How to turn off w3c in chromedriver to address the error unknown command: Cannot call non W3C standard command while in W3C

selenium google-chrome selenium-webdriver selenium-chromedriver webdriver-w3c-spec
Julie picture Julie · Jun 5, 2019 · Viewed 18.9k times · Source

With version 75 of Chrome just released, our tests no longer run properly. They give the stacktrace pasted below. We are using ruby on rails v. 5.1.6.2 with rspec, selenium-webdriver 3.8.0.

Stacktrace:

Selenium::WebDriver::Error::UnknownCommandError:
            unknown command: Cannot call non W3C standard command while in W3C mode
          # 0   chromedriver                        0x000000010c46e8e9 chromedriver + 3594473
          # 1   chromedriver                        0x000000010c3fe543 chromedriver + 3134787
          # 2   chromedriver                        0x000000010c1aa29f chromedriver + 692895
          # 3   chromedriver                        0x000000010c11a691 chromedriver + 104081
          # 4   chromedriver                        0x000000010c11b7d5 chromedriver + 108501
          # 5   chromedriver                        0x000000010c42d555 chromedriver + 3327317
          # 6   chromedriver                        0x000000010c438e60 chromedriver + 3374688
          # 7   chromedriver                        0x000000010c438bf8 chromedriver + 3374072
          # 8   chromedriver                        0x000000010c40cd39 chromedriver + 3194169
          # 9   chromedriver                        0x000000010c4396d8 chromedriver + 3376856
          # 10  chromedriver                        0x000000010c420f27 chromedriver + 3276583
          # 11  chromedriver                        0x000000010c456064 chromedriver + 3493988
          # 12  chromedriver                        0x000000010c474617 chromedriver + 3618327
          # 13  libsystem_pthread.dylib             0x00007fff7744c2eb _pthread_body + 126
          # 14  libsystem_pthread.dylib             0x00007fff7744f249 _pthread_start + 66
          # 15  libsystem_pthread.dylib             0x00007fff7744b40d thread_start + 13
          # /Users/julie/.rvm/gems/ruby-2.5.1/gems/selenium-webdriver-3.8.0/lib/selenium/webdriver/remote/response.rb:69:in `assert_ok'
          # /Users/julie/.rvm/gems/ruby-2.5.1/gems/selenium-webdriver-3.8.0/lib/selenium/webdriver/remote/response.rb:32:in `initialize'
          # /Users/julie/.rvm/gems/ruby-2.5.1/gems/selenium-webdriver-3.8.0/lib/selenium/webdriver/remote/http/common.rb:81:in `new'
          # /Users/julie/.rvm/gems/ruby-2.5.1/gems/selenium-webdriver-3.8.0/lib/selenium/webdriver/remote/http/common.rb:81:in `create_response'
          # /Users/julie/.rvm/gems/ruby-2.5.1/gems/selenium-webdriver-3.8.0/lib/selenium/webdriver/remote/http/default.rb:104:in `request'
          # /Users/julie/.rvm/gems/ruby-2.5.1/gems/selenium-webdriver-3.8.0/lib/selenium/webdriver/remote/http/common.rb:59:in `call'
          # /Users/julie/.rvm/gems/ruby-2.5.1/gems/selenium-webdriver-3.8.0/lib/selenium/webdriver/remote/bridge.rb:166:in `execute'
          # /Users/julie/.rvm/gems/ruby-2.5.1/gems/selenium-webdriver-3.8.0/lib/selenium/webdriver/remote/oss/bridge.rb:579:in `execute'
          # /Users/julie/.rvm/gems/ruby-2.5.1/gems/selenium-webdriver-3.8.0/lib/selenium/webdriver/remote/oss/bridge.rb:526:in `element_displayed?'
          # /Users/julie/.rvm/gems/ruby-2.5.1/gems/selenium-webdriver-3.8.0/lib/selenium/webdriver/common/element.rb:199:in `displayed?'
          # /Users/julie/.rvm/gems/ruby-2.5.1/gems/capybara-2.17.0/lib/capybara/selenium/node.rb:148:in `visible?'
          # /Users/julie/.rvm/gems/ruby-2.5.1/gems/capybara-2.17.0/lib/capybara/node/element.rb:269:in `block in visible?'
          # /Users/julie/.rvm/gems/ruby-2.5.1/gems/capybara-2.17.0/lib/capybara/node/base.rb:81:in `synchronize'
          # /Users/julie/.rvm/gems/ruby-2.5.1/gems/capybara-2.17.0/lib/capybara/node/element.rb:269:in `visible?'
          # /Users/julie/.rvm/gems/ruby-2.5.1/gems/capybara-2.17.0/lib/capybara/queries/selector_query.rb:84:in `matches_filters?'
          # /Users/julie/.rvm/gems/ruby-2.5.1/gems/capybara-2.17.0/lib/capybara/result.rb:29:in `block in initialize'

Our driver configuration:

File.write(LOG_FILE_PATH, '')
Selenium::WebDriver.logger.level = :debug
Selenium::WebDriver.logger.output = LOG_FILE_PATH
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'
  options.add_argument '--headless' if ENV.fetch("HEADLESS", nil).present?
  options.add_argument '--window-size=1600,2400'
  options.add_argument '-–allow-file-access-from-files' # TODO Julie - may help with file specs?
  options.add_preference('homepage', 'about:blank') # TODO is this working?
  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

UPDATE:

I was able to get our tests to work temporarily using capabilities = { "chromeOptions" => {'w3c' => false} }.

