Enable browser caching for blobs and variants (#30196)

activestorage/app/controllers/active_storage/blobs_controller.rb

@@ -5,6 +5,7 @@
 class ActiveStorage::BlobsController < ActionController::Base
   def show
     if blob = find_signed_blob
+      expires_in 5.minutes # service_url defaults to 5 minutes
       redirect_to blob.service_url(disposition: disposition_param)
     else
       head :not_found

activestorage/app/controllers/active_storage/variants_controller.rb

@@ -5,6 +5,7 @@
 class ActiveStorage::VariantsController < ActionController::Base
   def show
     if blob = find_signed_blob
+      expires_in 5.minutes # service_url defaults to 5 minutes
       redirect_to ActiveStorage::Variant.new(blob, decoded_variation).processed.service_url(disposition: disposition_param)
     else
       head :not_found

activestorage/test/controllers/blobs_controller_test.rb

@@ -0,0 +1,15 @@
+require "test_helper"
+require "database/setup"
+
+class ActiveStorage::BlobsControllerTest < ActionDispatch::IntegrationTest
+  setup do
+    @blob = create_image_blob filename: "racecar.jpg"
+  end
+
+  test "showing blob utilizes browser caching" do
+    get rails_blob_url(@blob)
+
+    assert_redirected_to(/racecar.jpg/)
+    assert_equal "max-age=300, private", @response.headers["Cache-Control"]
+  end
+end