fix(page): leave the window size to Chrome when window_size is nil

.rubocop.yml

@@ -55,7 +55,7 @@ Metrics/ModuleLength:
   Max: 602
 
 Metrics/PerceivedComplexity:
-  Max: 14
+  Max: 15
 
 plugins:
   - rubocop-rake

CHANGELOG.md

@@ -8,6 +8,8 @@
 - Ferrum is bumped to `~> 0.19.0`
 
 ### Fixed
+- `window_size: nil` raised `Ferrum::BrowserError: Invalid parameters` on every page instead of leaving the window
+  size to Chrome, so `start-maximized` couldn't be used [#278]
 - `Driver#reset!` kept the page it had cached when the browser failed to reset, so every later example raised
   `Session with given id not found` or `Browser is dead or given window is closed` instead of starting on a fresh
   page [#274], [rubycdp/ferrum#641]

docs/2-customization.md

@@ -58,6 +58,9 @@ Capybara::Cuprite::Driver.new(app, timeout: 15, process_timeout: 30)
 # Connect to a remote browser
 Capybara::Cuprite::Driver.new(app, url: "http://chrome:3333")
 
+# Leave the window size to Chrome, e.g. to start maximized in headful mode
+Capybara::Cuprite::Driver.new(app, headless: false, window_size: nil, browser_options: { "start-maximized" => nil })
+
 # Emulate an iPhone 14
 Capybara::Cuprite::Driver.new(app, emulate: :iphone_14)
 

docs/9-windows-frames.md

@@ -54,7 +54,8 @@ Returns inner width and height of the window.
 page.current_window.size # => [1024, 768]
 ```
 
-The window size is reset to `:window_size` at the end of every test.
+The window size is reset to `:window_size` at the end of every test. With `window_size: nil` Cuprite doesn't
+set the size, so Chrome's own one, or `start-maximized`, applies.
 
 ## Frames
 

lib/capybara/cuprite/page.rb

@@ -178,7 +178,7 @@ def prepare_page
         super
 
         width, height = @options.window_size
-        resize(width: width, height: height)
+        width && height ? resize(width: width, height: height) : set_viewport
         command("Network.setUserAgentOverride", userAgent: default_user_agent) if @options.device_user_agent
 
         if @options.url_blacklist.any?

spec/features/driver_spec.rb

@@ -230,6 +230,25 @@ def session_url(path)
         driver&.quit
       end
 
+      it "leaves the window size to the browser when the option is nil" do
+        Capybara.register_driver :cuprite_without_window_size do |app|
+          Capybara::Cuprite::Driver.new(app, window_size: nil)
+        end
+        driver = Capybara::Session.new(:cuprite_without_window_size, TestApp).driver
+        driver.visit(session_url("/"))
+        default_size = driver.evaluate_script("[window.innerWidth, window.innerHeight]")
+        expect(default_size).not_to eq([1024, 768])
+
+        driver.resize(800, 600)
+        expect(driver.evaluate_script("[window.innerWidth, window.innerHeight]")).to eq([800, 600])
+
+        driver.reset!
+        driver.visit(session_url("/"))
+        expect(driver.evaluate_script("[window.innerWidth, window.innerHeight]")).to eq(default_size)
+      ensure
+        driver&.quit
+      end
+
       shared_examples "render screen" do
         it "supports rendering the whole of a page that goes outside the viewport" do
           @session.visit("/cuprite/long_page")