1 files changed, 73 insertions, 0 deletions
diff --git a/lib/gitlab/import_export/json/legacy_writer.rb b/lib/gitlab/import_export/json/legacy_writer.rb
new file mode 100644
index 00000000000..c935e360a65
--- /dev/null
+++ b/lib/gitlab/import_export/json/legacy_writer.rb
@@ -0,0 +1,73 @@
+# frozen_string_literal: true
+
+module Gitlab
+  module ImportExport
+    module JSON
+      class LegacyWriter
+        include Gitlab::ImportExport::CommandLineUtil
+
+        attr_reader :path
+
+        def initialize(path)
+          @path = path
+          @last_array = nil
+          @keys = Set.new
+
+          mkdir_p(File.dirname(@path))
+          file.write('{}')
+        end
+
+        def close
+          @file&.close
+          @file = nil
+        end
+
+        def set(hash)
+          hash.each do |key, value|
+            write(key, value)
+          end
+        end
+
+        def write(key, value)
+          raise ArgumentError, "key '#{key}' already written" if @keys.include?(key)
+
+          # rewind by one byte, to overwrite '}'
+          file.pos = file.size - 1
+
+          file.write(',') if @keys.any?
+          file.write(key.to_json)
+          file.write(':')
+          file.write(value.to_json)
+          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
+      end
+    end
+  end
+end