feat(chromium): always inject paint-callback polyfill to cover waitDelay users

pkg/modules/chromium/browser.go

@@ -308,7 +308,6 @@ func (b *chromiumBrowser) Healthy(logger *slog.Logger) bool {
 func (b *chromiumBrowser) pdf(ctx context.Context, logger *slog.Logger, url, outputPath string, options PdfOptions) error {
 	// Note: no error wrapping because it leaks on errors we want to display to
 	// the end user.
-	installPaintPolyfill := options.WaitForExpression != "" || options.WaitForSelector != ""
 	return b.do(ctx, logger, url, options.Options, chromedp.Tasks{
 		network.Enable(),
 		fetch.Enable(),
@@ -318,7 +317,7 @@ func (b *chromiumBrowser) pdf(ctx context.Context, logger *slog.Logger, url, out
 		disableJavaScriptActionFunc(logger, b.arguments.disableJavaScript),
 		setCookiesActionFunc(logger, options.Cookies),
 		userAgentOverride(logger, options.UserAgent),
-		injectPaintCallbacksPolyfillActionFunc(logger, installPaintPolyfill),
+		injectPaintCallbacksPolyfillActionFunc(logger),
 		navigateActionFunc(logger, url, options.SkipNetworkIdleEvent, options.SkipNetworkAlmostIdleEvent),
 		hideDefaultWhiteBackgroundActionFunc(logger, options.OmitBackground, options.PrintBackground),
 		forceExactColorsActionFunc(logger, options.PrintBackground),
@@ -336,7 +335,6 @@ func (b *chromiumBrowser) pdf(ctx context.Context, logger *slog.Logger, url, out
 func (b *chromiumBrowser) screenshot(ctx context.Context, logger *slog.Logger, url, outputPath string, options ScreenshotOptions) error {
 	// Note: no error wrapping because it leaks on errors we want to display to
 	// the end user.
-	installPaintPolyfill := options.WaitForExpression != "" || options.WaitForSelector != ""
 	return b.do(ctx, logger, url, options.Options, chromedp.Tasks{
 		network.Enable(),
 		fetch.Enable(),
@@ -346,7 +344,7 @@ func (b *chromiumBrowser) screenshot(ctx context.Context, logger *slog.Logger, u
 		disableJavaScriptActionFunc(logger, b.arguments.disableJavaScript),
 		setCookiesActionFunc(logger, options.Cookies),
 		userAgentOverride(logger, options.UserAgent),
-		injectPaintCallbacksPolyfillActionFunc(logger, installPaintPolyfill),
+		injectPaintCallbacksPolyfillActionFunc(logger),
 		navigateActionFunc(logger, url, options.SkipNetworkIdleEvent, options.SkipNetworkAlmostIdleEvent),
 		hideDefaultWhiteBackgroundActionFunc(logger, options.OmitBackground, true),
 		forceExactColorsActionFunc(logger, true),

pkg/modules/chromium/paint_polyfill.go

@@ -124,15 +124,14 @@ const paintCallbacksPolyfill = `
 
 // injectPaintCallbacksPolyfillActionFunc installs the
 // [paintCallbacksPolyfill] via [page.AddScriptToEvaluateOnNewDocument]
-// so that it runs before any user script on the navigated page. When
+// so that it runs before any user script on the navigated page. The
-// install is false the action is a no-op and the page keeps the native
+// shim is installed unconditionally: the native rAF, ResizeObserver,
-// rAF, ResizeObserver, and IntersectionObserver implementations.
+// and IntersectionObserver APIs do not fire during Chromium's
-func injectPaintCallbacksPolyfillActionFunc(logger *slog.Logger, install bool) chromedp.ActionFunc {
+// headless-print render, so replacing them with timer-backed
+// implementations either restores the behavior the page expects or has
+// no effect when the page never calls them.
+func injectPaintCallbacksPolyfillActionFunc(logger *slog.Logger) chromedp.ActionFunc {
 	return func(ctx context.Context) error {
-		if !install {
-			logger.DebugContext(ctx, "paint-callbacks polyfill not requested")
-			return nil
-		}
 		logger.DebugContext(ctx, "inject paint-callbacks polyfill")
 		_, err := page.AddScriptToEvaluateOnNewDocument(paintCallbacksPolyfill).Do(ctx)
 		if err != nil {

test/integration/features/chromium_convert_html.feature

@@ -195,7 +195,7 @@ Feature: /forms/chromium/convert/html
       Wait delay > 2 seconds or expression window globalVar === 'ready' returns true.
       """
 
-  Scenario: POST /forms/chromium/convert/html (paint-callback polyfill fires rAF / ResizeObserver / IntersectionObserver when waitForExpression is set)
+  Scenario: POST /forms/chromium/convert/html (paint-callback polyfill fires rAF / ResizeObserver / IntersectionObserver with waitForExpression)
     Given I have a default Gotenberg container
     When I make a "POST" request to Gotenberg at the "/forms/chromium/convert/html" endpoint with the following form data and header(s):
       | files                     | testdata/paint-callbacks-html/index.html       | file   |
@@ -219,14 +219,30 @@ Feature: /forms/chromium/convert/html
       io-fired
       """
 
-  Scenario: POST /forms/chromium/convert/html (paint-callback polyfill skipped without a readiness signal)
+  Scenario: POST /forms/chromium/convert/html (paint-callback polyfill fires rAF / ResizeObserver / IntersectionObserver with waitDelay and emulatedMediaType=print)
-    Given I have a Gotenberg container with the following environment variable(s):
+    Given I have a default Gotenberg container
-      | LOG_LEVEL | debug |
     When I make a "POST" request to Gotenberg at the "/forms/chromium/convert/html" endpoint with the following form data and header(s):
-      | files | testdata/page-1-html/index.html | file |
+      | files                     | testdata/paint-callbacks-html/index.html | file   |
+      | waitDelay                 | 3s                                       | field  |
+      | emulatedMediaType         | print                                    | field  |
+      | Gotenberg-Output-Filename | foo                                      | header |
     Then the response status code should be 200
-    Then the Gotenberg container should log the following entries:
+    Then the response header "Content-Type" should be "application/pdf"
-      | paint-callbacks polyfill not requested |
+    Then there should be 1 PDF(s) in the response
+    Then there should be the following file(s) in the response:
+      | foo.pdf |
+    Then the "foo.pdf" PDF should have the following content at page 1:
+      """
+      raf-fired
+      """
+    Then the "foo.pdf" PDF should have the following content at page 1:
+      """
+      ro-fired
+      """
+    Then the "foo.pdf" PDF should have the following content at page 1:
+      """
+      io-fired
+      """
 
   Scenario: POST /forms/chromium/convert/html (Wait For Selector)
     Given I have a default Gotenberg container