Refactor JSON reader/writer for import/export

- adds `allowed_path` to strong validate `LegacyReader`
  and `LegacyWriter`
- does not change any of todays behaviour for data serialization
- makes the interface for reader and writer to accept
  `importable/exportable_path` that will be used by `ndjson`
  to store data in separate files
- moves consuming of attributes outside of the relation tree restorer
  to ease the way how we process them
- splits specs for `LegacyReader::User/File` and introduces
  shared example for that: this is also the majority of changes
  introduced by this MR in order to move them
- slightly code-formats and re-organises group and project
  import/export

lib/gitlab/import_export/group/tree_restorer.rb

@@ -4,12 +4,13 @@ module Gitlab
   module ImportExport
     module Group
       class TreeRestorer
+        include Gitlab::Utils::StrongMemoize
+
         attr_reader :user
         attr_reader :shared
         attr_reader :group
 
         def initialize(user:, shared:, group:, group_hash:)
-          @path = File.join(shared.export_path, 'group.json')
           @user = user
           @shared = shared
           @group = group
@@ -17,17 +18,14 @@ module Gitlab
         end
 
         def restore
-          @relation_reader ||=
-            if @group_hash.present?
-              ImportExport::JSON::LegacyReader::User.new(@group_hash, reader.group_relation_names)
-            else
-              ImportExport::JSON::LegacyReader::File.new(@path, reader.group_relation_names)
-            end
+          @group_attributes = relation_reader.consume_attributes(nil)
+          @group_members = relation_reader.consume_relation(nil, 'members')
+
+          # We need to remove `name` and `path` as we did consume it in previous pass
+          @group_attributes.delete('name')
+          @group_attributes.delete('path')
 
-          @group_members = @relation_reader.consume_relation('members')
-          @children = @relation_reader.consume_attribute('children')
-          @relation_reader.consume_attribute('name')
-          @relation_reader.consume_attribute('path')
+          @children = @group_attributes.delete('children')
 
           if members_mapper.map && restorer.restore
             @children&.each do |group_hash|
@@ -53,16 +51,32 @@ module Gitlab
 
         private
 
+        def relation_reader
+          strong_memoize(:relation_reader) do
+            if @group_hash.present?
+              ImportExport::JSON::LegacyReader::Hash.new(
+                @group_hash,
+                relation_names: reader.group_relation_names)
+            else
+              ImportExport::JSON::LegacyReader::File.new(
+                File.join(shared.export_path, 'group.json'),
+                relation_names: reader.group_relation_names)
+            end
+          end
+        end
+
         def restorer
           @relation_tree_restorer ||= RelationTreeRestorer.new(
-            user:             @user,
-            shared:           @shared,
-            importable:       @group,
-            relation_reader:  @relation_reader,
-            members_mapper:   members_mapper,
-            object_builder:   object_builder,
-            relation_factory: relation_factory,
-            reader:           reader
+            user:                  @user,
+            shared:                @shared,
+            relation_reader:       relation_reader,
+            members_mapper:        members_mapper,
+            object_builder:        object_builder,
+            relation_factory:      relation_factory,
+            reader:                reader,
+            importable:            @group,
+            importable_attributes: @group_attributes,
+            importable_path:       nil
           )
         end
 
@@ -88,7 +102,11 @@ module Gitlab
         end
 
         def members_mapper
-          @members_mapper ||= Gitlab::ImportExport::MembersMapper.new(exported_members: @group_members, user: @user, importable: @group)
+          @members_mapper ||= Gitlab::ImportExport::MembersMapper.new(
+            exported_members: @group_members,
+            user: @user,
+            importable: @group
+          )
         end
 
         def relation_factory

lib/gitlab/import_export/json/legacy_reader.rb

@@ -5,19 +5,25 @@ module Gitlab
     module JSON
       class LegacyReader
         class File < LegacyReader
-          def initialize(path, relation_names)
+          include Gitlab::Utils::StrongMemoize
+
+          def initialize(path, relation_names:, allowed_path: nil)
             @path = path
-            super(relation_names)
+            super(
+              relation_names: relation_names,
+              allowed_path: allowed_path)
           end
 
