packages/flutter_tools/lib/src/build_system/targets/web.dart - mirrors/flutter - Git at Google

 // Copyright 2014 The Flutter Authors. 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:math';

 import 'package:crypto/crypto.dart';
 import 'package:meta/meta.dart';
 import 'package:package_config/package_config.dart';

 import '../../artifacts.dart';
 import '../../base/file_system.dart';
 import '../../base/io.dart';
 import '../../build_info.dart';
 import '../../dart/language_version.dart';
 import '../../dart/package_map.dart';
 import '../../globals.dart' as globals;
 import '../../project.dart';
 import '../build_system.dart';
 import '../depfile.dart';
 import 'assets.dart';
 import 'common.dart';
 import 'localizations.dart';

 /// Whether web builds should call the platform initialization logic.
 const String kInitializePlatform = 'InitializePlatform';

 /// Whether the application has web plugins.
 const String kHasWebPlugins = 'HasWebPlugins';

 /// An override for the dart2js build mode.
 ///
 /// Valid values are O1 (lowest, profile default) to O4 (highest, release default).
 const String kDart2jsOptimization = 'Dart2jsOptimization';

 /// Whether to disable dynamic generation code to satisfy csp policies.
 const String kCspMode = 'cspMode';

 /// The caching strategy to use for service worker generation.
 const String kServiceWorkerStrategy = 'ServiceWorkerStrategy';

 /// Whether the dart2js build should output source maps.
 const String kSourceMapsEnabled = 'SourceMaps';

 /// The caching strategy for the generated service worker.
 enum ServiceWorkerStrategy {
   /// Download the app shell eagerly and all other assets lazily.
   /// Prefer the offline cached version.
   offlineFirst,
   /// Do not generate a service worker,
   none,
 }

 const String kOfflineFirst = 'offline-first';
 const String kNoneWorker = 'none';

 /// Convert a [value] into a [ServiceWorkerStrategy].
 ServiceWorkerStrategy _serviceWorkerStrategyFromString(String value) {
   switch (value) {
     case kNoneWorker:
       return ServiceWorkerStrategy.none;
     // offline-first is the default value for any invalid requests.
     default:
       return ServiceWorkerStrategy.offlineFirst;
   }
 }

 /// Generates an entry point for a web target.
 // Keep this in sync with build_runner/resident_web_runner.dart
 class WebEntrypointTarget extends Target {
   const WebEntrypointTarget();

   @override
   String get name => 'web_entrypoint';

   @override
   List<Target> get dependencies => const <Target>[];

   @override
   List<Source> get inputs => const <Source>[
     Source.pattern('{FLUTTER_ROOT}/packages/flutter_tools/lib/src/build_system/targets/web.dart'),
   ];

   @override
   List<Source> get outputs => const <Source>[
     Source.pattern('{BUILD_DIR}/main.dart'),
   ];

   @override
   Future<void> build(Environment environment) async {
     final String targetFile = environment.defines[kTargetFile];
     final bool shouldInitializePlatform = environment.defines[kInitializePlatform] == 'true';
     final bool hasPlugins = environment.defines[kHasWebPlugins] == 'true';
     final Uri importUri = environment.fileSystem.file(targetFile).absolute.uri;
     // TODO(jonahwilliams): support configuration of this file.
     const String packageFile = '.packages';
     final PackageConfig packageConfig = await loadPackageConfigWithLogging(
       environment.fileSystem.file(packageFile),
       logger: environment.logger,
     );
     final FlutterProject flutterProject = FlutterProject.current();
     final String languageVersion = determineLanguageVersion(
       environment.fileSystem.file(targetFile),
       packageConfig[flutterProject.manifest.appName],
     ) ?? '';

     // Use the PackageConfig to find the correct package-scheme import path
     // for the user application. If the application has a mix of package-scheme
     // and relative imports for a library, then importing the entrypoint as a
     // file-scheme will cause said library to be recognized as two distinct
     // libraries. This can cause surprising behavior as types from that library
     // will be considered distinct from each other.
     // By construction, this will only be null if the .packages file does not
     // have an entry for the user's application or if the main file is
     // outside of the lib/ directory.
     final String mainImport = packageConfig.toPackageUri(importUri)?.toString()
       ?? importUri.toString();

     String contents;
     if (hasPlugins) {
       final Uri generatedUri = environment.projectDir
         .childDirectory('lib')
         .childFile('generated_plugin_registrant.dart')
         .absolute
         .uri;
       final String generatedImport = packageConfig.toPackageUri(generatedUri)?.toString()
         ?? generatedUri.toString();
       contents = '''
 $languageVersion

 import 'dart:ui' as ui;

 import 'package:flutter_web_plugins/flutter_web_plugins.dart';

 import '$generatedImport';
 import '$mainImport' as entrypoint;

 Future<void> main() async {
   registerPlugins(webPluginRegistry);
   if ($shouldInitializePlatform) {
     await ui.webOnlyInitializePlatform();
   }
   entrypoint.main();
 }
 ''';
     } else {
       contents = '''
 $languageVersion

 import 'dart:ui' as ui;

 import '$mainImport' as entrypoint;

 Future<void> main() async {
   if ($shouldInitializePlatform) {
     await ui.webOnlyInitializePlatform();
   }
   entrypoint.main();
 }
 ''';
     }
     environment.buildDir.childFile('main.dart')
       .writeAsStringSync(contents);
   }
 }

