How to Send Progress Updates from a FastAPI Backend Server to the Client

What will you learn?

In this comprehensive tutorial, you will master the art of sending real-time progress updates from a FastAPI backend server to the client using WebSocket technology. You will understand the importance of keeping users informed during long-running tasks and learn how to implement efficient communication between the server and client for an enhanced user experience.

Introduction to the Problem and Solution

When developing web applications that involve time-consuming operations, it is vital to provide users with feedback on the progress of their requests. Without timely updates, users may perceive the application as unresponsive or malfunctioning. To address this challenge, we will delve into setting up a FastAPI backend server capable of delivering live progress updates to the client using WebSockets.

By leveraging WebSocket technology, we establish a bidirectional communication channel between the server and client, enabling seamless data exchange in real-time. Through this guide, you will discover how WebSockets can be integrated into your FastAPI application and learn how to send periodic messages from the server to the client.


from fastapi import FastAPI, WebSocket
import asyncio

app = FastAPI()

async def websocket_endpoint(websocket: WebSocket):
    await websocket.accept()
    for i in range(100):
        await websocket.send_json({"progress": i+1})
        await asyncio.sleep(0.1)  # Simulating a task delay
    await websocket.close()

# Copyright PHD


In this solution:

  • FastAPI Application Setup: Initialize a FastAPI instance.
  • WebSocket Route: Define a route at /ws for WebSocket connections.
  • Accepting Connections: Accept incoming WebSocket connections.
  • Sending Progress Updates: Send JSON objects containing progress updates.
  • Closing Connection: Close the WebSocket connection after completing all iterations.

The asynchronous nature of async/await ensures non-blocking execution, allowing concurrent tasks without hindering performance.

    1. What is FastAPI?

      • FastAPI is a modern Python web framework for building APIs based on standard Python type hints.
    2. What are WebSockets?

      • WebSockets facilitate full-duplex communication over a single TCP connection, enabling independent data transmission between clients and servers.
    3. Why use WebSockets instead of HTTP polling?

      • WebSockets offer efficient real-time bidirectional communication without excessive network traffic associated with multiple HTTP requests, ideal for constant data exchange scenarios like live feeds or chat systems.
    4. Can I send binary data over Websockets in FastAPI?

      • Yes! Utilize websocket.send_bytes(data) instead of send_json.
    5. Do all browsers support Websockets?

      • Most modern browsers support Websockets; however, always verify browser compatibility during development.
    6. Is it necessary to use async functions with FastAPI?

      • While not mandatory for all operations within FastAPI applications, asynchronous functions enhance concurrent task handling efficiency, especially for I/O-bound tasks.
    7. How do I handle errors in WebSocket connections in FastAPI?

      • Implement error handling within your endpoint function using try-except blocks around critical sections prone to errors.
    8. Can I integrate Websockets with frontend frameworks like React or Angular?

      • Absolutely! Libraries such as Socket.IO provide clients for various frontend frameworks facilitating seamless integration.
    9. Are there any limitations on message size when using Websockets?

      • Though protocols do not impose explicit limits on message size, practical constraints may exist based on browser/server configurations and system memory restrictions.
    10. How secure are WebSocket connections?

      • WebSocket connections initiate with an HTTP handshake that upgrades securely if both parties agree; ensuring encryption through wss:// URLs akin HTTPS enhances security measures.

Integrating real-time communications into your applications via technologies like WebSockets within robust frameworks such as FastAPI offers a simple yet powerful solution for enhancing user experience significantly while enabling seamless operation behind-the-scenes during lengthy tasks.

Remember: Prioritize thorough testing across diverse environments focusing on security aspects to ensure smooth deployments in production environments while upholding high standards of user privacy protection and application integrity.

Happy coding!

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