-          def valid?
+          def exist?
             ::File.exist?(@path)
           end
 
-          private
+          protected
 
           def tree_hash
-            @tree_hash ||= read_hash
+            strong_memoize(:tree_hash) do
+              read_hash
+            end
           end
 
           def read_hash
@@ -28,13 +34,15 @@ module Gitlab
           end
         end
 
-        class User < LegacyReader
-          def initialize(tree_hash, relation_names)
+        class Hash < LegacyReader
+          def initialize(tree_hash, relation_names:, allowed_path: nil)
             @tree_hash = tree_hash
-            super(relation_names)
+            super(
+              relation_names: relation_names,
+              allowed_path: allowed_path)
           end
 
-          def valid?
+          def exist?
             @tree_hash.present?
           end
 
@@ -43,11 +51,16 @@ module Gitlab
           attr_reader :tree_hash
         end
 
-        def initialize(relation_names)
+        def initialize(relation_names:, allowed_path:)
           @relation_names = relation_names.map(&:to_s)
+
+          # This is legacy reader, to be used in transition
+          # period before `.ndjson`,
+          # we strong validate what is being readed
+          @allowed_path = allowed_path
         end
 
-        def valid?
+        def exist?
           raise NotImplementedError
         end
 
@@ -55,15 +68,22 @@ module Gitlab
           true
         end
 
-        def root_attributes(excluded_attributes = [])
-          attributes.except(*excluded_attributes.map(&:to_s))
+        def consume_attributes(importable_path)
+          unless importable_path == @allowed_path
+            raise ArgumentError, "Invalid #{importable_path} passed to `consume_attributes`. Use #{@allowed_path} instead."
+          end
+
+          attributes
         end
 
-        def consume_relation(key)
+        def consume_relation(importable_path, key)
+          unless importable_path == @allowed_path
+            raise ArgumentError, "Invalid #{importable_name} passed to `consume_relation`. Use #{@allowed_path} instead."
+          end
+
           value = relations.delete(key)
 
           return value unless block_given?
-
           return if value.nil?
 
           if value.is_a?(Array)
@@ -75,17 +95,13 @@ module Gitlab
           end
         end
 
-        def consume_attribute(key)
-          attributes.delete(key)
-        end
-
         def sort_ci_pipelines_by_id
           relations['ci_pipelines']&.sort_by! { |hash| hash['id'] }
         end
 
         private
 
-        attr_reader :relation_names
+        attr_reader :relation_names, :allowed_path
 
         def tree_hash
           raise NotImplementedError

lib/gitlab/import_export/json/legacy_writer.rb

@@ -8,11 +8,15 @@ module Gitlab
 
         attr_reader :path
 
-        def initialize(path)
+        def initialize(path, allowed_path:)
           @path = path
-          @last_array = nil
           @keys = Set.new
 
+          # This is legacy writer, to be used in transition
+          # period before `.ndjson`,
+          # we strong validate what is being written
+          @allowed_path = allowed_path
+
           mkdir_p(File.dirname(@path))
           file.write('{}')
         end
@@ -22,12 +26,44 @@ module Gitlab
           @file = nil
         end
 
-        def set(hash)
+        def write_attributes(exportable_path, hash)
+          unless exportable_path == @allowed_path
+            raise ArgumentError, "Invalid #{exportable_path}"
+          end
+
           hash.each do |key, value|
             write(key, value)
           end
         end
 
