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Introduction

aiosignalr is a high-performance, asyncio-native implementation of the SignalR hub protocol for Python. It provides both a client and a server in one package, covering the WebSocket, Server-Sent Events and Long Polling transports with JSON and MessagePack message encoding.

SignalR is the real-time framework behind many .NET applications. aiosignalr lets Python services speak the same wire protocol, so they can interoperate with ASP.NET Core servers and clients, browsers using @microsoft/signalr, and any other SignalR implementation.

Why aiosignalr?​

  • Pure asyncio — no blocking calls, designed for high-concurrency event-driven Python services.
  • Full-duplex client and server over WebSocket, with transport fallback: the client negotiates transports in server-declared order (WebSocket → Server-Sent Events → Long Polling).
  • Both hub protocols: the JSON protocol (0x1E-delimited) and the MessagePack protocol (VarInt length-prefixed binary).
  • Complete client features: invoke, stream, fire-and-forget send, client-to-server upload streams, server method handlers, keep-alive pings, server-timeout detection, and automatic reconnect with a pluggable retry policy.
  • Complete server features: hub methods (single result and streaming), groups, broadcast to all / connection / group / user, client results, invocation cancellation, upload-stream parameters, negotiation and handshake protocol selection.
  • Stateful reconnect: the ASP.NET Core useAck / Ack / Sequence buffering protocol on both ends, preserving in-flight messages across a transport drop without loss or duplication.
  • Flexible hosting: a standalone asyncio server or an ASGI application you can mount in uvicorn / FastAPI.
  • Tested against the reference implementation: an interop test-suite runs aiosignalr against a real ASP.NET Core SignalR server and a real Microsoft.AspNetCore.SignalR.Client against aiosignalr.

Feature matrix​

AreaWebSocketServer-Sent EventsLong Polling
Server → client✔✔✔
Client → server✔ (duplex)HTTP POSTHTTP POST
JSON protocol✔✔✔
MessagePack protocol✔✘✔
Stateful reconnect✔✘✘

Compatibility​

aiosignalr speaks the standard SignalR protocol, so it interoperates with:

  • ASP.NET Core servers (MapHub) and clients (HubConnectionBuilder), including stateful reconnect.
  • @microsoft/signalr JavaScript clients.
  • Any SignalR implementation that follows the Transport Protocols and Hub Protocol specifications.

Requirements​

  • Python 3.11+.
  • aiohttp, websockets and msgpack (installed automatically).

Next steps​