public/dart/fuchsia_webview_flutter/lib/src/fuchsia_webview_platform_controller.dart - topaz - Git at Google

 // Copyright 2019 The Fuchsia 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:async';
 import 'dart:convert' show utf8;
 import 'dart:developer';

 import 'package:fidl/fidl.dart' as fidl;
 import 'package:fidl_fuchsia_web/fidl_async.dart' as fidl_web;
 import 'package:fidl_fuchsia_net_http/fidl_async.dart' as fidl_net;
 import 'package:webview_flutter/platform_interface.dart';
 import 'package:fuchsia_logger/logger.dart';

 import 'fuchsia_web_services.dart';
 import 'utils.dart' as utils;

 class _ChannelSubscription {
   StreamSubscription<String> subscription;
   final int id;
   _ChannelSubscription(this.id, {this.subscription});
 }

 /// Fuchsia [WebViewPlatformController] implementation that serves as the entry
 /// point for all [fuchsia_webview_flutter/webview.dart]'s apis
 class FuchsiaWebViewPlatformController extends WebViewPlatformController {
   /// Helper class to interact with fuchsia web services
   FuchsiaWebServices _fuchsiaWebServices;
   int _nextId = 0;
   var _currentState = fidl_web.NavigationState();
   // Reason: sdk_version_set_literal unsupported until version 2.2
   // ignore: prefer_collection_literals
   var _beforeLoadChannels = Set<String>();

   final WebViewPlatformCallbacksHandler _platformCallbacksHandler;
   final _javascriptChannelSubscriptions = <String, _ChannelSubscription>{};

   /// Initializes [FuchsiaWebViewPlatformController]
   FuchsiaWebViewPlatformController(this._platformCallbacksHandler,
       CreationParams creationParams, this._fuchsiaWebServices)
       : assert(_platformCallbacksHandler != null),
         super(_platformCallbacksHandler) {
     fuchsiaWebServices.setNavigationEventListener(
         _WebviewNavigationEventListener(_onNavigationStateChanged));
     updateSettings(creationParams.webSettings);
     _addBeforeLoadChannels(creationParams.javascriptChannelNames);
     if (creationParams.initialUrl != null) {
       loadUrl(creationParams.initialUrl, {});
     }
   }

   /// Returns [FuchsiaWebServices]
   FuchsiaWebServices get fuchsiaWebServices {
     return _fuchsiaWebServices ??= FuchsiaWebServices();
   }

   @override
   Future<void> addJavascriptChannels(Set<String> javascriptChannelNames) async {
     await _createChannelSubscriptions(javascriptChannelNames);
   }

   @override
   Future<bool> canGoBack() async {
     return _currentState.canGoBack;
   }

   @override
   Future<bool> canGoForward() async {
     return _currentState.canGoForward;
   }

   @override
   Future<void> clearCache() {
     throw UnimplementedError(
         'FuchsiaWebView clearCache is not implemented on the current platform');
   }

   @override
   Future<String> currentUrl() async {
     return _currentState.url;
   }

   @override
   Future<String> getTitle() async {
     return _currentState.title;
   }

   @override
   Future<String> evaluateJavascript(String javascriptString) async {
     return fuchsiaWebServices.evaluateJavascript(['*'], javascriptString);
   }

   @override
   Future<void> goBack() {
     return fuchsiaWebServices.navigationController.goBack();
   }

   @override
   Future<void> goForward() {
     return fuchsiaWebServices.navigationController.goForward();
   }

   @override
   Future<void> loadUrl(
     String url,
     Map<String, String> headers,
   ) async {
     assert(url != null);

     final headersList = <fidl_net.Header>[];
     if (headers != null) {
       headers.forEach((k, v) {
         headersList
             .add(fidl_net.Header(name: utf8.encode(k), value: utf8.encode(v)));
       });
     }

     return fuchsiaWebServices.navigationController.loadUrl(
         url,
         fidl_web.LoadUrlParams(
           type: fidl_web.LoadUrlReason.typed,
           headers: headersList,
         ));
   }

   @override
   Future<void> reload() {
     return fuchsiaWebServices.navigationController
         .reload(fidl_web.ReloadType.partialCache);
   }

   @override
   Future<void> removeJavascriptChannels(
       Set<String> javascriptChannelNames) async {
     for (final channelName in javascriptChannelNames) {
       if (_javascriptChannelSubscriptions.containsKey(channelName)) {
         await _javascriptChannelSubscriptions[channelName]
             .subscription
             .cancel();
         _javascriptChannelSubscriptions.remove(channelName);
         await fuchsiaWebServices
             .evaluateJavascript(['*'], 'window.$channelName = undefined;');
       }
     }
   }

