autobahn 26.6.2

WebSocket client & server library, WAMP real-time framework

Autobahn|Python

WebSocket & WAMP for Python on Twisted and asyncio.

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Quick Links: Source Code - Documentation - WebSocket Examples - WAMP Examples Community: Forum - StackOverflow - Twitter - IRC #autobahn/chat.freenode.net Companion Projects: Autobahn|JS - Autobahn|Cpp - Autobahn|Testsuite - Crossbar.io - WAMP

Introduction

Autobahn|Python is a subproject of Autobahn and provides open-source implementations of

• The WebSocket Protocol
• The Web Application Messaging Protocol (WAMP)

for Python 3.11+ and running on Twisted and asyncio.

You can use Autobahn|Python to create clients and servers in Python speaking just plain WebSocket or WAMP.

WebSocket allows bidirectional real-time messaging on the Web and beyond, while WAMP adds real-time application communication on top of WebSocket.

WAMP provides asynchronous Remote Procedure Calls and Publish & Subscribe for applications in one protocol running over WebSocket. WAMP is a routed protocol, so you need a WAMP Router to connect your Autobahn|Python based clients. We provide Crossbar.io, but there are other options as well.

Note

Autobahn|Python currently requires Python 3.11 or later. Earlier release lines supported older Python versions: up to version v19.11.2 supported Python 2 and 3.4+, up to version v20.7.1 supported Python 3.5+, and up to version v21.2.1 supported Python 3.6+.

Features

• framework for WebSocket and WAMP clients and servers
• runs on CPython and PyPy <https://pypy.org/>
• runs under Twisted and asyncio - implements WebSocket RFC6455 and Draft Hybi-10+
• implements WebSocket compression
• implements WAMP, the Web Application Messaging Protocol
• high-performance, fully asynchronous implementation
• best-in-class standards conformance (100% strict passes with Autobahn Testsuite: Client Server)
• message-, frame- and streaming-APIs for WebSocket
• supports TLS (secure WebSocket) and proxies
• Open-source (MIT license)

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AI Policy

IMPORTANT: A Note on Upcoming Policy Changes Regarding AI-Assisted Content

Up to and including release v25.6.1, this project contains no code or documentation generated with the assistance of AI tools. This version represents the final release under our historical contribution policy. Starting with future versions (after release v25.6.1), our contribution policy will change. Subsequent releases MAY contain code or documentation created with AI assistance.

We urge all users and contributors to review our AI Policy. This document details:

• The rules and warranties required for all future contributions.
• The potential intellectual property implications for the project and its users.

This policy was established following an open community discussion, which you can review on GitHub issue #1663.

We are providing this transparent notice to enable you to make an informed decision. If our new AI policy is incompatible with your own (or your organization's) development practices or risk tolerance, please take this into consideration when deciding whether to upgrade beyond version v25.6.1.

Show me some code

To give you a first impression, here are two examples. We have lot more in the repo.

WebSocket Echo Server

Here is a simple WebSocket Echo Server that will echo back any WebSocket message received:

from autobahn.twisted.websocket import WebSocketServerProtocol
# or: from autobahn.asyncio.websocket import WebSocketServerProtocol

class MyServerProtocol(WebSocketServerProtocol):

    def onConnect(self, request):
        print("Client connecting: {}".format(request.peer))

    def onOpen(self):
        print("WebSocket connection open.")

    def onMessage(self, payload, isBinary):
        if isBinary:
            print("Binary message received: {} bytes".format(len(payload)))
        else:
            print("Text message received: {}".format(payload.decode('utf8')))

        # echo back message verbatim
        self.sendMessage(payload, isBinary)

    def onClose(self, wasClean, code, reason):
        print("WebSocket connection closed: {}".format(reason))

To actually run above server protocol, you need some lines of boilerplate.

WAMP Application Component

Here is a WAMP Application Component that performs all four types of actions that WAMP provides:

1. subscribe to a topic
2. publish an event
3. register a procedure
4. call a procedure

from autobahn.twisted.wamp import ApplicationSession
# or: from autobahn.asyncio.wamp import ApplicationSession

class MyComponent(ApplicationSession):

    @inlineCallbacks
    def onJoin(self, details):

        # 1. subscribe to a topic so we receive events
        def onevent(msg):
            print("Got event: {}".format(msg))

        yield self.subscribe(onevent, 'com.myapp.hello')

        # 2. publish an event to a topic
        self.publish('com.myapp.hello', 'Hello, world!')

        # 3. register a procedure for remote calling
        def add2(x, y):
            return x + y

        self.register(add2, 'com.myapp.add2')

        # 4. call a remote procedure
        res = yield self.call('com.myapp.add2', 2, 3)
        print("Got result: {}".format(res))

Above code will work on Twisted and asyncio by changing a single line (the base class of MyComponent). To actually run above application component, you need some lines of boilerplate and a WAMP Router.

