Add support for more HTTP cache controls

From <https://tools.ietf.org/html/rfc5861>:

> The stale-if-error HTTP Cache-Control extension allows a cache to
> return a stale response when an error -- e.g., a 500 Internal Server
> Error, a network segment, or DNS failure -- is encountered, rather
> than returning a "hard" error.  This improves availability.
>
> The stale-while-revalidate HTTP Cache-Control extension allows a
> cache to immediately return a stale response while it revalidates it
> in the background, thereby hiding latency (both in the network and on
> the server) from clients.

These are useful, fully standardized parts of the HTTP protocol with
widespread support among CDN vendors. Supporting them will make it
easier to utilize reverse proxies and CDNs from Rails.

3 files changed, 28 insertions, 2 deletions

diff --git a/actionpack/lib/action_controller/metal/conditional_get.rb b/actionpack/lib/action_controller/metal/conditional_get.rb
index 06b6a95ff8..4be4557e2c 100644
--- a/actionpack/lib/action_controller/metal/conditional_get.rb
+++ b/actionpack/lib/action_controller/metal/conditional_get.rb
@@ -235,7 +235,9 @@ module ActionController
       response.cache_control.merge!(
         max_age: seconds,
         public: options.delete(:public),
-        must_revalidate: options.delete(:must_revalidate)
+        must_revalidate: options.delete(:must_revalidate),
+        stale_while_revalidate: options.delete(:stale_while_revalidate),
+        stale_if_error: options.delete(:stale_if_error),
       )
       options.delete(:private)
 
diff --git a/actionpack/lib/action_dispatch/http/cache.rb b/actionpack/lib/action_dispatch/http/cache.rb
index a8febc32b3..a7c7cfc1e5 100644
--- a/actionpack/lib/action_dispatch/http/cache.rb
+++ b/actionpack/lib/action_dispatch/http/cache.rb
@@ -202,13 +202,17 @@ module ActionDispatch
               self._cache_control = _cache_control + ", #{control[:extras].join(', ')}"
             end
           else
-            extras  = control[:extras]
+            extras = control[:extras]
             max_age = control[:max_age]
+            stale_while_revalidate = control[:stale_while_revalidate]
+            stale_if_error = control[:stale_if_error]
 
             options = []
             options << "max-age=#{max_age.to_i}" if max_age
             options << (control[:public] ? PUBLIC : PRIVATE)
             options << MUST_REVALIDATE if control[:must_revalidate]
+            options << "stale-while-revalidate=#{stale_while_revalidate.to_i}" if stale_while_revalidate
+            options << "stale-if-error=#{stale_if_error.to_i}" if stale_if_error
             options.concat(extras) if extras
 
             self._cache_control = options.join(", ")
diff --git a/actionpack/test/controller/render_test.rb b/actionpack/test/controller/render_test.rb
index 24c5761e41..6e3bd0596b 100644
--- a/actionpack/test/controller/render_test.rb
+++ b/actionpack/test/controller/render_test.rb
@@ -141,6 +141,16 @@ class TestController < ActionController::Base
     render action: "hello_world"
   end
 
+  def conditional_hello_with_expires_in_with_stale_while_revalidate
+    expires_in 1.minute, public: true, stale_while_revalidate: 5.minutes
+    render action: "hello_world"
+  end
+
+  def conditional_hello_with_expires_in_with_stale_if_error
+    expires_in 1.minute, public: true, stale_if_error: 5.minutes
+    render action: "hello_world"
+  end
+
   def conditional_hello_with_expires_in_with_public_with_more_keys
     expires_in 1.minute, :public => true, "s-maxage" => 5.hours
     render action: "hello_world"
@@ -358,6 +368,16 @@ class ExpiresInRenderTest < ActionController::TestCase
     assert_equal "max-age=60, public, must-revalidate", @response.headers["Cache-Control"]
   end
 
+  def test_expires_in_header_with_stale_while_revalidate
+    get :conditional_hello_with_expires_in_with_stale_while_revalidate
+    assert_equal "max-age=60, public, stale-while-revalidate=300", @response.headers["Cache-Control"]
+  end
+
+  def test_expires_in_header_with_stale_if_error
+    get :conditional_hello_with_expires_in_with_stale_if_error
+    assert_equal "max-age=60, public, stale-if-error=300", @response.headers["Cache-Control"]
+  end
+
   def test_expires_in_header_with_additional_headers
     get :conditional_hello_with_expires_in_with_public_with_more_keys
     assert_equal "max-age=60, public, s-maxage=18000", @response.headers["Cache-Control"]