Adding custom error response for when file upload is too large

lib/api/ci/secure_files.rb

@@ -60,6 +60,7 @@ module API
 
         route_setting :authentication, basic_auth_personal_access_token: true, job_token_allowed: true
         post ':id/secure_files' do
+  
           secure_file = user_project.secure_files.new(
             name: params[:name],
             permissions: params[:permissions] || :read_only
@@ -67,6 +68,8 @@ module API
 
           secure_file.file = params[:file]
 
+          file_too_large! unless secure_file.file.size < ::Ci::SecureFile::FILE_SIZE_LIMIT.to_i
+
           if secure_file.save
             present secure_file, with: Entities::Ci::SecureFile
           else

spec/requests/api/ci/secure_files_spec.rb

@@ -226,6 +226,21 @@ RSpec.describe API::Ci::SecureFiles do
 
         expect(response).to have_gitlab_http_status(:bad_request)
       end
+
+      it 'returns a 413 error when the file size is too large' do
+        allow_next_instance_of(Ci::SecureFile) do |instance|
+          allow(instance).to receive_message_chain(:file, :size).and_return(6.megabytes.to_i)
+        end
+
+        post_params = {
+          file: fixture_file_upload('spec/fixtures/ci_secure_files/upload-keystore.jks'),
+          name: 'upload-keystore.jks'
+        }
+
+        post api("/projects/#{project.id}/secure_files", user), params: post_params
+
+        expect(response).to have_gitlab_http_status(:payload_too_large)
+      end
     end
 
     context 'authorized user with invalid permissions' do