aiopquic 0.2.5

High-performance QUIC/HTTP3 library — picoquic-backed, qh3-compatible asyncio API

aiopquic - Async QUIC + WebTransport (picoquic)

aiopquic is a Python/Cython binding to picoquic, providing high-performance QUIC transport and WebTransport for asyncio applications.

Overview

aiopquic exposes picoquic's QUIC implementation through a lock-free SPSC ring buffer architecture that bridges the picoquic network thread with Python's asyncio event loop. It provides an asyncio QUIC/HTTP3 transport API in the spirit of aioquic (and its fork qh3) — similar shapes for QuicConfiguration, QuicConnection, connect / serve, and event types — plus a native WebTransport client/server layered on picoquic's H3 + h3zero. Not a drop-in replacement: semantics differ around backpressure (send_stream_data raises BufferError on full per-stream ring) and flow-control sizing.

Architecture

• SPSC Ring Buffers -- Lock-free single producer/single consumer rings for event passing between threads, separate TX and RX rings per TransportContext.
• TX path -- Asyncio pushes into per-stream byte ring; picoquic pulls at wire rate via prepare_to_send.
• RX path -- picoquic pushes per-event StreamChunks; ownership transfers at pop for 1-copy delivery.
• Cross-platform wake fd -- Linux eventfd for efficient asyncio add_reader() notification; pipe() self-pipe fallback on macOS / BSD.
• Dedicated Network Thread -- picoquic runs in its own thread via picoquic_start_network_thread().
• Cython Bridge -- Thin Cython layer over C callbacks, minimal overhead.
• WebTransport -- asyncio.webtransport.WebTransportSession (client + server) over picoquic's picowt_* API and h3zero.

Features

• QUIC client and server: connect, serve, QuicConnectionProtocol
• Stream data send/receive with FIN signaling, stream reset, stop_sending
• WebTransport client + server: serve_webtransport, WebTransportSession
• QUIC datagram TX + RX (note: WebTransport datagram TX not yet wired)
• Connection migration / 0-RTT (inherited from picoquic)
• Connection management: create, close, idle timeout, application close codes
• Per-cnx multiplexing on the server side via QuicEngine
• TLS keylog (NSS Key Log Format) for pcap decryption
• Native picoquic_ct / picohttp_ct subprocess smoke (catches upstream regressions on every submodule update)

Test Results

Tests pass on Linux and macOS. The interop suite is opt-in (network-dependent).

Suite	Coverage
test_spsc_ring	per-event malloc ring lifecycle
test_buffer	Cython Buffer
test_transport	Transport lifecycle, wake fd, wake-up, connection management
test_loopback	17 tests — handshake, streams, FIN, reset, datagrams, ALPN mismatch, idle timeout, app-close codes, stop_sending, many-streams stress, TX-ring overflow
test_asyncio	client/server stream + datagram exchange via connect / serve
test_baton_pattern	Pure-QUIC baton-style stream multiplexing (UNI ↔ BIDI)
test_native_picoquic	picoquic_ct / picohttp_ct subprocess driver
test_interop	Real public endpoints (opt-in)
tests/bench/	microbenches: ring push/pop, single-shot/sustained/parallel/bidirectional throughput, datagrams, RTT latency, handshake rate, byte-verifying object stress + stream churn + concurrent streams (opt-in via pytest tests/bench)

Performance

Single-host loopback on AMD Ryzen 7 PRO 7840U (Zen 4), Linux, Python 3.14, against the released wheel (manylinux_2_34, OpenSSL 3.5.1). Byte-perfect across every run.

Single-stream sustained (30s, lowlevel SPSC ring):

obj	obj/s	throughput	latency p50	latency p99
1 KiB	293K	2,400 Mbps	98 µs	834 µs
4 KiB	83K	2,732 Mbps	3,139 µs	4,798 µs
16 KiB	21K	2,746 Mbps	3,142 µs	5,029 µs

High-level API (QuicConnection.send_stream_data, what client libraries see, 30s):

obj	obj/s	throughput	latency p50
1 KiB	229K	1,875 Mbps	370 µs
4 KiB	74K	2,439 Mbps	3,488 µs
16 KiB	18K	2,424 Mbps	3,509 µs

Multi-stream (concurrent streams on one connection, line rate):

P × obj	streams complete	obj/s	throughput
64 × 4 KiB	64/64	97K	3,190 Mbps
256 × 4 KiB	256/256	91K	2,983 Mbps
64 × 16 KiB	64/64	42K	5,481 Mbps

Stream churn (open/send/FIN, byte-verifying):

streams × obj	streams/s	throughput
1000 × 4 obj × 256 B	48,654	399 Mbps
100 × 16 obj × 1 KiB	12,600	1,651 Mbps
200 × 64 obj × 4 KiB	1,723	3,614 Mbps

Installation

Wheels for cp312 / cp313 / cp314 on Linux (manylinux_2_34, glibc 2.34+) and macOS arm64 are published to PyPI:

uv pip install aiopquic     # or: pip install aiopquic

For older Linux (glibc 2.28–2.33) install via sdist; build toolchain required.

