dwds/lib/src/handlers/injected_handler.dart

// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

import 'dart:convert';
import 'dart:io';
import 'dart:isolate';

import 'package:crypto/crypto.dart';
import 'package:dwds/src/utilities/shared.dart';
import 'package:shelf/shelf.dart';

import '../../dwds.dart';

/// File extension that build_web_compilers will place the
/// [entrypointExtensionMarker] in.
const bootstrapJsExtension = '.bootstrap.js';

/// Marker placed by build_web_compilers for where to put injected JS code.
const entrypointExtensionMarker = '/* ENTRYPOINT_EXTENTION_MARKER */';

/// Marker placed by build_web_compilers for where to put injected JS code.
const mainExtensionMarker = '/* MAIN_EXTENSION_MARKER */';

const _clientScript = 'dwds/src/injected/client';

Handler Function(Handler) createInjectedHandler(
        ReloadConfiguration configuration,
        {String extensionHostname,
        int extensionPort}) =>
    (innerHandler) {
      return (Request request) async {
        if (request.url.path == '$_clientScript.js') {
          var uri = await Isolate.resolvePackageUri(
              Uri.parse('package:$_clientScript.js'));
          var result = await File(uri.toFilePath()).readAsString();
          return Response.ok(result, headers: {
            HttpHeaders.contentTypeHeader: 'application/javascript'
          });
        } else if (request.url.path.endsWith(bootstrapJsExtension)) {
          var ifNoneMatch = request.headers[HttpHeaders.ifNoneMatchHeader];
          if (ifNoneMatch != null) {
            // Disable caching of the inner hander by manually modifying the
            // if-none-match header before forwarding the request.
            request = request.change(headers: {
              HttpHeaders.ifNoneMatchHeader: '$ifNoneMatch\$injected',
            });
          }

          var response = await innerHandler(request);
          if (response.statusCode == HttpStatus.notFound) return response;
          var body = await response.readAsString();
          var etag = response.headers[HttpHeaders.etagHeader];
          var newHeaders = Map.of(response.headers);
          if (body.startsWith(entrypointExtensionMarker)) {
            // The requestedUri contains the hostname and port which gaurantees
            // uniqueness.
            var requestedUri = request.requestedUri;
            var appId =
                base64.encode(md5.convert(utf8.encode('$requestedUri')).bytes);
            var bodyLines = body.split('\n');
            var extensionIndex = bodyLines
                .indexWhere((line) => line.contains(mainExtensionMarker));
            body = bodyLines.sublist(0, extensionIndex).join('\n');
            // The line after the marker calls `main`. We prevent `main` from
            // being called and make it runnable through a global variable.
            var mainFunction = bodyLines[extensionIndex + 1]
                .replaceAll('main()', 'main')
                .trim();
            body += _injectedClientJs(configuration, appId, mainFunction,
                extensionHostname: extensionHostname,
                extensionPort: extensionPort);
            body += bodyLines.sublist(extensionIndex + 2).join('\n');
            // Change the hot restart handler to re-assign
            // `window.$dartRunMain` to the new main, instead of invoking it.
            body = body.replaceFirst(
                'child.main()', r'window.$dartRunMain = child.main');
            etag = base64.encode(md5.convert(body.codeUnits).bytes);
            newHeaders[HttpHeaders.etagHeader] = etag;
          }
          if (ifNoneMatch == etag) {
            return Response.notModified(headers: newHeaders);
          }
          return response.change(body: body, headers: newHeaders);
        } else {
          return innerHandler(request);
        }
      };
    };

String _injectedClientJs(
    ReloadConfiguration configuration, String appId, String mainFunction,
    {String extensionHostname, int extensionPort}) {
  var injectedBody = '''\n
            // Injected by webdev for build results support.
            window.\$dartAppId = "$appId";
            window.\$dartRunMain = $mainFunction;
            window.\$dartReloadConfiguration = "$configuration";
            window.\$dartLoader.forceLoadModule('$_clientScript');
            window.\$loadModuleConfig = "$loadModule";
            ''';
  if (extensionPort != null && extensionHostname != null) {
    injectedBody += '''
      window.\$extensionHostname = "$extensionHostname";
      window.\$extensionPort = "$extensionPort";
      ''';
  }
  return injectedBody;
}