Provided by: python3-socketio_5.0.3-2_all 
NAME
python-socketio - python-socketio Documentation
This projects implements Socket.IO clients and servers that can run standalone or integrated with a
variety of Python web frameworks.
GETTING STARTED
What is Socket.IO?
Socket.IO is a transport protocol that enables real-time bidirectional event-based communication between
clients (typically, though not always, web browsers) and a server. The official implementations of the
client and server components are written in JavaScript. This package provides Python implementations of
both, each with standard and asyncio variants.
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.
If you are using the Python client and server, the easiest way to ensure compatibility is to use the same
version of this package for the client and the server. If you are using this package with a different
client or server, then you must ensure the versions are compatible.
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 protocol │ Engine.IO protocol │ python-socketio │ python-engineio │
│ Socket.IO version │ revision │ revision │ version │ version │
├───────────────────┼─────────────────────┼─────────────────────┼─────────────────┼─────────────────┤
│ 0.9.x │ 1, 2 │ 1, 2 │ Not supported │ Not supported │
├───────────────────┼─────────────────────┼─────────────────────┼─────────────────┼─────────────────┤
│ 1.x and 2.x │ 3, 4 │ 3 │ 4.x │ 3.x │
├───────────────────┼─────────────────────┼─────────────────────┼─────────────────┼─────────────────┤
│ 3.x │ 5 │ 4 │ 5.x │ 4.x │
└───────────────────┴─────────────────────┴─────────────────────┴─────────────────┴─────────────────┘
Client Examples
The example that follows shows a simple Python client:
import socketio
sio = socketio.Client()
@sio.event
def connect():
print('connection established')
@sio.event
def my_message(data):
print('message received with ', data)
sio.emit('my response', {'response': 'my response'})
@sio.event
def disconnect():
print('disconnected from server')
sio.connect('http://localhost:5000')
sio.wait()
Client Features
• Can connect to other Socket.IO servers that are compatible with the JavaScript Socket.IO 1.x and 2.x
releases. Work to support release 3.x is in progress.
• Compatible with Python 3.5+.
• Two versions of the client, one for standard Python and another for asyncio.
• Uses an event-based architecture implemented with decorators that hides the details of the protocol.
• Implements HTTP long-polling and WebSocket transports.
• Automatically reconnects to the server if the connection is dropped.
Server Examples
The following application is a basic server example that uses the Eventlet asynchronous server:
import eventlet
import socketio
sio = socketio.Server()
app = socketio.WSGIApp(sio, static_files={
'/': {'content_type': 'text/html', 'filename': 'index.html'}
})
@sio.event
def connect(sid, environ):
print('connect ', sid)
@sio.event
def my_message(sid, data):
print('message ', data)
@sio.event
def disconnect(sid):
print('disconnect ', sid)
if __name__ == '__main__':
eventlet.wsgi.server(eventlet.listen(('', 5000)), app)
Below is a similar application, coded for asyncio (Python 3.5+ only) and the Uvicorn web server:
from aiohttp import web
import socketio
sio = socketio.AsyncServer()
app = web.Application()
sio.attach(app)
async def index(request):
"""Serve the client-side application."""
with open('index.html') as f:
return web.Response(text=f.read(), content_type='text/html')
@sio.event
def connect(sid, environ):
print("connect ", sid)
@sio.event
async def chat_message(sid, data):
print("message ", data)
await sio.emit('reply', room=sid)
@sio.event
def disconnect(sid):
print('disconnect ', sid)
app.router.add_static('/static', 'static')
app.router.add_get('/', index)
if __name__ == '__main__':
web.run_app(app)
Server Features
• Can connect to servers running other Socket.IO clients that are compatible with the JavaScript client
versions 1.x and 2.x. Work to support the 3.x release is in progress.
• Compatible with Python 3.5+.
• Two versions of the server, one for standard Python and another for asyncio.
• Supports large number of clients even on modest hardware due to being asynchronous.
• Can be hosted on any WSGI and ASGI web servers including Gunicorn, Uvicorn, eventlet and gevent.
• Can be integrated with WSGI applications written in frameworks such as Flask, Django, etc.
• Can be integrated with aiohttp, sanic and tornado asyncio applications.
• Broadcasting of messages to all connected clients, or to subsets of them assigned to "rooms".
• Optional support for multiple servers, connected through a messaging queue such as Redis or RabbitMQ.
• Send messages to clients from external processes, such as Celery workers or auxiliary scripts.
• Event-based architecture implemented with decorators that hides the details of the protocol.
• Support for HTTP long-polling and WebSocket transports.
• Support for XHR2 and XHR browsers.
• Support for text and binary messages.
• Support for gzip and deflate HTTP compression.
• Configurable CORS responses, to avoid cross-origin problems with browsers.
THE SOCKET.IO CLIENT
This package contains two Socket.IO clients:
• The socketio.Client() class creates a client compatible with the standard Python library.
• The socketio.AsyncClient() class creates a client compatible with the asyncio package.
The methods in the two clients are the same, with the only difference that in the asyncio client most
methods are implemented as coroutines.
Installation
To install the standard Python client along with its dependencies, use the following command:
pip install "python-socketio[client]"
If instead you plan on using the asyncio client, then use this:
pip install "python-socketio[asyncio_client]"
Creating a Client Instance
To instantiate an Socket.IO client, simply create an instance of the appropriate client class:
import socketio
# standard Python
sio = socketio.Client()
# asyncio
sio = socketio.AsyncClient()
Defining Event Handlers
The Socket.IO protocol is event based. When a server wants to communicate with a client it emits an
event. Each event has a name, and a list of arguments. The client registers event handler functions with
the socketio.Client.event() or socketio.Client.on() decorators:
@sio.event
def message(data):
print('I received a message!')
@sio.on('my message')
def on_message(data):
print('I received a message!')
In the first example the event name is obtained from the name of the handler function. The second example
is slightly more verbose, but it allows the event name to be different than the function name or to
include characters that are illegal in function names, such as spaces.
For the asyncio client, event handlers can be regular functions as above, or can also be coroutines:
@sio.event
async def message(data):
print('I received a message!')
The connect, connect_error and disconnect events are special; they are invoked automatically when a
client connects or disconnects from the server:
@sio.event
def connect():
print("I'm connected!")
@sio.event
def connect_error():
print("The connection failed!")
@sio.event
def disconnect():
print("I'm disconnected!")
Note that the disconnect handler is invoked for application initiated disconnects, server initiated
disconnects, or accidental disconnects, for example due to networking failures. In the case of an
accidental disconnection, the client is going to attempt to reconnect immediately after invoking the
disconnect handler. As soon as the connection is re-established the connect handler will be invoked once
again.
If the server includes arguments with an event, those are passed to the handler function as arguments.
Connecting to a Server
The connection to a server is established by calling the connect() method:
sio.connect('http://localhost:5000')
In the case of the asyncio client, the method is a coroutine:
await sio.connect('http://localhost:5000')
Upon connection, the server assigns the client a unique session identifier. The applicaction can find
this identifier in the sid attribute:
print('my sid is', sio.sid)
Emitting Events
The client can emit an event to the server using the emit() method:
sio.emit('my message', {'foo': 'bar'})
Or in the case of asyncio, as a coroutine:
await sio.emit('my message', {'foo': 'bar'})
The single argument provided to the method is the data that is passed on to the server. The data can be
of type str, bytes, dict, list or tuple. When sending a tuple, the elements in it need to be of any of
the other four allowed types. The elements of the tuple will be passed as multiple arguments to the
server-side event handler function.
The emit() method can be invoked inside an event handler as a response to a server event, or in any other
part of the application, including in background tasks.
Event Callbacks
When a server emits an event to a client, it can optionally provide a callback function, to be invoked as
a way of acknowledgment that the server has processed the event. While this is entirely managed by the
server, the client can provide a list of return values that are to be passed on to the callback function
set up by the server. This is achieved simply by returning the desired values from the handler function:
@sio.event
def my_event(sid, data):
# handle the message
return "OK", 123
Likewise, the client can request a callback function to be invoked after the server has processed an
event. The socketio.Server.emit() method has an optional callback argument that can be set to a callable.
If this argument is given, the callable will be invoked after the server has processed the event, and any
values returned by the server handler will be passed as arguments to this function.
Namespaces
The Socket.IO protocol supports multiple logical connections, all multiplexed on the same physical
connection. Clients can open multiple connections by specifying a different namespace on each. Namespaces
use a path syntax starting with a forward slash. A list of namespaces can be given by the client in the
connect() call. For example, this example creates two logical connections, the default one plus a second
connection under the /chat namespace:
sio.connect('http://localhost:5000', namespaces=['/chat'])
To define event handlers on a namespace, the namespace argument must be added to the corresponding
decorator:
@sio.event(namespace='/chat')
def my_custom_event(sid, data):
pass
@sio.on('connect', namespace='/chat')
def on_connect():
print("I'm connected to the /chat namespace!")
Likewise, the client can emit an event to the server on a namespace by providing its in the emit() call:
sio.emit('my message', {'foo': 'bar'}, namespace='/chat')
If the namespaces argument of the connect() call isn't given, any namespaces used in event handlers are
automatically connected.
Class-Based Namespaces
As an alternative to the decorator-based event handlers, the event handlers that belong to a namespace
can be created as methods of a subclass of socketio.ClientNamespace:
class MyCustomNamespace(socketio.ClientNamespace):
def on_connect(self):
pass
def on_disconnect(self):
pass
def on_my_event(self, data):
self.emit('my_response', data)
sio.register_namespace(MyCustomNamespace('/chat'))
For asyncio based servers, namespaces must inherit from socketio.AsyncClientNamespace, and can define
event handlers as coroutines if desired:
class MyCustomNamespace(socketio.AsyncClientNamespace):
def on_connect(self):
pass
def on_disconnect(self):
pass
async def on_my_event(self, data):
await self.emit('my_response', data)
sio.register_namespace(MyCustomNamespace('/chat'))
When class-based namespaces are used, any events received by the client are dispatched to a method named
as the event name with the on_ prefix. For example, event my_event will be handled by a method named
on_my_event. If an event is received for which there is no corresponding method defined in the namespace
class, then the event is ignored. All event names used in class-based namespaces must use characters that
are legal in method names.
As a convenience to methods defined in a class-based namespace, the namespace instance includes versions
of several of the methods in the socketio.Client and socketio.AsyncClient classes that default to the
proper namespace when the namespace argument is not given.
In the case that an event has a handler in a class-based namespace, and also a decorator-based function
handler, only the standalone function handler is invoked.
Disconnecting from the Server
At any time the client can request to be disconnected from the server by invoking the disconnect()
method:
sio.disconnect()
For the asyncio client this is a coroutine:
await sio.disconnect()
Managing Background Tasks
When a client connection to the server is established, a few background tasks will be spawned to keep the
connection alive and handle incoming events. The application running on the main thread is free to do any
work, as this is not going to prevent the functioning of the Socket.IO client.
If the application does not have anything to do in the main thread and just wants to wait until the
connection with the server ends, it can call the wait() method:
sio.wait()
Or in the asyncio version:
await sio.wait()
For the convenience of the application, a helper function is provided to start a custom background task:
def my_background_task(my_argument):
# do some background work here!
pass
sio.start_background_task(my_background_task, 123)
The arguments passed to this method are the background function and any positional or keyword arguments
to invoke the function with.
Here is the asyncio version:
async def my_background_task(my_argument):
# do some background work here!
pass
sio.start_background_task(my_background_task, 123)
Note that this function is not a coroutine, since it does not wait for the background function to end.
The background function must be a coroutine.