   @override
   Future<void> updateSettings(WebSettings settings) {
     if (settings.debuggingEnabled != null) {
       return fuchsiaWebServices.setJavaScriptLogLevel(settings.debuggingEnabled
           ? fidl_web.ConsoleLogLevel.debug
           : fidl_web.ConsoleLogLevel.none);
     }
     return Future.value();
   }

   /// Clears all cookies for all [WebView] instances.
   ///
   /// Returns true if cookies were present before clearing, else false.
   static Future<bool> clearCookies() {
     throw UnimplementedError(
         'FuchsiaWebView clearCookies is not implemented on the current platform');
   }

   /// Close all remaining subscriptions and connections.
   void dispose() {
     for (final entry in _javascriptChannelSubscriptions.entries) {
       entry.value.subscription.cancel();
     }
     fuchsiaWebServices.dispose();
   }

   /// Called when a navigation state event is received from the webview.
   Future<void> _onNavigationStateChanged(fidl_web.NavigationState state) async {
     _updateCurrentStateDiff(state);
     if (state.isMainDocumentLoaded != null && state.isMainDocumentLoaded) {
       await _establishCommunication(_beforeLoadChannels);
       _platformCallbacksHandler.onPageFinished(_currentState.url);
     }
   }

   /// Updates the current state with each field that is set in the new
   /// navigation state.
   void _updateCurrentStateDiff(fidl_web.NavigationState state) {
     _currentState = fidl_web.NavigationState(
       title: state.title ?? _currentState.title,
       url: state.url ?? _currentState.url,
       canGoBack: state.canGoBack ?? _currentState.canGoBack,
       canGoForward: state.canGoForward ?? _currentState.canGoForward,
       isMainDocumentLoaded:
           state.isMainDocumentLoaded ?? _currentState.isMainDocumentLoaded,
       pageType: state.pageType ?? _currentState.pageType,
     );
   }

   /// Registers the javascript channels that will be loaded when the page loads.
   /// Connection will be established when the page loads.
   Future<void> _addBeforeLoadChannels(
       Set<String> javascriptChannelNames) async {
     _beforeLoadChannels = javascriptChannelNames;
     await _createChannelSubscriptions(javascriptChannelNames, beforeLoad: true);
   }

   /// For each channel in [javascriptChannelNames] creates an object with the
   /// channel name on window in the frame. That object will contain a
   /// `postMessage` method. Messages sent through that method will be received
   /// here and notified back to the client of the webview.
   /// The process for each channel is:
   ///   1. Inject the script that will create the object on window to the
   ///      webview. This script will initially wait for a 'share-port' message.
   ///   2. postMessage 'share-port' to the frame.
   ///   3. The frame has a listener on window and will reply with a
   ///      share-port-ack and a port to which the frame will send messages.
   ///   4. Bind that port and start listening on it.
   ///   5. Notify the frame that we are ready to receive messages.
   ///   6. When a message arrives on that port it is sent to the client through
   ///      the platform callback.
   Future<void> _createChannelSubscriptions(Set<String> javascriptChannelNames,
       {bool beforeLoad}) async {
     for (final channelName in javascriptChannelNames) {
       // Close any connections to that object (if any existed)
       if (_javascriptChannelSubscriptions.containsKey(channelName)) {
         await _javascriptChannelSubscriptions[channelName]
             .subscription
             .cancel();
       } else {
         _javascriptChannelSubscriptions[channelName] =
             _ChannelSubscription(_nextId);
         _nextId += 1;
       }
     }

     // Create a JavaScript object with one postMessage method. This object
     // will be exposed on window.$channelName when the FIDL communication is
     // established. Any window.$channelName already set will be removed.
     // If before load, the connection will happen once the page loads.
     if (beforeLoad) {
       await Future.wait(javascriptChannelNames.map((channel) {
         // Reason: not supported until v2.2 and we need to support earlier
         // versions.
         // ignore: prefer_collection_literals
         final script = _scriptForChannels(Set.from([channel]));
         return fuchsiaWebServices.evaluateJavascriptBeforeLoad(
             _javascriptChannelSubscriptions[channel].id, ['*'], script);
       }));
       return;
     }

     final script = _scriptForChannels(javascriptChannelNames);
     await evaluateJavascript(script);

     await _establishCommunication(javascriptChannelNames);
   }

   Future<void> _establishCommunication(Set<String> javascriptChannelNames) {
     return Future.wait(javascriptChannelNames.map((channelName) async {
       // Creates the message channel connection.
       fidl_web.MessagePortProxy incomingPort;
       try {
         incomingPort = await _bindIncomingPort(channelName);
       } on Exception catch (e) {
         log.warning('Failed to bind incoming port for $channelName: $e');
         return;
       }

