WebSocket endpoint creation in FastAPI

Introduction

WebSocket endpoints let your app talk to users instantly without waiting. This is great for live chats or real-time updates.

You want to build a live chat app where messages appear instantly.

You need to show real-time notifications or alerts to users.

You want to update a dashboard with live data without refreshing the page.

You are making a multiplayer game that needs fast communication.

You want to stream data continuously, like stock prices or sensor info.

Syntax

FastAPI

from fastapi import FastAPI, WebSocket

app = FastAPI()

@app.websocket("/ws")
async def websocket_endpoint(websocket: WebSocket):
    await websocket.accept()
    while True:
        data = await websocket.receive_text()
        await websocket.send_text(f"Message text was: {data}")

Use @app.websocket("/path") to create a WebSocket endpoint.

Call await websocket.accept() to accept the connection before communication.

Examples

A simple WebSocket that accepts one message and replies back.

FastAPI

from fastapi import FastAPI, WebSocket

app = FastAPI()

@app.websocket("/chat")
async def chat(websocket: WebSocket):
    await websocket.accept()
    data = await websocket.receive_text()
    await websocket.send_text(f"You said: {data}")

This endpoint echoes back every message it receives in a loop.

FastAPI

from fastapi import FastAPI, WebSocket

app = FastAPI()

@app.websocket("/echo")
async def echo(websocket: WebSocket):
    await websocket.accept()
    while True:
        data = await websocket.receive_text()
        await websocket.send_text(data)

Sample Program

This program creates a WebSocket endpoint at /ws. It accepts connections, waits for text messages, and sends back a reply showing what was received.

FastAPI

from fastapi import FastAPI, WebSocket

app = FastAPI()

@app.websocket("/ws")
async def websocket_endpoint(websocket: WebSocket):
    await websocket.accept()
    while True:
        data = await websocket.receive_text()
        await websocket.send_text(f"Message text was: {data}")

Important Notes

Always call await websocket.accept() to start the connection.

Use await websocket.receive_text() to get messages from the client.

Use await websocket.send_text() to send messages back.

Summary

WebSocket endpoints let your app communicate instantly with users.

Use @app.websocket decorator to create them in FastAPI.

Remember to accept connections and handle messages asynchronously.