Trio WebSocket

This library implements both server and client aspects of the the WebSocket protocol, striving for safety, correctness, and ergonomics. It is based on the wsproto project, which is a Sans-IO state machine that implements the majority of the WebSocket protocol, including framing, codecs, and events. This library handles I/O using the Trio framework. This library passes the Autobahn Test Suite.

This README contains a brief introduction to the project. Full documentation is available here.

Alternatives

If you happen to only need a server, using Quart via the quart-trio extension may suffice. While trio-websocket is more flexible, Quart covers both HTTP and WebSocket within a single framework, and serving both from the same port is straightforward. There has yet to be a performance comparison.

Installation

This library requires Python 3.5 or greater. To install from PyPI:

pip install trio-websocket

Client Example

This example demonstrates how to open a WebSocket URL:

import trio
from sys import stderr
from trio_websocket import open_websocket_url


async def main():
    try:
        async with open_websocket_url('wss://echo.websocket.org') as ws:
            await ws.send_message('hello world!')
            message = await ws.get_message()
            print('Received message: %s' % message)
    except OSError as ose:
        print('Connection attempt failed: %s' % ose, file=stderr)

trio.run(main)

The WebSocket context manager connects automatically before entering the block and disconnects automatically before exiting the block. The full API offers a lot of flexibility and additional options.

Server Example

A WebSocket server requires a bind address, a port, and a coroutine to handle incoming connections. This example demonstrates an "echo server" that replies to each incoming message with an identical outgoing message.

import trio
from trio_websocket import serve_websocket, ConnectionClosed

async def echo_server(request):
    ws = await request.accept()
    while True:
        try:
            message = await ws.get_message()
            await ws.send_message(message)
        except ConnectionClosed:
            break

async def main():
    await serve_websocket(echo_server, '127.0.0.1', 8000, ssl_context=None)

trio.run(main)

The server's handler echo_server(…) receives a connection request object. This object can be used to inspect the client's request and modify the handshake, then it can be exchanged for an actual WebSocket object ws. Again, the full API offers a lot of flexibility and additional options.