PyWebTransport

An async-native WebTransport stack for Python

Features

• Sans-I/O Architecture: Powered by an ownership-driven Rust state machine decoupled from an autonomous threaded reactor via a lock-free IPC boundary.
• Transport Primitives: Full implementation of bidirectional streams, unidirectional streams, and unreliable datagrams.
• Structured Concurrency: Deterministic lifecycle management for connections and streams via asynchronous context managers.
• Zero-Copy I/O: End-to-end support for buffer protocols and memoryview to minimize data copying overhead.
• Application Framework: Declarative ServerApp featuring path-based routing and composable stateful middleware.

Installation

pip install pywebtransport

Quick Start

Server

import asyncio

from pywebtransport import Event, ServerApp, ServerConfig, WebTransportSession, WebTransportStream
from pywebtransport.types import EventType
from pywebtransport.utils import generate_self_signed_cert

generate_self_signed_cert(hostname="localhost")

app = ServerApp(config=ServerConfig(certfile="localhost.crt", keyfile="localhost.key"))


@app.route(path="/")
async def echo_handler(session: WebTransportSession) -> None:
    async def on_datagram(event: Event) -> None:
        if isinstance(event.data, dict) and (data := event.data.get("data")):
            await session.send_datagram(data=b"ECHO: " + data)

    session.events.on(event_type=EventType.DATAGRAM_RECEIVED, handler=on_datagram)

    try:
        async for stream in session.incoming_bidirectional_streams():
            asyncio.create_task(handle_stream(stream))
    finally:
        session.events.off(event_type=EventType.DATAGRAM_RECEIVED, handler=on_datagram)


async def handle_stream(stream: WebTransportStream) -> None:
    try:
        data = await stream.read_all()
        await stream.write_all(data=b"ECHO: " + data, end_stream=True)
    except Exception:
        pass


if __name__ == "__main__":
    app.run(host="127.0.0.1", port=4433)

Client

import asyncio
import ssl

from pywebtransport import ClientConfig, WebTransportClient
from pywebtransport.types import EventType


async def main() -> None:
    config = ClientConfig(verify_mode=ssl.CERT_NONE)

    async with WebTransportClient(config=config) as client:
        session = await client.connect(url="https://127.0.0.1:4433/")

        await session.send_datagram(data=b"Hello, Datagram!")

        event = await session.events.wait_for(event_type=EventType.DATAGRAM_RECEIVED)
        if isinstance(event.data, dict) and (data := event.data.get("data")):
            print(f"Datagram: {data!r}")

        stream = await session.create_bidirectional_stream()
        await stream.write_all(data=b"Hello, Stream!", end_stream=True)

        response = await stream.read_all()
        print(f"Stream: {response!r}")

        await session.close()


if __name__ == "__main__":
    try:
        asyncio.run(main())
    except KeyboardInterrupt:
        pass

Interoperability

Infrastructure

• Public Instance: https://interop.wtransport.org, Native Dual-Stack
• Container Image: ghcr.io/wtransport/interop-server:latest, UDP Port 4433

Endpoints

• /echo: Bidirectional stream and datagram reflection.
• /stats: Current session statistics and negotiated parameters.
• /status: Global server health and aggregate metrics.
• /webtransport/devious-baton: Devious Baton protocol state transition validation.

Sponsors

License

Distributed under the terms of the Apache License 2.0. See LICENSE for details.