Inject ::UploadedFile from Multipart middleware

I mistakenly concluded Rack::Multipart injects File instances into the
params. These should be UploadedFile instances. This reuses a mock
UploadedFile class we already had in GitLab.

lib/gitlab/middleware/multipart.rb

@@ -42,7 +42,7 @@ module Gitlab
 
             key, value = parsed_field.first
             if value.nil?
-              value = File.open(tmp_path)
+              value = open_file(tmp_path)
               @open_files << value
             else
               value = decorate_params_value(value, @request.params[key], tmp_path)
@@ -68,7 +68,7 @@ module Gitlab
 
           case path_value
           when nil
-            value_hash[path_key] = File.open(tmp_path)
+            value_hash[path_key] = open_file(tmp_path)
             @open_files << value_hash[path_key]
             value_hash
           when Hash
@@ -78,6 +78,10 @@ module Gitlab
             raise "unexpected path value: #{path_value.inspect}"
           end
         end
+
+        def open_file(path)
+          ::UploadedFile.new(path, File.basename(path), 'application/octet-stream')
+        end
       end
 
       def initialize(app)

spec/lib/gitlab/middleware/multipart_spec.rb

@@ -12,7 +12,7 @@ describe Gitlab::Middleware::Multipart do
 
       expect(app).to receive(:call) do |env|
         file = Rack::Request.new(env).params['file']
-        expect(file).to be_a(File)
+        expect(file).to be_a(::UploadedFile)
         expect(file.path).to eq(tempfile.path)
       end
 
@@ -39,7 +39,7 @@ describe Gitlab::Middleware::Multipart do
 
       expect(app).to receive(:call) do |env|
         file = Rack::Request.new(env).params['user']['avatar']
-        expect(file).to be_a(File)
+        expect(file).to be_a(::UploadedFile)
         expect(file.path).to eq(tempfile.path)
       end
 
@@ -54,7 +54,7 @@ describe Gitlab::Middleware::Multipart do
 
       expect(app).to receive(:call) do |env|
         file = Rack::Request.new(env).params['project']['milestone']['themesong']
-        expect(file).to be_a(File)
+        expect(file).to be_a(::UploadedFile)
         expect(file.path).to eq(tempfile.path)
       end