 /// Compiles a web entry point with dart2js.
 class Dart2JSTarget extends Target {
   const Dart2JSTarget();

   @override
   String get name => 'dart2js';

   @override
   List<Target> get dependencies => const <Target>[
     WebEntrypointTarget(),
     GenerateLocalizationsTarget(),
   ];

   @override
   List<Source> get inputs => const <Source>[
     Source.artifact(Artifact.flutterWebSdk),
     Source.artifact(Artifact.dart2jsSnapshot),
     Source.artifact(Artifact.engineDartBinary),
     Source.pattern('{BUILD_DIR}/main.dart'),
     Source.pattern('{PROJECT_DIR}/.packages'),
   ];

   @override
   List<Source> get outputs => const <Source>[];

   @override
   List<String> get depfiles => const <String>[
     'dart2js.d',
   ];

   @override
   Future<void> build(Environment environment) async {
     final BuildMode buildMode = getBuildModeForName(environment.defines[kBuildMode]);
     final bool sourceMapsEnabled = environment.defines[kSourceMapsEnabled] == 'true';

     final List<String> sharedCommandOptions = <String>[
       globals.artifacts.getArtifactPath(Artifact.engineDartBinary),
       '--disable-dart-dev',
       globals.artifacts.getArtifactPath(Artifact.dart2jsSnapshot),
       '--libraries-spec=${globals.fs.path.join(globals.artifacts.getArtifactPath(Artifact.flutterWebSdk), 'libraries.json')}',
       ...?decodeDartDefines(environment.defines, kExtraFrontEndOptions),
       if (buildMode == BuildMode.profile)
         '-Ddart.vm.profile=true'
       else
         '-Ddart.vm.product=true',
       for (final String dartDefine in decodeDartDefines(environment.defines, kDartDefines))
         '-D$dartDefine',
       if (!sourceMapsEnabled)
         '--no-source-maps',
     ];

     // Run the dart2js compilation in two stages, so that icon tree shaking can
     // parse the kernel file for web builds.
     final ProcessResult kernelResult = await globals.processManager.run(<String>[
       ...sharedCommandOptions,
       '-o',
       environment.buildDir.childFile('app.dill').path,
       '--packages=.packages',
       '--cfe-only',
       environment.buildDir.childFile('main.dart').path, // dartfile
     ]);
     if (kernelResult.exitCode != 0) {
       throw Exception(kernelResult.stdout + kernelResult.stderr);
     }

     final String dart2jsOptimization = environment.defines[kDart2jsOptimization];
     final File outputJSFile = environment.buildDir.childFile('main.dart.js');
     final bool csp = environment.defines[kCspMode] == 'true';

     final ProcessResult javaScriptResult = await environment.processManager.run(<String>[
       ...sharedCommandOptions,
       if (dart2jsOptimization != null) '-$dart2jsOptimization' else '-O4',
       if (buildMode == BuildMode.profile) '--no-minify',
       if (csp) '--csp',
       '-o',
       outputJSFile.path,
       environment.buildDir.childFile('app.dill').path, // dartfile
     ]);
     if (javaScriptResult.exitCode != 0) {
       throw Exception(javaScriptResult.stdout + javaScriptResult.stderr);
     }
     final File dart2jsDeps = environment.buildDir
       .childFile('app.dill.deps');
     if (!dart2jsDeps.existsSync()) {
       globals.printError('Warning: dart2js did not produced expected deps list at '
         '${dart2jsDeps.path}');
       return;
     }
     final DepfileService depfileService = DepfileService(
       fileSystem: globals.fs,
       logger: globals.logger,
     );
     final Depfile depfile = depfileService.parseDart2js(
       environment.buildDir.childFile('app.dill.deps'),
       outputJSFile,
     );
     depfileService.writeToFile(
       depfile,
       environment.buildDir.childFile('dart2js.d'),
     );
   }
 }

 /// Unpacks the dart2js compilation and resources to a given output directory.
 class WebReleaseBundle extends Target {
   const WebReleaseBundle();

   @override
   String get name => 'web_release_bundle';

   @override
   List<Target> get dependencies => const <Target>[
     Dart2JSTarget(),
   ];

   @override
   List<Source> get inputs => const <Source>[
     Source.pattern('{BUILD_DIR}/main.dart.js'),
     Source.pattern('{PROJECT_DIR}/pubspec.yaml'),
   ];

   @override
   List<Source> get outputs => const <Source>[
     Source.pattern('{OUTPUT_DIR}/main.dart.js'),
   ];

   @override
   List<String> get depfiles => const <String>[
     'dart2js.d',
     'flutter_assets.d',
     'web_resources.d',
   ];

   @override
   Future<void> build(Environment environment) async {
     for (final File outputFile in environment.buildDir.listSync(recursive: true).whereType<File>()) {
       final String basename = globals.fs.path.basename(outputFile.path);
       if (!basename.contains('main.dart.js')) {
         continue;
       }
       // Do not copy the deps file.
       if (basename.endsWith('.deps')) {
         continue;
       }
       outputFile.copySync(
         environment.outputDir.childFile(globals.fs.path.basename(outputFile.path)).path
       );
     }

     final String versionInfo = FlutterProject.current().getVersionInfo();
     environment.outputDir
         .childFile('version.json')
         .writeAsStringSync(versionInfo);
     final Directory outputDirectory = environment.outputDir.childDirectory('assets');
     outputDirectory.createSync(recursive: true);
     final Depfile depfile = await copyAssets(
       environment,
       environment.outputDir.childDirectory('assets'),
       targetPlatform: TargetPlatform.web_javascript,
     );
     final DepfileService depfileService = DepfileService(
       fileSystem: globals.fs,
       logger: globals.logger,
     );
     depfileService.writeToFile(
       depfile,
       environment.buildDir.childFile('flutter_assets.d'),
     );

     final Directory webResources = environment.projectDir
       .childDirectory('web');
     final List<File> inputResourceFiles = webResources
       .listSync(recursive: true)
       .whereType<File>()
       .toList();