After updating chromedriver, we began receiving the error "unknown error: DevToolsActivePort file doesn't exist". In order to fix this problem, we upgraded our selenium-webdriver gem to 3.142.3 and this fixed the issue, allowing us to use w3c without any additional parameters.

Answer

DebanjanB picture DebanjanB · Jun 5, 2019

First the solution

As promised by John Chen [Owner - WebDriver for Google Chrome] yesterday, new versions of ChromeDriver 75.0.3770.90 and 76.0.3809.25 have been released, and are now available at the ChromeDriver Downloads site. These versions include the following bug fixes over the previous releases of ChromeDriver 75 and 76:

  • Fixed a bug that incorrectly rejected POST requests with empty body in OSS mode
  • Added new endpoints for retrieving Chrome log

In addition, version 76.0.3809.25 also includes the following change:

  • Added endpoint for Is Displayed command in W3C mode

Email Snapshot

75_76

Details

It will be against the best practices to turn off w3c in chromedriver to address the error:

Selenium::WebDriver::Error::UnknownCommandError:
        unknown command: Cannot call non W3C standard command while in W3C mode

as the current implementation of ChromeDriver requests a W3C-compliant session to the client.

However, this error message implies that the ChromeDriver was unable to invoke a non W3C standard command while in W3C mode while initiating/spawning a new WebBrowser i.e. Chrome Browser session.

The main issue is, when ChromeDriver's client requests a W3C-compliant session, the response from ChromeDriver does not conform to the W3C spec, and causes errors in language APIs.

As per the discussion in ChromeDriver response in W3C mode is not standard compliant John Chen (Owner - WebDriver for Google Chrome) mentioned Simon Stewart (Creator - WebDriver) have updated that:

  • The new session response for a w3c session should look like:

    {
  "value": {
    "sessionId": "some-uuid",
    "capabilities": {
      "browserName": "chrome",
      ...
    }
  }
}

  • But when starting a new session with the w3c option set to true in the chromeOptions, the returned response looked like:

        {
      "sessionId": "af4656c27fb94485b7872e1fc616923a",
      "status": "ok",
      "value": {
        "browserName": "chrome",
        ...
      }
    }

Which is neither a correctly formed response for the JSON Wire Protocol (where "status" would be an integer), nor a correctly formed W3C response and without a correctly formed response, the w3c compatible cannot be used.

This revision and this commit addressed this issue.

This usecase

Presumably you are using ChromeDriver v75.x with Chrome v75.x and in case you are still seeing the error, you need to pass the ExperimentalOption w3c as true explicitly as follows:

  • Ruby code sample:

    capabilities = { "chromeOptions" => {'w3c' => true} }

  • Java code sample:

    import org.openqa.selenium.chrome.ChromeDriver;
import org.openqa.selenium.chrome.ChromeOptions;

public class W3c {
  public static void main(String[] args) throws Exception {
    ChromeOptions opt = new ChromeOptions();
    opt.setExperimentalOption("w3c", true);
    ChromeDriver driver = new ChromeDriver(opt);
    driver.get("https://www.google.co.in");
  }
}

  • Python code sample:

    from selenium import webdriver

opt = webdriver.ChromeOptions()
opt.add_experimental_option('w3c', True)
driver = webdriver.Chrome(chrome_options=opt)
driver.get('https://www.google.co.in')

Update

Till ChromeDriver v74.x, Chrome and ChromeDriver combo was running in w3c mode by default but there was bug with in the chromedriver/server/http_handler.cc. As per the details in goog:chromeOptions.w3c=false doesn't work for POST request with empty body:

Method HttpHandler::HandleCommand checks the value of the kW3CDefault constant instead of session goog:chromeOptions.w3c value. As a result, JSON Wire protocol support was broken, where POST requests with an empty body are allowed. JSON Wire protocol will be in demand until displayed endpoint is resumed in the w3c mode. It should be noted that W3C WebDriver specification doesn't forbid the use of 'displayed' endpoint and this feature is actively used in some APIs.

As Is Element Displayed command is not part of W3C spec, but is still used by some APIs, and its functionality can be difficult to replicate in those APIs. This Change List [revision and commit] re-enables this command in W3C mode to ease transition to W3C mode.

@John have already confirmed us to expect an update to ChromeDriver v75.0 tomorrow with the fix.

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