Avoid duplicating routes for HEAD requests.

Follow up to rails#15321

Instead of duplicating the routes, we will first match the HEAD request to
HEAD routes. If no match is found, we will then map the HEAD request to
GET routes.

2 files changed, 29 insertions, 17 deletions

diff --git a/actionpack/lib/action_dispatch/http/request.rb b/actionpack/lib/action_dispatch/http/request.rb
index f35289253b..c441f7f95b 100644
--- a/actionpack/lib/action_dispatch/http/request.rb
+++ b/actionpack/lib/action_dispatch/http/request.rb
@@ -105,6 +105,12 @@ module ActionDispatch
       @request_method ||= check_method(env["REQUEST_METHOD"])
     end
 
+    def request_method=(request_method) #:nodoc:
+      if check_method(request_method)
+        @request_method = env["REQUEST_METHOD"] = request_method
+      end
+    end
+
     # Returns a symbol form of the #request_method
     def request_method_symbol
       HTTP_METHOD_LOOKUP[request_method]
diff --git a/actionpack/lib/action_dispatch/journey/router.rb b/actionpack/lib/action_dispatch/journey/router.rb
index 21817b374c..9131b65380 100644
--- a/actionpack/lib/action_dispatch/journey/router.rb
+++ b/actionpack/lib/action_dispatch/journey/router.rb
@@ -101,11 +101,13 @@ module ActionDispatch
             r.path.match(req.path_info)
           }
 
-          if req.env["REQUEST_METHOD"] === "HEAD"
-            routes.concat get_routes_as_head(routes)
-          end
+          routes =
+            if req.request_method == "HEAD"
+              match_head_routes(routes, req)
+            else
+              match_routes(routes, req)
+            end
 
-          routes.select! { |r| r.matches?(req) }
           routes.sort_by!(&:precedence)
 
           routes.map! { |r|
@@ -118,19 +120,23 @@ module ActionDispatch
           }
         end
 
-        def get_routes_as_head(routes)
-          precedence = (routes.map(&:precedence).max || 0) + 1
-          routes.select { |r|
-            r.verb === "GET" && !(r.verb === "HEAD")
-          }.map! { |r|
-            Route.new(r.name,
-                      r.app,
-                      r.path,
-                      r.conditions.merge(request_method: "HEAD"),
-                      r.defaults).tap do |route|
-                        route.precedence = r.precedence + precedence
-                      end
-          }
+        def match_head_routes(routes, req)
+          head_routes = match_routes(routes, req)
+
+          if head_routes.empty?
+            begin
+              req.request_method = "GET"
+              match_routes(routes, req)
+            ensure
+              req.request_method = "HEAD"
+            end
+          else
+            head_routes
+          end
+        end
+
+        def match_routes(routes, req)
+          routes.select { |r| r.matches?(req) }
         end
     end
   end