     // Copy other resource files out of web/ directory.
     final List<File> outputResourcesFiles = <File>[];
     for (final File inputFile in inputResourceFiles) {
       final File outputFile = globals.fs.file(globals.fs.path.join(
         environment.outputDir.path,
         globals.fs.path.relative(inputFile.path, from: webResources.path)));
       if (!outputFile.parent.existsSync()) {
         outputFile.parent.createSync(recursive: true);
       }
       outputResourcesFiles.add(outputFile);
       // insert a random hash into the requests for service_worker.js. This is not a content hash,
       // because it would need to be the hash for the entire bundle and not just the resource
       // in question.
       if (environment.fileSystem.path.basename(inputFile.path) == 'index.html') {
         final String randomHash = Random().nextInt(4294967296).toString();
         final String resultString = inputFile.readAsStringSync()
           .replaceFirst(
             "navigator.serviceWorker.register('flutter_service_worker.js')",
             "navigator.serviceWorker.register('flutter_service_worker.js?v=$randomHash')",
           );
         outputFile.writeAsStringSync(resultString);
         continue;
       }
       inputFile.copySync(outputFile.path);
     }
     final Depfile resourceFile = Depfile(inputResourceFiles, outputResourcesFiles);
     depfileService.writeToFile(
       resourceFile,
       environment.buildDir.childFile('web_resources.d'),
     );
   }
 }

 /// Generate a service worker for a web target.
 class WebServiceWorker extends Target {
   const WebServiceWorker();

   @override
   String get name => 'web_service_worker';

   @override
   List<Target> get dependencies => const <Target>[
     Dart2JSTarget(),
     WebReleaseBundle(),
   ];

   @override
   List<String> get depfiles => const <String>[
     'service_worker.d',
   ];

   @override
   List<Source> get inputs => const <Source>[];

   @override
   List<Source> get outputs => const <Source>[];

   @override
   Future<void> build(Environment environment) async {
     final List<File> contents = environment.outputDir
       .listSync(recursive: true)
       .whereType<File>()
       .where((File file) => !file.path.endsWith('flutter_service_worker.js')
         && !globals.fs.path.basename(file.path).startsWith('.'))
       .toList();

     final Map<String, String> urlToHash = <String, String>{};
     for (final File file in contents) {
       // Do not force caching of source maps.
       if (file.path.endsWith('main.dart.js.map') ||
         file.path.endsWith('.part.js.map')) {
         continue;
       }
       final String url = globals.fs.path.toUri(
         globals.fs.path.relative(
           file.path,
           from: environment.outputDir.path),
         ).toString();
       final String hash = md5.convert(await file.readAsBytes()).toString();
       urlToHash[url] = hash;
       // Add an additional entry for the base URL.
       if (globals.fs.path.basename(url) == 'index.html') {
         urlToHash['/'] = hash;
       }
     }

     final File serviceWorkerFile = environment.outputDir
       .childFile('flutter_service_worker.js');
     final Depfile depfile = Depfile(contents, <File>[serviceWorkerFile]);
     final ServiceWorkerStrategy serviceWorkerStrategy = _serviceWorkerStrategyFromString(
       environment.defines[kServiceWorkerStrategy],
     );
     final String serviceWorker = generateServiceWorker(
       urlToHash,
       <String>[
         '/',
         'main.dart.js',
         'index.html',
         'assets/NOTICES',
         if (urlToHash.containsKey('assets/AssetManifest.json'))
           'assets/AssetManifest.json',
         if (urlToHash.containsKey('assets/FontManifest.json'))
           'assets/FontManifest.json',
       ],
       serviceWorkerStrategy: serviceWorkerStrategy,
     );
     serviceWorkerFile
       .writeAsStringSync(serviceWorker);
     final DepfileService depfileService = DepfileService(
       fileSystem: globals.fs,
       logger: globals.logger,
     );
     depfileService.writeToFile(
       depfile,
       environment.buildDir.childFile('service_worker.d'),
     );
   }
 }

 /// Generate a service worker with an app-specific cache name a map of
 /// resource files.
 ///
 /// The tool embeds file hashes directly into the worker so that the byte for byte
 /// invalidation will automatically reactivate workers whenever a new
 /// version is deployed.
 String generateServiceWorker(
   Map<String, String> resources,
   List<String> coreBundle, {
   @required ServiceWorkerStrategy serviceWorkerStrategy,
 }) {
   if (serviceWorkerStrategy == ServiceWorkerStrategy.none) {
     return '';
   }
   return '''
 'use strict';
 const MANIFEST = 'flutter-app-manifest';
 const TEMP = 'flutter-temp-cache';
 const CACHE_NAME = 'flutter-app-cache';
 const RESOURCES = {
   ${resources.entries.map((MapEntry<String, String> entry) => '"${entry.key}": "${entry.value}"').join(",\n")}
 };

