Support as=fetch in Early Hints preload

The spec doesn't prohibit as=fetch.

Bug: 1408649
Change-Id: I81c50de77b362c8fa1c6ecfcc8332bba4c5e5d66
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4177723
Reviewed-by: Yoav Weiss <yoavweiss@chromium.org>
Commit-Queue: Kenichi Ishibashi <bashi@chromium.org>
Reviewed-by: Takashi Toyoshima <toyoshim@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1098451}

content/browser/loader/navigation_early_hints_manager.cc

@@ -82,6 +82,7 @@ const net::NetworkTrafficAnnotationTag kEarlyHintsPreloadTrafficAnnotation =
 
 network::mojom::CSPDirectiveName LinkAsAttributeToCSPDirective(
     network::mojom::LinkAsAttribute attr) {
+  // https://w3c.github.io/webappsec-csp/#csp-directives
   switch (attr) {
     case network::mojom::LinkAsAttribute::kUnspecified:
       return network::mojom::CSPDirectiveName::Unknown;
@@ -93,6 +94,8 @@ network::mojom::CSPDirectiveName LinkAsAttributeToCSPDirective(
       return network::mojom::CSPDirectiveName::ScriptSrcElem;
     case network::mojom::LinkAsAttribute::kStyleSheet:
       return network::mojom::CSPDirectiveName::StyleSrcElem;
+    case network::mojom::LinkAsAttribute::kFetch:
+      return network::mojom::CSPDirectiveName::ConnectSrc;
   }
   NOTREACHED();
   return network::mojom::CSPDirectiveName::Unknown;
@@ -131,8 +134,9 @@ bool CheckContentSecurityPolicyForPreload(
   return true;
 }
 
-network::mojom::RequestDestination LinkAsAttributeToRequestDestination(
-    const network::mojom::LinkHeaderPtr& link) {
+absl::optional<network::mojom::RequestDestination>
+LinkAsAttributeToRequestDestination(const network::mojom::LinkHeaderPtr& link) {
+  // https://fetch.spec.whatwg.org/#concept-potential-destination-translate
   switch (link->as) {
     case network::mojom::LinkAsAttribute::kUnspecified:
       // For modulepreload, the request destination should be "script" when `as`
@@ -141,7 +145,7 @@ network::mojom::RequestDestination LinkAsAttributeToRequestDestination(
       if (link->rel == network::mojom::LinkRelAttribute::kModulePreload) {
         return network::mojom::RequestDestination::kScript;
       }
-      return network::mojom::RequestDestination::kEmpty;
+      return absl::nullopt;
     case network::mojom::LinkAsAttribute::kImage:
       return network::mojom::RequestDestination::kImage;
     case network::mojom::LinkAsAttribute::kFont:
@@ -150,6 +154,8 @@ network::mojom::RequestDestination LinkAsAttributeToRequestDestination(
       return network::mojom::RequestDestination::kScript;
     case network::mojom::LinkAsAttribute::kStyleSheet:
       return network::mojom::RequestDestination::kStyle;
+    case network::mojom::LinkAsAttribute::kFetch:
+      return network::mojom::RequestDestination::kEmpty;
   }
 }
 
@@ -166,6 +172,7 @@ net::RequestPriority CalculateRequestPriority(
     case network::mojom::LinkAsAttribute::kScript:
       return net::MEDIUM;
     case network::mojom::LinkAsAttribute::kImage:
+    case network::mojom::LinkAsAttribute::kFetch:
       return net::LOWEST;
     case network::mojom::LinkAsAttribute::kUnspecified:
       return net::IDLE;
@@ -513,12 +520,13 @@ void NavigationEarlyHintsManager::MaybePreloadHintedResource(
   if (!ShouldHandleResourceHints(link))
     return;
 
-  network::mojom::RequestDestination destination =
-      LinkAsAttributeToRequestDestination(link);
   // Step 2. If options's destination is not a destination, then return null.
   // https://html.spec.whatwg.org/multipage/semantics.html#create-a-link-request
-  if (destination == network::mojom::RequestDestination::kEmpty)
+  absl::optional<network::mojom::RequestDestination> destination =
+      LinkAsAttributeToRequestDestination(link);
+  if (!destination) {
     return;
+  }
 
   if (!CheckContentSecurityPolicyForPreload(link, content_security_policies))
     return;
@@ -535,7 +543,7 @@ void NavigationEarlyHintsManager::MaybePreloadHintedResource(
   network::ResourceRequest request;
   request.method = net::HttpRequestHeaders::kGetMethod;
   request.priority = CalculateRequestPriority(link);
-  request.destination = destination;
+  request.destination = *destination;
   request.url = link->href;
   request.site_for_cookies = site_for_cookies;
   request.request_initiator = origin_;

services/network/public/cpp/link_header_parser.cc

@@ -62,6 +62,8 @@ absl::optional<mojom::LinkAsAttribute> ParseAsAttribute(
     return mojom::LinkAsAttribute::kScript;
   } else if (value == "style") {
     return mojom::LinkAsAttribute::kStyleSheet;
+  } else if (value == "fetch") {
+    return mojom::LinkAsAttribute::kFetch;
   }
   return absl::nullopt;
 }

