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Introduction

Installation

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

pip install flask-socketio

Requirements

Flask-SocketIO is compatible with Python 3.8+. The asynchronous services that this package relies on can be selected among three choices:

  • The threading package from the Python standard library is the easier and most compatible solution, with full support of long-polling and WebSocket transports. The Flask development web server can be used during development, and Gunicorn in multi-threaded mode can be used in production deployments.
  • gevent is supported in a number of different configurations, also with support for the long-polling and WebSocket transports. The Flask development web server, gevent's own web server, Gunicorn (with the gevent worker) and uWSGI (in gevent mode) are all supported when using gevent.
  • eventlet used to be a good option with support for long-polling and WebSocket transports, but it is not actively maintained anymore, so gevent should be preferred. The Flask development web server, eventlet's own web server and Gunicorn (with the eventlet worker) are all supported when using eventlet.

The extension automatically detects which asynchronous framework to use based on what is installed. Preference is given to eventlet, followed by gevent. If neither eventlet nor gevent are installed, Python's threading package 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