 // The application shell files that are downloaded before a service worker can
 // start.
 const CORE = [
   ${coreBundle.map((String file) => '"$file"').join(',\n')}];
 // During install, the TEMP cache is populated with the application shell files.
 self.addEventListener("install", (event) => {
   self.skipWaiting();
   return event.waitUntil(
     caches.open(TEMP).then((cache) => {
       return cache.addAll(
         CORE.map((value) => new Request(value + '?revision=' + RESOURCES[value], {'cache': 'reload'})));
     })
   );
 });

 // During activate, the cache is populated with the temp files downloaded in
 // install. If this service worker is upgrading from one with a saved
 // MANIFEST, then use this to retain unchanged resource files.
 self.addEventListener("activate", function(event) {
   return event.waitUntil(async function() {
     try {
       var contentCache = await caches.open(CACHE_NAME);
       var tempCache = await caches.open(TEMP);
       var manifestCache = await caches.open(MANIFEST);
       var manifest = await manifestCache.match('manifest');
       // When there is no prior manifest, clear the entire cache.
       if (!manifest) {
         await caches.delete(CACHE_NAME);
         contentCache = await caches.open(CACHE_NAME);
         for (var request of await tempCache.keys()) {
           var response = await tempCache.match(request);
           await contentCache.put(request, response);
         }
         await caches.delete(TEMP);
         // Save the manifest to make future upgrades efficient.
         await manifestCache.put('manifest', new Response(JSON.stringify(RESOURCES)));
         return;
       }
       var oldManifest = await manifest.json();
       var origin = self.location.origin;
       for (var request of await contentCache.keys()) {
         var key = request.url.substring(origin.length + 1);
         if (key == "") {
           key = "/";
         }
         // If a resource from the old manifest is not in the new cache, or if
         // the MD5 sum has changed, delete it. Otherwise the resource is left
         // in the cache and can be reused by the new service worker.
         if (!RESOURCES[key] || RESOURCES[key] != oldManifest[key]) {
           await contentCache.delete(request);
         }
       }
       // Populate the cache with the app shell TEMP files, potentially overwriting
       // cache files preserved above.
       for (var request of await tempCache.keys()) {
         var response = await tempCache.match(request);
         await contentCache.put(request, response);
       }
       await caches.delete(TEMP);
       // Save the manifest to make future upgrades efficient.
       await manifestCache.put('manifest', new Response(JSON.stringify(RESOURCES)));
       return;
     } catch (err) {
       // On an unhandled exception the state of the cache cannot be guaranteed.
       console.error('Failed to upgrade service worker: ' + err);
       await caches.delete(CACHE_NAME);
       await caches.delete(TEMP);
       await caches.delete(MANIFEST);
     }
   }());
 });

 // The fetch handler redirects requests for RESOURCE files to the service
 // worker cache.
 self.addEventListener("fetch", (event) => {
   if (event.request.method !== 'GET') {
     return;
   }
   var origin = self.location.origin;
   var key = event.request.url.substring(origin.length + 1);
   // Redirect URLs to the index.html
   if (key.indexOf('?v=') != -1) {
     key = key.split('?v=')[0];
   }
   if (event.request.url == origin || event.request.url.startsWith(origin + '/#') || key == '') {
     key = '/';
   }
   // If the URL is not the RESOURCE list then return to signal that the
   // browser should take over.
   if (!RESOURCES[key]) {
     return;
   }
   // If the URL is the index.html, perform an online-first request.
   if (key == '/') {
     return onlineFirst(event);
   }
   event.respondWith(caches.open(CACHE_NAME)
     .then((cache) =>  {
       return cache.match(event.request).then((response) => {
         // Either respond with the cached resource, or perform a fetch and
         // lazily populate the cache.
         return response || fetch(event.request).then((response) => {
           cache.put(event.request, response.clone());
           return response;
         });
       })
     })
   );
 });

 self.addEventListener('message', (event) => {
   // SkipWaiting can be used to immediately activate a waiting service worker.
   // This will also require a page refresh triggered by the main worker.
   if (event.data === 'skipWaiting') {
     self.skipWaiting();
     return;
   }
   if (event.data === 'downloadOffline') {
     downloadOffline();
     return;
   }
 });

 // Download offline will check the RESOURCES for all files not in the cache
 // and populate them.
 async function downloadOffline() {
   var resources = [];
   var contentCache = await caches.open(CACHE_NAME);
   var currentContent = {};
   for (var request of await contentCache.keys()) {
     var key = request.url.substring(origin.length + 1);
     if (key == "") {
       key = "/";
     }
     currentContent[key] = true;
   }
   for (var resourceKey in Object.keys(RESOURCES)) {
     if (!currentContent[resourceKey]) {
       resources.push(resourceKey);
     }
   }
   return contentCache.addAll(resources);
 }

