Allow empty files to be uploaded

actionpack/lib/action_controller/url_encoded_pair_parser.rb

@@ -46,7 +46,7 @@ module ActionController
           when Array
             value.map { |v| get_typed_value(v) }
           when Hash
-            if value.has_key?(:tempfile) && value[:tempfile].size > 0
+            if value.has_key?(:tempfile) && value[:filename].any?
               upload = value[:tempfile]
               upload.extend(UploadedFile)
               upload.original_path = value[:filename]

actionpack/test/controller/request/multipart_params_parsing_test.rb

@@ -101,11 +101,19 @@ class MultipartParamsParsingTest < ActionController::IntegrationTest
     assert_equal 19756, files.size
   end
 
-  test "skips empty upload field" do
+  test "does not create tempfile if no file has been selected" do
+    params = parse_multipart('none')
+    assert_equal %w(files submit-name), params.keys.sort
+    assert_equal 'Larry', params['submit-name']
+    assert_equal nil, params['files']
+  end
+
+  test "parses empty upload file" do
     params = parse_multipart('empty')
     assert_equal %w(files submit-name), params.keys.sort
     assert_equal 'Larry', params['submit-name']
-    assert_equal nil, params['file']
+    assert params['files']
+    assert_equal "", params['files'].read
   end
 
   test "uploads and reads binary file" do

actionpack/test/fixtures/multipart/empty

@@ -3,7 +3,8 @@ Content-Disposition: form-data; name="submit-name"
 
 Larry
 --AaB03x
-Content-Disposition: form-data; name="files"; filename=""
+Content-Disposition: form-data; name="files"; filename="file1.txt"
+Content-Type: text/plain
 
 
 --AaB03x--

actionpack/test/fixtures/multipart/none

@@ -0,0 +1,9 @@
+--AaB03x
+Content-Disposition: form-data; name="submit-name"
+
+Larry
+--AaB03x
+Content-Disposition: form-data; name="files"; filename=""
+
+
+--AaB03x--