Lower case the link header

Since rack/rack@1fbcf54
the early hints will be checked against Rack::Link that requires all
headers to be lower cased.

Fixes rails#51961.

Author: rafaelfranca

actionpack/lib/action_dispatch/http/request.rb

@@ -230,11 +230,11 @@ def headers
     # start making preparations for processing the final response.
     #
     # If the env contains `rack.early_hints` then the server accepts HTTP2 push for
-    # Link headers.
+    # link headers.
     #
     # The `send_early_hints` method accepts a hash of links as follows:
     #
-    #     send_early_hints("Link" => "</style.css>; rel=preload; as=style\n</script.js>; rel=preload")
+    #     send_early_hints("link" => "</style.css>; rel=preload; as=style\n</script.js>; rel=preload")
     #
     # If you are using `javascript_include_tag` or `stylesheet_link_tag` the Early
     # Hints headers are included by default if supported.

actionpack/test/dispatch/request_test.rb

@@ -1412,8 +1412,8 @@ def setup
   end
 
   test "when early hints is set in the env link headers are sent" do
-    early_hints = @request.send_early_hints("Link" => "</style.css>; rel=preload; as=style\n</script.js>; rel=preload")
-    expected_hints = { "Link" => "</style.css>; rel=preload; as=style\n</script.js>; rel=preload" }
+    early_hints = @request.send_early_hints("link" => "</style.css>; rel=preload; as=style\n</script.js>; rel=preload")
+    expected_hints = { "link" => "</style.css>; rel=preload; as=style\n</script.js>; rel=preload" }
 
     assert_equal expected_hints, early_hints
   end

actionview/lib/action_view/helpers/asset_tag_helper.rb

@@ -657,11 +657,11 @@ def send_preload_links_header(preload_links, max_header_size: MAX_HEADER_SIZE)
           return if response_present && response.sending?
 
           if respond_to?(:request) && request
-            request.send_early_hints("Link" => preload_links.join("\n"))
+            request.send_early_hints("link" => preload_links.join("\n"))
           end
 
           if response_present
-            header = +response.headers["Link"].to_s
+            header = +response.headers["link"].to_s
             preload_links.each do |link|
               break if header.bytesize + link.bytesize > max_header_size
 
@@ -672,7 +672,7 @@ def send_preload_links_header(preload_links, max_header_size: MAX_HEADER_SIZE)
               end
             end
 
-            response.headers["Link"] = header
+            response.headers["link"] = header
           end
         end
     end

actionview/test/template/asset_tag_helper_test.rb

@@ -634,23 +634,23 @@ def test_should_set_preload_links
       stylesheet_link_tag("http://example.com/style.css")
       javascript_include_tag("http://example.com/all.js")
       expected = "<http://example.com/style.css>; rel=preload; as=style; nopush,<http://example.com/all.js>; rel=preload; as=script; nopush"
-      assert_equal expected, @response.headers["Link"]
+      assert_equal expected, @response.headers["link"]
     end
   end
 
   def test_should_not_set_preload_links_for_data_url
     with_preload_links_header do
       stylesheet_link_tag("data:text/css;base64,YWxlcnQoIkhlbGxvIik7")
       javascript_include_tag("data:text/javascript;base64,YWxlcnQoIkhlbGxvIik7")
-      assert_nil @response.headers["Link"]
+      assert_nil @response.headers["link"]
     end
   end
 
   def test_should_not_set_preload_links_if_opted_out_at_invokation
     with_preload_links_header do
       stylesheet_link_tag("http://example.com/style.css", preload_links_header: false)
       javascript_include_tag("http://example.com/all.js", preload_links_header: false)
-      assert_nil @response.headers["Link"]
+      assert_nil @response.headers["link"]
     end
   end
 
