How Can httpx Enhance Safe and Efficient Downstream HTTP Requests in FastAPI?

Making Downstream HTTP Requests Safely in FastAPI Using httpx

When making HTTP requests in FastAPI using the standard Python requests library, thread safety becomes a concern amidst concurrent requests. To address this issue effectively, consider employing httpx, a library that offers both thread safety and improved performance.

Using the httpx Async API

httpx comes with an asynchronous API, allowing you to easily make HTTP requests while efficiently handling multiple concurrent tasks. Here's an example of its usage within a FastAPI endpoint:

from httpx import AsyncClient
from fastapi import FastAPI, Request

app = FastAPI()

@app.on_event("startup")
async def startup_event():
    app.state.client = AsyncClient()

@app.on_event('shutdown')
async def shutdown_event():
    await app.state.client.aclose()

@app.get('/')
async def home(request: Request):
    client = request.state.client
    req = client.build_request('GET', 'https://www.example.com')
    r = await client.send(req, stream=True)
    return StreamingResponse(r.aiter_raw(), background=BackgroundTask(r.aclose))

In this example:

• startup_event() initializes and stores a shared httpx AsyncClient in the app's state.
• shutdown_event() gracefully closes the client upon application shutdown.
• home() performs an HTTP request to https://www.example.com using the shared client, making use of streaming to efficiently handle large responses.

Using the httpx Synchronous API

If defining endpoints with async def is not desired, opting for the synchronous API of httpx becomes necessary. This approach maintains thread safety and simplifies endpoint implementation:

from httpx import Client
from fastapi import FastAPI, Request

app = FastAPI()

@app.on_event("startup")
def startup_event():
    app.state.client = Client()

@app.on_event('shutdown')
async def shutdown_event():
    await app.state.client.aclose()

@app.get('/')
def home(request: Request):
    client = request.state.client
    req = client.build_request('GET', 'https://www.example.com')
    try:
        r = client.send(req)
        content_type = r.headers.get('content-type')
    except Exception as e:
        content_type = 'text/plain'
        e = str(e)

    if content_type == 'application/json':
        return r.json()
    elif content_type == 'text/plain':
        return PlainTextResponse(content=r.text)
    else:
        return Response(content=r.content)

In this example, the synchronous API handles HTTP requests within a try/except block, allowing for graceful handling of any exceptions that may arise during the request.

Additional Features and Considerations

• Async API Benefits: The async API provides superior performance and scales more efficiently with concurrent requests.
• Streaming Responses: Use streaming responses when dealing with large amounts of data in requests or responses.
• Controlling Connection Pool: You can optimize connection pool usage by setting the limits argument when creating the httpx client.
• Thread Safety: httpx is designed to be thread-safe, ensuring reliable execution across multiple threads.

By leveraging httpx and its features, you can confidently make downstream HTTP requests within FastAPI, handling multiple concurrent tasks seamlessly and ensuring application stability.

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