 // Attempt to download the resource online before falling back to
 // the offline cache.
 function onlineFirst(event) {
   return event.respondWith(
     fetch(event.request).then((response) => {
       return caches.open(CACHE_NAME).then((cache) => {
         cache.put(event.request, response.clone());
         return response;
       });
     }).catch((error) => {
       return caches.open(CACHE_NAME).then((cache) => {
         return cache.match(event.request).then((response) => {
           if (response != null) {
             return response;
           }
           throw error;
         });
       });
     })
   );
 }
 ''';
 }
	// Copyright 2014 The Flutter Authors. 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:math';

	import 'package:crypto/crypto.dart';
	import 'package:meta/meta.dart';
	import 'package:package_config/package_config.dart';

	import '../../artifacts.dart';
	import '../../base/file_system.dart';
	import '../../base/io.dart';
	import '../../build_info.dart';
	import '../../dart/language_version.dart';
	import '../../dart/package_map.dart';
	import '../../globals.dart' as globals;
	import '../../project.dart';
	import '../build_system.dart';
	import '../depfile.dart';
	import 'assets.dart';
	import 'common.dart';
	import 'localizations.dart';

	/// Whether web builds should call the platform initialization logic.
	const String kInitializePlatform = 'InitializePlatform';

	/// Whether the application has web plugins.
	const String kHasWebPlugins = 'HasWebPlugins';

	/// An override for the dart2js build mode.
	///
	/// Valid values are O1 (lowest, profile default) to O4 (highest, release default).
	const String kDart2jsOptimization = 'Dart2jsOptimization';

	/// Whether to disable dynamic generation code to satisfy csp policies.
	const String kCspMode = 'cspMode';

	/// The caching strategy to use for service worker generation.
	const String kServiceWorkerStrategy = 'ServiceWorkerStrategy';

	/// Whether the dart2js build should output source maps.
	const String kSourceMapsEnabled = 'SourceMaps';

	/// The caching strategy for the generated service worker.
	enum ServiceWorkerStrategy {
	/// Download the app shell eagerly and all other assets lazily.
	/// Prefer the offline cached version.
	offlineFirst,
	/// Do not generate a service worker,
	none,
	}

	const String kOfflineFirst = 'offline-first';
	const String kNoneWorker = 'none';

	/// Convert a [value] into a [ServiceWorkerStrategy].
	ServiceWorkerStrategy _serviceWorkerStrategyFromString(String value) {
	switch (value) {
	case kNoneWorker:
	return ServiceWorkerStrategy.none;
	// offline-first is the default value for any invalid requests.
	default:
	return ServiceWorkerStrategy.offlineFirst;
	}
	}

	/// Generates an entry point for a web target.
	// Keep this in sync with build_runner/resident_web_runner.dart
	class WebEntrypointTarget extends Target {
	const WebEntrypointTarget();

	@override
	String get name => 'web_entrypoint';

	@override
	List<Target> get dependencies => const <Target>[];

	@override
	List<Source> get inputs => const <Source>[
	Source.pattern('{FLUTTER_ROOT}/packages/flutter_tools/lib/src/build_system/targets/web.dart'),
	];

	@override
	List<Source> get outputs => const <Source>[
	Source.pattern('{BUILD_DIR}/main.dart'),
	];

	@override
	Future<void> build(Environment environment) async {
	final String targetFile = environment.defines[kTargetFile];
	final bool shouldInitializePlatform = environment.defines[kInitializePlatform] == 'true';
	final bool hasPlugins = environment.defines[kHasWebPlugins] == 'true';
	final Uri importUri = environment.fileSystem.file(targetFile).absolute.uri;
	// TODO(jonahwilliams): support configuration of this file.
	const String packageFile = '.packages';
	final PackageConfig packageConfig = await loadPackageConfigWithLogging(
	environment.fileSystem.file(packageFile),
	logger: environment.logger,
	);
	final FlutterProject flutterProject = FlutterProject.current();
	final String languageVersion = determineLanguageVersion(
	environment.fileSystem.file(targetFile),
	packageConfig[flutterProject.manifest.appName],
	) ?? '';

	// Use the PackageConfig to find the correct package-scheme import path
	// for the user application. If the application has a mix of package-scheme
	// and relative imports for a library, then importing the entrypoint as a
	// file-scheme will cause said library to be recognized as two distinct
	// libraries. This can cause surprising behavior as types from that library
	// will be considered distinct from each other.
	// By construction, this will only be null if the .packages file does not
	// have an entry for the user's application or if the main file is
	// outside of the lib/ directory.
	final String mainImport = packageConfig.toPackageUri(importUri)?.toString()
	?? importUri.toString();

	String contents;
	if (hasPlugins) {
	final Uri generatedUri = environment.projectDir
	.childDirectory('lib')
	.childFile('generated_plugin_registrant.dart')
	.absolute
	.uri;
	final String generatedImport = packageConfig.toPackageUri(generatedUri)?.toString()
	?? generatedUri.toString();
	contents = '''
	$languageVersion

	import 'dart:ui' as ui;

	import 'package:flutter_web_plugins/flutter_web_plugins.dart';

	import '$generatedImport';
	import '$mainImport' as entrypoint;

	Future<void> main() async {
	registerPlugins(webPluginRegistry);
	if ($shouldInitializePlatform) {
	await ui.webOnlyInitializePlatform();
	}
	entrypoint.main();
	}
	''';
	} else {
	contents = '''
	$languageVersion

	import 'dart:ui' as ui;

	import '$mainImport' as entrypoint;

	Future<void> main() async {
	if ($shouldInitializePlatform) {
	await ui.webOnlyInitializePlatform();
	}
	entrypoint.main();
	}
	''';
	}
	environment.buildDir.childFile('main.dart')
	.writeAsStringSync(contents);
	}
	}