       // Subscribe for incoming messages.
       final incomingMessagesStream = _startReceivingMessages(incomingPort);
       _javascriptChannelSubscriptions[channelName].subscription =
           incomingMessagesStream.listen(
         (message) async {
           _platformCallbacksHandler.onJavaScriptChannelMessage(
               channelName, message);
         },
       );

       // Notify of readiness
       await fuchsiaWebServices.postMessage(
           '*', 'share-port-$channelName-ready');
     }));
   }

   /// Communicates with the script injected by `_scriptForChannels` to get a port
   /// from the web page with which to communicate with the page. See comments on
   /// `_createChannelSubscriptions` for details on the process.
   Future<fidl_web.MessagePortProxy> _bindIncomingPort(String channel) async {
     final messagePort = fidl_web.MessagePortProxy();
     await fuchsiaWebServices.postMessage('*', 'share-port-$channel',
         outgoingMessagePortRequest: messagePort.ctrl.request());

     final msg = await messagePort.receiveMessage();
     final ackMsg = utils.bufferToString(msg.data);
     if (ackMsg != 'share-port-ack-$channel') {
       throw Exception('Expected "share-port-ack-$channel", got: "$ackMsg"');
     }
     if (msg.incomingTransfer == null || msg.incomingTransfer.isEmpty) {
       throw Exception('failed to provide an incoming message port');
     }
     final incomingMessagePort = fidl_web.MessagePortProxy();
     incomingMessagePort.ctrl.bind(msg.incomingTransfer[0].messagePort);
     return incomingMessagePort;
   }

   /// Script injected to the frame to create an object with the given name on
   /// window. See comments on `_createChannelSubscriptions` for details on the
   /// process.
   String _scriptForChannels(Set<String> channelNames) {
     return channelNames.map((channel) => '''
         (function() {
           class $channel {
             constructor() {
               this._messageChannel = null;
               this._pendingMessages = [];
               this._isReady = false;
             }

             postMessage(message) {
               if (this._isReady) {
                 this._messageChannel.port1.postMessage(message);
               } else {
                 this._pendingMessages.push(message);
               }
             }

             _ready() {
               for (const pendingMessage of this._pendingMessages) {
                 this._messageChannel.port1.postMessage(pendingMessage);
               }
               this._isReady = true;
               this._pendingMessages = [];
             }

             _setMessageChannel(channel) {
               this._messageChannel = channel;
             }
           }

           window.$channel = new $channel();

           function initializer$channel(event) {
             if (event.data) {
               if (event.data == 'share-port-$channel' && event.ports && event.ports.length > 0) {
                 console.log('Registering channel $channel');
                 const messageChannel = new MessageChannel();
                 window.$channel._setMessageChannel(messageChannel);
                 event.ports[0].postMessage('share-port-ack-$channel', [messageChannel.port2]);
               }
               if (event.data == 'share-port-$channel-ready') {
                 console.log('Channel $channel ready');
                 window.$channel._ready();
                 window.removeEventListener('message', initializer$channel, true);
               }
             }
           }
           window.addEventListener('message', initializer$channel, true);
         })();
       ''').join('\n');
   }

   /// Listens for messages on the incoming port and streams them.
   Stream<String> _startReceivingMessages(
       fidl_web.MessagePortProxy incomingMessagePort) async* {
     // ignore: literal_only_boolean_expressions
     while (true) {
       try {
         final msg = await incomingMessagePort.receiveMessage();
         yield utils.bufferToString(msg.data);
       } on fidl.FidlError {
         // Occurs when the incoming port is closed (ie navigate to another page).
         break;
       }
     }
   }
 }

 class _WebviewNavigationEventListener extends fidl_web.NavigationEventListener {
   final Future<void> Function(fidl_web.NavigationState state)
       navigationStateCallback;

   _WebviewNavigationEventListener(this.navigationStateCallback);

