Use of packet capturing tool Fiddler: simulating speed limit test process in weak network environment

One ： Why do you want to be a weak network test ？

　　 The actual customer site may have unstable network or low network speed , Bad network environment will lead to some problems bug, Some services are not even available . The internal R & D environment network of the company is usually relatively smooth , It's hard to reproduce this bug. To solve this problem , We need to test it in a weak network environment 、 Reproduce and fix problems .

　　 Two ： How to simulate bad network environment ？

　　 This article only uses fiddler For example , Let's get to know the others , No specific study .

　　 3、 ... and ：Fiddler How to simulate a weak network ？

　　Fiddler It's a HTTP Debug agent , It can Record All your computers and Internet Between HTTP Communications ,Fiddler You can also check all HTTP Communications , To set breakpoints , And modify all “ In and out ” The data of （ finger Cookie/HTML/JS/CSS Wait for the documents ）.

　　 utilize Fiddler To simulate the bad network environment , Implement a simple , More intuitive , The disadvantage is that it can only support those who use HTTP Services for communication and interaction .

　　 open fiddler, By default Rules –> Performances –> Simulate Modem Speeds Is unchecked , Normal network . Select this option （ Simulate optical cat network speed ） after , The network speed will become very slow , Opening a web page takes a long time to load . In this way, the weak network effect is realized .

Set up

　　 If you want to know （ Upload and download ） The specific value of network speed , You can use a tool speedtest, The speed measurement method is very simple , There are lots of tutorials on the Internet .

　　http://www.speedtest.net/ It's an English website , It should be a foreign version , Slow access . and Windows The system only supports Windows10 Download client , I am using Windows7 Use chrome Browser to install Speedtest The extender has to go over the wall , So... Is not recommended . Suggest visiting http://www.speedtest.cn/ Website , The speed measurement results are fast and in Chinese . Support mobile phone client APP download .

　　 Four ： Speed limit principle

　　Fiddler The speed limit is realized in the form of network delay , Network latency * Network speed = Number of bytes transferred .

　　 Click on Rules – Customize Rules（ Shortcut key Ctrl + R） open Fiddler ScriptEditor, Or directly click on the home page on the right FiddlerScript.

After opening the file ,Ctrl + F lookup m_SimulateModem Sign a , You can see the following code ：

　　if (m_SimulateModem) { // Delay sends by 300ms per KB uploaded. oSession["request-trickle-delay"] = "300"; // Delay receives by 150ms per KB downloaded. oSession["response-trickle-delay"] = "150"; }

　　 annotated ： request-trickle-delay The value in represents every KB How many milliseconds will be delayed when the data is uploaded ;response-trickle-delay It corresponds to every KB How many milliseconds will the data be delayed . For example, you need to simulate the upload speed 100KBps Network of , The upload delay is 1KB/100KBps=0.01s=100ms, Change to 100.

　　 When checked Simulate Modem Speeds when ,request-trickle-delay And response-trickle-delay It will be set , If the network speed is already quite fast , The value set here can approximately calculate the upload and download bandwidth after the simulation is turned on , For example, the default upload delay is 300ms The download delay is 150ms, It can be calculated that the approximate analog bandwidth is ：

　　 Upload bandwidth =(1 * 8/1000) /0.300 ≈ 0.027Mbps

　　 Download bandwidth =(1 * 8/1000) /0.150 ≈ 0.053Mbps

　　 In practice, the bandwidth obtained may have errors , Affected by various external factors, it will not be so accurate .

　　 It can be seen that the download bandwidth is twice that of upload , That is, the smaller the delay , More bandwidth . The bandwidth is inversely proportional to the delay here .

　　 5、 ... and ： Adjust network environment parameters

　　Fiddler default Simulate Modem Speeds The speed is too slow , The speed limit parameter can be adjusted , If you need to be faster, you can modify the configuration file Fiddler2ScriptsCustomRules.js.（ Don't forget to back up the original file if you modify it ） stay fiddler Official website http://www.fiddlerbook.com/Fiddler/dev/ScriptSamples.asp Reference examples can be found .

　　 Here are two simple ways to modify scripts , Choose one .

　　 Method 1

　　 Find the if (m_SimulateModem) sentence , Modify the code . The following script implements a random delay setting , So that the network bandwidth is not constant to a low speed value , It's a random jitter within a certain range ：

　　static function randInt(min, max) { return Math.round(Math.random()*(max-min)+min);}if (m_SimulateModem) { // Delay sends by 300ms per KB uploaded. oSession["request-trickle-delay"] = ""+randInt(1,50); // Delay receives by 150ms per KB downloaded. oSession["response-trickle-delay"] = ""+randInt(1,50);}

　　 Method 2

　　 Click on fiddlerScript Find... In the code onBeforeRequest, This defines what to do before sending a request . Add the following code to achieve delay ：

　　oSession["request-trickle-delay"]="3000"; // Request phase delay 3 second oSession["response-trickle-delay"]="3000"; // Response phase delay 3 second

Add code

　　 Choose one of the above two methods , Save the configuration file after modification （Ctrl+S） Or clear the cache （Rules –> Performances –>Disable Caching）, Check again Rules –> Performances –> Simulate Modem Speeds Speed measurement . Be careful ： Every time you edit and save the configuration file ,Simulate Modem Speeds The option will be cancelled , Please check again .

　　 After the speed limit is completed, be sure to uncheck , Otherwise it will affect the Internet . Like the second method, because the request and response are delayed 3 second , It will cause slow access to web pages .