Introduction

Installation

You can install this package in the usual way using pip:

pip install flask-socketio

Requirements

Flask-SocketIO is compatible with Python 3.6+. The asynchronous services that this package relies on can be selected among three choices:

  • eventlet is the best performant option, with support for long-polling and WebSocket transports.
  • gevent is supported in a number of different configurations. The long-polling transport is fully supported with the gevent package, but unlike eventlet, gevent does not have native WebSocket support. To add support for WebSocket there are currently two options. Installing the gevent-websocket package adds WebSocket support to gevent or one can use the uWSGI web server, which comes with WebSocket functionality. The use of gevent is also a performant option, but slightly lower than eventlet.
  • The Flask development server based on Werkzeug can be used as well, with the caveat that this web server is intended only for development use, so it should only be used to simplify the development workflow and not for production.

The extension automatically detects which asynchronous framework to use based on what is installed. Preference is given to eventlet, followed by gevent. For WebSocket support in gevent, uWSGI is preferred, followed by gevent-websocket. If neither eventlet nor gevent are installed, then the Flask development server is used.

If using multiple processes, a message queue service must be configured to allow the servers to coordinate operations such as broadcasting. The supported queues are Redis, RabbitMQ, Kafka, and any other message queues supported by the Kombu package.

On the client-side, the official Socket.IO Javascript client library can be used to establish a connection to the server. There are also official clients written in Swift, Java and C++. Unofficial clients may also work, as long as they implement the Socket.IO protocol. The python-socketio package (which provides the Socket.IO server implementation used by Flask-SocketIO) includes a Python client.

Version compatibility

The Socket.IO protocol has been through a number of revisions, and some of these introduced backward incompatible changes, which means that the client and the server must use compatible versions for everything to work.

The version compatibility chart below maps versions of this package to versions of the JavaScript reference implementation and the versions of the Socket.IO and Engine.IO protocols.

JavaScript Socket.IO version Socket.IO protocol revision Engine.IO protocol revision Flask-SocketIO version python-socketio version python-engineio version
0.9.x 1, 2 1, 2 Not supported Not supported Not supported
1.x and 2.x 3, 4 3 4.x 4.x 3.x
3.x and 4.x 5 4 5.x 5.x 4.x