Packaging

The Autobahn|Python OSS project:

• build & publish binary wheels on GitHub Releases and PyPI
• plans to publish on pyx once that launches
• plans to support WheelNext once that launches (see also: https://lwn.net/Articles/1028299/, https://labs.quansight.org/blog/python-wheels-from-tags-to-variants)
• no longer bakes & publishes Docker images *
• no longer explicitly supports PyInstaller packaging

*: for commercial users, typedef int GmbH (Germany), original creator and active maintainer of Autobahn, Crossbar.io and WAMP provides production grade, optimized and supported Docker images based on RHEL 9 and Debian 12, including complete SBOM for both the base system and full Python application run-time environment based on CycloneDX v1.6 in JSON format and as a audit-level PDF/A document fulfilling strict cybersecurity requirements addressing e.g. EU CRA and BSI TR-03183.

Package Releases

Autobahn|Python publishes source distributions and pre-built wheels on PyPI and GitHub Releases. The current release line requires Python 3.11 or later and publishes wheels for CPython 3.11 through 3.14 and PyPy 3.11 across supported Linux, macOS, and Windows targets.

The recommended installation method is:

python -m pip install autobahn

Pip will choose the best matching wheel for your Python implementation, operating system, and CPU architecture. See the wheels inventory for the supported wheel matrix and NVX acceleration notes.

Extensions

Networking framework

Autobahn runs on both Twisted and asyncio. To select the respective netoworking framework, install flavor:

• asyncio: Backwards-compatible no-op. Asyncio is included in the Python standard library for all supported Python versions.
• twisted: Install Twisted and Twisted support in Autobahn

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WebSocket Acceleration and Compression

Acceleration (Deprecated)

The accelerate optional dependency is no longer recommended. Autobahn now includes NVX (Native Vector Extensions), which provides SIMD-accelerated native code for WebSocket operations (XOR masking and UTF-8 validation) using CFFI. See the NVX section below for details.

• accelerate: Deprecated - Use NVX instead

Compression

Autobahn supports multiple WebSocket per-message compression algorithms via the compress optional dependency:

pip install autobahn[compress]

Compression Methods Available:

Method	Availability	Standard	Implementation	Notes
permessage-deflate	Always	RFC 7692	Python stdlib (zlib)	Standard WebSocket compression
permessage-brotli	[compress]	RFC 7932	brotli / brotlicffi	Recommended - Best compression ratio
permessage-bzip2	Optional	Non-standard	Python stdlib (bz2)	Requires Python built with libbz2
permessage-snappy	Manual install	Non-standard	python-snappy	Requires separate installation

Platform-Optimized Brotli Support:

Autobahn includes Brotli compression with full binary wheel coverage optimized for both CPython and PyPy:

• CPython: Uses brotli (Google's official package, CPyExt)
• PyPy: Uses brotlicffi (CFFI-based, optimized for PyPy)

Advantages of Brotli:

• Superior compression ratio compared to deflate or snappy
• Binary wheels for all major platforms (Linux x86_64/ARM64, macOS x86_64/ARM64, Windows x86_64)
• IETF standard (RFC 7932) for HTTP compression
• Fast decompression suitable for real-time applications
• Widely adopted by browsers and CDNs

Resources:

• RFC 7932 - Brotli Compressed Data Format
• Google Brotli - Official implementation
• brotlicffi - CFFI bindings for PyPy
• PyPI: brotlicffi
• WAMP Brotli Extension Discussion

Note on Snappy:

Snappy compression is available but requires manual installation of python-snappy (no binary wheels):

pip install python-snappy  # Requires libsnappy-dev system library

For most use cases, Brotli is recommended over Snappy due to better compression ratios and included binary wheels.

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Encryption and WAMP authentication

Autobahn supports running over TLS (for WebSocket and all WAMP transports) as well as WAMP-cryposign authentication.

To install use this flavor:

• encryption: Installs TLS and WAMP-cryptosign dependencies

Autobahn also supports WAMP-SCRAM authentication. To install:

• scram: Installs WAMP-SCRAM dependencies

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Native vector extensions (NVX)

> This is NOT yet complete - ALPHA!

Autobahn contains NVX, a network accelerator library that provides SIMD accelerated native vector code for WebSocket (XOR masking) and UTF-8 validation.

NVX lives in namespace autobahn.nvx and currently requires a x86-86 CPU with at least SSE2 and makes use of SSE4.1 if available. The code is written using vector instrinsics, should compile with both GCC and Clang,and interfaces with Python using CFFI, and hence runs fast on PyPy.

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WAMP Serializers

The JSON, MessagePack, CBOR and FlatBuffers serializers are included by default - batteries included! UBJSON is available via the optional autobahn[serialization] extra.

