lib/react/server_rendering/webpacker_manifest_container.rb

require 'open-uri'

module React
  module ServerRendering
    # Get a compiled file from Webpacker. It may come from:
    #
    # - webpack-dev-server
    # - compiled pack
    class WebpackerManifestContainer

      begin
        MAJOR, MINOR, PATCH, _ = Bundler.locked_gems.specs.find { |gem_spec| gem_spec.name == 'webpacker' || gem_spec.name == 'shakapacker' }.version.segments
      rescue
        MAJOR, MINOR, PATCH, _ = [0,0,0]
      end

      # This pattern matches the code that initializes the dev-server client.
      CLIENT_REQUIRE = %r{__webpack_require__\(.*webpack-dev-server\/client\/index\.js.*\n}

      def self.compatible?
        !!defined?(Webpacker)
      end

      if MAJOR < 3
        def find_asset(logical_path)
          # raises if not found
          asset_path = manifest.lookup(logical_path).to_s
          if asset_path.start_with?('http')
            # Get a file from the webpack-dev-server
            dev_server_asset = URI.open(asset_path).read
            # Remove `webpack-dev-server/client/index.js` code which causes ExecJS to 💥
            dev_server_asset.sub!(CLIENT_REQUIRE, '//\0')
            dev_server_asset
          else
            # Read the already-compiled pack:
            full_path = file_path(logical_path).to_s
            File.read(full_path)
          end
        end
      else
        def find_asset(logical_path)
          asset_path = Webpacker.manifest.lookup(logical_path).to_s
          if Webpacker.dev_server.running?
            ds = Webpacker.dev_server
            # Remove the protocol and host from the asset path. Sometimes webpacker includes this, sometimes it does not
            asset_path.slice!("#{ds.protocol}://#{ds.host_with_port}")
            dev_server_asset = URI.open("#{ds.protocol}://#{ds.host_with_port}#{asset_path}").read
            dev_server_asset.sub!(CLIENT_REQUIRE, '//\0')
            dev_server_asset
          else
            File.read(file_path(logical_path))
          end
        end
      end

      if MAJOR < 3
        def manifest
          Webpacker::Manifest
        end
      else
        def manifest
          Webpacker.manifest
        end
      end

      if MAJOR < 3
        def config
          Webpacker::Configuration
        end
      else
        def config
          Webpacker.config
        end
      end

      if (MAJOR == 1 && MINOR >= 2) || MAJOR == 2
        def file_path path
          manifest.lookup_path(path)
        end
      elsif MAJOR >= 3
        def file_path path
          ::Rails.root.join('public', manifest.lookup!(path)[1..-1])
        end
      else # 1.0 and 1.1 support
        def file_path path
          File.join(output_path, manifest.lookup(path).split('/')[2..-1])
        end
      end

      def output_path
        # Webpack1 /:output/:entry, Webpack3 /public/:output
        config.respond_to?(:output_path) ? config.output_path : 'public'
      end
    end
  end
end