The sleep() method is a second convenince function that is provided for the benefit of applications
working with background tasks of their own:
sio.sleep(2)
Or for asyncio:
await sio.sleep(2)
The single argument passed to the method is the number of seconds to sleep for.
Debugging and Troubleshooting
To help you debug issues, the client can be configured to output logs to the terminal:
import socketio
# standard Python
sio = socketio.Client(logger=True, engineio_logger=True)
# asyncio
sio = socketio.AsyncClient(logger=True, engineio_logger=True)
The logger argument controls logging related to the Socket.IO protocol, while engineio_logger controls
logs that originate in the low-level Engine.IO transport. These arguments can be set to True to output
logs to stderr, or to an object compatible with Python's logging package where the logs should be emitted
to. A value of False disables logging.
Logging can help identify the cause of connection problems, unexpected disconnections and other issues.
THE SOCKET.IO SERVER
This package contains two Socket.IO servers:
• The socketio.Server() class creates a server compatible with the Python standard library.
• The socketio.AsyncServer() class creates a server compatible with the asyncio package.
The methods in the two servers are the same, with the only difference that in the asyncio server most
methods are implemented as coroutines.
Installation
To install the Socket.IO server along with its dependencies, use the following command:
pip install python-socketio
In addition to the server, you will need to select an asynchronous framework or server to use along with
it. The list of supported packages is covered in the Deployment Strategies section.
Creating a Server Instance
A Socket.IO server is an instance of class socketio.Server. This instance can be transformed into a
standard WSGI application by wrapping it with the socketio.WSGIApp class:
import socketio
# create a Socket.IO server
sio = socketio.Server()
# wrap with a WSGI application
app = socketio.WSGIApp(sio)
For asyncio based servers, the socketio.AsyncServer class provides the same functionality, but in a
coroutine friendly format. If desired, The socketio.ASGIApp class can transform the server into a
standard ASGI application:
# create a Socket.IO server
sio = socketio.AsyncServer()
# wrap with ASGI application
app = socketio.ASGIApp(sio)
These two wrappers can also act as middlewares, forwarding any traffic that is not intended to the
Socket.IO server to another application. This allows Socket.IO servers to integrate easily into existing
WSGI or ASGI applications:
from wsgi import app # a Flask, Django, etc. application
app = socketio.WSGIApp(sio, app)
Serving Static Files
The Engine.IO server can be configured to serve static files to clients. This is particularly useful to
deliver HTML, CSS and JavaScript files to clients when this package is used without a companion web
framework.
Static files are configured with a Python dictionary in which each key/value pair is a static file
mapping rule. In its simplest form, this dictionary has one or more static file URLs as keys, and the
corresponding files in the server as values:
static_files = {
'/': 'latency.html',
'/static/socket.io.js': 'static/socket.io.js',
'/static/style.css': 'static/style.css',
}
With this example configuration, when the server receives a request for / (the root URL) it will return
the contents of the file latency.html in the current directory, and will assign a content type based on
the file extension, in this case text/html.
Files with the .html, .css, .js, .json, .jpg, .png, .gif and .txt file extensions are automatically
recognized and assigned the correct content type. For files with other file extensions or with no file
extension, the application/octet-stream content type is used as a default.
If desired, an explicit content type for a static file can be given as follows:
static_files = {
'/': {'filename': 'latency.html', 'content_type': 'text/plain'},
}
It is also possible to configure an entire directory in a single rule, so that all the files in it are
served as static files:
static_files = {
'/static': './public',
}
In this example any files with URLs starting with /static will be served directly from the public folder
in the current directory, so for example, the URL /static/index.html will return local file
./public/index.html and the URL /static/css/styles.css will return local file ./public/css/styles.css.
If a URL that ends in a / is requested, then a default filename of index.html is appended to it. In the
previous example, a request for the /static/ URL would return local file ./public/index.html. The default
filename to serve for slash-ending URLs can be set in the static files dictionary with an empty key:
static_files = {
'/static': './public',
'': 'image.gif',
}
With this configuration, a request for /static/ would return local file ./public/image.gif. A
non-standard content type can also be specified if needed:
static_files = {
'/static': './public',
'': {'filename': 'image.gif', 'content_type': 'text/plain'},
}
The static file configuration dictionary is given as the static_files argument to the socketio.WSGIApp or
socketio.ASGIApp classes:
# for standard WSGI applications
sio = socketio.Server()
app = socketio.WSGIApp(sio, static_files=static_files)
# for asyncio-based ASGI applications
sio = socketio.AsyncServer()
app = socketio.ASGIApp(sio, static_files=static_files)
The routing precedence in these two classes is as follows:
• First, the path is checked against the Socket.IO endpoint.
• Next, the path is checked against the static file configuration, if present.
• If the path did not match the Socket.IO endpoint or any static file, control is passed to the secondary
application if configured, else a 404 error is returned.
Note: static file serving is intended for development use only, and as such it lacks important features
such as caching. Do not use in a production environment.
Defining Event Handlers
The Socket.IO protocol is event based. When a client wants to communicate with the server it emits an
event. Each event has a name, and a list of arguments. The server registers event handler functions with
the socketio.Server.event() or socketio.Server.on() decorators:
@sio.event
def my_event(sid, data):
pass
@sio.on('my custom event')
def another_event(sid, data):
pass
In the first example the event name is obtained from the name of the handler function. The second example
is slightly more verbose, but it allows the event name to be different than the function name or to
include characters that are illegal in function names, such as spaces.
For asyncio servers, event handlers can optionally be given as coroutines:
@sio.event
async def my_event(sid, data):
pass
The sid argument is the Socket.IO session id, a unique identifier of each client connection. All the
events sent by a given client will have the same sid value.
The connect and disconnect events are special; they are invoked automatically when a client connects or
disconnects from the server:
@sio.event
def connect(sid, environ):
print('connect ', sid)
@sio.event
def disconnect(sid):
print('disconnect ', sid)
The connect event is an ideal place to perform user authentication, and any necessary mapping between
user entities in the application and the sid that was assigned to the client. The environ argument is a
dictionary in standard WSGI format containing the request information, including HTTP headers. After
inspecting the request, the connect event handler can return False to reject the connection with the
client.
Sometimes it is useful to pass data back to the client being rejected. In that case instead of returning
False socketio.exceptions.ConnectionRefusedError can be raised, and all of its arguments will be sent to
the client with the rejection message:
@sio.event
def connect(sid, environ):
raise ConnectionRefusedError('authentication failed')
Emitting Events
Socket.IO is a bidirectional protocol, so at any time the server can send an event to its connected
clients. The socketio.Server.emit() method is used for this task:
sio.emit('my event', {'data': 'foobar'})
Sometimes the server may want to send an event just to a particular client. This can be achieved by
adding a room argument to the emit call:
sio.emit('my event', {'data': 'foobar'}, room=user_sid)
The socketio.Server.emit() method takes an event name, a message payload of type str, bytes, list, dict
or tuple, and the recipient room. When sending a tuple, the elements in it need to be of any of the other
four allowed types. The elements of the tuple will be passed as multiple arguments to the client-side
event handler function. The room argument is used to identify the client that should receive the event,
and is set to the sid value assigned to that client's connection with the server. When omitted, the event
is broadcasted to all connected clients.
Event Callbacks
When a client sends an event to the server, it can optionally provide a callback function, to be invoked
as a way of acknowledgment that the server has processed the event. While this is entirely managed by the
client, the server can provide a list of values that are to be passed on to the callback function, simply
by returning them from the handler function:
@sio.event
def my_event(sid, data):
# handle the message
return "OK", 123
Likewise, the server can request a callback function to be invoked after a client has processed an event.
The socketio.Server.emit() method has an optional callback argument that can be set to a callable. If
this argument is given, the callable will be invoked after the client has processed the event, and any
values returned by the client will be passed as arguments to this function. Using callback functions when
broadcasting to multiple clients is not recommended, as the callback function will be invoked once for
each client that received the message.
Namespaces
The Socket.IO protocol supports multiple logical connections, all multiplexed on the same physical
connection. Clients can open multiple connections by specifying a different namespace on each. A
namespace is given by the client as a pathname following the hostname and port. For example, connecting
to http://example.com:8000/chat would open a connection to the namespace /chat.
Each namespace is handled independently from the others, with separate session IDs (sids), event handlers
and rooms. It is important that applications that use multiple namespaces specify the correct namespace
when setting up their event handlers and rooms, using the optional namespace argument available in all
the methods in the socketio.Server class:
@sio.event(namespace='/chat')
def my_custom_event(sid, data):
pass
@sio.on('my custom event', namespace='/chat')
def my_custom_event(sid, data):
pass
When emitting an event, the namespace optional argument is used to specify which namespace to send it on.
When the namespace argument is omitted, the default Socket.IO namespace, which is named /, is used.
Class-Based Namespaces
As an alternative to the decorator-based event handlers, the event handlers that belong to a namespace
can be created as methods of a subclass of socketio.Namespace:
class MyCustomNamespace(socketio.Namespace):
def on_connect(self, sid, environ):
pass
def on_disconnect(self, sid):
pass
def on_my_event(self, sid, data):
self.emit('my_response', data)
sio.register_namespace(MyCustomNamespace('/test'))
For asyncio based severs, namespaces must inherit from socketio.AsyncNamespace, and can define event
handlers as coroutines if desired:
class MyCustomNamespace(socketio.AsyncNamespace):
def on_connect(self, sid, environ):
pass
def on_disconnect(self, sid):
pass
async def on_my_event(self, sid, data):
await self.emit('my_response', data)
sio.register_namespace(MyCustomNamespace('/test'))
When class-based namespaces are used, any events received by the server are dispatched to a method named
as the event name with the on_ prefix. For example, event my_event will be handled by a method named
on_my_event. If an event is received for which there is no corresponding method defined in the namespace
class, then the event is ignored. All event names used in class-based namespaces must use characters that
are legal in method names.
As a convenience to methods defined in a class-based namespace, the namespace instance includes versions
of several of the methods in the socketio.Server and socketio.AsyncServer classes that default to the
proper namespace when the namespace argument is not given.
In the case that an event has a handler in a class-based namespace, and also a decorator-based function
handler, only the standalone function handler is invoked.
It is important to note that class-based namespaces are singletons. This means that a single instance of
a namespace class is used for all clients, and consequently, a namespace instance cannot be used to store
client specific information.
Rooms
To make it easy for the server to emit events to groups of related clients, the application can put its
clients into "rooms", and then address messages to these rooms.
In the previous section the room argument of the socketio.SocketIO.emit() method was used to designate a
specific client as the recipient of the event. This is because upon connection, a personal room for each
client is created and named with the sid assigned to the connection. The application is then free to
create additional rooms and manage which clients are in them using the socketio.Server.enter_room() and
socketio.Server.leave_room() methods. Clients can be in as many rooms as needed and can be moved between
rooms as often as necessary.
@sio.event
def begin_chat(sid):
sio.enter_room(sid, 'chat_users')
@sio.event
def exit_chat(sid):
sio.leave_room(sid, 'chat_users')
In chat applications it is often desired that an event is broadcasted to all the members of the room
except one, which is the originator of the event such as a chat message. The socketio.Server.emit()
method provides an optional skip_sid argument to indicate a client that should be skipped during the
broadcast.
@sio.event
def my_message(sid, data):
sio.emit('my reply', data, room='chat_users', skip_sid=sid)
User Sessions
The server can maintain application-specific information in a user session dedicated to each connected
client. Applications can use the user session to write any details about the user that need to be
preserved throughout the life of the connection, such as usernames or user ids.
