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This example demonstrates how to monitor network traffic by listening to Chrome DevTools Protocol (CDP) events. You can intercept HTTP requests and responses to debug, analyze, or modify network behavior.

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What it does

The script:
  1. Sets up handlers for network request and response events
  2. Navigates to Google and performs a search
  3. Logs all HTTP requests with their headers
  4. Logs all HTTP responses
  5. Downloads all URLs found on the page

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Complete code

from zendriver import cdp, loop, start


async def main() -> None:
    browser = await start()

    tab = browser.main_tab
    tab.add_handler(cdp.network.RequestWillBeSent, send_handler)
    tab.add_handler(cdp.network.ResponseReceived, receive_handler)

    tab = await browser.get("https://www.google.com/?hl=en")

    reject_btn = await tab.find("reject all", best_match=True)
    await reject_btn.click()

    search_inp = await tab.select("textarea")
    await search_inp.send_keys("undetected zendriver")

    search_btn = await tab.find("google search", True)
    await search_btn.click()

    for _ in range(10):
        await tab.scroll_down(50)

    await tab
    await tab.back()

    search_inp = await tab.select("textarea")

    for letter in "undetected zendriver":
        await search_inp.clear_input()
        await search_inp.send_keys(
            "undetected zendriver".replace(letter, letter.upper())
        )
        await tab.wait(0.1)

    all_urls = await tab.get_all_urls()
    for u in all_urls:
        print("downloading %s" % u)
        await tab.download_file(u)

    await tab.sleep(10)


async def receive_handler(event: cdp.network.ResponseReceived) -> None:
    print(event.response)


async def send_handler(event: cdp.network.RequestWillBeSent) -> None:
    r = event.request
    s = f"{r.method} {r.url}"
    for k, v in r.headers.items():
        s += f"\n\t{k} : {v}"
    print(s)


if __name__ == "__main__":
    loop().run_until_complete(main())

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Key techniques

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CDP event handlers

Add handlers to listen for Chrome DevTools Protocol events: 
tab.add_handler(cdp.network.RequestWillBeSent, send_handler)
tab.add_handler(cdp.network.ResponseReceived, receive_handler)

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Request inspection

Access detailed request information in your handler: 
async def send_handler(event: cdp.network.RequestWillBeSent) -> None:
    r = event.request
    print(f"{r.method} {r.url}")
    for k, v in r.headers.items():
        print(f"\t{k} : {v}")

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Response inspection

Access response data: 
async def receive_handler(event: cdp.network.ResponseReceived) -> None:
    print(event.response)

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URL extraction

Get all URLs from the current page: 
all_urls = await tab.get_all_urls()
for u in all_urls:
    await tab.download_file(u)
Use browser navigation controls: 
await tab.back()  # Go back in history

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Input manipulation

Clear and modify input fields: 
await search_inp.clear_input()
await search_inp.send_keys("new text")

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Running the example

  1. Save the code to a file (e.g., network_monitor.py)
  2. Run it with Python:
python network_monitor.py
  1. Watch the console output to see all network requests and responses

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Use cases

  • Debugging: See exactly what requests your automation is making
  • Performance analysis: Identify slow or failing requests
  • API inspection: Discover undocumented API endpoints
  • Security testing: Analyze headers and authentication flows
  • Data extraction: Capture API responses for further processing

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Available CDP events

You can listen to many other CDP events beyond network monitoring:
  • cdp.network.RequestWillBeSent - Before a request is sent
  • cdp.network.ResponseReceived - When a response is received
  • cdp.network.LoadingFinished - When a resource finishes loading
  • cdp.network.LoadingFailed - When a resource fails to load
  • cdp.page.FrameNavigated - When a frame navigates
  • And many more from the Chrome DevTools Protocol specification

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