Python FastAPI Websocket – The Ultimate Guide for Beginners

Introduction

Python is one of the most popular programming languages in the world. It is efficient, easy to learn, and has a vast library of modules that make it ideal for web development. FastAPI is a modern, fast (high-performance), web framework for building APIs with Python 3.7+ based on standard Python type hints. It is designed to be easy to use and to provide high performance. Websockets are a powerful tool for real-time communication between a client and a server. In this article, we will explore how to use Python FastAPI Websocket.

What is Python FastAPI Websocket?

Python FastAPI Websocket is a combination of Python FastAPI and websockets. FastAPI is a modern, fast (high-performance), web framework for building APIs with Python 3.7+ based on standard Python type hints. It is designed to be easy to use and to provide high performance. Websockets are a powerful tool for real-time communication between a client and a server. Together, they make a great combination for building real-time applications.

Setting up the Environment

To get started with Python FastAPI Websocket, you need to have Python 3.7+ installed on your machine. Once you have installed Python, you can use pip to install the required libraries. Here are the steps:

  1. Install FastAPI: pip install fastapi
  2. Install uvicorn: pip install uvicorn[standard]
  3. Install websockets: pip install websockets

Once you have installed these libraries, you are ready to start building your application.

Creating a Basic FastAPI Websocket Application

Here are the steps to create a basic FastAPI Websocket application:

  1. Create a new Python file, for example app.py.
  2. Import the required libraries:
  • from fastapi import FastAPI
  • import websockets
  • Create a FastAPI instance:
    • app = FastAPI()
  • Define a websocket route:
    • @app.websocket(“/ws”)
    • async def websocket_endpoint(websocket: websockets.WebSocketServerProtocol)
    • : await websocket.send(“Hello, world!”)
  • Start the application:
    • if __name__ == “__main__”:
    • uvicorn.run(app, host=”0.0.0.0″, port=8000)

    Now, if you run this application, it will start a WebSocket server that listens on port 8000. When a client connects to the /ws route, it will receive a “Hello, world!” message.

    Handling Incoming Messages

    Now that we have a basic application that can send messages, let’s see how we can handle incoming messages from the client:

    1. Modify the websocket route to handle incoming messages:
    • @app.websocket(“/ws”)
    • async def websocket_endpoint(websocket: websockets.WebSocketServerProtocol)
    • : await websocket.send(“Hello, world!”)
    • while True:
    • message = await websocket.recv()
    • await websocket.send(f”Message received: {message}”)

    Now, when a client sends a message to the server, the server will receive it and send back a response message.

    Handling Disconnections

    When a client disconnects from the server, we need to handle this event to avoid errors. Here’s how:

    1. Add a try-except block around the message handling code:
    • try:
    • while True:
    • message = await websocket.recv()
    • await websocket.send(f”Message received: {message}”)
    • except websockets.exceptions.ConnectionClosed:
    • print(“Connection closed”)

    Now, when a client disconnects from the server, the server will catch the ConnectionClosed exception and print a message to the console.

    Adding Authentication

    Now that we have a basic WebSocket server that can handle incoming messages, let’s see how we can add authentication to it:

    1. Create a function to authenticate the client:
    • async def authenticate(websocket: websockets.WebSocketServerProtocol) -> bool:
    • # TODO: Implement authentication logic here
    • return True
  • Modify the websocket route to authenticate the client:
    • @app.websocket(“/ws”)
    • async def websocket_endpoint(websocket: websockets.WebSocketServerProtocol)
    • : authenticated = await authenticate(websocket)
    • if authenticated:
    • await websocket.send(“Hello, world!”)
    • try:
    • while True:
    • message = await websocket.recv()
    • await websocket.send(f”Message received: {message}”)
    • except websockets.exceptions.ConnectionClosed:
    • print(“Connection closed”)

    Now, when a client connects to the server, the server will authenticate the client before sending any messages.

    Using Websocket Middleware

    FastAPI supports middleware, which allows you to modify incoming and outgoing requests and responses. We can use middleware to add headers, log requests, and more. Here’s how to use middleware with FastAPI Websocket:

    1. Create a middleware function:
    • async def middleware(websocket: websockets.WebSocketServerProtocol, next_handler):
    • # TODO: Implement middleware logic here
    • return await next_handler()
  • Add the middleware to the application:
    • app.add_websocket_middleware(middleware)

    Now, when a client connects to the server, the middleware function will be called before the websocket_endpoint function. This allows you to modify the websocket connection before it is established.

    Conclusion

    Python FastAPI Websocket is a powerful tool for building real-time applications. With FastAPI, you can easily create a high-performance WebSocket server that can handle incoming messages and authenticate clients. By using middleware, you can add custom logic to the websocket connection. FastAPI Websocket is a great choice for building real-time applications with Python.

    FAQ

    What is Python FastAPI?

    Python FastAPI is a modern, fast (high-performance), web framework for building APIs with Python 3.7+ based on standard Python type hints. It is designed to be easy to use and to provide high performance.

    What are Websockets?

    Websockets are a powerful tool for real-time communication between a client and a server. They allow bidirectional communication between the client and server in real-time.

    What is the difference between HTTP and Websockets?

    HTTP is a request-response protocol, where a client sends a request to a server and the server responds with a response. Websockets, on the other hand, allow bidirectional communication between the client and server in real-time.