+        def write_relation(exportable_path, key, value)
+          unless exportable_path == @allowed_path
+            raise ArgumentError, "Invalid #{exportable_path}"
+          end
+
+          write(key, value)
+        end
+
+        def write_relation_array(exportable_path, key, items)
+          unless exportable_path == @allowed_path
+            raise ArgumentError, "Invalid #{exportable_path}"
+          end
+
+          write(key, [])
+
+          # rewind by two bytes, to overwrite ']}'
+          file.pos = file.size - 2
+
+          items.each_with_index do |item, idx|
+            file.write(',') if idx > 0
+            file.write(item.to_json)
+          end
+
+          file.write(']}')
+        end
+
+        private
+
         def write(key, value)
           raise ArgumentError, "key '#{key}' already written" if @keys.include?(key)
 
@@ -41,29 +77,8 @@ module Gitlab
           file.write('}')
 
           @keys.add(key)
-          @last_array = nil
-          @last_array_count = nil
-        end
-
-        def append(key, value)
-          unless @last_array == key
-            write(key, [])
-
-            @last_array = key
-            @last_array_count = 0
-          end
-
-          # rewind by two bytes, to overwrite ']}'
-          file.pos = file.size - 2
-
-          file.write(',') if @last_array_count > 0
-          file.write(value.to_json)
-          file.write(']}')
-          @last_array_count += 1
         end
 
-        private
-
         def file
           @file ||= File.open(@path, "wb")
         end

lib/gitlab/import_export/json/streaming_serializer.rb

@@ -14,8 +14,9 @@ module Gitlab
           end
         end
 
-        def initialize(exportable, relations_schema, json_writer)
+        def initialize(exportable, relations_schema, json_writer, exportable_path:)
           @exportable = exportable
+          @exportable_path = exportable_path
           @relations_schema = relations_schema
           @json_writer = json_writer
         end
@@ -35,7 +36,7 @@ module Gitlab
         def serialize_root
           attributes = exportable.as_json(
             relations_schema.merge(include: nil, preloads: nil))
-          json_writer.set(attributes)
+          json_writer.write_attributes(@exportable_path, attributes)
         end
 
         def serialize_relation(definition)
@@ -53,20 +54,22 @@ module Gitlab
         end
 
         def serialize_many_relations(key, records, options)
-          key_preloads = preloads&.dig(key)
-          records = records.preload(key_preloads) if key_preloads
+          enumerator = Enumerator.new do |items|
+            key_preloads = preloads&.dig(key)
+            records = records.preload(key_preloads) if key_preloads
 
-          records.find_each(batch_size: BATCH_SIZE) do |record|
-            json = Raw.new(record.to_json(options))
-
-            json_writer.append(key, json)
+            records.find_each(batch_size: BATCH_SIZE) do |record|
+              items << Raw.new(record.to_json(options))
+            end
           end
+
+          json_writer.write_relation_array(@exportable_path, key, enumerator)
         end
 
         def serialize_single_relation(key, record, options)
           json = Raw.new(record.to_json(options))
 
-          json_writer.write(key, json)
+          json_writer.write_relation(@exportable_path, key, json)
         end
 
         def includes

lib/gitlab/import_export/project/tree_restorer.rb

@@ -4,6 +4,8 @@ module Gitlab
   module ImportExport
     module Project
       class TreeRestorer
+        include Gitlab::Utils::StrongMemoize
+
         attr_reader :user
         attr_reader :shared
         attr_reader :project
@@ -15,9 +17,8 @@ module Gitlab
         end
 
         def restore
-          @relation_reader = ImportExport::JSON::LegacyReader::File.new(File.join(shared.export_path, 'project.json'), reader.project_relation_names)
-
-          @project_members = @relation_reader.consume_relation('project_members')
+          @project_attributes = relation_reader.consume_attributes(importable_path)
+          @project_members = relation_reader.consume_relation(importable_path, 'project_members')
 
           if relation_tree_restorer.restore
             import_failure_service.with_retry(action: 'set_latest_merge_request_diff_ids!') do
@@ -35,16 +36,28 @@ module Gitlab
 
