Chromedriver remote-debugging-port with Selenium

Question

I am using Capybara Selenium to run headless Chrome, which works great, except I cannot figure out how to use remote debugging. When I add --remote-debugging-port=4444 or --remote-debugging-port=9222 or --remote-debugging-port=9521, Selenium no longer connects to the browser to run the test.

How do I get remote debugging to work? Here is my code for reference:

Capybara.register_driver :selenium do |app|
  # from https://github.com/SeleniumHQ/selenium/issues/3738
  capabilities = Selenium::WebDriver::Remote::Capabilities.chrome(loggingPrefs: {browser: 'ALL'})
  options = Selenium::WebDriver::Chrome::Options.new
  options.add_argument '--disable-infobars' # hide info bar about chrome automating test
  # if we don't use this flag, every selenium test will die with the error:
  # "unknown error: Chrome failed to start: exited abnormally"
  options.add_argument '--no-sandbox'
  # BREAKS THINGS if uncommented
  # options.add_argument '--remote-debugging-port=4444'
  options.add_argument '--headless'
  options.add_argument '--window-size=1600,2400'
  options.add_preference('profile.default_content_settings.popups', 0)
  options.add_preference('download.default_directory', DownloadHelpers::PATH.to_s)
  Capybara::Selenium::Driver.new(
    app,
    clear_local_storage: true,
    clear_session_storage: true,
    browser: :chrome,
    options: options,
    desired_capabilities: capabilities,
  )
end

Answer 1

Since chrome 67 and chromedriver 2.39, chromedriver now correctly uses the port you specify with --remote-debugging-port. This removes quite a bit of complexity from my answer above. The steps I now take, which work for my use case of needing to configure download settings using chrome_remote, are as follows:

It makes uses of a nodejs library, crmux - which allows multiple clients to connect to the remote debug port of chrome at the same time.

1. Get nodejs installed first: Nodejs v9.7.0 works fine
2. Install crmux by running npm install crmux -g

3. Before you start chromedriver (Capybara::Selenium::Driver.new), you need to spawn a separate thread that will fire up crmux, which will let both you and chromedriver communicate with chrome itself via the port you specified in Capybara (4444):

   crmux --port=4444 --listen=4444

4. You may want to add a sleep 3 after the spawn command in the main script/thread to give time for crmux to start before you continue with your test startup.

You can then use chrome_remote (for example) to access chrome using port 4444, while capybara is doing its thing.

Answer 2

Updating my ChromeDriver fixed it for me. I didn't have to do anything else. Before it would hang when attempting to start the test.

Specifically I was on ChromeDriver 2.36 and I upgraded to ChromeDriver 2.40. I don't think the Chrome version was a problem, since I was on Chrome 67 both before and after.

Here's how I'm registering the driver:

Capybara.register_driver :headless_chrome do |app|
  capabilities = Selenium::WebDriver::Remote::Capabilities.chrome(
    chromeOptions: { args: %w[headless window-size=1280,960 remote-debugging-port=9222] }
  )
  Capybara::Selenium::Driver.new(app, browser: :chrome, desired_capabilities: capabilities)
end

After that I ran my test with a debugger (binding.pry) placed where I wanted to inspect. Then when I hit the debugger I navigated to http://localhost:9222/ in a normal instance of Chrome and was able to follow a link to view what was happening in the headless Chrome instance, including the browser console output I needed.