   @override
   Future<void> onNavigationStateChanged(fidl_web.NavigationState state) async {
     await navigationStateCallback(state);
   }
 }
	// Copyright 2019 The Fuchsia 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:async';
	import 'dart:convert' show utf8;
	import 'dart:developer';

	import 'package:fidl/fidl.dart' as fidl;
	import 'package:fidl_fuchsia_web/fidl_async.dart' as fidl_web;
	import 'package:fidl_fuchsia_net_http/fidl_async.dart' as fidl_net;
	import 'package:webview_flutter/platform_interface.dart';
	import 'package:fuchsia_logger/logger.dart';

	import 'fuchsia_web_services.dart';
	import 'utils.dart' as utils;

	class _ChannelSubscription {
	StreamSubscription<String> subscription;
	final int id;
	_ChannelSubscription(this.id, {this.subscription});
	}

	/// Fuchsia [WebViewPlatformController] implementation that serves as the entry
	/// point for all [fuchsia_webview_flutter/webview.dart]'s apis
	class FuchsiaWebViewPlatformController extends WebViewPlatformController {
	/// Helper class to interact with fuchsia web services
	FuchsiaWebServices _fuchsiaWebServices;
	int _nextId = 0;
	var _currentState = fidl_web.NavigationState();
	// Reason: sdk_version_set_literal unsupported until version 2.2
	// ignore: prefer_collection_literals
	var _beforeLoadChannels = Set<String>();

	final WebViewPlatformCallbacksHandler _platformCallbacksHandler;
	final _javascriptChannelSubscriptions = <String, _ChannelSubscription>{};

	/// Initializes [FuchsiaWebViewPlatformController]
	FuchsiaWebViewPlatformController(this._platformCallbacksHandler,
	CreationParams creationParams, this._fuchsiaWebServices)
	: assert(_platformCallbacksHandler != null),
	super(_platformCallbacksHandler) {
	fuchsiaWebServices.setNavigationEventListener(
	_WebviewNavigationEventListener(_onNavigationStateChanged));
	updateSettings(creationParams.webSettings);
	_addBeforeLoadChannels(creationParams.javascriptChannelNames);
	if (creationParams.initialUrl != null) {
	loadUrl(creationParams.initialUrl, {});
	}
	}

	/// Returns [FuchsiaWebServices]
	FuchsiaWebServices get fuchsiaWebServices {
	return _fuchsiaWebServices ??= FuchsiaWebServices();
	}

	@override
	Future<void> addJavascriptChannels(Set<String> javascriptChannelNames) async {
	await _createChannelSubscriptions(javascriptChannelNames);
	}

	@override
	Future<bool> canGoBack() async {
	return _currentState.canGoBack;
	}

	@override
	Future<bool> canGoForward() async {
	return _currentState.canGoForward;
	}

	@override
	Future<void> clearCache() {
	throw UnimplementedError(
	'FuchsiaWebView clearCache is not implemented on the current platform');
	}

	@override
	Future<String> currentUrl() async {
	return _currentState.url;
	}

	@override
	Future<String> getTitle() async {
	return _currentState.title;
	}

	@override
	Future<String> evaluateJavascript(String javascriptString) async {
	return fuchsiaWebServices.evaluateJavascript(['*'], javascriptString);
	}

	@override
	Future<void> goBack() {
	return fuchsiaWebServices.navigationController.goBack();
	}

	@override
	Future<void> goForward() {
	return fuchsiaWebServices.navigationController.goForward();
	}

	@override
	Future<void> loadUrl(
	String url,
	Map<String, String> headers,
	) async {
	assert(url != null);

	final headersList = <fidl_net.Header>[];
	if (headers != null) {
	headers.forEach((k, v) {
	headersList
	.add(fidl_net.Header(name: utf8.encode(k), value: utf8.encode(v)));
	});
	}

	return fuchsiaWebServices.navigationController.loadUrl(
	url,
	fidl_web.LoadUrlParams(
	type: fidl_web.LoadUrlReason.typed,
	headers: headersList,
	));
	}

	@override
	Future<void> reload() {
	return fuchsiaWebServices.navigationController
	.reload(fidl_web.ReloadType.partialCache);
	}

	@override
	Future<void> removeJavascriptChannels(
	Set<String> javascriptChannelNames) async {
	for (final channelName in javascriptChannelNames) {
	if (_javascriptChannelSubscriptions.containsKey(channelName)) {
	await _javascriptChannelSubscriptions[channelName]
	.subscription
	.cancel();
	_javascriptChannelSubscriptions.remove(channelName);
	await fuchsiaWebServices
	.evaluateJavascript(['*'], 'window.$channelName = undefined;');
	}
	}
	}