         private
 
+        def relation_reader
+          strong_memoize(:relation_reader) do
+            ImportExport::JSON::LegacyReader::File.new(
+              File.join(shared.export_path, 'project.json'),
+              relation_names: reader.project_relation_names,
+              allowed_path: importable_path
+            )
+          end
+        end
+
         def relation_tree_restorer
           @relation_tree_restorer ||= RelationTreeRestorer.new(
             user: @user,
             shared: @shared,
-            importable: @project,
-            relation_reader: @relation_reader,
+            relation_reader: relation_reader,
             object_builder: object_builder,
             members_mapper: members_mapper,
             relation_factory: relation_factory,
-            reader: reader
+            reader: reader,
+            importable: @project,
+            importable_attributes: @project_attributes,
+            importable_path: importable_path
           )
         end
 
@@ -69,6 +82,10 @@ module Gitlab
         def import_failure_service
           @import_failure_service ||= ImportFailureService.new(@project)
         end
+
+        def importable_path
+          "project"
+        end
       end
     end
   end

lib/gitlab/import_export/project/tree_saver.rb

@@ -15,10 +15,17 @@ module Gitlab
         end
 
         def save
-          json_writer = ImportExport::JSON::LegacyWriter.new(@full_path)
-
-          serializer = ImportExport::JSON::StreamingSerializer.new(exportable, reader.project_tree, json_writer)
-          serializer.execute
+          json_writer = ImportExport::JSON::LegacyWriter.new(
+            @full_path,
+            allowed_path: "project"
+          )
+
+          ImportExport::JSON::StreamingSerializer.new(
+            exportable,
+            reader.project_tree,
+            json_writer,
+            exportable_path: "project"
+          ).execute
 
           true
         rescue => e

lib/gitlab/import_export/relation_tree_restorer.rb

@@ -11,7 +11,15 @@ module Gitlab
       attr_reader :importable
       attr_reader :relation_reader
 
-      def initialize(user:, shared:, importable:, relation_reader:, members_mapper:, object_builder:, relation_factory:, reader:)
+      def initialize( # rubocop:disable Metrics/ParameterLists
+        user:, shared:, relation_reader:,
+        members_mapper:, object_builder:,
+        relation_factory:,
+        reader:,
+        importable:,
+        importable_attributes:,
+        importable_path:
+      )
         @user = user
         @shared = shared
         @importable = importable
@@ -20,6 +28,8 @@ module Gitlab
         @object_builder = object_builder
         @relation_factory = relation_factory
         @reader = reader
+        @importable_attributes = importable_attributes
+        @importable_path = importable_path
       end
 
       def restore
@@ -57,7 +67,7 @@ module Gitlab
       end
 
       def process_relation!(relation_key, relation_definition)
-        @relation_reader.consume_relation(relation_key) do |data_hash, relation_index|
+        @relation_reader.consume_relation(@importable_path, relation_key) do |data_hash, relation_index|
           process_relation_item!(relation_key, relation_definition, relation_index, data_hash)
         end
       end
@@ -94,7 +104,7 @@ module Gitlab
       end
 
       def update_params!
-        params = @relation_reader.root_attributes(relations.keys)
+        params = @importable_attributes.except(*relations.keys.map(&:to_s))
         params = params.merge(present_override_params)
 
         # Cleaning all imported and overridden params

spec/lib/gitlab/import_export/json/legacy_reader/file_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+require_relative 'shared_example.rb'
+
+describe Gitlab::ImportExport::JSON::LegacyReader::File do
+  it_behaves_like 'import/export json legacy reader' do
+    let(:valid_path) { 'spec/fixtures/lib/gitlab/import_export/light/project.json' }
+    let(:data) { valid_path }
+    let(:json_data) { JSON.parse(File.read(valid_path)) }
+  end
+
+  describe '#exist?' do
+    let(:legacy_reader) do
+      described_class.new(path, relation_names: [])
+    end
+
+    subject { legacy_reader.exist? }
+
+    context 'given valid path' do
+      let(:path) { 'spec/fixtures/lib/gitlab/import_export/light/project.json' }
+
+      it { is_expected.to be true }
+    end
+
+    context 'given invalid path' do
+      let(:path) { 'spec/non-existing-folder/do-not-create-this-file.json' }
+
+      it { is_expected.to be false }
+    end
+  end
+end

