(200, headers);

  // After client opens connection send all nests as string
  const data = `data: ${JSON.stringify(nests)}\n\n`;
  res.write(data);

  // Generate an id based on timestamp and save res
  // object of client connection on clients list
  // Later we'll iterate it and send updates to each client
  const clientId = Date.now();
  const newClient = {
    id: clientId,
    res
  };
  clients.push(newClient);

  // When client closes connection we update the clients list
  // avoiding the disconnected one
  req.on('close', () => {
    console.log(`${clientId} Connection closed`);
    clients = clients.filter(c => c.id !== clientId);
  });
}

In this code, please notice the part where we have req.on('close', () => {...}) near the end of the snippet.

This allows listening to events on the request object. It could be a close event, an error event, etc.

I know that the .on() fonction is a Javascript specific function and is probably inherited by the reqobject. But I am hoping that someone could help me achieve the same thing with java-express .

Essentially, I am trying to keep track of each request until they are disconnected. And in the meantime, when I receive a POST request (in my Java code) that will have a channel property in the submitted data, I will send that to all the GET requests that were made with that same channel. I know that clients will stay connected because they are supposed to be using an EventSource() connection to connect to the server, which will in turn a response with a text/event-stream content type.

Thank you