[🐛 Bug]: Chrome extension windows are no longer included in window_handles - Remote debugging window

[rookes]

Description

When connecting to an existing session via remote debugging, Chrome extension windows are not included in driver.window_handles. This issue is new in the past few weeks, but I'm not sure exactly when it started.

To reproduce, open a chrome window with the option --remote-debugging-port=9222 , then run the code. The code prints out the title of every window in window_handles. Note that if there is any chrome extension tab open, it will not be included. I have tested this with multiple valid extensions, extension popups, and invalid extension URLs as well. All give the same result.

Example output with two tabs open: "chrome-extension://a" and the default "New Tab"
New Tab

Further, if the Chrome extension is the only tab open, then an error will be generated:

Traceback (most recent call last):
  File "C:\Users\username\Documents\test.py", line 8, in <module>
    driver = webdriver.Chrome(options=chrome_options)
  File "C:\Users\username\AppData\Roaming\Python\Python313\site-packages\selenium\webdriver\chrome\webdriver.py", line 45, in __init__   
    super().__init__(
    ~~~~~~~~~~~~~~~~^
        browser_name=DesiredCapabilities.CHROME["browserName"],
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    ...<3 lines>...
        keep_alive=keep_alive,
        ^^^^^^^^^^^^^^^^^^^^^^
    )
    ^
  File "C:\Users\username\AppData\Roaming\Python\Python313\site-packages\selenium\webdriver\chromium\webdriver.py", line 66, in __init__ 
    super().__init__(command_executor=executor, options=options)
    ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\username\AppData\Roaming\Python\Python313\site-packages\selenium\webdriver\remote\webdriver.py", line 250, in __init__  
    self.start_session(capabilities)
    ~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^
  File "C:\Users\username\AppData\Roaming\Python\Python313\site-packages\selenium\webdriver\remote\webdriver.py", line 342, in start_session
    response = self.execute(Command.NEW_SESSION, caps)["value"]
               ~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\username\AppData\Roaming\Python\Python313\site-packages\selenium\webdriver\remote\webdriver.py", line 429, in execute   
    self.error_handler.check_response(response)
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^
  File "C:\Users\username\AppData\Roaming\Python\Python313\site-packages\selenium\webdriver\remote\errorhandler.py", line 232, in check_response
    raise exception_class(message, screen, stacktrace)
selenium.common.exceptions.WebDriverException: Message: unknown error: unable to discover open window in chrome
  (Session info: chrome=136.0.7103.49)
Stacktrace:
        GetHandleVerifier [0x00007FF73A60A145+76773]
        GetHandleVerifier [0x00007FF73A60A1A0+76864]
        (No symbol) [0x00007FF73A3C8F7A]
        (No symbol) [0x00007FF73A3A0A95]
        (No symbol) [0x00007FF73A4552BE]
        (No symbol) [0x00007FF73A454710]
        (No symbol) [0x00007FF73A447133]
        (No symbol) [0x00007FF73A4104D1]
        (No symbol) [0x00007FF73A411263]
        GetHandleVerifier [0x00007FF73A8CA8ED+2962317]
        GetHandleVerifier [0x00007FF73A8C4EC2+2939234]
        GetHandleVerifier [0x00007FF73A8E2FF3+3062419]
        GetHandleVerifier [0x00007FF73A624B9A+185914]
        GetHandleVerifier [0x00007FF73A62C78F+217647]
        GetHandleVerifier [0x00007FF73A612A44+111844]
        GetHandleVerifier [0x00007FF73A612BF2+112274]
        GetHandleVerifier [0x00007FF73A5F8A79+5401]
        BaseThreadInitThunk [0x00007FFE49BAE8D7+23]
        RtlUserThreadStart [0x00007FFE4AD114FC+44]

Reproducible Code

# Before running: 
#    1. open Chrome window with --remote-debugging-port=9222
#    2. open any tab with an extension url (starts with "chrome-extension://")
#       Note that the chrome-extension url does not need to be valid to replicate issue
#    3. Optionally, open some other normal tabs

from selenium import webdriver
from selenium.webdriver.chrome.options import Options

chrome_options = Options()
chrome_options.add_experimental_option("debuggerAddress", "localhost:9222") # connect to existing session
driver = webdriver.Chrome(options=chrome_options)

window_handles = driver.window_handles

for handle in window_handles:
    driver.switch_to.window(handle)
    print(driver.title)

Debugging Logs

What version of Selenium are you currently using?