spec/lib/gitlab/import_export/json/legacy_reader/hash_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+require_relative 'shared_example.rb'
+
+describe Gitlab::ImportExport::JSON::LegacyReader::Hash do
+  it_behaves_like 'import/export json legacy reader' do
+    let(:path) { 'spec/fixtures/lib/gitlab/import_export/light/project.json' }
+
+    # the hash is modified by the `LegacyReader`
+    # we need to deep-dup it
+    let(:json_data) { JSON.parse(File.read(path)) }
+    let(:data) { JSON.parse(File.read(path)) }
+  end
+
+  describe '#exist?' do
+    let(:legacy_reader) do
+      described_class.new(tree_hash, relation_names: [])
+    end
+
+    subject { legacy_reader.exist? }
+
+    context 'tree_hash is nil' do
+      let(:tree_hash) { nil }
+
+      it { is_expected.to be_falsey }
+    end
+
+    context 'tree_hash presents' do
+      let(:tree_hash) { { "issues": [] } }
+
+      it { is_expected.to be_truthy }
+    end
+  end
+end

spec/lib/gitlab/import_export/json/legacy_reader/shared_example.rb

+# frozen_string_literal: true
+
+RSpec.shared_examples 'import/export json legacy reader' do
+  let(:relation_names) { [] }
+
+  let(:legacy_reader) do
+    described_class.new(
+      data,
+      relation_names: relation_names,
+      allowed_path: "project")
+  end
+
+  describe '#consume_attributes' do
+    context 'when valid path is passed' do
+      subject { legacy_reader.consume_attributes("project") }
+
+      context 'no excluded attributes' do
+        let(:excluded_attributes) { [] }
+        let(:relation_names) { [] }
+
+        it 'returns the whole tree from parsed JSON' do
+          expect(subject).to eq(json_data)
+        end
+      end
+
+      context 'some attributes are excluded' do
+        let(:relation_names) { %w[milestones labels] }
+
+        it 'returns hash without excluded attributes and relations' do
+          expect(subject).not_to include('milestones', 'labels')
+        end
+      end
+    end
+
+    context 'when invalid path is passed' do
+      it 'raises an exception' do
+        expect { legacy_reader.consume_attributes("invalid-path") }
+          .to raise_error(ArgumentError)
+      end
+    end
+  end
+
+  describe '#consume_relation' do
+    context 'when valid path is passed' do
+      let(:key) { 'description' }
+
+      context 'block not given' do
+        it 'returns value of the key' do
+          expect(legacy_reader).to receive(:relations).and_return({ key => 'test value' })
+          expect(legacy_reader.consume_relation("project", key)).to eq('test value')
+        end
+      end
+
+      context 'key has been consumed' do
+        before do
+          legacy_reader.consume_relation("project", key)
+        end
+
+        it 'does not yield' do
+          expect do |blk|
+            legacy_reader.consume_relation("project", key, &blk)
+          end.not_to yield_control
+        end
+      end
+
+      context 'value is nil' do
+        before do
+          expect(legacy_reader).to receive(:relations).and_return({ key => nil })
+        end
+
+        it 'does not yield' do
+          expect do |blk|
+            legacy_reader.consume_relation("project", key, &blk)
+          end.not_to yield_control
+        end
+      end
+
+      context 'value is not array' do
+        before do
+          expect(legacy_reader).to receive(:relations).and_return({ key => 'value' })
+        end
+
+        it 'yield the value with index 0' do
+          expect do |blk|
+            legacy_reader.consume_relation("project", key, &blk)
+          end.to yield_with_args('value', 0)
+        end
+      end
+
+      context 'value is an array' do
+        before do
+          expect(legacy_reader).to receive(:relations).and_return({ key => %w[item1 item2 item3] })
+        end
+
+        it 'yield each array element with index' do
+          expect do |blk|
+            legacy_reader.consume_relation("project", key, &blk)
+          end.to yield_successive_args(['item1', 0], ['item2', 1], ['item3', 2])
+        end
+      end
+    end
+
+    context 'when invalid path is passed' do
+      it 'raises an exception' do
+        expect { legacy_reader.consume_relation("invalid") }
+          .to raise_error(ArgumentError)
+      end
+    end
+  end
+end