services/network/public/cpp/link_header_parser_unittest.cc

@@ -135,15 +135,17 @@ TEST(LinkHeaderParserTest, LinkAsAttribute) {
   headers->AddHeader("link", "</image.jpg>; rel=preload; as=image");
   headers->AddHeader("link", "</script.js>; rel=preload; as=script");
   headers->AddHeader("link", "</style.css>; rel=preload; as=style");
+  headers->AddHeader("link", "</foo.json>; rel=preload; as=fetch; crossorigin");
 
   std::vector<mojom::LinkHeaderPtr> parsed_headers =
       ParseLinkHeaders(*headers, kBaseUrl);
-  ASSERT_EQ(parsed_headers.size(), 5UL);
+  ASSERT_EQ(parsed_headers.size(), 6UL);
   EXPECT_EQ(parsed_headers[0]->as, mojom::LinkAsAttribute::kUnspecified);
   EXPECT_EQ(parsed_headers[1]->as, mojom::LinkAsAttribute::kFont);
   EXPECT_EQ(parsed_headers[2]->as, mojom::LinkAsAttribute::kImage);
   EXPECT_EQ(parsed_headers[3]->as, mojom::LinkAsAttribute::kScript);
   EXPECT_EQ(parsed_headers[4]->as, mojom::LinkAsAttribute::kStyleSheet);
+  EXPECT_EQ(parsed_headers[5]->as, mojom::LinkAsAttribute::kFetch);
 }
 
 TEST(LinkHeaderParserTest, CrossOriginAttribute) {

services/network/public/mojom/link_header.mojom

@@ -19,12 +19,15 @@ enum LinkRelAttribute {
 };
 
 // Represents subset of possible values for `as` attribute of the Link header.
+// https://fetch.spec.whatwg.org/#concept-potential-destination
+// https://fetch.spec.whatwg.org/#concept-request-destination
 enum LinkAsAttribute {
   kUnspecified,
   kFont,
   kImage,
   kScript,
   kStyleSheet,
+  kFetch,
 };
 
 // Represents subset of possible values for `crossorigin` attribute.

third_party/blink/web_tests/external/wpt/loading/early-hints/preload-fetch.h2.window.js

@@ -0,0 +1,10 @@
+// META: script=resources/early-hints-helpers.sub.js
+
+test(() => {
+    const preloads = [{
+        "url": "empty.json?" + Date.now(),
+        "as_attr": "fetch",
+        "crossorigin_attr": "",
+    }];
+    navigateToTestWithEarlyHints("resources/preload-fetch.html", preloads);
+});

third_party/blink/web_tests/external/wpt/loading/early-hints/resources/early-hints-helpers.sub.js

@@ -14,6 +14,8 @@ const CROSS_ORIGIN_RESOURCES_URL = CROSS_ORIGIN + RESOURCES_PATH;
  * @property {string} url - A URL to preload. Note: This is relative to the
  *     `test_url` parameter of `navigateToTestWithEarlyHints()`.
  * @property {string} as_attr - `as` attribute of this preload.
+ * @property {string} [crossorigin_attr] - `crossorigin` attribute of this
+ *     preload.
  *
  * @param {string} test_url - URL of a test after the Early Hints response.
  * @param {Array<Preload>} preloads  - Preloads included in the Early Hints response.

third_party/blink/web_tests/external/wpt/loading/early-hints/resources/early-hints-test-loader.h2.py

@@ -18,6 +18,12 @@ def handle_headers(frame, request, response):
     for encoded_preload in request.GET.get_list(b"preloads"):
         preload = json.loads(encoded_preload.decode("utf-8"))
         header = "<{}>; rel=preload; as={}".format(preload["url"], preload["as_attr"])
+        if "crossorigin_attr" in preload:
+            crossorigin = preload["crossorigin_attr"]
+            if crossorigin:
+                header += "; crossorigin={}".format(crossorigin)
+            else:
+                header += "; crossorigin"
         preload_headers.append(header.encode())
 
     # Send a 103 response.

third_party/blink/web_tests/external/wpt/loading/early-hints/resources/empty.json

@@ -0,0 +1 @@
+{}

third_party/blink/web_tests/external/wpt/loading/early-hints/resources/empty.json.headers

@@ -0,0 +1,4 @@
+cache-control: max-age=600
+access-control-allow-origin: *
+timing-allow-origin: *
+cross-origin-resource-policy: cross-origin

third_party/blink/web_tests/external/wpt/loading/early-hints/resources/preload-fetch.html

@@ -0,0 +1,18 @@
+<!DOCTYPE html>
+<meta charset=utf-8>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="early-hints-helpers.sub.js"></script>
+<body>
+<script>
+promise_test(async (t) => {
+    const preloads = getPreloadsFromSearchParams();
+    assert_equals(preloads.length, 1);
+    const preload = preloads[0];
+
+    await fetch(preload.url).then((response) => response.json());
+    const name = new URL(preload.url, window.location);
+    assert_true(isPreloadedByEarlyHints(name));
+}, "Ensure early hints preload works for fetch()");
+</script>
+</body>