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Communicate with WebSockets

In addition to normal HTTP requests, you can connect to servers using WebSockets. WebSockets allow for two-way communication with a server without polling.

In this example, connect to a test WebSocket server sponsored by Lob.com. The server sends back the same message you send to it. This recipe uses the following steps:

  1. Connect to a WebSocket server.
  2. Listen for messages from the server.
  3. Send data to the server.
  4. Close the WebSocket connection.

1. Connect to a WebSocket server

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The web_socket_channel package provides the tools you need to connect to a WebSocket server.

The package provides a WebSocketChannel that allows you to both listen for messages from the server and push messages to the server.

In Flutter, use the following line to create a WebSocketChannel that connects to a server:

dart 
final channel = WebSocketChannel.connect(  Uri.parse('wss://echo.websocket.events'), );

2. Listen for messages from the server

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Now that you've established a connection, listen to messages from the server.

After sending a message to the test server, it sends the same message back.

In this example, use a StreamBuilder widget to listen for new messages, and a Text widget to display them.

dart 
StreamBuilder(  stream: channel.stream,  builder: (context, snapshot) {  return Text(snapshot.hasData ? '${snapshot.data}' : '');  }, ),

How this works

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The WebSocketChannel provides a Stream of messages from the server.

The Stream class is a fundamental part of the dart:async package. It provides a way to listen to async events from a data source. Unlike Future, which returns a single async response, the Stream class can deliver many events over time.

The StreamBuilder widget connects to a Stream and asks Flutter to rebuild every time it receives an event using the given builder() function.

3. Send data to the server

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To send data to the server, add() messages to the sink provided by the WebSocketChannel.

dart 
channel.sink.add('Hello!');

How this works

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The WebSocketChannel provides a StreamSink to push messages to the server.

The StreamSink class provides a general way to add sync or async events to a data source.

4. Close the WebSocket connection

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After you're done using the WebSocket, close the connection:

dart 
channel.sink.close();

Complete example

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dart 
import 'package:flutter/material.dart'; import 'package:web_socket_channel/web_socket_channel.dart'; ​ void main() => runApp(const MyApp()); ​ class MyApp extends StatelessWidget {  const MyApp({super.key}); ​  @override  Widget build(BuildContext context) {  const title = 'WebSocket Demo';  return const MaterialApp(  title: title,  home: MyHomePage(title: title),  );  } } ​ class MyHomePage extends StatefulWidget {  const MyHomePage({super.key, required this.title}); ​  final String title; ​  @override  State<MyHomePage> createState() => _MyHomePageState(); } ​ class _MyHomePageState extends State<MyHomePage> {  final TextEditingController _controller = TextEditingController();  final _channel = WebSocketChannel.connect(  Uri.parse('wss://echo.websocket.events'),  ); ​  @override  Widget build(BuildContext context) {  return Scaffold(  appBar: AppBar(title: Text(widget.title)),  body: Padding(  padding: const EdgeInsets.all(20),  child: Column(  crossAxisAlignment: CrossAxisAlignment.start,  children: [  Form(  child: TextFormField(  controller: _controller,  decoration: const InputDecoration(labelText: 'Send a message'),  ),  ),  const SizedBox(height: 24),  StreamBuilder(  stream: _channel.stream,  builder: (context, snapshot) {  return Text(snapshot.hasData ? '${snapshot.data}' : '');  },  ),  ],  ),  ),  floatingActionButton: FloatingActionButton(  onPressed: _sendMessage,  tooltip: 'Send message',  child: const Icon(Icons.send),  ), // This trailing comma makes auto-formatting nicer for build methods.  );  } ​  void _sendMessage() {  if (_controller.text.isNotEmpty) {  _channel.sink.add(_controller.text);  }  } ​  @override  void dispose() {  _channel.sink.close();  _controller.dispose();  super.dispose();  } }

Web sockets demo

Unless stated otherwise, the documentation on this site reflects Flutter 3.38.1. Page last updated on 2025-5-19. View source or report an issue.