@@ -659,7 +659,7 @@ def test_should_set_preload_links_if_opted_in_at_invokation
       stylesheet_link_tag("http://example.com/style.css", preload_links_header: true)
       javascript_include_tag("http://example.com/all.js", preload_links_header: true)
       expected = "<http://example.com/style.css>; rel=preload; as=style; nopush,<http://example.com/all.js>; rel=preload; as=script; nopush"
-      assert_equal expected, @response.headers["Link"]
+      assert_equal expected, @response.headers["link"]
     end
   end
 
@@ -669,15 +669,15 @@ def test_should_generate_links_under_the_max_size
         stylesheet_link_tag("http://example.com/style.css?#{i}")
         javascript_include_tag("http://example.com/all.js?#{i}")
       end
-      links = @response.headers["Link"].count(",")
+      links = @response.headers["link"].count(",")
       assert_equal 14, links
     end
   end
 
   def test_should_not_preload_links_with_defer
     with_preload_links_header do
       javascript_include_tag("http://example.com/all.js", defer: true)
-      assert_nil @response.headers["Link"]
+      assert_nil @response.headers["link"]
     end
   end
 
@@ -686,7 +686,7 @@ def test_should_allow_caller_to_remove_nopush
       stylesheet_link_tag("http://example.com/style.css", nopush: false)
       javascript_include_tag("http://example.com/all.js", nopush: false)
       expected = "<http://example.com/style.css>; rel=preload; as=style,<http://example.com/all.js>; rel=preload; as=script"
-      assert_equal expected, @response.headers["Link"]
+      assert_equal expected, @response.headers["link"]
     end
   end
 
@@ -695,23 +695,23 @@ def test_should_set_preload_links_with_cross_origin
       stylesheet_link_tag("http://example.com/style.css", crossorigin: "use-credentials")
       javascript_include_tag("http://example.com/all.js", crossorigin: true)
       expected = "<http://example.com/style.css>; rel=preload; as=style; crossorigin=use-credentials; nopush,<http://example.com/all.js>; rel=preload; as=script; crossorigin=anonymous; nopush"
-      assert_equal expected, @response.headers["Link"]
+      assert_equal expected, @response.headers["link"]
     end
   end
 
   def test_should_set_preload_links_with_rel_modulepreload
     with_preload_links_header do
       javascript_include_tag("http://example.com/all.js", type: "module")
       expected = "<http://example.com/all.js>; rel=modulepreload; as=script; nopush"
-      assert_equal expected, @response.headers["Link"]
+      assert_equal expected, @response.headers["link"]
     end
   end
 
   def test_should_set_preload_early_hints_with_rel_modulepreload
     with_preload_links_header do
       preload_link_tag("http://example.com/all.js", type: "module")
       expected = "<http://example.com/all.js>; rel=modulepreload; as=script; type=module"
-      assert_equal expected, @response.headers["Link"]
+      assert_equal expected, @response.headers["link"]
     end
   end
 
@@ -720,15 +720,15 @@ def test_should_set_preload_links_with_integrity_hashes
       stylesheet_link_tag("http://example.com/style.css", integrity: "sha256-AbpHGcgLb+kRsJGnwFEktk7uzpZOCcBY74+YBdrKVGs")
       javascript_include_tag("http://example.com/all.js", integrity: "sha256-AbpHGcgLb+kRsJGnwFEktk7uzpZOCcBY74+YBdrKVGs")
       expected = "<http://example.com/style.css>; rel=preload; as=style; integrity=sha256-AbpHGcgLb+kRsJGnwFEktk7uzpZOCcBY74+YBdrKVGs; nopush,<http://example.com/all.js>; rel=preload; as=script; integrity=sha256-AbpHGcgLb+kRsJGnwFEktk7uzpZOCcBY74+YBdrKVGs; nopush"
-      assert_equal expected, @response.headers["Link"]
+      assert_equal expected, @response.headers["link"]
     end
   end
 
   def test_should_not_preload_links_when_disabled
     with_preload_links_header(false) do
       stylesheet_link_tag("http://example.com/style.css")
       javascript_include_tag("http://example.com/all.js")
-      assert_nil @response.headers["Link"]
+      assert_nil @response.headers["link"]
     end
   end
 

guides/source/6_1_release_notes.md

@@ -176,7 +176,7 @@ Please refer to the [Changelog][action-view] for detailed changes.
 
