Response Bandwidth Limiter

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Response Bandwidth Limiter lets you configure a transfer speed limit for each endpoint in FastAPI and Starlette. The limit applies independently to each response.

It can also reject, delay, or throttle requests based on request counts. Group requests by IP address, API key, user, or another identifier, and use Redis to share counters across workers.

Installation

Requires Python 3.10 or later. For the FastAPI example below, install the library, FastAPI, and the Uvicorn server:

python -m pip install response-bandwidth-limiter fastapi uvicorn

For Starlette applications, see Installation and usage.

Quick Start

Save the following as main.py:

from fastapi import FastAPI, Request
from starlette.responses import PlainTextResponse

from response_bandwidth_limiter import ResponseBandwidthLimiter

app = FastAPI()
limiter = ResponseBandwidthLimiter()

@app.get("/download")
@limiter.limit(1024)  # 1024 bytes per second
async def download(request: Request):
    return PlainTextResponse("payload" * 4096)

limiter.init_app(app)

Register routes first, then call limiter.init_app(app) to install the middleware. Each response from /download is limited to 1,024 bytes per second; concurrent responses each have their own limit.

From the directory containing main.py, start the server:

python -m uvicorn main:app --host 127.0.0.1 --port 8000

Open http://127.0.0.1:8000/download in your browser. The response contains 28 KiB of repeated payload text and takes about 28 seconds to finish transferring at the configured rate. This delay is intentional.

Key Considerations

• Request counters and IP block / allow state are process-local by default. Use Redis to share them across workers; runtime configuration updates still remain process-local.
• Enable trusted_proxy_headers only behind a trusted reverse proxy that rewrites or sanitizes client IP headers.
• init_app() handles shutdown signals by default. Set install_signal_handlers=False to manage shutdown in your application. See Shutdown behavior for details.
• Actual transfer speed also depends on network conditions.

Documentation

Runnable examples are in example/.

Project

• Source code
• PyPI

Acknowledgements

This library was inspired by slowapi (MIT Licensed).

License

MPL-2.0