	@override
	Future<void> updateSettings(WebSettings settings) {
	if (settings.debuggingEnabled != null) {
	return fuchsiaWebServices.setJavaScriptLogLevel(settings.debuggingEnabled
	? fidl_web.ConsoleLogLevel.debug
	: fidl_web.ConsoleLogLevel.none);
	}
	return Future.value();
	}

	/// Clears all cookies for all [WebView] instances.
	///
	/// Returns true if cookies were present before clearing, else false.
	static Future<bool> clearCookies() {
	throw UnimplementedError(
	'FuchsiaWebView clearCookies is not implemented on the current platform');
	}

	/// Close all remaining subscriptions and connections.
	void dispose() {
	for (final entry in _javascriptChannelSubscriptions.entries) {
	entry.value.subscription.cancel();
	}
	fuchsiaWebServices.dispose();
	}

	/// Called when a navigation state event is received from the webview.
	Future<void> _onNavigationStateChanged(fidl_web.NavigationState state) async {
	_updateCurrentStateDiff(state);
	if (state.isMainDocumentLoaded != null && state.isMainDocumentLoaded) {
	await _establishCommunication(_beforeLoadChannels);
	_platformCallbacksHandler.onPageFinished(_currentState.url);
	}
	}

	/// Updates the current state with each field that is set in the new
	/// navigation state.
	void _updateCurrentStateDiff(fidl_web.NavigationState state) {
	_currentState = fidl_web.NavigationState(
	title: state.title ?? _currentState.title,
	url: state.url ?? _currentState.url,
	canGoBack: state.canGoBack ?? _currentState.canGoBack,
	canGoForward: state.canGoForward ?? _currentState.canGoForward,
	isMainDocumentLoaded:
	state.isMainDocumentLoaded ?? _currentState.isMainDocumentLoaded,
	pageType: state.pageType ?? _currentState.pageType,
	);
	}

	/// Registers the javascript channels that will be loaded when the page loads.
	/// Connection will be established when the page loads.
	Future<void> _addBeforeLoadChannels(
	Set<String> javascriptChannelNames) async {
	_beforeLoadChannels = javascriptChannelNames;
	await _createChannelSubscriptions(javascriptChannelNames, beforeLoad: true);
	}

	/// For each channel in [javascriptChannelNames] creates an object with the
	/// channel name on window in the frame. That object will contain a
	/// `postMessage` method. Messages sent through that method will be received
	/// here and notified back to the client of the webview.
	/// The process for each channel is:
	/// 1. Inject the script that will create the object on window to the
	/// webview. This script will initially wait for a 'share-port' message.
	/// 2. postMessage 'share-port' to the frame.
	/// 3. The frame has a listener on window and will reply with a
	/// share-port-ack and a port to which the frame will send messages.
	/// 4. Bind that port and start listening on it.
	/// 5. Notify the frame that we are ready to receive messages.
	/// 6. When a message arrives on that port it is sent to the client through
	/// the platform callback.
	Future<void> _createChannelSubscriptions(Set<String> javascriptChannelNames,
	{bool beforeLoad}) async {
	for (final channelName in javascriptChannelNames) {
	// Close any connections to that object (if any existed)
	if (_javascriptChannelSubscriptions.containsKey(channelName)) {
	await _javascriptChannelSubscriptions[channelName]
	.subscription
	.cancel();
	} else {
	_javascriptChannelSubscriptions[channelName] =
	_ChannelSubscription(_nextId);
	_nextId += 1;
	}
	}

	// Create a JavaScript object with one postMessage method. This object
	// will be exposed on window.$channelName when the FIDL communication is
	// established. Any window.$channelName already set will be removed.
	// If before load, the connection will happen once the page loads.
	if (beforeLoad) {
	await Future.wait(javascriptChannelNames.map((channel) {
	// Reason: not supported until v2.2 and we need to support earlier
	// versions.
	// ignore: prefer_collection_literals
	final script = _scriptForChannels(Set.from([channel]));
	return fuchsiaWebServices.evaluateJavascriptBeforeLoad(
	_javascriptChannelSubscriptions[channel].id, ['*'], script);
	}));
	return;
	}

	final script = _scriptForChannels(javascriptChannelNames);
	await evaluateJavascript(script);

	await _establishCommunication(javascriptChannelNames);
	}

	Future<void> _establishCommunication(Set<String> javascriptChannelNames) {
	return Future.wait(javascriptChannelNames.map((channelName) async {
	// Creates the message channel connection.
	fidl_web.MessagePortProxy incomingPort;
	try {
	incomingPort = await _bindIncomingPort(channelName);
	} on Exception catch (e) {
	log.warning('Failed to bind incoming port for $channelName: $e');
	return;
	}

