Encode Gitaly diff patches properly

lib/gitlab/git/diff.rb

@@ -318,7 +318,7 @@ module Gitlab
       end
 
       def init_from_gitaly(diff)
-        @diff = diff.patch if diff.respond_to?(:patch)
+        @diff = encode!(diff.patch) if diff.respond_to?(:patch)
         @new_path = encode!(diff.to_path.dup)
         @old_path = encode!(diff.from_path.dup)
         @a_mode = diff.old_mode.to_s(8)

lib/gitlab/gitaly_client/diff_stitcher.rb

@@ -13,7 +13,10 @@ module Gitlab
         @rpc_response.each do |diff_msg|
           if current_diff.nil?
             diff_params = diff_msg.to_h.slice(*GitalyClient::Diff::FIELDS)
-            diff_params[:patch] = diff_msg.raw_patch_data
+            # gRPC uses frozen strings by default, and we need to have an unfrozen string as it
+            # gets processed further down the line. So we unfreeze the first chunk of the patch
+            # in case it's the only chunk we receive for this diff.
+            diff_params[:patch] = diff_msg.raw_patch_data.dup
 
             current_diff = GitalyClient::Diff.new(diff_params)
           else

spec/lib/gitlab/git/diff_spec.rb

@@ -175,6 +175,14 @@ EOT
           expect(diff).to be_too_large
         end
       end
+
+      context 'when the patch passed is not UTF-8-encoded' do
+        let(:raw_patch) { @raw_diff_hash[:diff].encode(Encoding::ASCII_8BIT) }
+
+        it 'encodes diff patch to UTF-8' do
+          expect(diff.diff.encoding).to eq(Encoding::UTF_8)
+        end
+      end
     end
   end