	/// Compiles a web entry point with dart2js.
	class Dart2JSTarget extends Target {
	const Dart2JSTarget();

	@override
	String get name => 'dart2js';

	@override
	List<Target> get dependencies => const <Target>[
	WebEntrypointTarget(),
	GenerateLocalizationsTarget(),
	];

	@override
	List<Source> get inputs => const <Source>[
	Source.artifact(Artifact.flutterWebSdk),
	Source.artifact(Artifact.dart2jsSnapshot),
	Source.artifact(Artifact.engineDartBinary),
	Source.pattern('{BUILD_DIR}/main.dart'),
	Source.pattern('{PROJECT_DIR}/.packages'),
	];

	@override
	List<Source> get outputs => const <Source>[];

	@override
	List<String> get depfiles => const <String>[
	'dart2js.d',
	];

	@override
	Future<void> build(Environment environment) async {
	final BuildMode buildMode = getBuildModeForName(environment.defines[kBuildMode]);
	final bool sourceMapsEnabled = environment.defines[kSourceMapsEnabled] == 'true';

	final List<String> sharedCommandOptions = <String>[
	globals.artifacts.getArtifactPath(Artifact.engineDartBinary),
	'--disable-dart-dev',
	globals.artifacts.getArtifactPath(Artifact.dart2jsSnapshot),
	'--libraries-spec=${globals.fs.path.join(globals.artifacts.getArtifactPath(Artifact.flutterWebSdk), 'libraries.json')}',
	...?decodeDartDefines(environment.defines, kExtraFrontEndOptions),
	if (buildMode == BuildMode.profile)
	'-Ddart.vm.profile=true'
	else
	'-Ddart.vm.product=true',
	for (final String dartDefine in decodeDartDefines(environment.defines, kDartDefines))
	'-D$dartDefine',
	if (!sourceMapsEnabled)
	'--no-source-maps',
	];

	// Run the dart2js compilation in two stages, so that icon tree shaking can
	// parse the kernel file for web builds.
	final ProcessResult kernelResult = await globals.processManager.run(<String>[
	...sharedCommandOptions,
	'-o',
	environment.buildDir.childFile('app.dill').path,
	'--packages=.packages',
	'--cfe-only',
	environment.buildDir.childFile('main.dart').path, // dartfile
	]);
	if (kernelResult.exitCode != 0) {
	throw Exception(kernelResult.stdout + kernelResult.stderr);
	}

	final String dart2jsOptimization = environment.defines[kDart2jsOptimization];
	final File outputJSFile = environment.buildDir.childFile('main.dart.js');
	final bool csp = environment.defines[kCspMode] == 'true';

	final ProcessResult javaScriptResult = await environment.processManager.run(<String>[
	...sharedCommandOptions,
	if (dart2jsOptimization != null) '-$dart2jsOptimization' else '-O4',
	if (buildMode == BuildMode.profile) '--no-minify',
	if (csp) '--csp',
	'-o',
	outputJSFile.path,
	environment.buildDir.childFile('app.dill').path, // dartfile
	]);
	if (javaScriptResult.exitCode != 0) {
	throw Exception(javaScriptResult.stdout + javaScriptResult.stderr);
	}
	final File dart2jsDeps = environment.buildDir
	.childFile('app.dill.deps');
	if (!dart2jsDeps.existsSync()) {
	globals.printError('Warning: dart2js did not produced expected deps list at '
	'${dart2jsDeps.path}');
	return;
	}
	final DepfileService depfileService = DepfileService(
	fileSystem: globals.fs,
	logger: globals.logger,
	);
	final Depfile depfile = depfileService.parseDart2js(
	environment.buildDir.childFile('app.dill.deps'),
	outputJSFile,
	);
	depfileService.writeToFile(
	depfile,
	environment.buildDir.childFile('dart2js.d'),
	);
	}
	}

	/// Unpacks the dart2js compilation and resources to a given output directory.
	class WebReleaseBundle extends Target {
	const WebReleaseBundle();

	@override
	String get name => 'web_release_bundle';

	@override
	List<Target> get dependencies => const <Target>[
	Dart2JSTarget(),
	];

	@override
	List<Source> get inputs => const <Source>[
	Source.pattern('{BUILD_DIR}/main.dart.js'),
	Source.pattern('{PROJECT_DIR}/pubspec.yaml'),
	];

	@override
	List<Source> get outputs => const <Source>[
	Source.pattern('{OUTPUT_DIR}/main.dart.js'),
	];

	@override
	List<String> get depfiles => const <String>[
	'dart2js.d',
	'flutter_assets.d',
	'web_resources.d',
	];

	@override
	Future<void> build(Environment environment) async {
	for (final File outputFile in environment.buildDir.listSync(recursive: true).whereType<File>()) {
	final String basename = globals.fs.path.basename(outputFile.path);
	if (!basename.contains('main.dart.js')) {
	continue;
	}
	// Do not copy the deps file.
	if (basename.endsWith('.deps')) {
	continue;
	}
	outputFile.copySync(
	environment.outputDir.childFile(globals.fs.path.basename(outputFile.path)).path
	);
	}

	final String versionInfo = FlutterProject.current().getVersionInfo();
	environment.outputDir
	.childFile('version.json')
	.writeAsStringSync(versionInfo);
	final Directory outputDirectory = environment.outputDir.childDirectory('assets');
	outputDirectory.createSync(recursive: true);
	final Depfile depfile = await copyAssets(
	environment,
	environment.outputDir.childDirectory('assets'),
	targetPlatform: TargetPlatform.web_javascript,
	);
	final DepfileService depfileService = DepfileService(
	fileSystem: globals.fs,
	logger: globals.logger,
	);
	depfileService.writeToFile(
	depfile,
	environment.buildDir.childFile('flutter_assets.d'),
	);

	final Directory webResources = environment.projectDir
	.childDirectory('web');
	final List<File> inputResourceFiles = webResources
	.listSync(recursive: true)
	.whereType<File>()
	.toList();