spec/lib/gitlab/import_export/json/legacy_reader_spec.rb

-# frozen_string_literal: true
-
-require 'spec_helper'
-
-describe Gitlab::ImportExport::JSON::LegacyReader::User do
-  let(:relation_names) { [] }
-  let(:legacy_reader) { described_class.new(tree_hash, relation_names) }
-
-  describe '#valid?' do
-    subject { legacy_reader.valid? }
-
-    context 'tree_hash not present' do
-      let(:tree_hash) { nil }
-
-      it { is_expected.to be false }
-    end
-
-    context 'tree_hash presents' do
-      let(:tree_hash) { { "issues": [] } }
-
-      it { is_expected.to be true }
-    end
-  end
-end
-
-describe Gitlab::ImportExport::JSON::LegacyReader::File do
-  let(:fixture) { 'spec/fixtures/lib/gitlab/import_export/light/project.json' }
-  let(:project_tree) { JSON.parse(File.read(fixture)) }
-  let(:relation_names) { [] }
-  let(:legacy_reader) { described_class.new(path, relation_names) }
-
-  describe '#valid?' do
-    subject { legacy_reader.valid? }
-
-    context 'given valid path' do
-      let(:path) { fixture }
-
-      it { is_expected.to be true }
-    end
-
-    context 'given invalid path' do
-      let(:path) { 'spec/non-existing-folder/do-not-create-this-file.json' }
-
-      it { is_expected.to be false }
-    end
-  end
-
-  describe '#root_attributes' do
-    let(:path) { fixture }
-
-    subject { legacy_reader.root_attributes(excluded_attributes) }
-
-    context 'No excluded attributes' do
-      let(:excluded_attributes) { [] }
-      let(:relation_names) { [] }
-
-      it 'returns the whole tree from parsed JSON' do
-        expect(subject).to eq(project_tree)
-      end
-    end
-
-    context 'Some attributes are excluded' do
-      let(:excluded_attributes) { %w[milestones labels issues services snippets] }
-      let(:relation_names) { %w[import_type archived] }
-
-      it 'returns hash without excluded attributes and relations' do
-        expect(subject).not_to include('milestones', 'labels', 'issues', 'services', 'snippets', 'import_type', 'archived')
-      end
-    end
-  end
-
-  describe '#consume_relation' do
-    let(:path) { fixture }
-    let(:key) { 'description' }
-
-    context 'block not given' do
-      it 'returns value of the key' do
-        expect(legacy_reader).to receive(:relations).and_return({ key => 'test value' })
-        expect(legacy_reader.consume_relation(key)).to eq('test value')
-      end
-    end
-
-    context 'key has been consumed' do
-      before do
-        legacy_reader.consume_relation(key)
-      end
-
-      it 'does not yield' do
-        expect do |blk|
-          legacy_reader.consume_relation(key, &blk)
-        end.not_to yield_control
-      end
-    end
-
-    context 'value is nil' do
-      before do
-        expect(legacy_reader).to receive(:relations).and_return({ key => nil })
-      end
-
-      it 'does not yield' do
-        expect do |blk|
-          legacy_reader.consume_relation(key, &blk)
-        end.not_to yield_control
-      end
-    end
-
-    context 'value is not array' do
-      before do
-        expect(legacy_reader).to receive(:relations).and_return({ key => 'value' })
-      end
-
-      it 'yield the value with index 0' do
-        expect do |blk|
-          legacy_reader.consume_relation(key, &blk)
-        end.to yield_with_args('value', 0)
-      end
-    end
-
-    context 'value is an array' do
-      before do
-        expect(legacy_reader).to receive(:relations).and_return({ key => %w[item1 item2 item3] })
-      end
-
-      it 'yield each array element with index' do
-        expect do |blk|
-          legacy_reader.consume_relation(key, &blk)
-        end.to yield_successive_args(['item1', 0], ['item2', 1], ['item3', 2])
-      end
-    end
-  end
-
-  describe '#tree_hash' do
-    let(:path) { fixture }
-
-    subject { legacy_reader.send(:tree_hash) }
-
-    it 'parses the JSON into the expected tree' do
-      expect(subject).to eq(project_tree)
-    end
-
-    context 'invalid JSON' do
-      let(:path) { 'spec/fixtures/lib/gitlab/import_export/invalid_json/project.json' }
-
-      it 'raise Exception' do
-        expect { subject }.to raise_exception(Gitlab::ImportExport::Error, 'Incorrect JSON format')
-      end
-    end
-  end
-end

