Node.js: Long-polling with EventEmitter and Express 4.x | Catching request close

I'm long-polling node.js route with JQuery's ajax request (xhr). This sends a GET request to my Express server and listens for message bus events. I'm setting a timeout on that GET request (as my proxy would kill long requests). So after the timeout, an abort event should be sent by the client to the server.

I want to catch that abort/close/finish event and remove the relevant message bus listener/subscriber.

But I struggle. I tried req.on("close"..) and the on-finished npm module, but that didn't work for me. I'm also not much more clever after reading the http documentation of node: https://nodejs.org/api/http.html.

Any ideas how to tackle this beast? Or better ways to remove listeners to prevent memory leaks?

Server side essentials:

// server.js
var express = require("express");
var EventEmitter = require("events").EventEmitter;
var messageBus = new EventEmitter();
messageBus.setMaxListeners(20);

var REST_PORT = (process.env.PORT || 5000);
var app = express();

app.get("/events", (req, res) => {
    var listener = function(res) {
        messageBus.once("message", function(data) {
            res.status(200).json(data);
        });
    };
    req.on("abort", function() { //I tried also "aborted", "close", "closed", "finish", "finished"..no luck
        messageBus.removeListener("message", listener);
    });

    listener(res);
    console.log("Total listeners to 'message' events:", messageBus.listeners("message").length);
});

// other messageBus.emit logic ..

app.listen(REST_PORT, () => {
    console.log("Application ready on port " + REST_PORT);
});

Client side essentials:

//client.js
$.ajax({
    method: "GET",
    async: true,
    url: "/events",
    success: function(data) {
        callback(data);
    },
    complete: function(request, status, err) {
        if (status == "timeout" || status == "success") {
            console.log("LOG: Normal long-polling timeout or successful poll, continuing.");
            longPoll();
        } else {
            console.warn("WARN: Server probably offline, retrying in 2 sec.");
            setTimeout(function() {
                longPoll();
            }, 2000);
        }
    },
    timeout: 30000
});

Thank you!

via flaesh