Bug 1853116 - Early Hints: don't preload fonts when gfx.downloadable_fonts.enabled false r=necko-reviewers,kershaw

Differential Revision: https://phabricator.services.mozilla.com/D188231

netwerk/protocol/http/EarlyHintPreloader.cpp

@@ -10,6 +10,7 @@
 #include "HttpChannelParent.h"
 #include "MainThreadUtils.h"
 #include "NeckoCommon.h"
+#include "gfxPlatform.h"
 #include "mozilla/CORSMode.h"
 #include "mozilla/dom/Element.h"
 #include "mozilla/dom/nsCSPContext.h"
@@ -219,6 +220,11 @@ void EarlyHintPreloader::MaybeCreateAndInsertPreload(
     return;
   }
 
+  if (destination == ASDestination::DESTINATION_FONT &&
+      !gfxPlatform::GetPlatform()->DownloadableFontsEnabled()) {
+    return;
+  }
+
   nsCOMPtr<nsIURI> uri;
   NS_ENSURE_SUCCESS_VOID(
       NS_NewURI(getter_AddRefs(uri), aLinkHeader.mHref, nullptr, aBaseURI));

netwerk/test/browser/browser_103_preload.js

@@ -11,13 +11,10 @@ Services.prefs.setBoolPref(
   false
 );
 
-const {
-  request_count_checking,
-  test_hint_preload_internal,
-  test_hint_preload,
-} = ChromeUtils.importESModule(
-  "resource://testing-common/early_hint_preload_test_helper.sys.mjs"
-);
+const { request_count_checking, test_preload_url, test_hint_preload } =
+  ChromeUtils.importESModule(
+    "resource://testing-common/early_hint_preload_test_helper.sys.mjs"
+  );
 
 // TODO testing:
 //  * Abort main document load while early hint is still loading -> early hint should be aborted
@@ -34,6 +31,22 @@ add_task(async function test_103_preload_disabled() {
   Services.prefs.setBoolPref("network.early-hints.enabled", true);
 });
 
+add_task(async function test_103_font_disabled() {
+  let url =
+    "https://example.com/browser/netwerk/test/browser/early_hint_asset_html.sjs?hinted=1&as=font";
+  Services.prefs.setBoolPref("gfx.downloadable_fonts.enabled", false);
+  await test_preload_url("font_loading_disabled", url, {
+    hinted: 0,
+    normal: 0,
+  });
+  Services.prefs.setBoolPref("gfx.downloadable_fonts.enabled", true);
+  await test_preload_url("font_loading_enabled", url, {
+    hinted: 1,
+    normal: 0,
+  });
+  Services.prefs.clearUserPref("gfx.downloadable_fonts.enabled");
+});
+
 // Preload with same origin in secure context with mochitest http proxy
 add_task(async function test_103_preload_https() {
   await test_hint_preload(

netwerk/test/browser/early_hint_preload_test_helper.sys.mjs

@@ -129,3 +129,31 @@ export async function test_preload_hint_and_request(input, expected_results) {
   gBrowser.removeCurrentTab();
   Services.cache2.clear();
 }
+
+// simple loading of one url and then checking the request count against the
+// passed expected count
+export async function test_preload_url(testName, url, expectedRequestCount) {
+  // reset the count
+  let headers = new Headers();
+  headers.append("X-Early-Hint-Count-Start", "");
+  await fetch(
+    "http://example.com/browser/netwerk/test/browser/early_hint_pixel_count.sjs",
+    { headers }
+  );
+
+  await BrowserTestUtils.withNewTab(
+    {
+      gBrowser,
+      url,
+      waitForLoad: true,
+    },
+    async function () {}
+  );
+
+  let gotRequestCount = await fetch(
+    "http://example.com/browser/netwerk/test/browser/early_hint_pixel_count.sjs"
+  ).then(response => response.json());
+
+  await request_count_checking(testName, gotRequestCount, expectedRequestCount);
+  Services.cache2.clear();
+}