How do I simulate different network conditions in Headless Chromium?

Simulating different network conditions is particularly useful when you want to test how your web application performs under various bandwidth limitations, latency levels, or packet loss scenarios. In headless Chromium, you can control network conditions by using the Chrome DevTools Protocol (CDP).

The DevTools Protocol allows for instrumentation of the browser by sending commands and receiving events. One of the domains in this protocol is the Network domain, which provides the ability to emulate custom network conditions.

To simulate different network conditions using headless Chromium, you will typically use a browser automation library that supports CDP, such as Puppeteer for Node.js or Pyppeteer for Python.

Here's how you can do it in both JavaScript with Puppeteer and Python with Pyppeteer:

JavaScript with Puppeteer

First, you need to install Puppeteer:

npm install puppeteer

Then you can use the following code example to run headless Chromium with simulated network conditions:

const puppeteer = require('puppeteer');

(async () => {
  const browser = await puppeteer.launch();
  const page = await browser.newPage();

  // Connect to Chrome DevTools
  const client = await page.target().createCDPSession();

  // Enable Network domain
  await client.send('Network.enable');

  // Set network conditions
  await client.send('Network.emulateNetworkConditions', {
    // Network connectivity is absent
    offline: false,
    // Download speed (bytes/s)
    downloadThroughput: 1500 * 1024 / 8,
    // Upload speed (bytes/s)
    uploadThroughput: 750 * 1024 / 8,
    // Latency (ms)
    latency: 100
  });

  // Go to desired page
  await page.goto('https://example.com');

  // Do whatever you need to do here...

  // Close browser
  await browser.close();
})();

Python with Pyppeteer

First, you need to install Pyppeteer:

pip install pyppeteer

Then you can use the following code example to run headless Chromium with simulated network conditions:

import asyncio
from pyppeteer import launch

async def emulate_network_conditions():
    browser = await launch()
    page = await browser.newPage()

    # Connect to Chrome DevTools
    client = await page.target.createCDPSession()

    # Enable Network domain
    await client.send('Network.enable')

    # Set network conditions
    await client.send('Network.emulateNetworkConditions', {
        # Network connectivity is absent
        'offline': False,
        # Download speed (bytes/s)
        'downloadThroughput': 1500 * 1024 / 8,
        # Upload speed (bytes/s)
        'uploadThroughput': 750 * 1024 / 8,
        # Latency (ms)
        'latency': 100
    })

    # Go to desired page
    await page.goto('https://example.com')

    # Do whatever you need to do here...

    # Close browser
    await browser.close()

asyncio.get_event_loop().run_until_complete(emulate_network_conditions())

Both of these examples demonstrate how to emulate network conditions in headless Chromium using the respective automation libraries. The emulateNetworkConditions command requires parameters to define the network conditions, including offline, downloadThroughput, uploadThroughput, and latency. You can adjust these values to simulate various network conditions.

Remember that network emulation will only affect the page controlled by the current CDP session. If you open additional pages or tabs, you will need to set up network conditions for each one individually.