Issue #2158 - Part 5: Guard preload links support with a preference

This is enabled by default.

dom/base/nsContentUtils.cpp

@@ -295,6 +295,7 @@ bool nsContentUtils::sGettersDecodeURLHash = false;
 bool nsContentUtils::sPrivacyResistFingerprinting = false;
 bool nsContentUtils::sSendPerformanceTimingNotifications = false;
 bool nsContentUtils::sUseActivityCursor = false;
+bool nsContentUtils::sPreloadEnabled = true;
 
 uint32_t nsContentUtils::sHandlingInputTimeout = 1000;
 
@@ -633,6 +634,9 @@ nsContentUtils::Init()
   Preferences::AddBoolVarCache(&sUseActivityCursor,
                                "ui.use_activity_cursor", false);
 
+  Preferences::AddBoolVarCache(&sPreloadEnabled,
+                               "network.preload", true);
+
   Element::InitCCCallbacks();
 
   nsCOMPtr<nsIUUIDGenerator> uuidGenerator =
@@ -4125,6 +4129,10 @@ void
 nsContentUtils::DispatchEventForPreloadURI(nsIDOMNode* aNode,
                                            nsContentPolicyType& aPolicyType)
 {
+  if (!IsPreloadEnabled()) {
+    return;
+  }
+
   nsCOMPtr<nsINode> domNode = do_QueryInterface(aNode);
   if (domNode && domNode->IsInComposedDoc()) {
     bool success = aPolicyType != nsIContentPolicy::TYPE_INVALID;
@@ -7396,6 +7404,12 @@ nsContentUtils::GPCEnabled()
   return nsContentUtils::sGPCEnabled;
 }
 
+bool
+nsContentUtils::IsPreloadEnabled()
+{
+  return nsContentUtils::sPreloadEnabled;
+}
+
 mozilla::LogModule*
 nsContentUtils::DOMDumpLog()
 {

dom/base/nsContentUtils.h

@@ -2149,6 +2149,11 @@ public:
     return sUseActivityCursor;
   }
 
+  /**
+   * Returns true if the preload service is enabled.
+   */
+  static bool IsPreloadEnabled();
+
   /**
    * Return true if this doc is controlled by a ServiceWorker.
    */
@@ -2969,6 +2974,7 @@ private:
   static bool sPrivacyResistFingerprinting;
   static bool sSendPerformanceTimingNotifications;
   static bool sUseActivityCursor;
+  static bool sPreloadEnabled;
   static uint32_t sCookiesLifetimePolicy;
   static uint32_t sCookiesBehavior;
 

modules/libpref/init/all.js

@@ -1906,6 +1906,9 @@ pref("network.ftp.idleConnectionTimeout", 300);
 // all other values are treated like 2
 pref("network.dir.format", 2);
 
+// enables the preload service (i.e., preloading of <link rel="preload"> URLs).
+pref("network.preload", true);
+
 // enables the prefetch service (i.e., prefetching of <link rel="next"> URLs).
 pref("network.prefetch-next", true);
 

parser/html/nsHtml5TreeBuilderCppSupplement.h

@@ -230,7 +230,7 @@ nsHtml5TreeBuilder::createElement(int32_t aNamespace,
                 mSpeculativeLoadQueue.AppendElement()->InitPreconnect(
                   url, crossOrigin);
               }
-            } else if (rel.LowerCaseEqualsASCII("preload")) {
+            } else if (rel.LowerCaseEqualsASCII("preload") && nsContentUtils::IsPreloadEnabled()) {
               nsHtml5String url =
                 aAttributes->getValue(nsHtml5AttributeName::ATTR_HREF);
               if (url) {