Cache content_sha256 field for Files API

Changelog: performance

lib/api/files.rb

@@ -35,10 +35,9 @@ module API
         not_found!('Commit') unless @commit
 
         @repo = user_project.repository
-        @blob = @repo.blob_at(@commit.sha, params[:file_path])
+        @blob = @repo.blob_at(@commit.sha, params[:file_path], limit: Gitlab::Git::Blob::LFS_POINTER_MAX_SIZE)
 
         not_found!('File') unless @blob
-        @blob.load_all_data!
       end
 
       def commit_response(attrs)
@@ -48,13 +47,21 @@ module API
         }
       end
 
+      def content_sha
+        Rails.cache.fetch("blob_content_sha256:#{user_project.full_path}:#{@blob.id}") do
+          @blob.load_all_data!
+
+          Digest::SHA256.hexdigest(@blob.data)
+        end
+      end
+
       def blob_data
         {
           file_name: @blob.name,
           file_path: @blob.path,
           size: @blob.size,
           encoding: "base64",
-          content_sha256: Digest::SHA256.hexdigest(@blob.data),
+          content_sha256: content_sha,
           ref: params[:ref],
           blob_id: @blob.id,
           commit_id: @commit.id,
@@ -154,6 +161,8 @@ module API
       get ":id/repository/files/:file_path", requirements: FILE_ENDPOINT_REQUIREMENTS do
         assign_file_vars!
 
+        @blob.load_all_data!
+
         data = blob_data
 
         set_http_headers(data)

spec/requests/api/files_spec.rb

@@ -95,6 +95,19 @@ RSpec.describe API::Files do
         expect(response.headers['X-Gitlab-Content-Sha256']).to eq('c440cd09bae50c4632cc58638ad33c6aa375b6109d811e76a9cc3a613c1e8887')
       end
 
+      it 'caches sha256 of the content', :use_clean_rails_redis_caching do
+        head api(route(file_path), current_user, **options), params: params
+
+        expect(Rails.cache.fetch("blob_content_sha256:#{project.full_path}:#{response.headers['X-Gitlab-Blob-Id']}"))
+          .to eq('c440cd09bae50c4632cc58638ad33c6aa375b6109d811e76a9cc3a613c1e8887')
+
+        expect_next_instance_of(Gitlab::Git::Blob) do |instance|
+          expect(instance).not_to receive(:load_all_data!)
+        end
+
+        head api(route(file_path), current_user, **options), params: params
+      end
+
       it 'returns file by commit sha' do
         # This file is deleted on HEAD
         file_path = "files%2Fjs%2Fcommit%2Ejs%2Ecoffee"