Data got emit twice in socket.io engine about artillery-core HOT 2 OPEN

module.exports = {
    initConversation: initConversation,
    sendMessage: sendMessage
};

const artillery = require('artillery-core');

function initConversation(context, events, done) {
    events.emit("request");
    let startedAt = process.hrtime();
    context.sockets["/"].emit("message",
        {
            "action": "START_NEW_CONVERSATION", "dataType": "UNK", "data": {}, "conversationInfo": { "channelId": context.vars.channelId, "channelToken": context.vars.channelToken, "recipientId": context.vars.recipientId, "chatId": null, "senderId": null }
        });
    return processSender(context, events, done, startedAt);
}

function processSender(context, events, done, startedAt) {
    context.sockets["/"].on("message", function (res) {
        try {
            context.vars.senderId = res.conversationInfo.senderId;
        } catch (error) { // do something
        }

        if (context.vars.senderId) {
            markEndTime(events, context, startedAt);
            context.sockets["/"].off("message");
            return done();
        }
    });
}

function sendMessage(context, events, done) {
    events.emit("request");
    const startedAt = process.hrtime();
    context.sockets["/"].emit("message",
        {
            "action": "UNK", "dataType": "TEXT", "data": "Hello from JS", "conversationInfo": { "channelId": context.vars.channelId, "channelToken": context.vars.channelToken, "recipientId": context.vars.recipientId, "chatId": context.vars.channelId + '-' + context.vars.senderId, "senderId": context.vars.senderId }
        });
    return waitForResponse(context, events, done, startedAt, startTime);
}

function waitForResponse(context, events, done, startedAt, startTime) {
    context.sockets["/"].on("message", function (res) {
        if (res.action == "UNK") {
            markEndTime(events, context, startedAt);
            context.sockets["/"].off("message");
            return done();        
        }
    });
}

function markEndTime(ee, context, startedAt) {
    let endedAt = process.hrtime(startedAt);
    let delta = (endedAt[0] * 1e9) + endedAt[1];
    ee.emit('response', delta, 0, context._uid);
}