The save_session() and get_session() methods are used to store and retrieve information in the user
session:
@sio.event
def connect(sid, environ):
username = authenticate_user(environ)
sio.save_session(sid, {'username': username})
@sio.event
def message(sid, data):
session = sio.get_session(sid)
print('message from ', session['username'])
For the asyncio server, these methods are coroutines:
@sio.event
async def connect(sid, environ):
username = authenticate_user(environ)
await sio.save_session(sid, {'username': username})
@sio.event
async def message(sid, data):
session = await sio.get_session(sid)
print('message from ', session['username'])
The session can also be manipulated with the session() context manager:
@sio.event
def connect(sid, environ):
username = authenticate_user(environ)
with sio.session(sid) as session:
session['username'] = username
@sio.event
def message(sid, data):
with sio.session(sid) as session:
print('message from ', session['username'])
For the asyncio server, an asynchronous context manager is used:
@sio.event
def connect(sid, environ):
username = authenticate_user(environ)
async with sio.session(sid) as session:
session['username'] = username
@sio.event
def message(sid, data):
async with sio.session(sid) as session:
print('message from ', session['username'])
The get_session(), save_session() and session() methods take an optional namespace argument. If this
argument isn't provided, the session is attached to the default namespace.
Note: the contents of the user session are destroyed when the client disconnects. In particular, user
session contents are not preserved when a client reconnects after an unexpected disconnection from the
server.
Using a Message Queue
When working with distributed applications, it is often necessary to access the functionality of the
Socket.IO from multiple processes. There are two specific use cases:
• Applications that use work queues such as Celery may need to emit an event to a client once a
background job completes. The most convenient place to carry out this task is the worker process that
handled this job.
• Highly available applications may want to use horizontal scaling of the Socket.IO server to be able to
handle very large number of concurrent clients.
As a solution to the above problems, the Socket.IO server can be configured to connect to a message queue
such as Redis or RabbitMQ, to communicate with other related Socket.IO servers or auxiliary workers.
Redis
To use a Redis message queue, a Python Redis client must be installed:
# socketio.Server class
pip install redis
# socketio.AsyncServer class
pip install aioredis
The Redis queue is configured through the socketio.RedisManager and socketio.AsyncRedisManager classes.
These classes connect directly to the Redis store and use the queue's pub/sub functionality:
# socketio.Server class
mgr = socketio.RedisManager('redis://')
sio = socketio.Server(client_manager=mgr)
# socketio.AsyncServer class
mgr = socketio.AsyncRedisManager('redis://')
sio = socketio.AsyncServer(client_manager=mgr)
The client_manager argument instructs the server to connect to the given message queue, and to coordinate
with other processes connected to the queue.
Kombu
Kombu is a Python package that provides access to RabbitMQ and many other message queues. It can be
installed with pip:
pip install kombu
To use RabbitMQ or other AMQP protocol compatible queues, that is the only required dependency. But for
other message queues, Kombu may require additional packages. For example, to use a Redis queue via Kombu,
the Python package for Redis needs to be installed as well:
pip install redis
The queue is configured through the socketio.KombuManager:
mgr = socketio.KombuManager('amqp://')
sio = socketio.Server(client_manager=mgr)
The connection URL passed to the KombuManager constructor is passed directly to Kombu's Connection
object, so the Kombu documentation should be consulted for information on how to build the correct URL
for a given message queue.
Note that Kombu currently does not support asyncio, so it cannot be used with the socketio.AsyncServer
class.
Kafka
Apache Kafka is supported through the kafka-python package:
pip install kafka-python
Access to Kafka is configured through the socketio.KafkaManager class:
mgr = socketio.KafkaManager('kafka://')
sio = socketio.Server(client_manager=mgr)
Note that Kafka currently does not support asyncio, so it cannot be used with the socketio.AsyncServer
class.
AioPika
A RabbitMQ message queue is supported in asyncio applications through the AioPika package:: You need to
install aio_pika with pip:
pip install aio_pika
The RabbitMQ queue is configured through the socketio.AsyncAioPikaManager class:
mgr = socketio.AsyncAioPikaManager('amqp://')
sio = socketio.AsyncServer(client_manager=mgr)
Emitting from external processes
To have a process other than a server connect to the queue to emit a message, the same client manager
classes can be used as standalone objects. In this case, the write_only argument should be set to True to
disable the creation of a listening thread, which only makes sense in a server. For example:
# connect to the redis queue as an external process
external_sio = socketio.RedisManager('redis://', write_only=True)
# emit an event
external_sio.emit('my event', data={'foo': 'bar'}, room='my room')
Debugging and Troubleshooting
To help you debug issues, the server can be configured to output logs to the terminal:
import socketio
# standard Python
sio = socketio.Server(logger=True, engineio_logger=True)
# asyncio
sio = socketio.AsyncServer(logger=True, engineio_logger=True)
The logger argument controls logging related to the Socket.IO protocol, while engineio_logger controls
logs that originate in the low-level Engine.IO transport. These arguments can be set to True to output
logs to stderr, or to an object compatible with Python's logging package where the logs should be emitted
to. A value of False disables logging.
Logging can help identify the cause of connection problems, 400 responses, bad performance and other
issues.
Deployment Strategies
The following sections describe a variety of deployment strategies for Socket.IO servers.
Aiohttp
Aiohttp is a framework with support for HTTP and WebSocket, based on asyncio. Support for this framework
is limited to Python 3.5 and newer.
Instances of class socketio.AsyncServer will automatically use aiohttp for asynchronous operations if the
library is installed. To request its use explicitly, the async_mode option can be given in the
constructor:
sio = socketio.AsyncServer(async_mode='aiohttp')
A server configured for aiohttp must be attached to an existing application:
app = web.Application()
sio.attach(app)
The aiohttp application can define regular routes that will coexist with the Socket.IO server. A typical
pattern is to add routes that serve a client application and any associated static files.
The aiohttp application is then executed in the usual manner:
if __name__ == '__main__':
web.run_app(app)
Tornado
Tornado is a web framework with support for HTTP and WebSocket. Support for this framework requires
Python 3.5 and newer. Only Tornado version 5 and newer are supported, thanks to its tight integration
with asyncio.
Instances of class socketio.AsyncServer will automatically use tornado for asynchronous operations if the
library is installed. To request its use explicitly, the async_mode option can be given in the
constructor:
sio = socketio.AsyncServer(async_mode='tornado')
A server configured for tornado must include a request handler for Socket.IO:
app = tornado.web.Application(
[
(r"/socket.io/", socketio.get_tornado_handler(sio)),
],
# ... other application options
)
The tornado application can define other routes that will coexist with the Socket.IO server. A typical
pattern is to add routes that serve a client application and any associated static files.
The tornado application is then executed in the usual manner:
app.listen(port)
tornado.ioloop.IOLoop.current().start()
Sanic
Sanic is a very efficient asynchronous web server for Python 3.5 and newer.
Instances of class socketio.AsyncServer will automatically use Sanic for asynchronous operations if the
framework is installed. To request its use explicitly, the async_mode option can be given in the
constructor:
sio = socketio.AsyncServer(async_mode='sanic')
A server configured for aiohttp must be attached to an existing application:
app = Sanic()
sio.attach(app)
The Sanic application can define regular routes that will coexist with the Socket.IO server. A typical
pattern is to add routes that serve a client application and any associated static files.
The Sanic application is then executed in the usual manner:
if __name__ == '__main__':
app.run()
It has been reported that the CORS support provided by the Sanic extension sanic-cors is incomaptible
with this package's own support for this protocol. To disable CORS support in this package and let Sanic
take full control, initialize the server as follows:
sio = socketio.AsyncServer(async_mode='sanic', cors_allowed_origins=[])
On the Sanic side you will need to enable the CORS_SUPPORTS_CREDENTIALS setting in addition to any other
configuration that you use:
app.config['CORS_SUPPORTS_CREDENTIALS'] = True
Uvicorn, Daphne, and other ASGI servers
The socketio.ASGIApp class is an ASGI compatible application that can forward Socket.IO traffic to an
socketio.AsyncServer instance:
sio = socketio.AsyncServer(async_mode='asgi')
app = socketio.ASGIApp(sio)
The application can then be deployed with any ASGI compatible web server.
Eventlet
Eventlet is a high performance concurrent networking library for Python 2 and 3 that uses coroutines,
enabling code to be written in the same style used with the blocking standard library functions. An
Socket.IO server deployed with eventlet has access to the long-polling and WebSocket transports.
Instances of class socketio.Server will automatically use eventlet for asynchronous operations if the
library is installed. To request its use explicitly, the async_mode option can be given in the
constructor:
sio = socketio.Server(async_mode='eventlet')
A server configured for eventlet is deployed as a regular WSGI application using the provided
socketio.WSGIApp:
app = socketio.WSGIApp(sio)
import eventlet
eventlet.wsgi.server(eventlet.listen(('', 8000)), app)
Eventlet with Gunicorn
An alternative to running the eventlet WSGI server as above is to use gunicorn, a fully featured pure
Python web server. The command to launch the application under gunicorn is shown below:
$ gunicorn -k eventlet -w 1 module:app
Due to limitations in its load balancing algorithm, gunicorn can only be used with one worker process, so
the -w option cannot be set to a value higher than 1. A single eventlet worker can handle a large number
of concurrent clients, each handled by a greenlet.
Eventlet provides a monkey_patch() function that replaces all the blocking functions in the standard
library with equivalent asynchronous versions. While python-socketio does not require monkey patching,
other libraries such as database drivers are likely to require it.
Gevent
Gevent is another asynchronous framework based on coroutines, very similar to eventlet. An Socket.IO
server deployed with gevent has access to the long-polling transport. If project gevent-websocket is
installed, the WebSocket transport is also available.
Instances of class socketio.Server will automatically use gevent for asynchronous operations if the
library is installed and eventlet is not installed. To request gevent to be selected explicitly, the
async_mode option can be given in the constructor:
sio = socketio.Server(async_mode='gevent')
A server configured for gevent is deployed as a regular WSGI application using the provided
socketio.WSGIApp:
app = socketio.WSGIApp(sio)
from gevent import pywsgi
pywsgi.WSGIServer(('', 8000), app).serve_forever()
If the WebSocket transport is installed, then the server must be started as follows:
from gevent import pywsgi
from geventwebsocket.handler import WebSocketHandler
app = socketio.WSGIApp(sio)
pywsgi.WSGIServer(('', 8000), app,
handler_class=WebSocketHandler).serve_forever()
Gevent with Gunicorn
An alternative to running the gevent WSGI server as above is to use gunicorn, a fully featured pure
Python web server. The command to launch the application under gunicorn is shown below:
$ gunicorn -k gevent -w 1 module:app
Or to include WebSocket:
$ gunicorn -k geventwebsocket.gunicorn.workers.GeventWebSocketWorker -w 1 module: app
Same as with eventlet, due to limitations in its load balancing algorithm, gunicorn can only be used with
one worker process, so the -w option cannot be higher than 1. A single gevent worker can handle a large
number of concurrent clients through the use of greenlets.
Gevent provides a monkey_patch() function that replaces all the blocking functions in the standard
library with equivalent asynchronous versions. While python-socketio does not require monkey patching,
other libraries such as database drivers are likely to require it.
uWSGI
When using the uWSGI server in combination with gevent, the Socket.IO server can take advantage of
uWSGI's native WebSocket support.
Instances of class socketio.Server will automatically use this option for asynchronous operations if both
gevent and uWSGI are installed and eventlet is not installed. To request this asynchronous mode
explicitly, the async_mode option can be given in the constructor:
# gevent with uWSGI
sio = socketio.Server(async_mode='gevent_uwsgi')
A complete explanation of the configuration and usage of the uWSGI server is beyond the scope of this
documentation. The uWSGI server is a fairly complex package that provides a large and comprehensive set
of options. It must be compiled with WebSocket and SSL support for the WebSocket transport to be
available. As way of an introduction, the following command starts a uWSGI server for the latency.py
example on port 5000:
$ uwsgi --http :5000 --gevent 1000 --http-websockets --master --wsgi-file latency.py --callable app
Standard Threads
While not comparable to eventlet and gevent in terms of performance, the Socket.IO server can also be
configured to work with multi-threaded web servers that use standard Python threads. This is an ideal
setup to use with development servers such as Werkzeug. Only the long-polling transport is currently
available when using standard threads.