From source

git clone https://github.com/gmarzot/aiopquic.git
cd aiopquic
git submodule update --init --recursive
./bootstrap_python.sh    # creates .venv with uv-managed Python 3.14t and pins cython 3.2+
source .venv/bin/activate
./build_picoquic.sh      # builds picotls, picoquic, native test drivers
uv pip install -e '.[dev]'    # or: pip install -e '.[dev]'

On macOS, set OPENSSL_ROOT_DIR if Homebrew OpenSSL is not auto-detected (the build script tries openssl@3 then openssl@1.1).

Usage

Low-level Transport API

from aiopquic._binding._transport import TransportContext

server = TransportContext()
server.start(port=4433, cert_file="cert.pem", key_file="key.pem", alpn="moq-00", is_client=False)

client = TransportContext()
client.start(port=0, alpn="moq-00", is_client=True)
client.create_client_connection("127.0.0.1", 4433, sni="localhost", alpn="moq-00")

Asyncio API

from aiopquic.asyncio.client import connect
from aiopquic.quic.configuration import QuicConfiguration

configuration = QuicConfiguration(alpn_protocols=["myproto"], is_client=True)

async with connect("server", 4433, configuration=configuration) as protocol:
    quic = protocol._quic
    stream_id = quic.get_next_available_stream_id()
    quic.send_stream_data(stream_id, payload, end_stream=True)
    protocol.transmit()

payload is opaque bytes; the library doesn't impose framing. Consumers that want HTTP/3 layer on top of aiopquic's picowt-backed h3zero plumbing; consumers that want WebTransport use serve_webtransport / connect_webtransport. Most direct users of the asyncio API ship their own protocol bytes (MoQT, custom binary frames, etc.).

WebTransport

from aiopquic.asyncio.webtransport import (
    serve_webtransport, WebTransportSession,
)
# See src/aiopquic/asyncio/webtransport.py and tests/ for full examples.

Development

uv pip install -e '.[dev]'    # or: pip install -e '.[dev]'
python -m pytest tests/ -v -m "not interop and not native"

# Microbenches (opt-in)
python -m pytest tests/bench

Known Limitations

• Free-threaded Python (3.14t) not yet supported -- the TX-ring producer side, TransportContext lifecycle, and the WebTransport engine state currently rely on the GIL for serialization. FT support deferred until a per-context locking audit lands.
• STOP_SENDING error codes surface as 0 today: picoquic's public stream-error getter only returns the RESET_STREAM code. STOP_SENDING's code lives in stream->remote_stop_error in picoquic_internal.h (no public getter). A small helper that pulls the field is straightforward future work — see TODO in src/aiopquic/_binding/c/callback.h.
• Per-stream wrapper cleanup before connection close -- per-stream aiopquic_stream_ctx_t* wrappers are freed at connection close rather than at stream RESET/FIN. Bounded leak per cnx; flagged for follow-up.

TODO

• Windows support (eventfd alternative — IOCP / WSAEventSelect on the wake-fd path)
• Free-threaded Python (3.14t) support after producer-side locking audit
• STOP_SENDING error-code surfacing helper (read remote_stop_error from picoquic_internal.h)
• Per-stream wrapper cleanup on RESET/FIN before connection close
• WebTransport datagram TX path through the C bridge
• Datagram benches: latency percentiles, payload-size sweep, loss / jitter under load (today's bench_datagram is fire-and-count throughput only)
• Pure stream open/close microbench (lifecycle rate without payload, separate from bench_stream_churn_highlevel which bundles writes + FIN)
• Submit aiopquic to the QUIC interop runner for cross-implementation coverage

Resources

• picoquic -- QUIC implementation by Christian Huitema
• picotls -- TLS 1.3 implementation
• Media Over QUIC Working Group

---

A Marz Research project.
Author: G. S. Marzot <[e-mail]>

License

MIT License -- see LICENSE