Overview

Uvicorn 0.14, released on June 1, 2021, adds WebSocket max message size configuration and asyncio streams support for HTTP transport.

Main Features

WebSocket max size

The --ws-max-size parameter limits the size of incoming WebSocket messages, protecting the server against excessively large payloads.

python 
# Launch with WebSocket limit at 1 MB
# uvicorn app:app --ws-max-size 1048576

import uvicorn

uvicorn.run(
    'app:app',
    ws_max_size=1_048_576,  # 1 MB
    host='0.0.0.0',
    port=8000,
)

Asyncio streams

The HTTP transport can use asyncio streams (asyncio.streams), providing an alternative to low-level transport for certain use cases.

python 
# Minimal ASGI application
async def app(scope, receive, send):
    if scope['type'] == 'http':
        await send({'type': 'http.response.start',
                    'status': 200,
                    'headers': [[b'content-type', b'text/plain']]})
        await send({'type': 'http.response.body',
                    'body': b'Hello from Uvicorn 0.14'})

Sources