问Node.js:使用EventEmitter和Express 4.x的长轮询捕获请求关闭

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// 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.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
});