Implement WebSocket for the browser (#1142)

Author: brianquinlan

.github/workflows/dart.yml

@@ -0,0 +1,5 @@
+// Copyright (c) 2024, 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.
+
+export 'src/browser_web_socket.dart' show BrowserWebSocket;

pkgs/web_socket/lib/browser_web_socket.dart

@@ -1 +1,5 @@
+// Copyright (c) 2024, 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.
+
 export 'src/io_web_socket.dart' show IOWebSocket;

pkgs/web_socket/lib/io_web_socket.dart

@@ -0,0 +1,128 @@
+// Copyright (c) 2024, 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:async';
+import 'dart:js_interop';
+import 'dart:typed_data';
+
+import 'package:web/web.dart' as web;
+
+import '../web_socket.dart';
+import 'utils.dart';
+
+/// A [WebSocket] using the browser WebSocket API.
+///
+/// Usable when targeting the browser using either JavaScript or WASM.
+class BrowserWebSocket implements WebSocket {
+  final web.WebSocket _webSocket;
+  final _events = StreamController<WebSocketEvent>();
+
+  static Future<BrowserWebSocket> connect(Uri url) async {
+    final webSocket = web.WebSocket(url.toString())..binaryType = 'arraybuffer';
+    final browserSocket = BrowserWebSocket._(webSocket);
+    final webSocketConnected = Completer<BrowserWebSocket>();
+
+    if (webSocket.readyState == web.WebSocket.OPEN) {
+      webSocketConnected.complete(browserSocket);
+    } else {
+      if (webSocket.readyState == web.WebSocket.CLOSING ||
+          webSocket.readyState == web.WebSocket.CLOSED) {
+        webSocketConnected.completeError(WebSocketException(
+            'Unexpected WebSocket state: ${webSocket.readyState}, '
+            'expected CONNECTING (0) or OPEN (1)'));
+      } else {
+        // The socket API guarantees that only a single open event will be
+        // emitted.
+        unawaited(webSocket.onOpen.first.then((_) {
+          webSocketConnected.complete(browserSocket);
+        }));
+      }
+    }
+
+    unawaited(webSocket.onError.first.then((e) {
+      // Unfortunately, the underlying WebSocket API doesn't expose any
+      // specific information about the error itself.
+      if (!webSocketConnected.isCompleted) {
+        final error = WebSocketException('Failed to connect WebSocket');
+        webSocketConnected.completeError(error);
+      } else {
+        browserSocket._closed(1006, 'error');
+      }
+    }));
+
+    webSocket.onMessage.listen((e) {
+      if (browserSocket._events.isClosed) return;
+
+      final eventData = e.data!;
+      late WebSocketEvent data;
+      if (eventData.typeofEquals('string')) {
+        data = TextDataReceived((eventData as JSString).toDart);
+      } else if (eventData.typeofEquals('object') &&
+          (eventData as JSObject).instanceOfString('ArrayBuffer')) {
+        data = BinaryDataReceived(
+            (eventData as JSArrayBuffer).toDart.asUint8List());
+      } else {
+        throw StateError('unexpected message type: ${eventData.runtimeType}');
+      }
+      browserSocket._events.add(data);
+    });
+
+    unawaited(webSocket.onClose.first.then((event) {
+      if (!webSocketConnected.isCompleted) {
+        webSocketConnected.complete(browserSocket);
+      }
+      browserSocket._closed(event.code, event.reason);
+    }));
+
+    return webSocketConnected.future;
+  }
+
+  void _closed(int? code, String? reason) {
+    if (_events.isClosed) return;
+    _events.add(CloseReceived(code, reason ?? ''));
+    unawaited(_events.close());
+  }
+
+  BrowserWebSocket._(this._webSocket);
+
+  @override
+  void sendBytes(Uint8List b) {
+    if (_events.isClosed) {
+      throw StateError('WebSocket is closed');
+    }
+    // Silently discards the data if the connection is closed.
+    _webSocket.send(b.jsify()!);
+  }
+
+  @override
+  void sendText(String s) {
+    if (_events.isClosed) {
+      throw StateError('WebSocket is closed');
+    }
+    // Silently discards the data if the connection is closed.
+    _webSocket.send(s.jsify()!);
+  }
+
+  @override
+  Future<void> close([int? code, String? reason]) async {
+    if (_events.isClosed) {
+      throw StateError('WebSocket is closed');
+    }
+
+    checkCloseCode(code);
+    checkCloseReason(reason);
+
+    unawaited(_events.close());
+    if ((code, reason) case (final closeCode?, final closeReason?)) {
+      _webSocket.close(closeCode, closeReason);
+    } else if (code case final closeCode?) {
+      _webSocket.close(closeCode);
+    } else {
+      _webSocket.close();
+    }
+  }
+
+  @override
+  Stream<WebSocketEvent> get events => _events.stream;
+}