advanced patterns when using AsyncIO with WebSocket in Python 3.9 and FastAPI
Does anyone know how to I'm working on a project and hit a roadblock. This might be a silly question, but I'm working with an unexpected scenario while trying to implement WebSocket connections using FastAPI and AsyncIO in Python 3.9. I have set up a basic WebSocket endpoint, but when I try to connect, I receive a `websockets.exceptions.InvalidStatusCode: 400` behavior, which indicates a bad request. Here’s a simplified version of my code: ```python from fastapi import FastAPI, WebSocket from fastapi.responses import HTMLResponse app = FastAPI() html = """ <!DOCTYPE html> <html lang="en"> <head> <title>WebSocket Test</title> </head> <body> <h1>WebSocket Test</h1> <button onclick="connect()">Connect</button> <script> var socket; function connect() { socket = new WebSocket('ws://localhost:8000/ws'); socket.onmessage = function(event) { console.log(event.data); }; } </script> </body> </html> """ @app.get('/') async def get(): return HTMLResponse(html) @app.websocket('/ws') async def websocket_endpoint(websocket: WebSocket): await websocket.accept() await websocket.send_text('Hello, WebSocket!') await websocket.close() ``` When I run the FastAPI app using `uvicorn main:app --reload`, the server starts without any errors. However, upon trying to connect from my HTML page, I notice that it fails with the mentioned behavior. I ensured that I am navigating to the correct URL (`http://localhost:8000/`). I’ve double-checked my FastAPI version (0.68.1) and Uvicorn version (0.15.0), and I also tried using the `ws://` protocol in the JavaScript, which I believe is correct for WebSocket connections. I’ve looked through the FastAPI documentation but haven’t found anything that might explain this behavior. Is there something obvious that I might be missing, or could it be a configuration scenario? Any insights on how to resolve this would be greatly appreciated. This is for a web app running on Windows 10. Any pointers in the right direction? The project is a mobile app built with Python. I'm working on a REST API that needs to handle this. What are your experiences with this? I'd really appreciate any guidance on this.