spec/lib/gitlab/import_export/json/legacy_writer_spec.rb

@@ -5,20 +5,37 @@ require 'spec_helper'
 describe Gitlab::ImportExport::JSON::LegacyWriter do
   let(:path) { "#{Dir.tmpdir}/legacy_writer_spec/test.json" }
 
-  subject { described_class.new(path) }
+  subject do
+    described_class.new(path, allowed_path: "project")
+  end
 
   after do
     FileUtils.rm_rf(path)
   end
 
-  describe "#write" do
+  describe "#write_attributes" do
+    it "writes correct json" do
+      expected_hash = { "key" => "value_1", "key_1" => "value_2" }
+      subject.write_attributes("project", expected_hash)
+
+      expect(subject_json).to eq(expected_hash)
+    end
+
+    context 'when invalid path is used' do
+      it 'raises an exception' do
+        expect { subject.write_attributes("invalid", { "key" => "value" }) }
+          .to raise_error(ArgumentError)
+      end
+    end
+  end
+
+  describe "#write_relation" do
     context "when key is already written" do
       it "raises exception" do
-        key = "key"
-        value = "value"
-        subject.write(key, value)
+        subject.write_relation("project", "key", "old value")
 
-        expect { subject.write(key, "new value") }.to raise_exception("key '#{key}' already written")
+        expect { subject.write_relation("project", "key", "new value") }
+          .to raise_exception("key 'key' already written")
       end
     end
 
@@ -27,53 +44,58 @@ describe Gitlab::ImportExport::JSON::LegacyWriter do
         it "writes correct json" do
           expected_hash = { "key" => "value_1", "key_1" => "value_2" }
           expected_hash.each do |key, value|
-            subject.write(key, value)
+            subject.write_relation("project", key, value)
           end
-          subject.close
 
-          expect(saved_json(path)).to eq(expected_hash)
+          expect(subject_json).to eq(expected_hash)
         end
       end
     end
+
+    context 'when invalid path is used' do
+      it 'raises an exception' do
+        expect { subject.write_relation("invalid", "key", "value") }
+          .to raise_error(ArgumentError)
+      end
+    end
   end
 
-  describe "#append" do
-    context "when key is already written" do
-      it "appends values under a given key" do
-        key = "key"
-        values = %w(value_1 value_2)
-        expected_hash = { key => values }
-        values.each do |value|
-          subject.append(key, value)
-        end
-        subject.close
+  describe "#write_relation_array" do
+    context 'when array is used' do
+      it 'writes correct json' do
+        subject.write_relation_array("project", "key", ["value"])
 
-        expect(saved_json(path)).to eq(expected_hash)
+        expect(subject_json).to eq({ "key" => ["value"] })
       end
     end
 
