smarter Last-Modified header based on template mtime

app.rb

@@ -93,6 +93,8 @@ def page_title title = nil
   end
 end
 
+require_relative 'lib/auto_last_modified'
+
 before do
   page_title "Pretty RFC"
 end
@@ -112,9 +114,8 @@ def page_title title = nil
 end
 
 get "/" do
-  cache_control :public
-  last_modified File.mtime('views/index.erb')
-  erb :index
+  expires 5 * 60, :public
+  erb :index, auto_last_modified: true
 end
 
 get "/search" do
@@ -131,12 +132,11 @@ def page_title title = nil
 end
 
 get "/:doc_id" do
+  expires 5 * 60, :public
+
   @rfc = RfcDocument.fetch(params[:doc_id]) { not_found }
   redirect to(@rfc.id) unless request.path == "/#{@rfc.id}"
 
-  cache_control :public
-  last_modified @rfc.last_modified
-
   @rfc.make_pretty href_resolver
-  erb :show
+  erb :show, auto_last_modified: @rfc.last_modified
 end

lib/auto_last_modified.rb

@@ -0,0 +1,35 @@
+require 'sinatra/base'
+
+# Adds functionality to template rendering methods to call last_modified with
+# the template's timestamp before actually rendering it.
+#
+# Examples
+#
+#   erb :index, auto_last_modified: true
+#
+#   # with extra timestamp:
+#   erb :show, auto_last_modified: @item.updated_at
+module AutoLastModified
+  module TiltExt
+    def mtime
+      @mtime ||= File.mtime file
+    end
+  end
+
+  module SinatraExt
+    private
+    def compile_template(engine, data, options, views)
+      set_mtime = options.delete :auto_last_modified
+      template = super
+      if set_mtime
+        mtime = template.mtime
+        mtime = set_mtime if set_mtime.respond_to? :hour and set_mtime > mtime
+        last_modified mtime
+      end
+      template
+    end
+  end
+
+  Tilt::Template.send :include, TiltExt
+  Sinatra::Base.send  :include, SinatraExt
+end