package:web_socket_channel provides cross-platform
StreamChannel wrappers for WebSocket connections.
It provides a cross-platform
WebSocketChannel API, a cross-platform implementation of
that API that communicates over an underlying StreamChannel,
an implementation that wraps dart:io's WebSocket
class, and a similar implementation that wraps
dart:html's.
It also provides constants for the WebSocket protocol's pre-defined status codes
in the status.dart library. It's strongly recommended that users
import this library with the prefix status.
import 'package:web_socket_channel/web_socket_channel.dart';
import 'package:web_socket_channel/status.dart' as status;
main() async {
final wsUrl = Uri.parse('ws://example.com');
final channel = WebSocketChannel.connect(wsUrl);
await channel.ready;
channel.stream.listen((message) {
channel.sink.add('received!');
channel.sink.close(status.goingAway);
});
}The WebSocketChannel class's most important role is as the
interface for WebSocket stream channels across all implementations and all
platforms. In addition to the base StreamChannel interface, it adds a
protocol getter that returns the negotiated protocol for the
socket, as well as closeCode and closeReason
getters that provide information about why the socket closed.
The channel's sink property is also special. It returns a
WebSocketSink, which is just like a StreamSink except that
its close() method supports optional closeCode and
closeReason parameters. These parameters allow the caller to signal to the
other socket exactly why they're closing the connection.
WebSocketChannel also works as a cross-platform implementation of the
WebSocket protocol. The WebSocketChannel.connect constructor
connects to a listening server using the appropriate implementation for the
platform. The WebSocketChannel() constructor takes an underlying
StreamChannel over which it communicates using the WebSocket
protocol. It also provides the static signKey() method to make it
easier to implement the initial WebSocket handshake. These are used in the
shelf_web_socket package to support WebSockets in a
cross-platform way.