Dart Socket

last modified April 4, 2025

The Socket class in Dart provides TCP network communication functionality. It's part of the dart:io library and enables both client and server network operations.

Sockets support bidirectional communication between endpoints. They can transfer raw bytes or text data over TCP/IP networks with various events.

Basic Definition

A Socket represents a TCP network connection between two endpoints. It provides streams for reading and writing data asynchronously.

Key features include event-based data handling, connection management, and support for both IPv4 and IPv6 addresses. Sockets work with Streams.

Basic Socket Client

This example shows a simple TCP client that connects to a server.

import 'dart:io';

void main() async {
  try {
    var socket = await Socket.connect('localhost', 8080);
    print('Connected to server');
    
    socket.write('Hello from Dart client');
    socket.destroy();
  } catch (e) {
    print('Error: $e');
  }
}

We create a socket connection to localhost on port 8080. After sending a message, we close the connection. Error handling catches connection issues.

$ dart main.dart
Connected to server

Socket with Data Listening

This example demonstrates reading data from a socket connection.

import 'dart:io';
import 'dart:convert';

void main() async {
  var socket = await Socket.connect('example.com', 80);
  
  socket.write('GET / HTTP/1.1\r\nHost: example.com\r\n\r\n');
  
  socket.listen(
    (List<int> data) {
      print(utf8.decode(data));
    },
    onDone: () {
      print('Connection closed');
      socket.destroy();
    }
  );
}

We connect to a web server and send an HTTP request. The listen callback handles incoming data. The connection closes automatically when complete.

$ dart main.dart
HTTP/1.1 200 OK
Content-Type: text/html; charset=UTF-8
...
Connection closed

Socket Server

This example creates a simple TCP server that accepts client connections.

import 'dart:io';

void main() async {
  var server = await ServerSocket.bind('127.0.0.1', 8080);
  print('Server listening on ${server.address}:${server.port}');
  
  server.listen((Socket socket) {
    socket.write('Hello from server!\n');
    socket.close();
  });
}

The server binds to localhost port 8080. For each client connection, it sends a greeting and closes. ServerSocket manages multiple clients.

$ dart main.dart
Server listening on 127.0.0.1:8080

Bidirectional Communication

This example shows a chat-like bidirectional socket communication.

import 'dart:io';
import 'dart:async';

void main() async {
  var socket = await Socket.connect('localhost', 8080);
  
  socket.listen(
    (data) => print('Server: ${String.fromCharCodes(data)}'),
    onDone: () => socket.destroy()
  );
  
  var input = stdin.transform(utf8.decoder);
  await for (var message in input) {
    socket.write(message);
  }
}

The client connects to a server and listens for messages. It also reads user input from console and sends it to the server. UTF-8 handles text.

$ dart main.dart
Hello
Server: Hi there!
How are you?
Server: I'm fine, thanks!

Socket with Timeout

This example demonstrates socket connection with timeout handling.

import 'dart:io';

void main() async {
  try {
    var socket = await Socket.connect('localhost', 8080)
      .timeout(Duration(seconds: 5));
    
    socket.write('Quick message');
    await socket.flush();
    socket.destroy();
    
    print('Message sent successfully');
  } on SocketException catch (e) {
    print('Socket error: $e');
  } on TimeoutException {
    print('Connection timed out');
  }
}

The connection attempt will timeout after 5 seconds if unsuccessful. We handle both socket errors and timeout exceptions separately.

$ dart main.dart
Connection timed out

Best Practices

• Error handling: Always handle SocketException and other errors
• Resource cleanup: Call destroy() or close() when done
• Buffering: Use flush() for important writes
• Encoding: Specify text encoding when needed
• Timeouts: Set reasonable timeouts for operations

Source

Dart Socket Documentation

This tutorial covered Dart's Socket class with practical examples showing client/server communication, data handling, and error management.

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

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