javascript - 带有 PubSub 的 Socket.io:多页面刷新后几乎没有实时数据显示
问题描述
我正在尝试使用 Google PubSub、Node js 和 Google App Engine 可视化流数据。我正在做的只是:
- 每 1 秒将消息流推送到 PubSub 主题(使用 python 脚本)
- 创建对该主题的订阅
- 创建一个简单的 web 应用程序,它监听订阅,解析每个传入的消息,并以实时条形图的形式显示到浏览器(使用 node js、socket.io 和 fusionchart)
我遵循了本教程:https : //www.fusioncharts.com/blog/visualize-real-time-data-socket-io-charts/,唯一的区别是我使用 PubSub 而不是 PubNub,同时遵循此文档:https://cloud.google.com/pubsub/docs/quickstart-client-libraries#pubsub-client-libraries-nodejs用于“接收消息”部分。
它实际上有效,当我每 1 秒发布 10 条消息时,图表将每 1 秒实时显示 10 条消息。这是我运行应用程序时图表的样子:
问题是它仅在我第一次运行应用程序并打开页面时才有效。当我刷新页面并推送另外 10 条新消息时,数据显示需要更长的时间。当它最终出现时,仅显示 10 条消息中的 5 条。如果我尝试刷新同一页面,显示的数据会越来越少,甚至在某些时候都不会出现。
我通过控制台跟踪每条传入和传出的消息,似乎一切正常。推送了 10 条消息,收到了 10 条消息。只是出于某种原因,每次刷新后显示的越来越少。
这是我的 app.js 代码:
var express = require('express');
var app = require('express')();
var http = require('http').Server(app);
//creates a new socket.io instance attached to the http server.
var io = require('socket.io')(http);
// Imports the Google Cloud client library
const PubSub = require('@google-cloud/pubsub');
// Your Google Cloud Platform project ID
const projectId = 'myprojecthere';
//Provide the absolute path to the dist directory.
app.use(express.static(__dirname + '/dist'));
//On get request send 'index.html' page as a response.
app.get('/', function(req, res) {
res.sendFile(__dirname +'/index.html');
});
//Whenever someone connects this gets executed
//original : connection
io.on('connection', function (socket) {
console.log(`Enter io connection`);
console.log(' %s sockets connected', io.engine.clientsCount)
// Instantiates a client
const pubsub = new PubSub({
projectId: projectId,
key: """censored"""
});
var strData;
/**
* TODO(developer): Uncomment the following lines to run the sample.
* https://cloud.google.com/pubsub/docs/pull#pubsub-pull-messages-async-nodejs
*/
const subscriptionName = 'testing_subscription';
const topicName = 'testing';
const timeout = 50;
// References an existing subscription
//var topic = pubsub.topic(topicName)
const subscription = pubsub.subscription(subscriptionName);
//Function to format time and date
function formatDatetime (TimeStamp){
var formatted = (TimeStamp.getHours()) + ':' + (TimeStamp.getMinutes()) + ':' + (TimeStamp.getSeconds()) + ':' + (TimeStamp.getMilliseconds());
return formatted;
}
// Create an event handler to handle messages
let messageCount = 0;
const messageHandler = message => {
console.log(`Received message: ${message.id}`);
console.log(`\tData: ${message.data}`);
console.log(`\tAttributes: ${message.attributes}`);
var obj = JSON.parse(message.data);
console.log(`\tTimeStamp: ${obj.messages.timestamp}`);
console.log(`\tAmount: ${obj.messages.amount}`);
messageCount += 1;
console.log(`Message count : ${messageCount}`);
message.ack();
console.log(`Message Acknowledged`);
// This doesn't ack the message, but allows more messages to be retrieved
// if your limit was hit or if you don't want to ack the message.
