Initial support for <link rel="prefetch"> (#33345)

* Properly store link relations

Signed-off-by: Simon Wülker <simon.wuelker@arcor.de>

* Send fetch request for prefetch links

We don't actually *do* anything with the response yet
(handle errors etc) but its a first step.

Signed-off-by: Simon Wülker <simon.wuelker@arcor.de>

* Fire load/error events for prefetch loads

Signed-off-by: Simon Wülker <simon.wuelker@arcor.de>

* Set prefetch destination/cors setting correctly

Signed-off-by: Simon Wülker <simon.wuelker@arcor.de>

* Update WPT expectations

Signed-off-by: Simon Wülker <simon.wuelker@arcor.de>

* Fix ./mach test-tidy errors

Signed-off-by: Simon Wülker <simon.wuelker@arcor.de>

* Set correct "Accept" value for prefetch requests

Signed-off-by: Simon Wülker <simon.wuelker@arcor.de>

* Add spec text to individual steps

Signed-off-by: Simon Wülker <simon.wuelker@arcor.de>

---------

Signed-off-by: Simon Wülker <simon.wuelker@arcor.de>

components/script/link_relations.rs

@@ -0,0 +1,131 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+use html5ever::{local_name, namespace_url, ns};
+use malloc_size_of::malloc_size_of_is_0;
+use style::str::HTML_SPACE_CHARACTERS;
+
+use crate::dom::types::Element;
+
+bitflags::bitflags! {
+    #[derive(Clone, Copy, Debug)]
+    pub struct LinkRelations: u32 {
+        const ALTERNATE = 1;
+        const AUTHOR = 1 << 1;
+        const BOOKMARK = 1 << 2;
+        const CANONICAL = 1 << 3;
+        const DNS_PREFETCH = 1 << 4;
+        const EXPECT = 1 << 5;
+        const EXTERNAL = 1 << 6;
+        const HELP = 1 << 7;
+        const ICON = 1 << 8;
+        const LICENSE = 1 << 9;
+        const NEXT = 1 << 10;
+        const MANIFEST = 1 << 11;
+        const MODULE_PRELOAD = 1 << 12;
+        const NO_FOLLOW = 1 << 13;
+        const NO_OPENER = 1 << 14;
+        const NO_REFERRER = 1 << 15;
+        const OPENER = 1 << 16;
+        const PING_BACK = 1 << 17;
+        const PRECONNECT = 1 << 18;
+        const PREFETCH = 1 << 19;
+        const PRELOAD = 1 << 20;
+        const PREV = 1 << 21;
+        const PRIVACY_POLICY = 1 << 22;
+        const SEARCH = 1 << 23;
+        const STYLESHEET = 1 << 24;
+        const TAG = 1 << 25;
+        const TermsOfService = 1 << 26;
+    }
+}
+
+impl LinkRelations {
+    pub fn for_element(element: &Element) -> Self {
+        let rel = element.get_attribute(&ns!(), &local_name!("rel")).map(|e| {
+            let value = e.value();
+            (**value).to_owned()
+        });
+
+        // FIXME: for a, area and form elements we need to allow a different
+        //        set of attributes
+        let mut relations = rel
+            .map(|attribute| {
+                attribute
+                    .split(HTML_SPACE_CHARACTERS)
+                    .map(Self::from_single_keyword_for_link_element)
+                    .collect()
+            })
+            .unwrap_or(Self::empty());
+
+        // For historical reasons, "rev=made" is treated as if the "author" relation was specified
+        let has_legacy_author_relation = element
+            .get_attribute(&ns!(), &local_name!("rev"))
+            .is_some_and(|rev| &**rev.value() == "made");
+        if has_legacy_author_relation {
+            relations |= Self::AUTHOR;
+        }
+
+        relations
+    }
+
+    /// Parse one of the relations allowed for the `<link>` element
+    ///
+    /// If the keyword is invalid then `Self::empty` is returned.
+    fn from_single_keyword_for_link_element(keyword: &str) -> Self {
+        if keyword.eq_ignore_ascii_case("alternate") {
+            Self::ALTERNATE
+        } else if keyword.eq_ignore_ascii_case("canonical") {
+            Self::CANONICAL
+        } else if keyword.eq_ignore_ascii_case("author") {
+            Self::AUTHOR
+        } else if keyword.eq_ignore_ascii_case("dns-prefetch") {
+            Self::DNS_PREFETCH
+        } else if keyword.eq_ignore_ascii_case("expect") {
+            Self::EXPECT
+        } else if keyword.eq_ignore_ascii_case("help") {
+            Self::HELP
+        } else if keyword.eq_ignore_ascii_case("icon") ||
+            keyword.eq_ignore_ascii_case("shortcut icon") ||
+            keyword.eq_ignore_ascii_case("apple-touch-icon")
+        {
+            // TODO: "apple-touch-icon" is not in the spec. Where did it come from? Do we need it?
+            //       There is also "apple-touch-icon-precomposed" listed in
+            //       https://github.com/servo/servo/blob/e43e4778421be8ea30db9d5c553780c042161522/components/script/dom/htmllinkelement.rs#L452-L467
+            Self::ICON
+        } else if keyword.eq_ignore_ascii_case("manifest") {
+            Self::MANIFEST
+        } else if keyword.eq_ignore_ascii_case("modulepreload") {
+            Self::MODULE_PRELOAD
+        } else if keyword.eq_ignore_ascii_case("license") ||
+            keyword.eq_ignore_ascii_case("copyright")
+        {
+            Self::LICENSE
+        } else if keyword.eq_ignore_ascii_case("next") {
+            Self::NEXT
+        } else if keyword.eq_ignore_ascii_case("pingback") {
+            Self::PING_BACK
+        } else if keyword.eq_ignore_ascii_case("preconnect") {
+            Self::PRECONNECT
+        } else if keyword.eq_ignore_ascii_case("prefetch") {
+            Self::PREFETCH
+        } else if keyword.eq_ignore_ascii_case("preload") {
+            Self::PRELOAD
+        } else if keyword.eq_ignore_ascii_case("prev") || keyword.eq_ignore_ascii_case("previous") {
+            Self::PREV
+        } else if keyword.eq_ignore_ascii_case("privacy-policy") {
+            Self::PRIVACY_POLICY
+        } else if keyword.eq_ignore_ascii_case("search") {
+            Self::SEARCH
+        } else if keyword.eq_ignore_ascii_case("stylesheet") {
+            Self::STYLESHEET
+        } else if keyword.eq_ignore_ascii_case("terms-of-service") {
+            Self::TermsOfService
+        } else {
+            Self::empty()
+        }
+    }
+}
+
+malloc_size_of_is_0!(LinkRelations);