Add send_git_patch helper

app/controllers/projects/merge_requests_controller.rb

@@ -58,14 +58,17 @@ class Projects::MergeRequestsController < Projects::ApplicationController
     respond_to do |format|
       format.html
-      format.json   { render json: @merge_request }
+      
+      format.json do
+        render json: @merge_request
+      end
+
       format.patch  do
-        headers.store(*Gitlab::Workhorse.send_git_patch(@project.repository,
-                                                        @merge_request.diff_base_commit.id,
-                                                        @merge_request.last_commit.id))
-        headers['Content-Disposition'] = 'inline'
-        head :ok
+        return render_404 unless @merge_request.diff_refs
+
+        send_git_patch @project.repository, @merge_request.diff_refs
       end
+
       format.diff do
         return render_404 unless @merge_request.diff_refs

app/helpers/workhorse_helper.rb

-# Helpers to send Git blobs, diffs or archives through Workhorse.
+# Helpers to send Git blobs, diffs, patches or archives through Workhorse.
 # Workhorse will also serve files when using `send_file`.
 module WorkhorseHelper
   # Send a Git blob through Workhorse
@@ -16,6 +16,13 @@ module WorkhorseHelper
     head :ok
   end
+  # Send a Git patch through Workhorse
+  def send_git_patch(repository, diff_refs)
+    headers.store(*Gitlab::Workhorse.send_git_patch(repository, diff_refs))
+    headers['Content-Disposition'] = 'inline'
+    head :ok
+  end
+
   # Archive a Git repository and send it through Workhorse
   def send_git_archive(repository, ref:, format:)
     headers.store(*Gitlab::Workhorse.send_git_archive(repository, ref: ref, format: format))

lib/gitlab/workhorse.rb

@@ -50,11 +50,11 @@ module Gitlab
         ]
       end
-      def send_git_patch(repository, from, to)
+      def send_git_patch(repository, diff_refs)
         params = {
           'RepoPath'  => repository.path_to_repo,
-          'ShaFrom'   => from,
-          'ShaTo'     => to
+          'ShaFrom'   => diff_refs.start_sha,
+          'ShaTo'     => diff_refs.head_sha
         }
         [

spec/controllers/projects/merge_requests_controller_spec.rb

@@ -103,7 +103,7 @@ describe Projects::MergeRequestsController do
             id: merge_request.iid,
             format: :patch)
-        expect(response.headers['Gitlab-Workhorse-Send-Data']).to start_with("git-format-patch:")
+        expect(response.headers[Gitlab::Workhorse::SEND_DATA_HEADER]).to start_with("git-format-patch:")
       end
     end
   end