// message.nack();
// Get creation timestamp
var x = new Date(obj.messages.timestamp);
// Time formatting for x-axis in chart
var formatted = formatDatetime(x);
var Count = obj.messages.amount;
console.log(`Extracting Timestamp: ${formatted}`);
console.log(`Counts : ${Count}`);
strData = {"label": formatted,
"value": Count
}
socket.emit('news', strData);
console.log(``);
};
// Listen for new messages until timeout is hit
subscription.on(`message`, messageHandler);
setTimeout(() => {
console.log(`Enter timeout`);
//subscription.removeListener('message', messageHandler);
console.log(`0 message(s) received.`);
var x = new Date();
var formatted = formatDatetime(x);
var Count = 0;
console.log(`Extracting Timestamp: ${formatted}`)
strData = {"label": formatted,
"value": Count
}
console.log(`strData : ${strData}`)
console.log(``);
socket.emit('news', strData);
}, timeout);
//other handling
if ( typeof strData == 'undefined') {
console.log(`Something else happened`)
var x = new Date();
var formatted = formatDatetime(x);
console.log(`Extracting Timestamp: ${formatted}`)
strData = {"label": formatted,
"value": 9
}
socket.emit('news', strData);
}
console.log(`strData : ${strData}`);
console.log(``);
});
//server listening on port 8080
http.listen(8080, function() {
console.log('listening on *:8080');
});
这是我用来显示图表的代码:
/*globals io */
var FusionCharts = require("fusioncharts");
require("fusioncharts/fusioncharts.charts")(FusionCharts);
require("fusioncharts/fusioncharts.widgets")(FusionCharts);
var socket = io();
var transactionChart = new FusionCharts({
id: "mychart",
type: 'realtimecolumn',
width: '700',
height: '350',
dataFormat: 'json',
dataSource: {
"chart": {
"caption": "Streaming Data Visualization",
"subCaption": "Testing",
"yaxismaxvalue": "10",
"numdisplaysets": "10",
"yAxisName":"Quantity",
"labeldisplay": "rotate",
"showLegend":"0",
"showValues": "0",
"numbersuffix": "Kg",
"showlabels": "1",
/*This parameter lets you set whether you want the latest value (received from server) to be displayed on the chart or not*/
"showRealTimeValue": "0",
/*For this parameter, you can specify the number of seconds after which the chart will look for new data. This process will happen continuously - i.e., if you specify 5 seconds here, the chart will look for new data every 5 seconds*/
"refreshInterval":".1",
/*If you want the chart to keep polling for new data every x seconds and queue it, you can specify that x seconds as updateInterval. This helps you poll at different intervals and then draw at another interval (specified as refreshInterval)*/
"updateInterval":".1",
"yAxisNamePadding":"10",
//Cosmetics
"paletteColors" : "#0075c2,#1aaf5d",
"baseFontColor" : "#333333",
"baseFont" : "Helvetica Neue,Arial",
"captionFontSize" : "14",
"subcaptionFontSize" : "14",
"subcaptionFontBold" : "0",
"showBorder" : "0",
"bgColor" : "#ffffff",
"showShadow" : "0",
"canvasBgColor" : "#ffffff",
"canvasBorderAlpha" : "0",
"divlineAlpha" : "100",
"divlineColor" : "#999999",
"divlineThickness" : "1",
"divLineIsDashed" : "1",
"divLineDashLen" : "1",
"divLineGapLen" : "1",
"usePlotGradientColor" : "0",
"showplotborder" : "0",
"valueFontColor" : "#ffffff",
"placeValuesInside" : "1",
"rotateValues" : "1",
"showXAxisLine" : "1",
"xAxisLineThickness" : "1",
"xAxisLineColor" : "#999999",
"showAlternateHGridColor" : "0",
"legendBgAlpha" : "0",
"legendBorderAlpha" : "0",
"legendShadow" : "0",
"legendItemFontSize" : "10",
"legendItemFontColor" : "#666666"
},
"categories": [
{
"category": [
{ "label": "Start" }
]
}
],
"dataset": [
{
"seriesname": "",
"alpha": "100",
"data": [
{ "value": "3" }
]
}
]
}
}).render("chart-container");
//On connection with socket, will start receiving the data
socket.connect('http://localhost:8080/');
socket.on('news', function (data) {
function updateData() {
//Converting the fetched data in FusionCharts format
var strData = "&label=" + data.label + "&value=" + data.value;
//feeding the data to the real time chart
FusionCharts.items.mychart.feedData(strData);
}
//calling the update method
updateData();
});
这是我的 index.html 代码:
<!DOCTYPE html>
<html>
<head>
<title>Hello world</title>
<script src="/socket.io/socket.io.js"></script>
</head>
<body>
<div id="chart-container">FusionCharts will render here</div>
<script src="bundle.js"></script>
</body>
</html>
我对 Javascript 还是很陌生,以前从未在网络应用程序上工作过。我可能错过了关于事情如何运作的重要知识。但我确实有些怀疑,虽然我不确定。
可能是因为每次我刷新页面时都会建立一个新的套接字连接,并且丢失的消息实际上是由以前的连接接收的(因此它不显示)?
我尝试过的几个解决方案仍然无效: Node.js Socket.io 页面刷新多个连接
任何人都可以帮助我吗?
解决方案
我碰巧找到了解决我自己问题的有效方法。
不完全确定原因,但发生了以下情况:每当我刷新页面时,旧的套接字连接将被断开,并会创建一个新的套接字连接。这个新的套接字将监听相同的订阅。
虽然旧套接字的状态在页面刷新期间似乎断开了连接,但由于某种原因它仍然侦听相同的订阅。这会导致 10 条消息在两个或多个连接之间拆分(取决于页面刷新次数)。
但是,浏览器上显示的只是最新的连接。这可能看起来像是消息丢失了,而实际上它们分布在许多(看不见的)连接上。当我尝试打印每条消息结束的“套接字 ID”时,这一点很明显。
所以我所做的基本上是在套接字断开连接期间添加一个小处理:
//on Disconnect
socket.on('disconnect', function () {
console.log("LOG: just disconnected: " + socket.id);
subscription.removeListener('message', messageHandler);
所以每当一个socket断开连接时,它也会停止监听订阅,新的socket会收到一整套消息。
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