4.31.0

The following statements are true

• This applies to the most recent version of Selenium (we can't fix old versions)
• This hasn't already been reported (I searched and didn't find it)
• All information necessary to reproduce the issue has been provided above

Did this work for you before?

Yes this is a regression

If yes, what version of Selenium did it work with?

4.29.0

Operating System

Windows

Selenium Language Binding

Python

Which browsers are you experiencing the issue with?

Chrome

Are you using Selenium Grid?

No

[selenium-ci]

@rookes, thank you for creating this issue. We will troubleshoot it as soon as we can.

Selenium Triage Team: remember to follow the Triage Guide

[cgoldberg]

Did this work for you before?
Yes this is a regression

If yes, what version of Selenium did it work with?
4.29.0

Does it still work with selenium 4.29 and Chrome 136? Or were you using an older version of Chrome/ChromeDriver when it worked?

[rookes]

Does it still work with selenium 4.29 and Chrome 136? Or were you using an older version of Chrome/ChromeDriver when it worked?

No, 4.29 has the same issues with 136, it seems to be due to a Chrome update. I was using an older version of chrome when it worked, 135.xx

[cgoldberg]

So nothing has changed in the window handle code on the Selenium side, so this is a regression in either Chrome or Chromedriver.

[selenium-ci]

Hi, @rookes.
This issue has been determined to require fixes in ChromeDriver.

You can see if the feature is passing in the Web Platform Tests.

If it is something new, please create an issue with the ChromeDriver team.
Feel free to comment the issues that you raise back in this issue. Thank you.

[slhck]

FWIW this has been reported here: https://groups.google.com/g/chromedriver-users/c/4367H-1kHwU

Since I haven't found any official bug report I created one here: https://issues.chromium.org/issues/416666972

[slhck]

Ahah, since ChromeDriver v136, a new enableExtensionTargets capability is required to be set:

let driver = await new Builder()
  .forBrowser("chrome")
  .setChromeOptions(
    new chrome.Options({
      'goog:chromeOptions': {
        'enableExtensionTargets': true,
      }
    })
    .addArguments([
      `load-extension=./test-extension`
    ])
    .setChromeBinaryPath(chromeBinary)
  )
  .setChromeService(new chrome.ServiceBuilder(chromeDriverBinary))
  .build();

See also the PSA by the ChromeDriver team and the example code here.

It seems to me that this should be documented somewhere in Selenium as well, just to make life easier for others running into this issue.

[rookes]

Thanks for looking into this, I'm glad it's an easy fix!

So does the error calling window_handles need to be addressed? When enableExtensionTargets is off and the only windows open are extension windows, there will be an error generated (see original post for example trace). It seems like ideally this call would just return an empty list or something like that. Is that something that needs to be handled on the ChromeDriver side too?

[mrchinhdev]

Ahah, since ChromeDriver v136, a new enableExtensionTargets capability is required to be set:

let driver = await new Builder()
.forBrowser("chrome")
.setChromeOptions(
new chrome.Options({
'goog:chromeOptions': {
'enableExtensionTargets': true,
}
})
.addArguments([
load-extension=./test-extension
])
.setChromeBinaryPath(chromeBinary)
)
.setChromeService(new chrome.ServiceBuilder(chromeDriverBinary))
.build();
See also the PSA by the ChromeDriver team and the example code here.

It seems to me that this should be documented somewhere in Selenium as well, just to make life easier for others running into this issue.

I had to log into my GitHub account to say that this works.
The code you need to use to correctly count the number of Chrome tabs is:

options.add_experimental_option('enableExtensionTargets', True)

[slhck]

So does the error calling window_handles need to be addressed? When enableExtensionTargets is off and the only windows open are extension windows, there will be an error generated (see original post for example trace). It seems like ideally this call would just return an empty list or something like that. Is that something that needs to be handled on the ChromeDriver side too?

I personally don't think Selenium should treat this in any specific way and instead continue raising the underlying ChromeDriver error. As a developer, that exception would have probably pointed me in the right direction, whereas an empty list would have certainly caused more confusion.