Instances of class socketio.Server will automatically use the threading mode if neither eventlet nor
gevent are not installed. To request the threading mode explicitly, the async_mode option can be given in
the constructor:
sio = socketio.Server(async_mode='threading')
A server configured for threading is deployed as a regular web application, using any WSGI complaint
multi-threaded server. The example below deploys an Socket.IO application combined with a Flask web
application, using Flask's development web server based on Werkzeug:
sio = socketio.Server(async_mode='threading')
app = Flask(__name__)
app.wsgi_app = socketio.WSGIApp(sio, app.wsgi_app)
# ... Socket.IO and Flask handler functions ...
if __name__ == '__main__':
app.run(threaded=True)
When using the threading mode, it is important to ensure that the WSGI server can handle multiple
concurrent requests using threads, since a client can have up to two outstanding requests at any given
time. The Werkzeug server is single-threaded by default, so the threaded=True option is required.
Note that servers that use worker processes instead of threads, such as gunicorn, do not support a
Socket.IO server configured in threading mode.
Scalability Notes
Socket.IO is a stateful protocol, which makes horizontal scaling more difficult. To deploy a cluster of
Socket.IO processes hosted on one or multiple servers, the following conditions must be met:
• Each Socket.IO process must be able to handle multiple requests concurrently. This is required because
long-polling clients send two requests in parallel. Worker processes that can only handle one request
at a time are not supported.
• The load balancer must be configured to always forward requests from a client to the same worker
process. Load balancers call this sticky sessions, or session affinity.
• The worker processes need to communicate with each other to coordinate complex operations such as
broadcasts. This is done through a configured message queue. See the section on using message queues
for details.
Cross-Origin Controls
For security reasons, this server enforces a same-origin policy by default. In practical terms, this
means the following:
• If an incoming HTTP or WebSocket request includes the Origin header, this header must match the scheme
and host of the connection URL. In case of a mismatch, a 400 status code response is returned and the
connection is rejected.
• No restrictions are imposed on incoming requests that do not include the Origin header.
If necessary, the cors_allowed_origins option can be used to allow other origins. This argument can be
set to a string to set a single allowed origin, or to a list to allow multiple origins. A special value
of '*' can be used to instruct the server to allow all origins, but this should be done with care, as
this could make the server vulnerable to Cross-Site Request Forgery (CSRF) attacks.
API REFERENCE
Client class
class socketio.Client(reconnection=True, reconnection_attempts=0, reconnection_delay=1,
reconnection_delay_max=5, randomization_factor=0.5, logger=False, json=None, **kwargs)
A Socket.IO client.
This class implements a fully compliant Socket.IO web client with support for websocket and
long-polling transports.
Parameters
• reconnection -- True if the client should automatically attempt to reconnect to the
server after an interruption, or False to not reconnect. The default is True.
• reconnection_attempts -- How many reconnection attempts to issue before giving up, or 0
for infinity attempts. The default is 0.
• reconnection_delay -- How long to wait in seconds before the first reconnection attempt.
Each successive attempt doubles this delay.
• reconnection_delay_max -- The maximum delay between reconnection attempts.
• randomization_factor -- Randomization amount for each delay between reconnection
attempts. The default is 0.5, which means that each delay is randomly adjusted by +/-
50%.
• logger -- To enable logging set to True or pass a logger object to use. To disable
logging set to False. The default is False. Note that fatal errors are logged even when
logger is False.
• json -- An alternative json module to use for encoding and decoding packets. Custom json
modules must have dumps and loads functions that are compatible with the standard library
versions.
The Engine.IO configuration supports the following settings:
Parameters
• request_timeout -- A timeout in seconds for requests. The default is 5 seconds.
• ssl_verify -- True to verify SSL certificates, or False to skip SSL certificate
verification, allowing connections to servers with self signed certificates. The default
is True.
• engineio_logger -- To enable Engine.IO logging set to True or pass a logger object to
use. To disable logging set to False. The default is False. Note that fatal errors are
logged even when engineio_logger is False.
call(event, data=None, namespace=None, timeout=60)
Emit a custom event to a client and wait for the response.
Parameters
• event -- The event name. It can be any string. The event names 'connect',
'message' and 'disconnect' are reserved and should not be used.
• data -- The data to send to the server. Data can be of type str, bytes, list or
dict. To send multiple arguments, use a tuple where each element is of one of the
types indicated above.
• namespace -- The Socket.IO namespace for the event. If this argument is omitted
the event is emitted to the default namespace.
• timeout -- The waiting timeout. If the timeout is reached before the client
acknowledges the event, then a TimeoutError exception is raised.
Note: this method is not thread safe. If multiple threads are emitting at the same time on
the same client connection, messages composed of multiple packets may end up being sent in
an incorrect sequence. Use standard concurrency solutions (such as a Lock object) to
prevent this situation.
connect(url, headers={}, transports=None, namespaces=None, socketio_path='socket.io')
Connect to a Socket.IO server.
Parameters
• url -- The URL of the Socket.IO server. It can include custom query string
parameters if required by the server.
• headers -- A dictionary with custom headers to send with the connection request.
• transports -- The list of allowed transports. Valid transports are 'polling' and
'websocket'. If not given, the polling transport is connected first, then an
upgrade to websocket is attempted.
• namespaces -- The namespaces to connect as a string or list of strings. If not
given, the namespaces that have registered event handlers are connected.
• socketio_path -- The endpoint where the Socket.IO server is installed. The default
value is appropriate for most cases.
Note: The connection mechannism occurs in the background and will complete at some point
after this function returns. The connection will be established when the connect event is
invoked.
Example usage:
sio = socketio.Client()
sio.connect('http://localhost:5000')
disconnect()
Disconnect from the server.
emit(event, data=None, namespace=None, callback=None)
Emit a custom event to one or more connected clients.
Parameters
• event -- The event name. It can be any string. The event names 'connect',
'message' and 'disconnect' are reserved and should not be used.
• data -- The data to send to the server. Data can be of type str, bytes, list or
dict. To send multiple arguments, use a tuple where each element is of one of the
types indicated above.
• namespace -- The Socket.IO namespace for the event. If this argument is omitted
the event is emitted to the default namespace.
• callback -- If given, this function will be called to acknowledge the the server
has received the message. The arguments that will be passed to the function are
those provided by the server.
Note: this method is not thread safe. If multiple threads are emitting at the same time on
the same client connection, messages composed of multiple packets may end up being sent in
an incorrect sequence. Use standard concurrency solutions (such as a Lock object) to
prevent this situation.
event(*args, **kwargs)
Decorator to register an event handler.
This is a simplified version of the on() method that takes the event name from the
decorated function.
Example usage:
@sio.event
def my_event(data):
print('Received data: ', data)
The above example is equivalent to:
@sio.on('my_event')
def my_event(data):
print('Received data: ', data)
A custom namespace can be given as an argument to the decorator:
@sio.event(namespace='/test')
def my_event(data):
print('Received data: ', data)
get_sid(namespace=None)
Return the sid associated with a connection.
Parameters
namespace -- The Socket.IO namespace. If this argument is omitted the handler is
associated with the default namespace. Note that unlike previous versions, the
current version of the Socket.IO protocol uses different sid values per namespace.
This method returns the sid for the requested namespace as a string.
on(event, handler=None, namespace=None)
Register an event handler.
Parameters
• event -- The event name. It can be any string. The event names 'connect',
'message' and 'disconnect' are reserved and should not be used.
• handler -- The function that should be invoked to handle the event. When this
parameter is not given, the method acts as a decorator for the handler function.
• namespace -- The Socket.IO namespace for the event. If this argument is omitted
the handler is associated with the default namespace.
Example usage:
# as a decorator:
@sio.on('connect')
def connect_handler():
print('Connected!')
# as a method:
def message_handler(msg):
print('Received message: ', msg)
sio.send( 'response')
sio.on('message', message_handler)
The 'connect' event handler receives no arguments. The 'message' handler and handlers for
custom event names receive the message payload as only argument. Any values returned from a
message handler will be passed to the client's acknowledgement callback function if it
exists. The 'disconnect' handler does not take arguments.
register_namespace(namespace_handler)
Register a namespace handler object.
Parameters
namespace_handler -- An instance of a Namespace subclass that handles all the event
traffic for a namespace.
send(data, namespace=None, callback=None)
Send a message to one or more connected clients.
This function emits an event with the name 'message'. Use emit() to issue custom event
names.
Parameters
• data -- The data to send to the server. Data can be of type str, bytes, list or
dict. To send multiple arguments, use a tuple where each element is of one of the
types indicated above.
• namespace -- The Socket.IO namespace for the event. If this argument is omitted
the event is emitted to the default namespace.
• callback -- If given, this function will be called to acknowledge the the server
has received the message. The arguments that will be passed to the function are
those provided by the server.
sleep(seconds=0)
Sleep for the requested amount of time using the appropriate async model.
This is a utility function that applications can use to put a task to sleep without having
to worry about using the correct call for the selected async mode.
start_background_task(target, *args, **kwargs)
Start a background task using the appropriate async model.
This is a utility function that applications can use to start a background task using the
method that is compatible with the selected async mode.
Parameters
• target -- the target function to execute.
• args -- arguments to pass to the function.
• kwargs -- keyword arguments to pass to the function.
This function returns an object compatible with the Thread class in the Python standard
library. The start() method on this object is already called by this function.
transport()
Return the name of the transport used by the client.
The two possible values returned by this function are 'polling' and 'websocket'.
wait() Wait until the connection with the server ends.
Client applications can use this function to block the main thread during the life of the
connection.
AsyncClient class
class socketio.AsyncClient(reconnection=True, reconnection_attempts=0, reconnection_delay=1,
reconnection_delay_max=5, randomization_factor=0.5, logger=False, json=None, **kwargs)
A Socket.IO client for asyncio.
This class implements a fully compliant Socket.IO web client with support for websocket and
long-polling transports.
Parameters
• reconnection -- True if the client should automatically attempt to reconnect to the
server after an interruption, or False to not reconnect. The default is True.
• reconnection_attempts -- How many reconnection attempts to issue before giving up, or 0
for infinity attempts. The default is 0.
• reconnection_delay -- How long to wait in seconds before the first reconnection attempt.
Each successive attempt doubles this delay.
• reconnection_delay_max -- The maximum delay between reconnection attempts.
• randomization_factor -- Randomization amount for each delay between reconnection
attempts. The default is 0.5, which means that each delay is randomly adjusted by +/-
50%.
• logger -- To enable logging set to True or pass a logger object to use. To disable
logging set to False. The default is False. Note that fatal errors are logged even when
logger is False.
• json -- An alternative json module to use for encoding and decoding packets. Custom json
modules must have dumps and loads functions that are compatible with the standard library
versions.
The Engine.IO configuration supports the following settings:
Parameters
• request_timeout -- A timeout in seconds for requests. The default is 5 seconds.
• ssl_verify -- True to verify SSL certificates, or False to skip SSL certificate
verification, allowing connections to servers with self signed certificates. The default
is True.
• engineio_logger -- To enable Engine.IO logging set to True or pass a logger object to
use. To disable logging set to False. The default is False. Note that fatal errors are
logged even when engineio_logger is False.
async call(event, data=None, namespace=None, timeout=60)
Emit a custom event to a client and wait for the response.
