Sockets in Dart - Client/Server Communication

What are Sockets?

Sockets are communication endpoints that let different processes exchange data, whether on the same machine or over a network. In Dart, socket-based communication is fundamental for client-server applications, real-time chat, multiplayer games and more.

Bidirectional Communication

Client and server can send and receive data simultaneously

Real Time

Instant communication without needing to refresh

Client/Server Architecture

Multiple clients can connect to the same server

Socket Architecture

Client

Server

Solicitud del cliente

Respuesta del servidor

Necessary Imports:

import 'dart:io';      // Para sockets TCPimport 'dart:convert';  // Para codificación/decodificación

Creating a Socket Server

1. Import dependencies

We import the necessary libraries to handle sockets and input/output.

2. Bind the server

We specify the IP address and port where the server will listen for connections.

3. Handle connections

We listen for incoming connections and handle the received data.

4. Handle multiple clients

We keep a list of connected clients for broadcasting.

Complete Server:

import 'dart:io';

void main() async {
  // Paso 2: Vincular servidor al puerto 3456  final server = await ServerSocket.bind(
    InternetAddress.loopbackIPv4, // 127.0.0.1
    3456
  );
  
  List clientes = [];
  
  print('Servidor iniciado en ${server.address.address}:${server.port}');

  // Paso 3: Escuchar conexiones entrantes  server.listen((Socket cliente) {
    print("Cliente conectado desde ${cliente.remoteAddress.address}");
    
    // Enviar mensaje de bienvenida    cliente.write("¡Bienvenido a este servidor! \n");
    
    // Paso 4: Añadir cliente a la lista    clientes.add(cliente);
    
    // Escuchar mensajes del cliente    cliente.listen(
      (List data) {
        String mensaje = String.fromCharCodes(data).trim();
        print('Mensaje recibido: ${mensaje}');
        
        // Responder al cliente        cliente.write("Mensaje recibido \n");
        
        // Broadcast a otros clientes        for (var user in clientes) {
          if (user != cliente) {
            user.write("Cliente dice: \$mensaje \n");
          }
        }
        
        // Comando especial 'info'        if (mensaje == "info") {
          cliente.write("Clientes conectados: \${clientes.length} \n");
        }
      },
      
      onDone: () {
        print('Cliente desconectado');
        clientes.remove(cliente);
      },
      
      onError: (error) {
        print("Error: ${error}");
        clientes.remove(cliente);
      },
    );
  });
}

Creating a Socket Client

1. Connect to the server

We establish a connection to the server using an IP address and port.

2. Configure listeners

We set up handlers to receive data from the server.

3. Read user input

We capture console input to send to the server.

4. Handle disconnection

We implement logic to close the connection cleanly.

Complete Client:

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

void main() async {
  // Paso 1: Conectar al servidor  final socket = await Socket.connect('127.0.0.1', 3456);
  
  print("Conectado al servidor");
  socket.write("Cliente conectado");

  // Paso 2: Escuchar respuestas del servidor  socket.listen(
    (List data) {
      String mensaje = String.fromCharCodes(data).trim();
      print("Server: \${mensaje}");
    },
    
    onDone: () {
      print('Conexión perdida con el servidor');
      exit(0);
    },
    
    onError: (error) {
      print("Error: ${error}");
    },
  );

  // Paso 3: Leer entrada del usuario  stdin.transform(utf8.decoder).listen((String texto) {
    texto = texto.trim();
    
    // Paso 4: Manejar comando 'exit'    if (texto == 'exit') {
      print('Desconectando...');
      socket.write('Cliente cerró la conexión');
      socket.close();
      exit(0);
    } else if (texto.isNotEmpty) {
      // Enviar mensaje al servidor      socket.write(texto);
    }
  });
}

Socket Chat Simulator

Server Status:

Offline

Clientes Conectados:

0

Message Type:

Message:

Real-Time Logs:

Simulación de Sockets

— □ ×

[12:00:00] SERVIDOR: Servidor iniciado en 127.0.0.1:3456

[12:00:05] SISTEMA: Usa 'info' para ver clientes conectados

$

Connected Clients

Key Properties and Methods

ServerSocket.bind()

Creates and binds a server socket to an address and port

InternetAddress int port Future

Socket.connect()

Connects a client to a server socket

String host int port Future

.listen()

Listens for incoming data on the socket

Function callback onDone onError

.write()

Sends data through the socket

String data List data

.close()

Closes the socket's connection

void

.remoteAddress

Address of the connected client

InternetAddress

Common Use Cases

💬 Real-Time Chat

Instant messaging applications with multiple connected users.

🎮 Multiplayer Games

Real-time state synchronization between players.

📊 Real-Time Monitoring

Dashboard systems that show instantly updated data.

🤖 Communication between Microservices

Data exchange between different components of a distributed system.

Best Practices

🔒 Error Handling

Always implement onError and onDone to handle unexpected disconnections.

💾 Resource Cleanup

Remove disconnected clients from the list to avoid memory leaks.

📨 Data Encoding

Use utf8.decoder/encoder to correctly handle special characters.

⚡ Async/Await

Use asynchronous programming to avoid blocking the main thread.

Exercises to Practice

Exercise 1: Basic Chat

Modify the server so it sends the sender's client name along with each message to all others.

Hint: Store names alongside the sockets and add the name to the broadcast message

Exercise 2: Special Commands

Add commands like "/users" to list users and "/pm [user]" for private messages.

Hint: Check if the message starts with "/" and process it as a command

Exercise 3: Server with Authentication

Implement a system where clients must authenticate with a username/password before chatting.

Hint: When connecting, request credentials before adding to the general list

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