-    context "when key is not already written" do
-      it "writes correct json" do
-        expected_hash = { "key" => ["value"] }
-        subject.append("key", "value")
-        subject.close
+    context 'when enumerable is used' do
+      it 'writes correct json' do
+        values = %w(value1 value2)
+
+        enumerator = Enumerator.new do |items|
+          values.each { |value| items << value }
+        end
+
+        subject.write_relation_array("project", "key", enumerator)
 
-        expect(saved_json(path)).to eq(expected_hash)
+        expect(subject_json).to eq({ "key" => values })
       end
     end
-  end
 
-  describe "#set" do
-    it "writes correct json" do
-      expected_hash = { "key" => "value_1", "key_1" => "value_2" }
-      subject.set(expected_hash)
-      subject.close
+    context "when key is already written" do
+      it "raises an exception" do
+        subject.write_relation_array("project", "key", %w(old_value))
 
-      expect(saved_json(path)).to eq(expected_hash)
+        expect { subject.write_relation_array("project", "key", %w(new_value)) }
+          .to raise_error(ArgumentError)
+      end
     end
   end
 
-  def saved_json(filename)
-    ::JSON.parse(IO.read(filename))
+  def subject_json
+    subject.close
+
+    ::JSON.parse(IO.read(subject.path))
   end
 end

spec/lib/gitlab/import_export/relation_tree_restorer_spec.rb

@@ -14,23 +14,24 @@ describe Gitlab::ImportExport::RelationTreeRestorer do
 
   let(:user) { create(:user) }
   let(:shared) { Gitlab::ImportExport::Shared.new(importable) }
-  let(:members_mapper) { Gitlab::ImportExport::MembersMapper.new(exported_members: {}, user: user, importable: importable) }
+  let(:attributes) { {} }
 
-  let(:importable_hash) do
-    json = IO.read(path)
-    ActiveSupport::JSON.decode(json)
+  let(:members_mapper) do
+    Gitlab::ImportExport::MembersMapper.new(exported_members: {}, user: user, importable: importable)
   end
 
   let(:relation_tree_restorer) do
     described_class.new(
-      user:             user,
-      shared:           shared,
-      relation_reader:  relation_reader,
-      importable:       importable,
-      object_builder:   object_builder,
-      members_mapper:   members_mapper,
-      relation_factory: relation_factory,
-      reader:           reader
+      user:                  user,
+      shared:                shared,
+      relation_reader:       relation_reader,
+      object_builder:        object_builder,
+      members_mapper:        members_mapper,
+      relation_factory:      relation_factory,
+      reader:                reader,
+      importable:            importable,
+      importable_path:       nil,
+      importable_attributes: attributes
     )
   end
 
@@ -100,7 +101,14 @@ describe Gitlab::ImportExport::RelationTreeRestorer do
     let(:reader) { Gitlab::ImportExport::Reader.new(shared: shared) }
 
     context 'using legacy reader' do
-      let(:relation_reader) { Gitlab::ImportExport::JSON::LegacyReader::File.new(path, reader.project_relation_names) }
+      let(:relation_reader) do
+        Gitlab::ImportExport::JSON::LegacyReader::File.new(
+          path,
+          relation_names: reader.project_relation_names
+        )
+      end
+
+      let(:attributes) { relation_reader.consume_attributes(nil) }
 
       it_behaves_like 'import project successfully'
 
@@ -119,7 +127,7 @@ describe Gitlab::ImportExport::RelationTreeRestorer do
     let(:importable) { create(:group, parent: group) }
     let(:object_builder) { Gitlab::ImportExport::Group::ObjectBuilder }
     let(:relation_factory) { Gitlab::ImportExport::Group::RelationFactory }
-    let(:relation_reader) { Gitlab::ImportExport::JSON::LegacyReader::File.new(path, reader.group_relation_names) }
+    let(:relation_reader) { Gitlab::ImportExport::JSON::LegacyReader::File.new(path, relation_names: reader.group_relation_names) }
     let(:reader) do
       Gitlab::ImportExport::Reader.new(
         shared: shared,