use 303 for redirects from post for HTTP/1.1 (fixes ajax redirects in Internet Explorer 9)

lib/sinatra/base.rb

@@ -113,7 +113,11 @@ module Sinatra
 
     # Halt processing and redirect to the URI provided.
     def redirect(uri, *args)
-      status 302
+      if env['HTTP_VERSION'] == 'HTTP/1.1' and env["REQUEST_METHOD"] != 'GET'
+        status 303
+      else
+        status 302
+      end
 
       # According to RFC 2616 section 14.30, "the field value consists of a
       # single absolute URI"

test/helpers_test.rb

@@ -207,6 +207,22 @@ class HelpersTest < Test::Unit::TestCase
       assert_equal 'http://example.org:444/foo', response['Location']
     end
 
+    it 'uses 303 for post requests if request is HTTP 1.1' do
+      mock_app { post('/') { redirect '/'} }
+      post '/', {}, 'HTTP_VERSION' => 'HTTP/1.1'
+      assert_equal 303, status
+      assert_equal '', body
+      assert_equal 'http://example.org/', response['Location']
+    end
+
+    it 'uses 302 for post requests if request is HTTP 1.0' do
+      mock_app { post('/') { redirect '/'} }
+      post '/', {}, 'HTTP_VERSION' => 'HTTP/1.0'
+      assert_equal 302, status
+      assert_equal '', body
+      assert_equal 'http://example.org/', response['Location']
+    end
+
     it 'works behind a reverse proxy' do
       mock_app do
         get '/' do