From 5bb2e6597a038a9a8dc3de8df10ad92756487e3b Mon Sep 17 00:00:00 2001
From: Andreas Kling <kling@serenityos.org>
Date: Mon, 27 Sep 2021 02:06:37 +0200
Subject: [PATCH] LibWeb: Preload resources hinted by <link rel="preload">

If a page is nice enough to give us some preload hints, we can tell
RequestServer to get started on downloading the resources right away,
instead of waiting until discovering them later on during parsing.
---
 Userland/Libraries/LibWeb/HTML/HTMLLinkElement.cpp | 9 +++++++++
 Userland/Libraries/LibWeb/HTML/HTMLLinkElement.h   | 3 +++
 2 files changed, 12 insertions(+)

diff --git a/Userland/Libraries/LibWeb/HTML/HTMLLinkElement.cpp b/Userland/Libraries/LibWeb/HTML/HTMLLinkElement.cpp
index 1d3d24da6f..4811a8319f 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLLinkElement.cpp
+++ b/Userland/Libraries/LibWeb/HTML/HTMLLinkElement.cpp
@@ -36,6 +36,13 @@ void HTMLLinkElement::inserted()
         if (auto sheet = m_css_loader.style_sheet())
             document().style_sheets().add_sheet(sheet.release_nonnull());
     }
+
+    if (m_relationship & Relationship::Preload) {
+        // FIXME: Respect the "as" attribute.
+        LoadRequest request;
+        request.set_url(attribute(HTML::AttributeNames::href));
+        m_preload_resource = ResourceLoader::the().load_resource(Resource::Type::Generic, request);
+    }
 }
 
 void HTMLLinkElement::parse_attribute(const FlyString& name, const String& value)
@@ -48,6 +55,8 @@ void HTMLLinkElement::parse_attribute(const FlyString& name, const String& value
                 m_relationship |= Relationship::Stylesheet;
             else if (part == "alternate")
                 m_relationship |= Relationship::Alternate;
+            else if (part == "preload")
+                m_relationship |= Relationship::Preload;
         }
     }
 }
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLLinkElement.h b/Userland/Libraries/LibWeb/HTML/HTMLLinkElement.h
index 7c0a88fa36..aebd3a38d1 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLLinkElement.h
+++ b/Userland/Libraries/LibWeb/HTML/HTMLLinkElement.h
@@ -32,9 +32,12 @@ private:
         enum {
             Alternate = 1 << 0,
             Stylesheet = 1 << 1,
+            Preload = 1 << 2,
         };
     };
 
+    RefPtr<Resource> m_preload_resource;
+
     CSSLoader m_css_loader;
     unsigned m_relationship { 0 };
 };