Parameters
• event -- The event name. It can be any string. The event names 'connect',
'message' and 'disconnect' are reserved and should not be used.
• data -- The data to send to the server. Data can be of type str, bytes, list or
dict. To send multiple arguments, use a tuple where each element is of one of the
types indicated above.
• namespace -- The Socket.IO namespace for the event. If this argument is omitted
the event is emitted to the default namespace.
• timeout -- The waiting timeout. If the timeout is reached before the client
acknowledges the event, then a TimeoutError exception is raised.
Note: this method is not designed to be used concurrently. If multiple tasks are emitting
at the same time on the same client connection, then messages composed of multiple packets
may end up being sent in an incorrect sequence. Use standard concurrency solutions (such as
a Lock object) to prevent this situation.
Note 2: this method is a coroutine.
async connect(url, headers={}, transports=None, namespaces=None, socketio_path='socket.io')
Connect to a Socket.IO server.
Parameters
• url -- The URL of the Socket.IO server. It can include custom query string
parameters if required by the server.
• headers -- A dictionary with custom headers to send with the connection request.
• transports -- The list of allowed transports. Valid transports are 'polling' and
'websocket'. If not given, the polling transport is connected first, then an
upgrade to websocket is attempted.
• namespaces -- The namespaces to connect as a string or list of strings. If not
given, the namespaces that have registered event handlers are connected.
• socketio_path -- The endpoint where the Socket.IO server is installed. The default
value is appropriate for most cases.
Note: this method is a coroutine.
Note: The connection mechannism occurs in the background and will complete at some point
after this function returns. The connection will be established when the connect event is
invoked.
Example usage:
sio = socketio.AsyncClient()
sio.connect('http://localhost:5000')
async disconnect()
Disconnect from the server.
Note: this method is a coroutine.
async emit(event, data=None, namespace=None, callback=None)
Emit a custom event to one or more connected clients.
Parameters
• event -- The event name. It can be any string. The event names 'connect',
'message' and 'disconnect' are reserved and should not be used.
• data -- The data to send to the server. Data can be of type str, bytes, list or
dict. To send multiple arguments, use a tuple where each element is of one of the
types indicated above.
• namespace -- The Socket.IO namespace for the event. If this argument is omitted
the event is emitted to the default namespace.
• callback -- If given, this function will be called to acknowledge the the server
has received the message. The arguments that will be passed to the function are
those provided by the server.
Note: this method is not designed to be used concurrently. If multiple tasks are emitting
at the same time on the same client connection, then messages composed of multiple packets
may end up being sent in an incorrect sequence. Use standard concurrency solutions (such as
a Lock object) to prevent this situation.
Note 2: this method is a coroutine.
event(*args, **kwargs)
Decorator to register an event handler.
This is a simplified version of the on() method that takes the event name from the
decorated function.
Example usage:
@sio.event
def my_event(data):
print('Received data: ', data)
The above example is equivalent to:
@sio.on('my_event')
def my_event(data):
print('Received data: ', data)
A custom namespace can be given as an argument to the decorator:
@sio.event(namespace='/test')
def my_event(data):
print('Received data: ', data)
get_sid(namespace=None)
Return the sid associated with a connection.
Parameters
namespace -- The Socket.IO namespace. If this argument is omitted the handler is
associated with the default namespace. Note that unlike previous versions, the
current version of the Socket.IO protocol uses different sid values per namespace.
This method returns the sid for the requested namespace as a string.
on(event, handler=None, namespace=None)
Register an event handler.
Parameters
• event -- The event name. It can be any string. The event names 'connect',
'message' and 'disconnect' are reserved and should not be used.
• handler -- The function that should be invoked to handle the event. When this
parameter is not given, the method acts as a decorator for the handler function.
• namespace -- The Socket.IO namespace for the event. If this argument is omitted
the handler is associated with the default namespace.
Example usage:
# as a decorator:
@sio.on('connect')
def connect_handler():
print('Connected!')
# as a method:
def message_handler(msg):
print('Received message: ', msg)
sio.send( 'response')
sio.on('message', message_handler)
The 'connect' event handler receives no arguments. The 'message' handler and handlers for
custom event names receive the message payload as only argument. Any values returned from a
message handler will be passed to the client's acknowledgement callback function if it
exists. The 'disconnect' handler does not take arguments.
register_namespace(namespace_handler)
Register a namespace handler object.
Parameters
namespace_handler -- An instance of a Namespace subclass that handles all the event
traffic for a namespace.
async send(data, namespace=None, callback=None)
Send a message to one or more connected clients.
This function emits an event with the name 'message'. Use emit() to issue custom event
names.
Parameters
• data -- The data to send to the server. Data can be of type str, bytes, list or
dict. To send multiple arguments, use a tuple where each element is of one of the
types indicated above.
• namespace -- The Socket.IO namespace for the event. If this argument is omitted
the event is emitted to the default namespace.
• callback -- If given, this function will be called to acknowledge the the server
has received the message. The arguments that will be passed to the function are
those provided by the server.
Note: this method is a coroutine.
async sleep(seconds=0)
Sleep for the requested amount of time using the appropriate async model.
This is a utility function that applications can use to put a task to sleep without having
to worry about using the correct call for the selected async mode.
Note: this method is a coroutine.
start_background_task(target, *args, **kwargs)
Start a background task using the appropriate async model.
This is a utility function that applications can use to start a background task using the
method that is compatible with the selected async mode.
Parameters
• target -- the target function to execute.
• args -- arguments to pass to the function.
• kwargs -- keyword arguments to pass to the function.
This function returns an object compatible with the Thread class in the Python standard
library. The start() method on this object is already called by this function.
transport()
Return the name of the transport used by the client.
The two possible values returned by this function are 'polling' and 'websocket'.
async wait()
Wait until the connection with the server ends.
Client applications can use this function to block the main thread during the life of the
connection.
Note: this method is a coroutine.
Server class
class socketio.Server(client_manager=None, logger=False, json=None, async_handlers=True,
always_connect=False, **kwargs)
A Socket.IO server.
This class implements a fully compliant Socket.IO web server with support for websocket and
long-polling transports.
Parameters
• client_manager -- The client manager instance that will manage the client list. When this
is omitted, the client list is stored in an in-memory structure, so the use of multiple
connected servers is not possible.
• logger -- To enable logging set to True or pass a logger object to use. To disable
logging set to False. The default is False. Note that fatal errors are logged even when
logger is False.
• json -- An alternative json module to use for encoding and decoding packets. Custom json
modules must have dumps and loads functions that are compatible with the standard library
versions.
• async_handlers -- If set to True, event handlers for a client are executed in separate
threads. To run handlers for a client synchronously, set to False. The default is True.
• always_connect -- When set to False, new connections are provisory until the connect
handler returns something other than False, at which point they are accepted. When set to
True, connections are immediately accepted, and then if the connect handler returns False
a disconnect is issued. Set to True if you need to emit events from the connect handler
and your client is confused when it receives events before the connection acceptance. In
any other case use the default of False.
• kwargs -- Connection parameters for the underlying Engine.IO server.
The Engine.IO configuration supports the following settings:
Parameters
• async_mode -- The asynchronous model to use. See the Deployment section in the
documentation for a description of the available options. Valid async modes are
"threading", "eventlet", "gevent" and "gevent_uwsgi". If this argument is not given,
"eventlet" is tried first, then "gevent_uwsgi", then "gevent", and finally "threading".
The first async mode that has all its dependencies installed is then one that is chosen.
• ping_timeout -- The time in seconds that the client waits for the server to respond
before disconnecting. The default is 60 seconds.
• ping_interval -- The interval in seconds at which the client pings the server. The
default is 25 seconds.
• max_http_buffer_size -- The maximum size of a message when using the polling transport.
The default is 100,000,000 bytes.
• allow_upgrades -- Whether to allow transport upgrades or not. The default is True.
• http_compression -- Whether to compress packages when using the polling transport. The
default is True.
• compression_threshold -- Only compress messages when their byte size is greater than this
value. The default is 1024 bytes.
• cookie -- Name of the HTTP cookie that contains the client session id. If set to None, a
cookie is not sent to the client. The default is 'io'.
• cors_allowed_origins -- Origin or list of origins that are allowed to connect to this
server. Only the same origin is allowed by default. Set this argument to '*' to allow all
origins, or to [] to disable CORS handling.
• cors_credentials -- Whether credentials (cookies, authentication) are allowed in requests
to this server. The default is True.
• monitor_clients -- If set to True, a background task will ensure inactive clients are
closed. Set to False to disable the monitoring task (not recommended). The default is
True.
• engineio_logger -- To enable Engine.IO logging set to True or pass a logger object to
use. To disable logging set to False. The default is False. Note that fatal errors are
logged even when engineio_logger is False.
call(event, data=None, to=None, sid=None, namespace=None, timeout=60, **kwargs)
Emit a custom event to a client and wait for the response.
Parameters
• event -- The event name. It can be any string. The event names 'connect',
'message' and 'disconnect' are reserved and should not be used.
• data -- The data to send to the client or clients. Data can be of type str, bytes,
list or dict. To send multiple arguments, use a tuple where each element is of one
of the types indicated above.
• to -- The session ID of the recipient client.
• sid -- Alias for the to parameter.
• namespace -- The Socket.IO namespace for the event. If this argument is omitted
the event is emitted to the default namespace.
• timeout -- The waiting timeout. If the timeout is reached before the client
acknowledges the event, then a TimeoutError exception is raised.
• ignore_queue -- Only used when a message queue is configured. If set to True, the
event is emitted to the client directly, without going through the queue. This is
more efficient, but only works when a single server process is used. It is
recommended to always leave this parameter with its default value of False.
Note: this method is not thread safe. If multiple threads are emitting at the same time to
the same client, then messages composed of multiple packets may end up being sent in an
incorrect sequence. Use standard concurrency solutions (such as a Lock object) to prevent
this situation.
close_room(room, namespace=None)
Close a room.
This function removes all the clients from the given room.
Parameters
• room -- Room name.
• namespace -- The Socket.IO namespace for the event. If this argument is omitted
the default namespace is used.
disconnect(sid, namespace=None, ignore_queue=False)
Disconnect a client.
Parameters
• sid -- Session ID of the client.
• namespace -- The Socket.IO namespace to disconnect. If this argument is omitted
the default namespace is used.
• ignore_queue -- Only used when a message queue is configured. If set to True, the
disconnect is processed locally, without broadcasting on the queue. It is
recommended to always leave this parameter with its default value of False.
emit(event, data=None, to=None, room=None, skip_sid=None, namespace=None, callback=None, **kwargs)
Emit a custom event to one or more connected clients.
Parameters
• event -- The event name. It can be any string. The event names 'connect',
'message' and 'disconnect' are reserved and should not be used.
• data -- The data to send to the client or clients. Data can be of type str, bytes,
list or dict. To send multiple arguments, use a tuple where each element is of one
of the types indicated above.
• to -- The recipient of the message. This can be set to the session ID of a client
to address only that client, or to to any custom room created by the application
to address all the clients in that room, If this argument is omitted the event is
broadcasted to all connected clients.
• room -- Alias for the to parameter.
• skip_sid -- The session ID of a client to skip when broadcasting to a room or to
all clients. This can be used to prevent a message from being sent to the sender.
To skip multiple sids, pass a list.
• namespace -- The Socket.IO namespace for the event. If this argument is omitted
the event is emitted to the default namespace.
• callback -- If given, this function will be called to acknowledge the the client
has received the message. The arguments that will be passed to the function are
those provided by the client. Callback functions can only be used when addressing
an individual client.
