add support for If-Unmodified-Since

CHANGES

@@ -85,6 +85,8 @@
  * The `last_modified` helper does not stop execution and change the status code
    if the status code is something different than 200. (Konstantin Haase)
 
+ * Added support for If-Unmodified-Since header. (Konstantin Haase)
+
  * `Sinatra::Base.run!` now prints to stderr rather than stdout. (Andrew
    Armenia)
 

lib/sinatra/base.rb

@@ -355,12 +355,19 @@ module Sinatra
       return unless time
       time = time_for time
       response['Last-Modified'] = time.httpdate
+      return if env['HTTP_IF_NONE_MATCH']
 
-      if status == 200 and not env['HTTP_IF_NONE_MATCH']
+      if status == 200 and env['HTTP_IF_MODIFIED_SINCE']
         # compare based on seconds since epoch
         since = Time.httpdate(env['HTTP_IF_MODIFIED_SINCE']).to_i
         halt 304 if since >= time.to_i
       end
+
+      if (success? or status == 412) and env['HTTP_IF_UNMODIFIED_SINCE']
+        # compare based on seconds since epoch
+        since = Time.httpdate(env['HTTP_IF_UNMODIFIED_SINCE']).to_i
+        halt 412 if since < time.to_i
+      end
     rescue ArgumentError
     end
 

test/helpers_test.rb

@@ -969,6 +969,20 @@ class HelpersTest < Test::Unit::TestCase
             assert_equal '', body
           end
         end
+
+        context "If-Unmodified-Since" do
+          it 'results in 200 if resource has not been modified' do
+            get '/', {}, { 'HTTP_IF_UNMODIFIED_SINCE' => 'Sun, 26 Sep 2030 23:43:52 GMT' }
+            assert_equal 200, status
+            assert_equal 'Boo!', body
+          end
+
+          it 'results in 412 if resource has been modified' do
+            get '/', {}, { 'HTTP_IF_UNMODIFIED_SINCE' => Time.at(0).httpdate }
+            assert_equal 412, status
+            assert_equal '', body
+          end
+        end
       end
     end
   end