FastAPI Backend Development Bootcamp · Lección

Implementación de WebSockets en FastAPI

Aprenda a añadir endpoints WebSocket a su aplicación FastAPI y a gestionar las conexiones.

Implementación de WebSockets en FastAPI es una lección gratuita de FastAPI Backend Development Bootcamp en CoddyKit. Esta es la lección 2 de 4. Puedes leer la lección completa abajo gratuitamente — luego la practicas en el navegador con un editor de código integrado y un tutor de IA 24/7. Forma parte de la ruta de aprendizaje de FastAPI Backend Development Bootcamp, y tu progreso se sincroniza en la web y la app de CoddyKit. El curso de FastAPI Backend Development Bootcamp incluye 4 lecciones en total.

Partes de esta lección aún no han sido traducidas y se muestran en inglés.

Real-time with FastAPI WebSockets

Welcome to implementing WebSockets with FastAPI! WebSockets provide a persistent, full-duplex communication channel between a client and a server.

Full-duplex: Both client and server can send and receive messages simultaneously.
Real-time: Ideal for applications needing instant updates, like chat, live dashboards, or gaming.

FastAPI has excellent built-in support for WebSockets, leveraging Python's async/await features.

Defining a WebSocket Endpoint

Just like HTTP endpoints, you define WebSocket endpoints using a decorator. Instead of @app.get() or @app.post(), you use @app.websocket().

Your endpoint function must be async def and accept a websocket: WebSocket parameter. This WebSocket object is your primary tool for interaction.

The first step inside your function is always to await websocket.accept() to establish the connection.

Your First WebSocket Connection

Let's create our first WebSocket endpoint. This simple example accepts a connection, sends a welcome message, and then closes the connection.

Notice the @app.websocket("/ws") decorator and the async def function, which are key for WebSocket handling.

Try running this example and observe the connection:

from fastapi import FastAPI, WebSocket

app = FastAPI()

@app.websocket("/ws")
async def websocket_endpoint(websocket: WebSocket):
    await websocket.accept()
    await websocket.send_text("Welcome! Connection established.")
    await websocket.close()

Handling WebSocket Disconnections

WebSocket connections can be interrupted for various reasons (client closes tab, network error). It's crucial to handle these disconnections gracefully.

FastAPI raises a WebSocketDisconnect exception when a client disconnects. You can catch this exception to perform cleanup tasks, like removing the client from a list of active connections.

Wrap your WebSocket communication logic in a try...except WebSocketDisconnect block.

Receiving Messages from Clients

Once connected, your server can receive messages from the client. The WebSocket object provides methods for this:

await websocket.receive_text(): For receiving string data.
await websocket.receive_bytes(): For receiving binary data.
await websocket.receive_json(): For receiving JSON data (requires python-multipart).

These operations are asynchronous, so always use await.

Echoing Client Messages Back

This example demonstrates a simple 'echo' server. It accepts a connection, then continuously receives messages from the client and sends them back.

The while True loop keeps the connection open, and the try...except WebSocketDisconnect handles when the client leaves.

from fastapi import FastAPI, WebSocket, WebSocketDisconnect

app = FastAPI()

@app.websocket("/ws/echo")
async def websocket_echo(websocket: WebSocket):
    await websocket.accept()
    try:
        while True:
            data = await websocket.receive_text()
            print(f"Received from client: {data}")
            await websocket.send_text(f"Server echoed: {data}")
    except WebSocketDisconnect:
        print("Client disconnected.")

Sending Messages to Clients

Similarly, your server can send messages to the client. The WebSocket object offers:

await websocket.send_text("your message"): To send string data.
await websocket.send_bytes(b"your bytes"): To send binary data.
await websocket.send_json({"key": "value"}): To send JSON data.

Remember to await these calls. It's common to send a response right after receiving a message.

Working with JSON Data

For structured data, sending and receiving JSON is preferred. FastAPI's WebSocket object handles serialization/deserialization for you.

Sending: Pass a Python dict to send_json().
Receiving: receive_json() returns a Python dict.

This simplifies data exchange compared to manually parsing strings.

Simple Connection Manager

For applications with multiple clients, you'll need to manage active connections. A common pattern is to use a class to keep track of all connected WebSocket objects.

This manager can then be used to add/remove connections and send messages to specific clients or broadcast to all.

from fastapi import WebSocket

class ConnectionManager:
    def __init__(self):
        self.active_connections: list[WebSocket] = []

    async def connect(self, websocket: WebSocket):
        await websocket.accept()
        self.active_connections.append(websocket)

    def disconnect(self, websocket: WebSocket):
        self.active_connections.remove(websocket)

    async def send_personal_message(self, message: str, websocket: WebSocket):
        await websocket.send_text(message)

# In a real app, you'd integrate 'manager' into your FastAPI endpoint
manager = ConnectionManager()

WebSocket Interaction Check

You've learned the basics of setting up and interacting with WebSocket connections in FastAPI.

Let's check your understanding of accepting new connections.

Recap: Implementing WebSockets

You've successfully learned how to implement WebSockets in FastAPI!

Use @app.websocket() to define endpoints.
Always await websocket.accept() to establish the connection.
Handle disconnections with try...except WebSocketDisconnect.
Use await websocket.receive_text() and await websocket.send_text() for communication.
For structured data, send_json() and receive_json() are your friends.

Next, you'll build a real-time chat application to put these concepts into practice!

Preguntas frecuentes

¿La lección «Implementación de WebSockets en FastAPI» es gratis?

Sí — el texto completo de «Implementación de WebSockets en FastAPI» es gratis para leer aquí en la web. Para practicarla de forma interactiva (editor de código integrado y tutor de IA 24/7) y desbloquear el resto del curso de FastAPI Backend Development Bootcamp, actualiza a CoddyKit PRO. El curso de FastAPI Backend Development Bootcamp incluye 4 lecciones en total.

¿Qué aprenderé en «Implementación de WebSockets en FastAPI»?

Aprenda a añadir endpoints WebSocket a su aplicación FastAPI y a gestionar las conexiones. Practicas FastAPI Backend Development Bootcamp con código real que ejecutas directamente en el navegador, y un tutor de IA 24/7 responde tus preguntas mientras trabajas en la lección.

¿Necesito experiencia previa para empezar FastAPI Backend Development Bootcamp?

No se requiere experiencia previa. FastAPI Backend Development Bootcamp en CoddyKit está estructurado para principiantes hasta estudiantes avanzados, así que puedes empezar aquí o desde el inicio y avanzar a tu ritmo. Esta es la lección 2 de 4.

¿Cuánto tiempo toma la lección «Implementación de WebSockets en FastAPI»?

La mayoría de las lecciones de CoddyKit toman alrededor de 5–10 minutos. Cada una es compacta e interactiva, así que avanzas constantemente y retomas exactamente por donde dejaste en la web y la app.

¿Puedo escribir y ejecutar código en esta lección de FastAPI Backend Development Bootcamp?

Sí. Cada lección de FastAPI Backend Development Bootcamp incluye un editor de código integrado, así que escribes y ejecutas código real directamente en tu navegador y obtienes retroalimentación instantánea de IA — sin configuración local necesaria.

Todas las lecciones de este curso

Fundamentos del protocolo WebSocket
Implementación de WebSockets en FastAPI
Construcción de una aplicación de chat en tiempo real
Escalado de WebSockets con un backplane Pub/Sub

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