Encode remote root ref

lib/gitlab/gitaly_client/remote_service.rb

 module Gitlab
   module GitalyClient
     class RemoteService
+      include Gitlab::EncodingHelper
+
       MAX_MSG_SIZE = 128.kilobytes.freeze
 
       def self.exists?(remote_url)
@@ -61,7 +63,7 @@ module Gitlab
         response = GitalyClient.call(@storage, :remote_service,
                                      :find_remote_root_ref, request)
 
-        response.ref.presence
+        encode_utf8(response.ref)
       end
 
       def update_remote_mirror(ref_name, only_branches_matching)

spec/lib/gitlab/git/repository_spec.rb

@@ -591,6 +591,10 @@ describe Gitlab::Git::Repository, :seed_helper do
       expect(repository.find_remote_root_ref('origin')).to eq 'master'
     end
 
+    it 'returns UTF-8' do
+      expect(repository.find_remote_root_ref('origin')).to be_utf8
+    end
+
     it 'returns nil when remote name is nil' do
       expect_any_instance_of(Gitlab::GitalyClient::RemoteService)
         .not_to receive(:find_remote_root_ref)

spec/lib/gitlab/gitaly_client/remote_service_spec.rb

@@ -54,6 +54,15 @@ describe Gitlab::GitalyClient::RemoteService do
 
       expect(client.find_remote_root_ref('origin')).to eq 'master'
     end
+
+    it 'ensure ref is a valid UTF-8 string' do
+      expect_any_instance_of(Gitaly::RemoteService::Stub)
+        .to receive(:find_remote_root_ref)
+        .with(gitaly_request_with_path(storage_name, relative_path), kind_of(Hash))
+        .and_return(double(ref: "an_invalid_ref_\xE5"))
+
+      expect(client.find_remote_root_ref('origin')).to eq "an_invalid_ref_å"
+    end
   end
 
   describe '#update_remote_mirror' do