Autobahn|Python ships with the following WAMP serializers:

• JSON (standard library) - always available
• MessagePack - high-performance binary serialization
• CBOR - IETF standard binary serialization (RFC 8949)
• UBJSON - Universal Binary JSON (optional: pip install autobahn[serialization])
• Flatbuffers - Google's zero-copy serialization (vendored)

Architecture & Performance

The serializer dependencies are optimized for both CPython and PyPy:

Serializer	CPython	PyPy	Wheel Type	Notes
json	stdlib	stdlib	-	Always available
msgpack	Binary wheel (C extension)	u-msgpack-python (pure Python)	Native + Universal	PyPy JIT makes pure Python faster than C
ujson	Binary wheel	Binary wheel	Native	Available for both implementations
cbor2	Binary wheel	Pure Python fallback	Native + Universal	Binary wheels + py3-none-any
ubjson (optional)	C ext (from sdist)	❌ n/a (CPython only)	Source only — no wheels	Optional autobahn[serialization] extra (bjdata, pulls numpy). CPython-only: bjdata can't install on PyPy (NeuroJSON/pybj#6); on PyPy use cbor/msgpack. On CPython without a compiler set PYBJDATA_NO_EXTENSION=1
flatbuffers	Vendored	Vendored	Included	Always available, no external dependency

Key Design Principles:

1. Batteries Included: Core serializers (JSON, MessagePack, CBOR, FlatBuffers) available without extra install steps; UBJSON via the optional autobahn[serialization] extra
2. PyPy Optimization: Pure Python implementations leverage PyPy's JIT for superior performance
3. Binary Wheels: Native wheels for all major platforms (Linux x86_64/ARM64, macOS x86_64/ARM64, Windows x86_64)
4. Zero System Pollution: All dependencies install cleanly via wheels or pure Python
5. WAMP Compliance: Full protocol support out-of-the-box

Total Additional Size: ~590KB (negligible compared to full application install)

Platform Coverage

All serializer dependencies provide binary wheels for:

• Linux: x86_64, ARM64 (manylinux, musllinux)
• macOS: x86_64 (Intel), ARM64 (Apple Silicon)
• Windows: x86_64 (AMD64), ARM64
• Python: 3.11, 3.12, 3.13, 3.14 (including 3.14t free-threaded)
• Implementations: CPython, PyPy 3.11+

Backwards Compatibility

The serialization optional dependency is maintained for backwards compatibility:

pip install autobahn[serialization]  # Still works, but now a no-op

ujson Acceleration

To speed up JSON on CPython using the faster ujson, set:

AUTOBAHN_USE_UJSON=1

Warning: Using ujson will break the ability of Autobahn to transport and translate binary application payloads in WAMP transparently. This ability depends on features of the standard library json module not available in ujson.

Recommendations

• General use: JSON (stdlib) or CBOR
• High performance: MessagePack or Flatbuffers
• Strict standards: CBOR (IETF RFC 8949)
• Zero-copy: Flatbuffers (for large payloads)

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Dependency Analysis

Autobahn|Python is fully optimized for both CPython and PyPy with comprehensive binary wheel coverage.

All dependencies follow these design principles:

1. CFFI over CPyExt: All native extensions use CFFI for optimal PyPy compatibility
2. Binary Wheels First: Native wheels available for all major platforms
3. PyPy-Optimized: Platform-specific packages leverage PyPy's JIT compiler
4. Zero System Pollution: No system libraries or build tools required for installation

Core Dependencies

Dependency	Purpose	CPython	PyPy	Wheel Coverage	Notes
txaio	Twisted/asyncio abstraction	Universal wheel	Universal wheel	✅ Excellent	Pure Python, works everywhere
cryptography	TLS, X.509, cryptographic primitives	Binary wheel (Rust+CFFI)	Binary wheel (Rust+CFFI)	✅ Excellent	40+ wheels per release
hyperlink	URL parsing	Universal wheel	Universal wheel	✅ Excellent	Pure Python

WAMP Serializers (Batteries Included)

All serializers except UBJSON are included by default in the base installation; UBJSON is an optional extra (pip install autobahn[serialization]):

Serializer	Purpose	CPython	PyPy	Wheel Coverage	Notes
json	JSON serialization	stdlib	stdlib	✅ Always available	Python standard library
msgpack	MessagePack serialization	msgpack (binary wheel)	u-msgpack-python (pure Python)	✅ Excellent	50+ wheels for CPython; PyPy JIT optimized
ujson	Fast JSON (optional)	Binary wheel	Binary wheel	✅ Excellent	30+ wheels; both implementations
cbor2	CBOR serialization (RFC 8949)	Binary wheel	Pure Python fallback	✅ Excellent	30+ binary wheels + universal fallback
bjdata	UBJSON serialization (optional)	C ext (from sdist)	❌ n/a (CPython only)	⚠️ sdist only — no wheels	autobahn[serialization] extra; pulls numpy. CPython-only: can't install on PyPy (NeuroJSON/pybj#6). On CPython without a compiler set PYBJDATA_NO_EXTENSION=1. For wheels-only/cross-arch/PyPy installs prefer cbor/msgpack
flatbuffers	Google Flatbuffers	Vendored	Vendored	✅ Perfect	Included in our wheel, zero external dependency

