FastAPI Yieldable Response

A middleware for FastAPI that sends early responses from route handlers.

Overview

FastAPI Yieldable Response allows you to send immediate responses to clients while continuing to execute background processing in your route handlers. This is particularly useful when you want to:

• Send quick acknowledgments to clients before performing time-consuming operations
• Improve perceived response times by returning data immediately
• Execute cleanup or logging tasks after the response has been sent

Installation

pip install fastapi_yieldable_response

Quick Start

from fastapi import FastAPI
from fastapi_yieldable_response import yieldable_response

app = FastAPI()

@app.get("/")
@yieldable_response
async def root():
    # This response is sent immediately to the client
    yield {"message": "Hello!"}
    
    # This code runs in the background after the response is sent
    import time
    time.sleep(2)
    print("Background task completed!")

How It Works

The @yieldable_response decorator transforms your route handler into a function that:

1. Immediate Response: The first yield statement sends an immediate response to the client
2. Background Execution: Any code after the yield continues executing as a background task
3. Automatic Cleanup: Uses FastAPI's BackgroundTasks to ensure proper resource management

Features

•  Zero Dependencies: Only requires FastAPI (no additional dependencies)
•  Async/Sync Support: Works with both async and sync route handlers
•  Type Safety: Maintains original function signatures and type hints
•  FastAPI Integration: Uses FastAPI's built-in BackgroundTasks system
•  Simple API: Just add the decorator to your existing routes

Usage Examples

Async Route Handler

@app.get("/async-example")
@yieldable_response
async def async_example():
    yield {"status": "processing", "id": 123}
    
    # Background processing
    await some_async_operation()
    await send_notification()

Sync Route Handler

@app.get("/sync-example/{item_id}")
@yieldable_response
def sync_example(item_id: str):
    yield {"message": f"Processing item {item_id}"}
    
    # Background processing
    process_item(item_id)
    log_operation(item_id)

With Path Parameters

@app.get("/users/{user_id}")
@yieldable_response
async def get_user(user_id: int):
    # Send immediate response
    yield {"user_id": user_id, "status": "found"}
    
    # Log access in background
    await log_user_access(user_id)
    await update_analytics(user_id)

Requirements

• Python 3.10+
• FastAPI 0.68.0+

License

MIT License - see LICENSE file for details.

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.

Repository

• Homepage: https://github.com/lucamattiazzi/fastapi_yieldable_response
• Issues: https://github.com/lucamattiazzi/fastapi_yieldable_response/issues