【发布时间】：2012-08-20 19:38:06
【问题描述】：
我编写了一个代码，告诉我一个数据包从server to client 到达所花费的时间，以及从client to server to client 再次到达所花费的总时间。这是我的代码。
客户端：
<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>Ping</title>
<script src="/socket.io/socket.io.js"></script>
<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/1.7.2/jquery.min.js"></script>
<script>
$(document).ready(function(e) {
var socket = io.connect('http://pingme.jit.su:80/', {secure: false});
$('#button').click(function(e) {
e.preventDefault();
$(this).attr('disabled','disabled');
var time = (new Date()).getTime();
socket.emit('ping', time);
});
socket.on('pong', function(data) {
var time2 = (new Date()).getTime();
var lat = time2 - data.server;
var roundtrip = time2 - data.init;
var str = '<br><br><strong>From Server</strong>: '+lat+' ms<br><strong>Roundtrip</strong>: '+roundtrip+' ms<br><br>';
$('#res').prepend(str);
$('#button').removeAttr('disabled');
});
});
</script>
</head>
<body style="margin:0;">
<input type="button" name="Button" id="button" value="Latency">
<div id="res"></div>
</body>
</html>
服务器端：
var app = require('http').createServer(handler)
, io = require('socket.io').listen(app)
, fs = require('fs')
, path = require('path')
, url = require("url")
, querystring = require("querystring");
app.listen(8080);
io.configure('development', function(){
io.set('transports', ['xhr-polling']);
});
io.configure('production', function(){
io.set('transports', ['xhr-polling']);
});
var static = require('node-static');
var fileServer = new static.Server('.', { cache: false });
function handler (request, response) {
var pathname = url.parse(request.url).pathname;
if(pathname == '/') {
pathname = '/app.html';
}
request.addListener('end', function () {
fileServer.serveFile(pathname, 200, {}, request, response, function(err, result) {
if(err) {
console.log(err);
console.log(err.status);
}
else
console.log(result);
});
});
}
io.sockets.on('connection', function (socket) {
socket.on('ping',function(data) {
var time = (new Date()).getTime();
socket.emit('pong', {server:time, init:data});
});
});
这个问题在本地运行良好，显示以下输出：
From Server: 4 ms
Roundtrip: 11 ms
From Server: 10 ms
Roundtrip: 15 ms
在 Nodejitsu 上部署后运行时出现异常结果。它给了我以下输出：
From Server: 2223 ms
Roundtrip: 956 ms
From Server: 2265 ms
Roundtrip: 915 ms
数据包从服务器传输的时间怎么可能比整个往返时间长？我认为这是由于服务器和客户端之间的时间差异。你觉得是什么？
【问题讨论】：