 *   Make `locals` argument required on `ActionView::Template#initialize`.
 
-*   The `javascript_include_tag` and `stylesheet_link_tag` asset helpers generate a `Link` header that gives hints to modern browsers about preloading assets. This can be disabled by setting `config.action_view.preload_links_header` to `false`.
+*   The `javascript_include_tag` and `stylesheet_link_tag` asset helpers generate a `link` header that gives hints to modern browsers about preloading assets. This can be disabled by setting `config.action_view.preload_links_header` to `false`.
 
 Action Mailer
 -------------

guides/source/configuring.md

@@ -2219,7 +2219,7 @@ Determines whether to annotate rendered view with template file names. This defa
 
 #### `config.action_view.preload_links_header`
 
-Determines whether `javascript_include_tag` and `stylesheet_link_tag` will generate a `Link` header that preload assets.
+Determines whether `javascript_include_tag` and `stylesheet_link_tag` will generate a `link` header that preload assets.
 
 The default value depends on the `config.load_defaults` target version:
 

railties/test/application/configuration_test.rb

@@ -3188,7 +3188,7 @@ class ::DummyDestroyAssociationAsyncJob; end
       assert_equal false, ActionView::Helpers::AssetTagHelper.apply_stylesheet_media_default
     end
 
-    test "stylesheet_link_tag sets the Link header by default" do
+    test "stylesheet_link_tag sets the link header by default" do
       app_file "app/controllers/pages_controller.rb", <<-RUBY
       class PagesController < ApplicationController
         def index
@@ -3207,10 +3207,10 @@ def index
 
       get "/"
       assert_match %r[<link rel="stylesheet" href="/application.css" />], last_response.body
-      assert_equal "</application.css>; rel=preload; as=style; nopush", last_response.headers["Link"]
+      assert_equal "</application.css>; rel=preload; as=style; nopush", last_response.headers["link"]
     end
 
-    test "stylesheet_link_tag doesn't set the Link header when disabled" do
+    test "stylesheet_link_tag doesn't set the link header when disabled" do
       app_file "config/initializers/action_view.rb", <<-RUBY
         Rails.application.config.action_view.preload_links_header = false
       RUBY
@@ -3233,10 +3233,10 @@ def index
 
       get "/"
       assert_match %r[<link rel="stylesheet" href="/application.css" />], last_response.body
-      assert_nil last_response.headers["Link"]
+      assert_nil last_response.headers["link"]
     end
 
-    test "javascript_include_tag sets the Link header by default" do
+    test "javascript_include_tag sets the link header by default" do
       app_file "app/controllers/pages_controller.rb", <<-RUBY
       class PagesController < ApplicationController
         def index
@@ -3255,10 +3255,10 @@ def index
 
       get "/"
       assert_match %r[<script src="/application.js"></script>], last_response.body
-      assert_equal "</application.js>; rel=preload; as=script; nopush", last_response.headers["Link"]
+      assert_equal "</application.js>; rel=preload; as=script; nopush", last_response.headers["link"]
     end
 
-    test "javascript_include_tag doesn't set the Link header when disabled" do
+    test "javascript_include_tag doesn't set the link header when disabled" do
       app_file "config/initializers/action_view.rb", <<-RUBY
         Rails.application.config.action_view.preload_links_header = false
       RUBY
@@ -3281,7 +3281,7 @@ def index
 
       get "/"
       assert_match %r[<script src="/application.js"></script>], last_response.body
-      assert_nil last_response.headers["Link"]
+      assert_nil last_response.headers["link"]
     end
 
     test "ActiveJob::Base.retry_jitter is 0.15 by default for new apps" do