	// Subscribe for incoming messages.
	final incomingMessagesStream = _startReceivingMessages(incomingPort);
	_javascriptChannelSubscriptions[channelName].subscription =
	incomingMessagesStream.listen(
	(message) async {
	_platformCallbacksHandler.onJavaScriptChannelMessage(
	channelName, message);
	},
	);

	// Notify of readiness
	await fuchsiaWebServices.postMessage(
	'*', 'share-port-$channelName-ready');
	}));
	}

	/// Communicates with the script injected by `_scriptForChannels` to get a port
	/// from the web page with which to communicate with the page. See comments on
	/// `_createChannelSubscriptions` for details on the process.
	Future<fidl_web.MessagePortProxy> _bindIncomingPort(String channel) async {
	final messagePort = fidl_web.MessagePortProxy();
	await fuchsiaWebServices.postMessage('*', 'share-port-$channel',
	outgoingMessagePortRequest: messagePort.ctrl.request());

	final msg = await messagePort.receiveMessage();
	final ackMsg = utils.bufferToString(msg.data);
	if (ackMsg != 'share-port-ack-$channel') {
	throw Exception('Expected "share-port-ack-$channel", got: "$ackMsg"');
	}
	if (msg.incomingTransfer == null \|\| msg.incomingTransfer.isEmpty) {
	throw Exception('failed to provide an incoming message port');
	}
	final incomingMessagePort = fidl_web.MessagePortProxy();
	incomingMessagePort.ctrl.bind(msg.incomingTransfer[0].messagePort);
	return incomingMessagePort;
	}

	/// Script injected to the frame to create an object with the given name on
	/// window. See comments on `_createChannelSubscriptions` for details on the
	/// process.
	String _scriptForChannels(Set<String> channelNames) {
	return channelNames.map((channel) => '''
	(function() {
	class $channel {
	constructor() {
	this._messageChannel = null;
	this._pendingMessages = [];
	this._isReady = false;
	}

	postMessage(message) {
	if (this._isReady) {
	this._messageChannel.port1.postMessage(message);
	} else {
	this._pendingMessages.push(message);
	}
	}

	_ready() {
	for (const pendingMessage of this._pendingMessages) {
	this._messageChannel.port1.postMessage(pendingMessage);
	}
	this._isReady = true;
	this._pendingMessages = [];
	}

	_setMessageChannel(channel) {
	this._messageChannel = channel;
	}
	}

	window.$channel = new $channel();

	function initializer$channel(event) {
	if (event.data) {
	if (event.data == 'share-port-$channel' && event.ports && event.ports.length > 0) {
	console.log('Registering channel $channel');
	const messageChannel = new MessageChannel();
	window.$channel._setMessageChannel(messageChannel);
	event.ports[0].postMessage('share-port-ack-$channel', [messageChannel.port2]);
	}
	if (event.data == 'share-port-$channel-ready') {
	console.log('Channel $channel ready');
	window.$channel._ready();
	window.removeEventListener('message', initializer$channel, true);
	}
	}
	}
	window.addEventListener('message', initializer$channel, true);
	})();
	''').join('\n');
	}

	/// Listens for messages on the incoming port and streams them.
	Stream<String> _startReceivingMessages(
	fidl_web.MessagePortProxy incomingMessagePort) async* {
	// ignore: literal_only_boolean_expressions
	while (true) {
	try {
	final msg = await incomingMessagePort.receiveMessage();
	yield utils.bufferToString(msg.data);
	} on fidl.FidlError {
	// Occurs when the incoming port is closed (ie navigate to another page).
	break;
	}
	}
	}
	}

	class _WebviewNavigationEventListener extends fidl_web.NavigationEventListener {
	final Future<void> Function(fidl_web.NavigationState state)
	navigationStateCallback;

	_WebviewNavigationEventListener(this.navigationStateCallback);

	@override
	Future<void> onNavigationStateChanged(fidl_web.NavigationState state) async {
	await navigationStateCallback(state);
	}
	}