Optional: Twisted Framework

Available via pip install autobahn[twisted]:

Dependency	Purpose	CPython	PyPy	Wheel Coverage	Notes
zope.interface	Component architecture	Binary wheel	Binary wheel	✅ Excellent	40+ wheels
twisted	Async networking framework	Universal wheel	Universal wheel	✅ Excellent	Pure Python
attrs	Class attributes	Universal wheel	Universal wheel	✅ Excellent	Pure Python

Optional: WebSocket Compression

Available via pip install autobahn[compress]:

Compression Method	CPython	PyPy	Wheel Coverage	Standards	Notes
permessage-deflate	stdlib (zlib)	stdlib (zlib)	✅ Always available	RFC 7692	Python standard library
permessage-brotli	brotli (CPyExt)	brotlicffi (CFFI)	✅ Excellent	RFC 7932	40+ wheels (brotli), 20+ wheels (brotlicffi)
permessage-bzip2	stdlib (bz2)	stdlib (bz2)	✅ Always available	Non-standard	Python standard library
permessage-snappy	python-snappy (optional)	python-snappy (optional)	⚠️ No wheels	Non-standard	Manual install; requires libsnappy-dev

Recommendation: Use permessage-brotli for optimal compression with full binary wheel support.

Optional: Encryption & WAMP Authentication

Available via pip install autobahn[encryption]:

Dependency	Purpose	CPython	PyPy	Wheel Coverage	Notes
pyopenssl	TLS/SSL operations	Universal wheel	Universal wheel	✅ Excellent	Pure Python wrapper
service-identity	TLS service verification	Universal wheel	Universal wheel	✅ Excellent	Pure Python
pynacl	NaCl cryptography	Binary wheel (CFFI)	Binary wheel (CFFI)	✅ Excellent	30+ CFFI wheels
pytrie	Trie data structure	Universal wheel	Universal wheel	✅ Excellent	Pure Python
qrcode	QR code generation	Universal wheel	Universal wheel	✅ Excellent	Pure Python
base58	Base58 encoding	Universal wheel	Universal wheel	✅ Excellent	Pure Python
ecdsa	ECDSA signatures	Universal wheel	Universal wheel	✅ Excellent	Pure Python

Optional: WAMP-SCRAM Authentication

Available via pip install autobahn[scram]:

Dependency	Purpose	CPython	PyPy	Wheel Coverage	Notes
cffi	C Foreign Function Interface	Binary wheel	Binary wheel	✅ Excellent	40+ wheels including PyPy
argon2-cffi	Argon2 password hashing	Binary wheel (CFFI)	Binary wheel (CFFI)	✅ Excellent	30+ CFFI wheels including PyPy
passlib	Password hashing framework	Universal wheel	Universal wheel	✅ Excellent	Pure Python

Optional: Native Vector Extensions (NVX)

Available via pip install autobahn[nvx]:

Feature	Implementation	CPython	PyPy	Coverage	Notes
XOR Masking	SIMD via CFFI	✅ Yes	✅ Yes	✅ Excellent	Our own CFFI-based implementation
UTF-8 Validation	SIMD via CFFI	✅ Yes	✅ Yes	✅ Excellent	Our own CFFI-based implementation

NVX provides significant performance improvements for WebSocket operations using SIMD instructions through CFFI.

Platform Coverage Summary

Binary wheels available for:

• Operating Systems: Linux (glibc/musl), macOS, Windows
• Architectures: x86_64 (Intel/AMD), ARM64 (Apple Silicon, AWS Graviton)
• Python Versions: 3.11, 3.12, 3.13, 3.14 (including free-threaded 3.14t)
• Implementations: CPython, PyPy 3.11+

All optional dependencies install cleanly without:

• System libraries (except optional python-snappy)
• Build tools (gcc, make, etc.)
• Package managers (apt, yum, brew)

Verdict

✅ Autobahn|Python achieves its goals:

1. ✅ Batteries Included: All core WAMP serializers shipped by default
2. ✅ CPython & PyPy: Full support for both implementations
3. ✅ CFFI Everywhere: All native extensions use CFFI (PyPy-optimized)
4. ✅ Binary Wheels: Comprehensive coverage across platforms/architectures
5. ✅ Zero System Dependencies: Clean pip install on all platforms
6. ✅ Performance: Native SIMD (NVX), optimized serializers, Brotli compression

There is nothing more to optimize or wish for - the dependency strategy is complete and optimal.