• ignore_queue -- Only used when a message queue is configured. If set to True, the
event is emitted to the clients directly, without going through the queue. This
is more efficient, but only works when a single server process is used. It is
recommended to always leave this parameter with its default value of False.
Note: this method is not thread safe. If multiple threads are emitting at the same time to
the same client, then messages composed of multiple packets may end up being sent in an
incorrect sequence. Use standard concurrency solutions (such as a Lock object) to prevent
this situation.
enter_room(sid, room, namespace=None)
Enter a room.
This function adds the client to a room. The emit() and send() functions can optionally
broadcast events to all the clients in a room.
Parameters
• sid -- Session ID of the client.
• room -- Room name. If the room does not exist it is created.
• namespace -- The Socket.IO namespace for the event. If this argument is omitted
the default namespace is used.
event(*args, **kwargs)
Decorator to register an event handler.
This is a simplified version of the on() method that takes the event name from the
decorated function.
Example usage:
@sio.event
def my_event(data):
print('Received data: ', data)
The above example is equivalent to:
@sio.on('my_event')
def my_event(data):
print('Received data: ', data)
A custom namespace can be given as an argument to the decorator:
@sio.event(namespace='/test')
def my_event(data):
print('Received data: ', data)
get_environ(sid, namespace=None)
Return the WSGI environ dictionary for a client.
Parameters
• sid -- The session of the client.
• namespace -- The Socket.IO namespace. If this argument is omitted the default
namespace is used.
get_session(sid, namespace=None)
Return the user session for a client.
Parameters
• sid -- The session id of the client.
• namespace -- The Socket.IO namespace. If this argument is omitted the default
namespace is used.
The return value is a dictionary. Modifications made to this dictionary are not guaranteed
to be preserved unless save_session() is called, or when the session context manager is
used.
handle_request(environ, start_response)
Handle an HTTP request from the client.
This is the entry point of the Socket.IO application, using the same interface as a WSGI
application. For the typical usage, this function is invoked by the Middleware instance,
but it can be invoked directly when the middleware is not used.
Parameters
• environ -- The WSGI environment.
• start_response -- The WSGI start_response function.
This function returns the HTTP response body to deliver to the client as a byte sequence.
leave_room(sid, room, namespace=None)
Leave a room.
This function removes the client from a room.
Parameters
• sid -- Session ID of the client.
• room -- Room name.
• namespace -- The Socket.IO namespace for the event. If this argument is omitted
the default namespace is used.
on(event, handler=None, namespace=None)
Register an event handler.
Parameters
• event -- The event name. It can be any string. The event names 'connect',
'message' and 'disconnect' are reserved and should not be used.
• handler -- The function that should be invoked to handle the event. When this
parameter is not given, the method acts as a decorator for the handler function.
• namespace -- The Socket.IO namespace for the event. If this argument is omitted
the handler is associated with the default namespace.
Example usage:
# as a decorator:
@socket_io.on('connect', namespace='/chat')
def connect_handler(sid, environ):
print('Connection request')
if environ['REMOTE_ADDR'] in blacklisted:
return False # reject
# as a method:
def message_handler(sid, msg):
print('Received message: ', msg)
eio.send(sid, 'response')
socket_io.on('message', namespace='/chat', handler=message_handler)
The handler function receives the sid (session ID) for the client as first argument. The
'connect' event handler receives the WSGI environment as a second argument, and can return
False to reject the connection. The 'message' handler and handlers for custom event names
receive the message payload as a second argument. Any values returned from a message
handler will be passed to the client's acknowledgement callback function if it exists. The
'disconnect' handler does not take a second argument.
register_namespace(namespace_handler)
Register a namespace handler object.
Parameters
namespace_handler -- An instance of a Namespace subclass that handles all the event
traffic for a namespace.
rooms(sid, namespace=None)
Return the rooms a client is in.
Parameters
• sid -- Session ID of the client.
• namespace -- The Socket.IO namespace for the event. If this argument is omitted
the default namespace is used.
save_session(sid, session, namespace=None)
Store the user session for a client.
Parameters
• sid -- The session id of the client.
• session -- The session dictionary.
• namespace -- The Socket.IO namespace. If this argument is omitted the default
namespace is used.
send(data, to=None, room=None, skip_sid=None, namespace=None, callback=None, **kwargs)
Send a message to one or more connected clients.
This function emits an event with the name 'message'. Use emit() to issue custom event
names.
Parameters
• data -- The data to send to the client or clients. Data can be of type str, bytes,
list or dict. To send multiple arguments, use a tuple where each element is of one
of the types indicated above.
• to -- The recipient of the message. This can be set to the session ID of a client
to address only that client, or to to any custom room created by the application
to address all the clients in that room, If this argument is omitted the event is
broadcasted to all connected clients.
• room -- Alias for the to parameter.
• skip_sid -- The session ID of a client to skip when broadcasting to a room or to
all clients. This can be used to prevent a message from being sent to the sender.
To skip multiple sids, pass a list.
• namespace -- The Socket.IO namespace for the event. If this argument is omitted
the event is emitted to the default namespace.
• callback -- If given, this function will be called to acknowledge the the client
has received the message. The arguments that will be passed to the function are
those provided by the client. Callback functions can only be used when addressing
an individual client.
• ignore_queue -- Only used when a message queue is configured. If set to True, the
event is emitted to the clients directly, without going through the queue. This
is more efficient, but only works when a single server process is used. It is
recommended to always leave this parameter with its default value of False.
session(sid, namespace=None)
Return the user session for a client with context manager syntax.
Parameters
sid -- The session id of the client.
This is a context manager that returns the user session dictionary for the client. Any
changes that are made to this dictionary inside the context manager block are saved back to
the session. Example usage:
@sio.on('connect')
def on_connect(sid, environ):
username = authenticate_user(environ)
if not username:
return False
with sio.session(sid) as session:
session['username'] = username
@sio.on('message')
def on_message(sid, msg):
with sio.session(sid) as session:
print('received message from ', session['username'])
sleep(seconds=0)
Sleep for the requested amount of time using the appropriate async model.
This is a utility function that applications can use to put a task to sleep without having
to worry about using the correct call for the selected async mode.
start_background_task(target, *args, **kwargs)
Start a background task using the appropriate async model.
This is a utility function that applications can use to start a background task using the
method that is compatible with the selected async mode.
Parameters
• target -- the target function to execute.
• args -- arguments to pass to the function.
• kwargs -- keyword arguments to pass to the function.
This function returns an object compatible with the Thread class in the Python standard
library. The start() method on this object is already called by this function.
transport(sid)
Return the name of the transport used by the client.
The two possible values returned by this function are 'polling' and 'websocket'.
Parameters
sid -- The session of the client.
AsyncServer class
class socketio.AsyncServer(client_manager=None, logger=False, json=None, async_handlers=True, **kwargs)
A Socket.IO server for asyncio.
This class implements a fully compliant Socket.IO web server with support for websocket and
long-polling transports, compatible with the asyncio framework on Python 3.5 or newer.
Parameters
• client_manager -- The client manager instance that will manage the client list. When this
is omitted, the client list is stored in an in-memory structure, so the use of multiple
connected servers is not possible.
• logger -- To enable logging set to True or pass a logger object to use. To disable
logging set to False. Note that fatal errors are logged even when logger is False.
• json -- An alternative json module to use for encoding and decoding packets. Custom json
modules must have dumps and loads functions that are compatible with the standard library
versions.
• async_handlers -- If set to True, event handlers are executed in separate threads. To run
handlers synchronously, set to False. The default is True.
• kwargs -- Connection parameters for the underlying Engine.IO server.
The Engine.IO configuration supports the following settings:
Parameters
• async_mode -- The asynchronous model to use. See the Deployment section in the
documentation for a description of the available options. Valid async modes are
"aiohttp". If this argument is not given, an async mode is chosen based on the installed
packages.
• ping_timeout -- The time in seconds that the client waits for the server to respond
before disconnecting.
• ping_interval -- The interval in seconds at which the client pings the server.
• max_http_buffer_size -- The maximum size of a message when using the polling transport.
• allow_upgrades -- Whether to allow transport upgrades or not.
• http_compression -- Whether to compress packages when using the polling transport.
• compression_threshold -- Only compress messages when their byte size is greater than this
value.
• cookie -- Name of the HTTP cookie that contains the client session id. If set to None, a
cookie is not sent to the client.
• cors_allowed_origins -- Origin or list of origins that are allowed to connect to this
server. Only the same origin is allowed by default. Set this argument to '*' to allow all
origins, or to [] to disable CORS handling.
• cors_credentials -- Whether credentials (cookies, authentication) are allowed in requests
to this server.
• monitor_clients -- If set to True, a background task will ensure inactive clients are
closed. Set to False to disable the monitoring task (not recommended). The default is
True.
• engineio_logger -- To enable Engine.IO logging set to True or pass a logger object to
use. To disable logging set to False. Note that fatal errors are logged even when
engineio_logger is False.
attach(app, socketio_path='socket.io')
Attach the Socket.IO server to an application.
async call(event, data=None, to=None, sid=None, namespace=None, timeout=60, **kwargs)
Emit a custom event to a client and wait for the response.
Parameters
• event -- The event name. It can be any string. The event names 'connect',
'message' and 'disconnect' are reserved and should not be used.
• data -- The data to send to the client or clients. Data can be of type str, bytes,
list or dict. To send multiple arguments, use a tuple where each element is of one
of the types indicated above.
• to -- The session ID of the recipient client.
• sid -- Alias for the to parameter.
• namespace -- The Socket.IO namespace for the event. If this argument is omitted
the event is emitted to the default namespace.
• timeout -- The waiting timeout. If the timeout is reached before the client
acknowledges the event, then a TimeoutError exception is raised.
• ignore_queue -- Only used when a message queue is configured. If set to True, the
event is emitted to the client directly, without going through the queue. This is
more efficient, but only works when a single server process is used. It is
recommended to always leave this parameter with its default value of False.
Note: this method is not designed to be used concurrently. If multiple tasks are emitting
at the same time to the same client connection, then messages composed of multiple packets
may end up being sent in an incorrect sequence. Use standard concurrency solutions (such as
a Lock object) to prevent this situation.
Note 2: this method is a coroutine.
async close_room(room, namespace=None)
Close a room.
This function removes all the clients from the given room.
Parameters
• room -- Room name.
• namespace -- The Socket.IO namespace for the event. If this argument is omitted
the default namespace is used.
Note: this method is a coroutine.
async disconnect(sid, namespace=None, ignore_queue=False)
Disconnect a client.
Parameters
• sid -- Session ID of the client.
• namespace -- The Socket.IO namespace to disconnect. If this argument is omitted
the default namespace is used.
• ignore_queue -- Only used when a message queue is configured. If set to True, the
disconnect is processed locally, without broadcasting on the queue. It is
recommended to always leave this parameter with its default value of False.
Note: this method is a coroutine.
async emit(event, data=None, to=None, room=None, skip_sid=None, namespace=None, callback=None,
**kwargs)
Emit a custom event to one or more connected clients.
Parameters
• event -- The event name. It can be any string. The event names 'connect',
'message' and 'disconnect' are reserved and should not be used.
• data -- The data to send to the client or clients. Data can be of type str, bytes,
list or dict. To send multiple arguments, use a tuple where each element is of one
of the types indicated above.
• to -- The recipient of the message. This can be set to the session ID of a client
to address only that client, or to to any custom room created by the application
to address all the clients in that room, If this argument is omitted the event is
broadcasted to all connected clients.
• room -- Alias for the to parameter.
• skip_sid -- The session ID of a client to skip when broadcasting to a room or to
all clients. This can be used to prevent a message from being sent to the sender.
• namespace -- The Socket.IO namespace for the event. If this argument is omitted
the event is emitted to the default namespace.
