Como lidar com desconexões e reconexões
Implemente a lógica do cliente e do servidor para detectar desconexões e tentar reconectar automaticamente.
Como lidar com desconexões e reconexões é uma aula grátis de WebSockets & Realtime Systems Programming no CoddyKit. Esta é a aula 1 de 4. Você pode ler a aula completa abaixo gratuitamente — depois pratica ao vivo no navegador com um editor de código integrado e um tutor de IA 24/7. Faz parte do caminho de aprendizado de WebSockets & Realtime Systems Programming, e seu progresso é sincronizado entre a web e o app CoddyKit. O curso de WebSockets & Realtime Systems Programming inclui 4 aulas no total.
Partes desta aula ainda não foram traduzidas e aparecem em inglês.
Why Connections Drop
In the real world, network connections aren't always perfect. WebSockets, despite being persistent, can break due to many reasons.
Ignoring these disconnections can lead to unresponsive applications and a poor user experience. This lesson explores how to gracefully handle these interruptions.
Causes of Connection Loss
What makes a WebSocket connection drop?
- Network Issues: Wi-Fi drops, internet outages, proxy problems.
- Server Restarts: The server application might restart for updates or maintenance.
- Client Offline: The user closes their browser, loses power, or puts their device to sleep.
- Idle Timeouts: Some proxies or firewalls might close idle connections.
Client Detects Disconnects
On the client side, the browser's native WebSocket API provides events to notify you about connection status changes.
The most important event for detecting a disconnection is the onclose event. It fires when the connection is either gracefully closed by the server or abruptly lost.
Simple Reconnect Attempt
When onclose fires, you can immediately try to reconnect. This simple approach works for temporary glitches but can be problematic.
Try running this basic client-side example:
let ws;
function connect() {
ws = new WebSocket("ws://localhost:8080");
ws.onopen = () => console.log("Connected!");
ws.onmessage = (event) => console.log("Received:", event.data);
ws.onerror = (error) => console.error("WebSocket Error:", error);
ws.onclose = () => {
console.log("Disconnected. Reconnecting...");
setTimeout(connect, 1000); // Try again in 1 second
};
}
connect();Why Simple Retries Fail
Continuously trying to reconnect immediately (e.g., every 1 second) can overwhelm both the client and the server.
- Client Resource Drain: Constant connection attempts consume CPU and network resources.
- Server Overload: If many clients disconnect and then flood the server with reconnect requests, it can lead to a Denial of Service (DoS) situation.
- No Backoff: It doesn't account for prolonged outages.
Smart Reconnection: Backoff
To prevent overloading and provide a better experience, we use reconnection backoff strategies.
A backoff strategy introduces delays between reconnection attempts, and these delays typically increase with each failed attempt. This gives the server time to recover and prevents a "thundering herd" problem.
Exponential Backoff Logic
Exponential backoff is a common and effective strategy. It means the delay between retries increases exponentially.
- First retry: 1 second
- Second retry: 2 seconds
- Third retry: 4 seconds
- Fourth retry: 8 seconds
You usually cap the maximum delay to prevent excessively long waits and add some random "jitter" to avoid synchronized retries.
Client with Exponential Backoff
Let's enhance our client-side code to use exponential backoff with a maximum delay and some random jitter. Try running it!
let ws;
let reconnectInterval = 1000; // Start with 1 second
const maxReconnectInterval = 30000; // Max 30 seconds
let reconnectTimer;
function connect() {
ws = new WebSocket("ws://localhost:8080");
ws.onopen = () => {
console.log("Connected!");
reconnectInterval = 1000; // Reset on successful connection
clearTimeout(reconnectTimer);
};
ws.onmessage = (event) => console.log("Received:", event.data);
ws.onerror = (error) => console.error("WebSocket Error:", error);
ws.onclose = () => {
console.log(`Disconnected. Retrying in ${reconnectInterval / 1000}s...`);
reconnectTimer = setTimeout(connect, reconnectInterval);
reconnectInterval = Math.min(reconnectInterval * 2, maxReconnectInterval);
// Add some random jitter (e.g., +/- 10%) for better distribution
reconnectInterval += (Math.random() - 0.5) * reconnectInterval * 0.2;
reconnectInterval = Math.floor(reconnectInterval);
};
}
connect();Server-Side Disconnects
The server also needs to know when a client disconnects. This is crucial for cleaning up resources, updating connected user lists, or stopping data streams for that client.
Using a library like ws in Node.js, the WebSocket server emits a 'close' event on the individual client connection object when it disconnects.
Server Cleanup on Disconnect
Here's a basic Node.js WebSocket server example showing how to handle client disconnections and remove them from an active connections list.
const WebSocket = require('ws');
const wss = new WebSocket.Server({ port: 8080 });
let clients = new Set();
wss.on('connection', function connection(ws) {
clients.add(ws);
console.log('Client connected. Total:', clients.size);
ws.on('message', function incoming(message) {
console.log('received: %s', message);
});
ws.on('close', function close() {
clients.delete(ws);
console.log('Client disconnected. Total:', clients.size);
});
ws.send('Welcome!');
});
console.log('WebSocket server started on port 8080');Check Your Understanding
Consider a client-side WebSocket application that needs to handle disconnections robustly.
Which of the following are good practices for implementing a reconnection strategy?
Recap: Robust Connections
We've explored how crucial it is to handle disconnections in realtime applications. Both client and server play a role in maintaining connection resilience.
- Clients use
oncloseto detect disconnections. - Exponential backoff with jitter and a max delay prevents server overload during reconnections.
- Servers use
on('close')to clean up resources when clients leave.
These strategies ensure your realtime apps remain responsive and reliable, even in unstable network conditions.
Perguntas Frequentes
A aula “Como lidar com desconexões e reconexões” é grátis?
Sim — o texto completo de “Como lidar com desconexões e reconexões” é grátis para ler aqui na web. Para praticá-la interativamente (um editor de código integrado e um tutor de IA 24/7) e desbloquear o restante do curso de WebSockets & Realtime Systems Programming, atualize para CoddyKit PRO. O curso de WebSockets & Realtime Systems Programming inclui 4 aulas no total.
O que vou aprender em “Como lidar com desconexões e reconexões”?
Implemente a lógica do cliente e do servidor para detectar desconexões e tentar reconectar automaticamente. Você pratica WebSockets & Realtime Systems Programming com código prático que executa diretamente no navegador, e um tutor de IA 24/7 responde suas dúvidas enquanto trabalha na aula.
Preciso ter experiência prévia para começar WebSockets & Realtime Systems Programming?
Nenhuma experiência prévia é necessária. WebSockets & Realtime Systems Programming no CoddyKit é estruturado para alunos iniciantes até avançados, então você pode começar aqui ou desde o início e aprender no seu ritmo. Esta é a aula 1 de 4.
Quanto tempo leva a aula “Como lidar com desconexões e reconexões”?
A maioria das aulas CoddyKit leva cerca de 5–10 minutos. Cada uma é compacta e interativa, então você faz progresso constante e retoma exatamente de onde parou entre web e app.
Posso escrever e executar código nesta aula de WebSockets & Realtime Systems Programming?
Sim. Cada aula de WebSockets & Realtime Systems Programming inclui um editor de código integrado, então você escreve e executa código real direto no navegador e recebe feedback de IA instantaneamente — nenhuma configuração local necessária.
Todas as aulas deste curso
- Como lidar com desconexões e reconexões
- Propagação e recuperação robustas de erros
- Sinais de atividade e manutenção da conexão
- Confirmação de mensagens e garantias de entrega