Fiddler has been preset to provide the option of simulating Modem speed, its location is at:
Rules->Performances->Simulate Modem Speeds
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After checking this option, all the traffic proxied by Fiddler will become normal with a 56k modem.
To visually observe the effect of the speed limit, it is best to use a speed test tool running in the browser. Here, it is recommended to use the "http://www.speedtest.cn/" online speed test tool for testing.
Adjust parameters for simulating harsh network environments
Directly simulating the modem speed is really slow. In fact, even in the case of poor signal, the mobile network speed of the mobile phone has exceeded the modem speed of 56k, so the simulated environment with the default configuration does not necessarily meet the requirements. At this time, it is necessary to adjust the parameters of the speed limit.
Fiddler itself provides a configuration file for adjusting these parameters, click:
Rules – Customize Rules...
to open the CustomRules.js file (Fiddler2Scripts located in the document directory of the user directory by default), the suffix is js. Find the "m_SimulateModem" flag in the edit content:
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";
}This flag controls the setting of the two parameter values of oSession. When Simulate Modem Speeds is checked, request-trickle-delay and response-trickle-delay will be set, where the value in request-trickle-delay represents each How many milliseconds will be delayed when KB data is uploaded, and response-trickle-delay corresponds to how many milliseconds will be delayed when downloading each KB of data. If the network speed is already quite fast, the value set here can be approximated The upload and download bandwidth after the simulation is turned on. For example, the download delay is 150ms by default, and the upload delay is 300ms. Correspondingly, the approximate analog bandwidth can be calculated as: upload bandwidth=(1*8/1000)
/0.300≈0.053 Mbps
download bandwidth=(1*8/1000)/0.150≈0.027Mbps
Write a custom script
to further expand the logic in CustomRules.js. Refer to the Jscript documentation to add more custom logic in the simulated harsh environment. Here is the implementation A random delay is set, so that the network bandwidth is not constant at a low-speed value, but will jitter randomly 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);
}By further extending CutionRules.js, many required harsh environment simulation scenarios can be realized. If the scene is more complex, you can also write C# plug-in code to further control the behavior of Fiddler by writing Fiddler plug-ins. I won’t go into details here. up.
Limitations of Fiddler's simulation of harsh network environments
Fiddler's speed limit is relatively simple and flexible, and its configuration is more convenient. However, because it is an HTTP proxy at the application layer, it can only simulate the behavior on this layer. For some complex network layers Bad situations such as packet loss and retransmission cannot be simulated well, and the application of other protocols is not supported.