	// Copy other resource files out of web/ directory.
	final List<File> outputResourcesFiles = <File>[];
	for (final File inputFile in inputResourceFiles) {
	final File outputFile = globals.fs.file(globals.fs.path.join(
	environment.outputDir.path,
	globals.fs.path.relative(inputFile.path, from: webResources.path)));
	if (!outputFile.parent.existsSync()) {
	outputFile.parent.createSync(recursive: true);
	}
	outputResourcesFiles.add(outputFile);
	// insert a random hash into the requests for service_worker.js. This is not a content hash,
	// because it would need to be the hash for the entire bundle and not just the resource
	// in question.
	if (environment.fileSystem.path.basename(inputFile.path) == 'index.html') {
	final String randomHash = Random().nextInt(4294967296).toString();
	final String resultString = inputFile.readAsStringSync()
	.replaceFirst(
	"navigator.serviceWorker.register('flutter_service_worker.js')",
	"navigator.serviceWorker.register('flutter_service_worker.js?v=$randomHash')",
	);
	outputFile.writeAsStringSync(resultString);
	continue;
	}
	inputFile.copySync(outputFile.path);
	}
	final Depfile resourceFile = Depfile(inputResourceFiles, outputResourcesFiles);
	depfileService.writeToFile(
	resourceFile,
	environment.buildDir.childFile('web_resources.d'),
	);
	}
	}

	/// Generate a service worker for a web target.
	class WebServiceWorker extends Target {
	const WebServiceWorker();

	@override
	String get name => 'web_service_worker';

	@override
	List<Target> get dependencies => const <Target>[
	Dart2JSTarget(),
	WebReleaseBundle(),
	];

	@override
	List<String> get depfiles => const <String>[
	'service_worker.d',
	];

	@override
	List<Source> get inputs => const <Source>[];

	@override
	List<Source> get outputs => const <Source>[];

	@override
	Future<void> build(Environment environment) async {
	final List<File> contents = environment.outputDir
	.listSync(recursive: true)
	.whereType<File>()
	.where((File file) => !file.path.endsWith('flutter_service_worker.js')
	&& !globals.fs.path.basename(file.path).startsWith('.'))
	.toList();

	final Map<String, String> urlToHash = <String, String>{};
	for (final File file in contents) {
	// Do not force caching of source maps.
	if (file.path.endsWith('main.dart.js.map') \|\|
	file.path.endsWith('.part.js.map')) {
	continue;
	}
	final String url = globals.fs.path.toUri(
	globals.fs.path.relative(
	file.path,
	from: environment.outputDir.path),
	).toString();
	final String hash = md5.convert(await file.readAsBytes()).toString();
	urlToHash[url] = hash;
	// Add an additional entry for the base URL.
	if (globals.fs.path.basename(url) == 'index.html') {
	urlToHash['/'] = hash;
	}
	}

	final File serviceWorkerFile = environment.outputDir
	.childFile('flutter_service_worker.js');
	final Depfile depfile = Depfile(contents, <File>[serviceWorkerFile]);
	final ServiceWorkerStrategy serviceWorkerStrategy = _serviceWorkerStrategyFromString(
	environment.defines[kServiceWorkerStrategy],
	);
	final String serviceWorker = generateServiceWorker(
	urlToHash,
	<String>[
	'/',
	'main.dart.js',
	'index.html',
	'assets/NOTICES',
	if (urlToHash.containsKey('assets/AssetManifest.json'))
	'assets/AssetManifest.json',
	if (urlToHash.containsKey('assets/FontManifest.json'))
	'assets/FontManifest.json',
	],
	serviceWorkerStrategy: serviceWorkerStrategy,
	);
	serviceWorkerFile
	.writeAsStringSync(serviceWorker);
	final DepfileService depfileService = DepfileService(
	fileSystem: globals.fs,
	logger: globals.logger,
	);
	depfileService.writeToFile(
	depfile,
	environment.buildDir.childFile('service_worker.d'),
	);
	}
	}

	/// Generate a service worker with an app-specific cache name a map of
	/// resource files.
	///
	/// The tool embeds file hashes directly into the worker so that the byte for byte
	/// invalidation will automatically reactivate workers whenever a new
	/// version is deployed.
	String generateServiceWorker(
	Map<String, String> resources,
	List<String> coreBundle, {
	@required ServiceWorkerStrategy serviceWorkerStrategy,
	}) {
	if (serviceWorkerStrategy == ServiceWorkerStrategy.none) {
	return '';
	}
	return '''
	'use strict';
	const MANIFEST = 'flutter-app-manifest';
	const TEMP = 'flutter-temp-cache';
	const CACHE_NAME = 'flutter-app-cache';
	const RESOURCES = {
	${resources.entries.map((MapEntry<String, String> entry) => '"${entry.key}": "${entry.value}"').join(",\n")}
	};

