Network throttling with chrome and selenium

问题

Google Chrome 38 introduced the new "Device Mode & Mobile Emulation" functionality in devtools. In addition to choosing a device for emulation, it is also possible to emulate different network conditions:

Optimizing your site's performance under varying network conditions is a key aspect of developing for a mobile audience.

Device mode's network conditioning allows you to test your site on a variety of network connections, including Edge, 3G, and even offline. Select a connection from the preset dropdown to apply network throttling and latency manipulation.

For example, we can set it to be like in good old days - GPRS 50 Kbps:

Now we have a good use case for it - we have an internal application for network speed testing. And this new emulation functionality is very helpful for manual testing. But, we'd like to automate it.

Question is:

Is it possible to start chrome via selenium with specified network conditions? Is it something that can be controlled through chrome preferences or command-line arguments?

There are certainly multiple options to simulate slow internet connection, but the question is specifically about chrome+selenium.

回答1:

The API to control network emulation were added to ChromeDriver. And should be available for quite a while now. According to comment in the linked issue you should use version at least 2.26 because of some bugfix.

According to Selenium changelog bindings are available for these languages:

JavaScript as of version 3.4.0 (commit)
Python as of version 3.5.0 (commit)
Ruby as of version 3.11.0 (commit)
C# as of version 4 (commit)

If you need these binding in other languages you should probably open issue/contribute implementation similar to one of the above.

Example usage from Python is below:

driver.set_network_conditions(
    offline=False,
    latency=5,  # additional latency (ms)
    download_throughput=500 * 1024,  # maximal throughput
    upload_throughput=500 * 1024)  # maximal throughput

回答2:

No, it is not possible to control Network Connectivity Emulation through Chrome preferences or command-line arguments. Network Connectivity Emulation is part of the build-in Chrome debugger. One way way in solving this is to control the debugger. This can be done via an extension or by directly controlling the debugger, see explanation. However, this will not work with WebDriver. The reason for this is that there can only be one "debug" session and WebDriver is already using it, see explanation. Since there is no public interface, there is also no way to control it via WebDriver.

For Device Mode & Mobile Emulation which is also part of the build-in debugger, there is a public interface (details), and thus can be controlled. This can be done through WebDriver Capabilities. Two options 1) Specify a device name 2) Enter your own parameters (limited).

回答3:

Indeed C# Selenium latest (3.11) has NetworkConditions added. Now you can use it like this:

     var driver = new ChromeDriver(pathToDriver);
     driver.NetworkConditions = new ChromeNetworkConditions()
     {  DownloadThroughput = 5000, UploadThroughput = 5000, Latency = TimeSpan.FromMilliseconds(5) };

The problem is it's not yet usable because of the bug

https://github.com/SeleniumHQ/selenium/issues/5693

So .Net guys will have to wait until 3.12 Selenium Release.

回答4:

While this is a very welcome and useful bit of functionality, for serious testing I think the conventional methods of network simulation are still the way to go.

I am aware of 2 solutions in addition to those already linked - the Charles web proxy (very useful tool - commercial) and implementing your own recipe using Linux Traffic Control (e.g. see chapter 6 of LAMPe2e).

By interfering with the network connections rather than the browser, you then get a proper measure of the impact independently of the browser in use.

Why do you just want to use the Chrome functionality?

回答5:

You can use this method to run your test case in specified network conditions

protected void networkThrotting() throws IOException {
  Map map = new HashMap();
  map.put("offline", false);
  map.put("latency", 5);
  map.put("download_throughput", 500);
  map.put("upload_throughput", 1024);


  CommandExecutor executor = ((ChromeDriver)driver).getCommandExecutor();
  Response response = executor.execute(
        new Command(((ChromeDriver)driver).getSessionId(),    "setNetworkConditions", ImmutableMap.of("network_conditions", ImmutableMap.copyOf(map)))
  );
}