• callback -- If given, this function will be called to acknowledge the the client
has received the message. The arguments that will be passed to the function are
those provided by the client. Callback functions can only be used when addressing
an individual client.
• ignore_queue -- Only used when a message queue is configured. If set to True, the
event is emitted to the clients directly, without going through the queue. This
is more efficient, but only works when a single server process is used. It is
recommended to always leave this parameter with its default value of False.
Note: this method is not designed to be used concurrently. If multiple tasks are emitting
at the same time to the same client connection, then messages composed of multiple packets
may end up being sent in an incorrect sequence. Use standard concurrency solutions (such as
a Lock object) to prevent this situation.
Note 2: this method is a coroutine.
enter_room(sid, room, namespace=None)
Enter a room.
This function adds the client to a room. The emit() and send() functions can optionally
broadcast events to all the clients in a room.
Parameters
• sid -- Session ID of the client.
• room -- Room name. If the room does not exist it is created.
• namespace -- The Socket.IO namespace for the event. If this argument is omitted
the default namespace is used.
event(*args, **kwargs)
Decorator to register an event handler.
This is a simplified version of the on() method that takes the event name from the
decorated function.
Example usage:
@sio.event
def my_event(data):
print('Received data: ', data)
The above example is equivalent to:
@sio.on('my_event')
def my_event(data):
print('Received data: ', data)
A custom namespace can be given as an argument to the decorator:
@sio.event(namespace='/test')
def my_event(data):
print('Received data: ', data)
get_environ(sid, namespace=None)
Return the WSGI environ dictionary for a client.
Parameters
• sid -- The session of the client.
• namespace -- The Socket.IO namespace. If this argument is omitted the default
namespace is used.
async get_session(sid, namespace=None)
Return the user session for a client.
Parameters
• sid -- The session id of the client.
• namespace -- The Socket.IO namespace. If this argument is omitted the default
namespace is used.
The return value is a dictionary. Modifications made to this dictionary are not guaranteed
to be preserved. If you want to modify the user session, use the session context manager
instead.
async handle_request(*args, **kwargs)
Handle an HTTP request from the client.
This is the entry point of the Socket.IO application. This function returns the HTTP
response body to deliver to the client.
Note: this method is a coroutine.
leave_room(sid, room, namespace=None)
Leave a room.
This function removes the client from a room.
Parameters
• sid -- Session ID of the client.
• room -- Room name.
• namespace -- The Socket.IO namespace for the event. If this argument is omitted
the default namespace is used.
on(event, handler=None, namespace=None)
Register an event handler.
Parameters
• event -- The event name. It can be any string. The event names 'connect',
'message' and 'disconnect' are reserved and should not be used.
• handler -- The function that should be invoked to handle the event. When this
parameter is not given, the method acts as a decorator for the handler function.
• namespace -- The Socket.IO namespace for the event. If this argument is omitted
the handler is associated with the default namespace.
Example usage:
# as a decorator:
@socket_io.on('connect', namespace='/chat')
def connect_handler(sid, environ):
print('Connection request')
if environ['REMOTE_ADDR'] in blacklisted:
return False # reject
# as a method:
def message_handler(sid, msg):
print('Received message: ', msg)
eio.send(sid, 'response')
socket_io.on('message', namespace='/chat', handler=message_handler)
The handler function receives the sid (session ID) for the client as first argument. The
'connect' event handler receives the WSGI environment as a second argument, and can return
False to reject the connection. The 'message' handler and handlers for custom event names
receive the message payload as a second argument. Any values returned from a message
handler will be passed to the client's acknowledgement callback function if it exists. The
'disconnect' handler does not take a second argument.
register_namespace(namespace_handler)
Register a namespace handler object.
Parameters
namespace_handler -- An instance of a Namespace subclass that handles all the event
traffic for a namespace.
rooms(sid, namespace=None)
Return the rooms a client is in.
Parameters
• sid -- Session ID of the client.
• namespace -- The Socket.IO namespace for the event. If this argument is omitted
the default namespace is used.
async save_session(sid, session, namespace=None)
Store the user session for a client.
Parameters
• sid -- The session id of the client.
• session -- The session dictionary.
• namespace -- The Socket.IO namespace. If this argument is omitted the default
namespace is used.
async send(data, to=None, room=None, skip_sid=None, namespace=None, callback=None, **kwargs)
Send a message to one or more connected clients.
This function emits an event with the name 'message'. Use emit() to issue custom event
names.
Parameters
• data -- The data to send to the client or clients. Data can be of type str, bytes,
list or dict. To send multiple arguments, use a tuple where each element is of one
of the types indicated above.
• to -- The recipient of the message. This can be set to the session ID of a client
to address only that client, or to to any custom room created by the application
to address all the clients in that room, If this argument is omitted the event is
broadcasted to all connected clients.
• room -- Alias for the to parameter.
• skip_sid -- The session ID of a client to skip when broadcasting to a room or to
all clients. This can be used to prevent a message from being sent to the sender.
• namespace -- The Socket.IO namespace for the event. If this argument is omitted
the event is emitted to the default namespace.
• callback -- If given, this function will be called to acknowledge the the client
has received the message. The arguments that will be passed to the function are
those provided by the client. Callback functions can only be used when addressing
an individual client.
• ignore_queue -- Only used when a message queue is configured. If set to True, the
event is emitted to the clients directly, without going through the queue. This
is more efficient, but only works when a single server process is used. It is
recommended to always leave this parameter with its default value of False.
Note: this method is a coroutine.
session(sid, namespace=None)
Return the user session for a client with context manager syntax.
Parameters
sid -- The session id of the client.
This is a context manager that returns the user session dictionary for the client. Any
changes that are made to this dictionary inside the context manager block are saved back to
the session. Example usage:
@eio.on('connect')
def on_connect(sid, environ):
username = authenticate_user(environ)
if not username:
return False
with eio.session(sid) as session:
session['username'] = username
@eio.on('message')
def on_message(sid, msg):
async with eio.session(sid) as session:
print('received message from ', session['username'])
async sleep(seconds=0)
Sleep for the requested amount of time using the appropriate async model.
This is a utility function that applications can use to put a task to sleep without having
to worry about using the correct call for the selected async mode.
Note: this method is a coroutine.
start_background_task(target, *args, **kwargs)
Start a background task using the appropriate async model.
This is a utility function that applications can use to start a background task using the
method that is compatible with the selected async mode.
Parameters
• target -- the target function to execute. Must be a coroutine.
• args -- arguments to pass to the function.
• kwargs -- keyword arguments to pass to the function.
The return value is a asyncio.Task object.
Note: this method is a coroutine.
transport(sid)
Return the name of the transport used by the client.
The two possible values returned by this function are 'polling' and 'websocket'.
Parameters
sid -- The session of the client.
ConnectionRefusedError class
WSGIApp class
class socketio.WSGIApp(socketio_app, wsgi_app=None, static_files=None, socketio_path='socket.io')
WSGI middleware for Socket.IO.
This middleware dispatches traffic to a Socket.IO application. It can also serve a list of static
files to the client, or forward unrelated HTTP traffic to another WSGI application.
Parameters
• socketio_app -- The Socket.IO server. Must be an instance of the socketio.Server class.
• wsgi_app -- The WSGI app that receives all other traffic.
• static_files -- A dictionary with static file mapping rules. See the documentation for
details on this argument.
• socketio_path -- The endpoint where the Socket.IO application should be installed. The
default value is appropriate for most cases.
Example usage:
import socketio
import eventlet
from . import wsgi_app
sio = socketio.Server()
app = socketio.WSGIApp(sio, wsgi_app)
eventlet.wsgi.server(eventlet.listen(('', 8000)), app)
ASGIApp class
class socketio.ASGIApp(socketio_server, other_asgi_app=None, static_files=None,
socketio_path='socket.io', on_startup=None, on_shutdown=None)
ASGI application middleware for Socket.IO.
This middleware dispatches traffic to an Socket.IO application. It can also serve a list of static
files to the client, or forward unrelated HTTP traffic to another ASGI application.
Parameters
• socketio_server -- The Socket.IO server. Must be an instance of the socketio.AsyncServer
class.
• static_files -- A dictionary with static file mapping rules. See the documentation for
details on this argument.
• other_asgi_app -- A separate ASGI app that receives all other traffic.
• socketio_path -- The endpoint where the Socket.IO application should be installed. The
default value is appropriate for most cases.
• on_startup -- function to be called on application startup; can be coroutine
• on_shutdown -- function to be called on application shutdown; can be coroutine
Example usage:
import socketio
import uvicorn
sio = socketio.AsyncServer()
app = engineio.ASGIApp(sio, static_files={
'/': 'index.html',
'/static': './public',
})
uvicorn.run(app, host='127.0.0.1', port=5000)
Middleware class (deprecated)
class socketio.Middleware(socketio_app, wsgi_app=None, socketio_path='socket.io')
This class has been renamed to WSGIApp and is now deprecated.
ClientNamespace class
class socketio.ClientNamespace(namespace=None)
Base class for client-side class-based namespaces.
A class-based namespace is a class that contains all the event handlers for a Socket.IO namespace.
The event handlers are methods of the class with the prefix on_, such as on_connect,
on_disconnect, on_message, on_json, and so on.
Parameters
namespace -- The Socket.IO namespace to be used with all the event handlers defined in this
class. If this argument is omitted, the default namespace is used.
disconnect()
Disconnect from the server.
The only difference with the socketio.Client.disconnect() method is that when the namespace
argument is not given the namespace associated with the class is used.
emit(event, data=None, namespace=None, callback=None)
Emit a custom event to the server.
The only difference with the socketio.Client.emit() method is that when the namespace
argument is not given the namespace associated with the class is used.
send(data, room=None, skip_sid=None, namespace=None, callback=None)
Send a message to the server.
The only difference with the socketio.Client.send() method is that when the namespace
argument is not given the namespace associated with the class is used.
trigger_event(event, *args)
Dispatch an event to the proper handler method.
In the most common usage, this method is not overloaded by subclasses, as it performs the
routing of events to methods. However, this method can be overriden if special dispatching
rules are needed, or if having a single method that catches all events is desired.
Namespace class
class socketio.Namespace(namespace=None)
Base class for server-side class-based namespaces.
A class-based namespace is a class that contains all the event handlers for a Socket.IO namespace.
The event handlers are methods of the class with the prefix on_, such as on_connect,
on_disconnect, on_message, on_json, and so on.
Parameters
namespace -- The Socket.IO namespace to be used with all the event handlers defined in this
class. If this argument is omitted, the default namespace is used.
close_room(room, namespace=None)
Close a room.
The only difference with the socketio.Server.close_room() method is that when the namespace
argument is not given the namespace associated with the class is used.
disconnect(sid, namespace=None)
Disconnect a client.
The only difference with the socketio.Server.disconnect() method is that when the namespace
argument is not given the namespace associated with the class is used.
emit(event, data=None, room=None, skip_sid=None, namespace=None, callback=None)
Emit a custom event to one or more connected clients.
The only difference with the socketio.Server.emit() method is that when the namespace
argument is not given the namespace associated with the class is used.
enter_room(sid, room, namespace=None)
Enter a room.
The only difference with the socketio.Server.enter_room() method is that when the namespace
argument is not given the namespace associated with the class is used.
get_session(sid, namespace=None)
Return the user session for a client.
The only difference with the socketio.Server.get_session() method is that when the
namespace argument is not given the namespace associated with the class is used.
leave_room(sid, room, namespace=None)
Leave a room.
The only difference with the socketio.Server.leave_room() method is that when the namespace
argument is not given the namespace associated with the class is used.
rooms(sid, namespace=None)
Return the rooms a client is in.