	// The application shell files that are downloaded before a service worker can
	// start.
	const CORE = [
	${coreBundle.map((String file) => '"$file"').join(',\n')}];
	// During install, the TEMP cache is populated with the application shell files.
	self.addEventListener("install", (event) => {
	self.skipWaiting();
	return event.waitUntil(
	caches.open(TEMP).then((cache) => {
	return cache.addAll(
	CORE.map((value) => new Request(value + '?revision=' + RESOURCES[value], {'cache': 'reload'})));
	})
	);
	});

	// During activate, the cache is populated with the temp files downloaded in
	// install. If this service worker is upgrading from one with a saved
	// MANIFEST, then use this to retain unchanged resource files.
	self.addEventListener("activate", function(event) {
	return event.waitUntil(async function() {
	try {
	var contentCache = await caches.open(CACHE_NAME);
	var tempCache = await caches.open(TEMP);
	var manifestCache = await caches.open(MANIFEST);
	var manifest = await manifestCache.match('manifest');
	// When there is no prior manifest, clear the entire cache.
	if (!manifest) {
	await caches.delete(CACHE_NAME);
	contentCache = await caches.open(CACHE_NAME);
	for (var request of await tempCache.keys()) {
	var response = await tempCache.match(request);
	await contentCache.put(request, response);
	}
	await caches.delete(TEMP);
	// Save the manifest to make future upgrades efficient.
	await manifestCache.put('manifest', new Response(JSON.stringify(RESOURCES)));
	return;
	}
	var oldManifest = await manifest.json();
	var origin = self.location.origin;
	for (var request of await contentCache.keys()) {
	var key = request.url.substring(origin.length + 1);
	if (key == "") {
	key = "/";
	}
	// If a resource from the old manifest is not in the new cache, or if
	// the MD5 sum has changed, delete it. Otherwise the resource is left
	// in the cache and can be reused by the new service worker.
	if (!RESOURCES[key] \|\| RESOURCES[key] != oldManifest[key]) {
	await contentCache.delete(request);
	}
	}
	// Populate the cache with the app shell TEMP files, potentially overwriting
	// cache files preserved above.
	for (var request of await tempCache.keys()) {
	var response = await tempCache.match(request);
	await contentCache.put(request, response);
	}
	await caches.delete(TEMP);
	// Save the manifest to make future upgrades efficient.
	await manifestCache.put('manifest', new Response(JSON.stringify(RESOURCES)));
	return;
	} catch (err) {
	// On an unhandled exception the state of the cache cannot be guaranteed.
	console.error('Failed to upgrade service worker: ' + err);
	await caches.delete(CACHE_NAME);
	await caches.delete(TEMP);
	await caches.delete(MANIFEST);
	}
	}());
	});

	// The fetch handler redirects requests for RESOURCE files to the service
	// worker cache.
	self.addEventListener("fetch", (event) => {
	if (event.request.method !== 'GET') {
	return;
	}
	var origin = self.location.origin;
	var key = event.request.url.substring(origin.length + 1);
	// Redirect URLs to the index.html
	if (key.indexOf('?v=') != -1) {
	key = key.split('?v=')[0];
	}
	if (event.request.url == origin \|\| event.request.url.startsWith(origin + '/#') \|\| key == '') {
	key = '/';
	}
	// If the URL is not the RESOURCE list then return to signal that the
	// browser should take over.
	if (!RESOURCES[key]) {
	return;
	}
	// If the URL is the index.html, perform an online-first request.
	if (key == '/') {
	return onlineFirst(event);
	}
	event.respondWith(caches.open(CACHE_NAME)
	.then((cache) => {
	return cache.match(event.request).then((response) => {
	// Either respond with the cached resource, or perform a fetch and
	// lazily populate the cache.
	return response \|\| fetch(event.request).then((response) => {
	cache.put(event.request, response.clone());
	return response;
	});
	})
	})
	);
	});

	self.addEventListener('message', (event) => {
	// SkipWaiting can be used to immediately activate a waiting service worker.
	// This will also require a page refresh triggered by the main worker.
	if (event.data === 'skipWaiting') {
	self.skipWaiting();
	return;
	}
	if (event.data === 'downloadOffline') {
	downloadOffline();
	return;
	}
	});

	// Download offline will check the RESOURCES for all files not in the cache
	// and populate them.
	async function downloadOffline() {
	var resources = [];
	var contentCache = await caches.open(CACHE_NAME);
	var currentContent = {};
	for (var request of await contentCache.keys()) {
	var key = request.url.substring(origin.length + 1);
	if (key == "") {
	key = "/";
	}
	currentContent[key] = true;
	}
	for (var resourceKey in Object.keys(RESOURCES)) {
	if (!currentContent[resourceKey]) {
	resources.push(resourceKey);
	}
	}
	return contentCache.addAll(resources);
	}

	// Attempt to download the resource online before falling back to
	// the offline cache.
	function onlineFirst(event) {
	return event.respondWith(
	fetch(event.request).then((response) => {
	return caches.open(CACHE_NAME).then((cache) => {
	cache.put(event.request, response.clone());
	return response;
	});
	}).catch((error) => {
	return caches.open(CACHE_NAME).then((cache) => {
	return cache.match(event.request).then((response) => {
	if (response != null) {
	return response;
	}
	throw error;
	});
	});
	})
	);
	}
	''';
	}