The web_socket_channel
package provides 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 should be imported with the prefix status
.
import 'package:web_socket_channel/web_socket_channel.dart';
import 'package:web_socket_channel/status.dart' as status;
main() async {
var channel = IOWebSocketChannel.connect(Uri.parse('ws://localhost:1234'));
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.