The only difference with the socketio.Server.rooms() method is that when the namespace
argument is not given the namespace associated with the class is used.
save_session(sid, session, namespace=None)
Store the user session for a client.
The only difference with the socketio.Server.save_session() method is that when the
namespace argument is not given the namespace associated with the class is used.
send(data, room=None, skip_sid=None, namespace=None, callback=None)
Send a message to one or more connected clients.
The only difference with the socketio.Server.send() method is that when the namespace
argument is not given the namespace associated with the class is used.
session(sid, namespace=None)
Return the user session for a client with context manager syntax.
The only difference with the socketio.Server.session() method is that when the namespace
argument is not given the namespace associated with the class is used.
trigger_event(event, *args)
Dispatch an event to the proper handler method.
In the most common usage, this method is not overloaded by subclasses, as it performs the
routing of events to methods. However, this method can be overriden if special dispatching
rules are needed, or if having a single method that catches all events is desired.
AsyncClientNamespace class
class socketio.AsyncClientNamespace(namespace=None)
Base class for asyncio client-side class-based namespaces.
A class-based namespace is a class that contains all the event handlers for a Socket.IO namespace.
The event handlers are methods of the class with the prefix on_, such as on_connect,
on_disconnect, on_message, on_json, and so on. These can be regular functions or coroutines.
Parameters
namespace -- The Socket.IO namespace to be used with all the event handlers defined in this
class. If this argument is omitted, the default namespace is used.
async disconnect()
Disconnect a client.
The only difference with the socketio.Client.disconnect() method is that when the namespace
argument is not given the namespace associated with the class is used.
Note: this method is a coroutine.
async emit(event, data=None, namespace=None, callback=None)
Emit a custom event to the server.
The only difference with the socketio.Client.emit() method is that when the namespace
argument is not given the namespace associated with the class is used.
Note: this method is a coroutine.
async send(data, namespace=None, callback=None)
Send a message to the server.
The only difference with the socketio.Client.send() method is that when the namespace
argument is not given the namespace associated with the class is used.
Note: this method is a coroutine.
async trigger_event(event, *args)
Dispatch an event to the proper handler method.
In the most common usage, this method is not overloaded by subclasses, as it performs the
routing of events to methods. However, this method can be overriden if special dispatching
rules are needed, or if having a single method that catches all events is desired.
Note: this method is a coroutine.
AsyncNamespace class
class socketio.AsyncNamespace(namespace=None)
Base class for asyncio server-side class-based namespaces.
A class-based namespace is a class that contains all the event handlers for a Socket.IO namespace.
The event handlers are methods of the class with the prefix on_, such as on_connect,
on_disconnect, on_message, on_json, and so on. These can be regular functions or coroutines.
Parameters
namespace -- The Socket.IO namespace to be used with all the event handlers defined in this
class. If this argument is omitted, the default namespace is used.
async close_room(room, namespace=None)
Close a room.
The only difference with the socketio.Server.close_room() method is that when the namespace
argument is not given the namespace associated with the class is used.
Note: this method is a coroutine.
async disconnect(sid, namespace=None)
Disconnect a client.
The only difference with the socketio.Server.disconnect() method is that when the namespace
argument is not given the namespace associated with the class is used.
Note: this method is a coroutine.
async emit(event, data=None, room=None, skip_sid=None, namespace=None, callback=None)
Emit a custom event to one or more connected clients.
The only difference with the socketio.Server.emit() method is that when the namespace
argument is not given the namespace associated with the class is used.
Note: this method is a coroutine.
enter_room(sid, room, namespace=None)
Enter a room.
The only difference with the socketio.Server.enter_room() method is that when the namespace
argument is not given the namespace associated with the class is used.
async get_session(sid, namespace=None)
Return the user session for a client.
The only difference with the socketio.Server.get_session() method is that when the
namespace argument is not given the namespace associated with the class is used.
Note: this method is a coroutine.
leave_room(sid, room, namespace=None)
Leave a room.
The only difference with the socketio.Server.leave_room() method is that when the namespace
argument is not given the namespace associated with the class is used.
rooms(sid, namespace=None)
Return the rooms a client is in.
The only difference with the socketio.Server.rooms() method is that when the namespace
argument is not given the namespace associated with the class is used.
async save_session(sid, session, namespace=None)
Store the user session for a client.
The only difference with the socketio.Server.save_session() method is that when the
namespace argument is not given the namespace associated with the class is used.
Note: this method is a coroutine.
async send(data, room=None, skip_sid=None, namespace=None, callback=None)
Send a message to one or more connected clients.
The only difference with the socketio.Server.send() method is that when the namespace
argument is not given the namespace associated with the class is used.
Note: this method is a coroutine.
session(sid, namespace=None)
Return the user session for a client with context manager syntax.
The only difference with the socketio.Server.session() method is that when the namespace
argument is not given the namespace associated with the class is used.
async trigger_event(event, *args)
Dispatch an event to the proper handler method.
In the most common usage, this method is not overloaded by subclasses, as it performs the
routing of events to methods. However, this method can be overriden if special dispatching
rules are needed, or if having a single method that catches all events is desired.
Note: this method is a coroutine.
BaseManager class
class socketio.BaseManager
Manage client connections.
This class keeps track of all the clients and the rooms they are in, to support the broadcasting
of messages. The data used by this class is stored in a memory structure, making it appropriate
only for single process services. More sophisticated storage backends can be implemented by
subclasses.
close_room(room, namespace)
Remove all participants from a room.
connect(eio_sid, namespace)
Register a client connection to a namespace.
disconnect(sid, namespace)
Register a client disconnect from a namespace.
emit(event, data, namespace, room=None, skip_sid=None, callback=None, **kwargs)
Emit a message to a single client, a room, or all the clients connected to the namespace.
enter_room(sid, namespace, room, eio_sid=None)
Add a client to a room.
get_namespaces()
Return an iterable with the active namespace names.
get_participants(namespace, room)
Return an iterable with the active participants in a room.
get_rooms(sid, namespace)
Return the rooms a client is in.
initialize()
Invoked before the first request is received. Subclasses can add their initialization code
here.
leave_room(sid, namespace, room)
Remove a client from a room.
pre_disconnect(sid, namespace)
Put the client in the to-be-disconnected list.
This allows the client data structures to be present while the disconnect handler is
invoked, but still recognize the fact that the client is soon going away.
trigger_callback(sid, id, data)
Invoke an application callback.
PubSubManager class
class socketio.PubSubManager(channel='socketio', write_only=False, logger=None)
Manage a client list attached to a pub/sub backend.
This is a base class that enables multiple servers to share the list of clients, with the servers
communicating events through a pub/sub backend. The use of a pub/sub backend also allows any
client connected to the backend to emit events addressed to Socket.IO clients.
The actual backends must be implemented by subclasses, this class only provides a pub/sub generic
framework.
Parameters
channel -- The channel name on which the server sends and receives notifications.
close_room(room, namespace=None)
Remove all participants from a room.
emit(event, data, namespace=None, room=None, skip_sid=None, callback=None, **kwargs)
Emit a message to a single client, a room, or all the clients connected to the namespace.
This method takes care or propagating the message to all the servers that are connected
through the message queue.
The parameters are the same as in Server.emit().
initialize()
Invoked before the first request is received. Subclasses can add their initialization code
here.
KombuManager class
class socketio.KombuManager(url='amqp://guest:guest@localhost:5672//', channel='socketio',
write_only=False, logger=None, connection_options=None, exchange_options=None, queue_options=None,
producer_options=None)
Client manager that uses kombu for inter-process messaging.
This class implements a client manager backend for event sharing across multiple processes, using
RabbitMQ, Redis or any other messaging mechanism supported by kombu.
To use a kombu backend, initialize the Server instance as follows:
url = 'amqp://user:password@hostname:port//'
server = socketio.Server(client_manager=socketio.KombuManager(url))
Parameters
• url -- The connection URL for the backend messaging queue. Example connection URLs are
'amqp://guest:guest@localhost:5672//' and 'redis://localhost:6379/' for RabbitMQ and
Redis respectively. Consult the kombu documentation for more on how to construct
connection URLs.
• channel -- The channel name on which the server sends and receives notifications. Must be
the same in all the servers.
• write_only -- If set ot True, only initialize to emit events. The default of False
initializes the class for emitting and receiving.
• connection_options -- additional keyword arguments to be passed to kombu.Connection().
• exchange_options -- additional keyword arguments to be passed to kombu.Exchange().
• queue_options -- additional keyword arguments to be passed to kombu.Queue().
• producer_options -- additional keyword arguments to be passed to kombu.Producer().
initialize()
Invoked before the first request is received. Subclasses can add their initialization code
here.
RedisManager class
class socketio.RedisManager(url='redis://localhost:6379/0', channel='socketio', write_only=False,
logger=None, redis_options=None)
Redis based client manager.
This class implements a Redis backend for event sharing across multiple processes. Only kept here
as one more example of how to build a custom backend, since the kombu backend is perfectly
adequate to support a Redis message queue.
To use a Redis backend, initialize the Server instance as follows:
url = 'redis://hostname:port/0'
server = socketio.Server(client_manager=socketio.RedisManager(url))
Parameters
• url -- The connection URL for the Redis server. For a default Redis store running on the
same host, use redis://.
• channel -- The channel name on which the server sends and receives notifications. Must be
the same in all the servers.
• write_only -- If set ot True, only initialize to emit events. The default of False
initializes the class for emitting and receiving.
• redis_options -- additional keyword arguments to be passed to Redis.from_url().
initialize()
Invoked before the first request is received. Subclasses can add their initialization code
here.
KafkaManager class
class socketio.KafkaManager(url='kafka://localhost:9092', channel='socketio', write_only=False)
Kafka based client manager.
This class implements a Kafka backend for event sharing across multiple processes.
To use a Kafka backend, initialize the Server instance as follows:
url = 'kafka://hostname:port'
server = socketio.Server(client_manager=socketio.KafkaManager(url))
Parameters
• url -- The connection URL for the Kafka server. For a default Kafka store running on the
same host, use kafka://.
• channel -- The channel name (topic) on which the server sends and receives notifications.
Must be the same in all the servers.
• write_only -- If set ot True, only initialize to emit events. The default of False
initializes the class for emitting and receiving.
AsyncManager class
class socketio.AsyncManager
Manage a client list for an asyncio server.
async close_room(room, namespace)
Remove all participants from a room.
Note: this method is a coroutine.
connect(eio_sid, namespace)
Register a client connection to a namespace.
disconnect(sid, namespace)
Register a client disconnect from a namespace.
async emit(event, data, namespace, room=None, skip_sid=None, callback=None, **kwargs)
Emit a message to a single client, a room, or all the clients connected to the namespace.
Note: this method is a coroutine.
enter_room(sid, namespace, room, eio_sid=None)
Add a client to a room.
get_namespaces()
Return an iterable with the active namespace names.
get_participants(namespace, room)
Return an iterable with the active participants in a room.
get_rooms(sid, namespace)
Return the rooms a client is in.
initialize()
Invoked before the first request is received. Subclasses can add their initialization code
here.
leave_room(sid, namespace, room)
Remove a client from a room.
pre_disconnect(sid, namespace)
Put the client in the to-be-disconnected list.
This allows the client data structures to be present while the disconnect handler is
invoked, but still recognize the fact that the client is soon going away.
async trigger_callback(sid, id, data)
Invoke an application callback.
Note: this method is a coroutine.
AsyncRedisManager class
class socketio.AsyncRedisManager(url='redis://localhost:6379/0', channel='socketio', write_only=False,
logger=None)
Redis based client manager for asyncio servers.
This class implements a Redis backend for event sharing across multiple processes. Only kept here
as one more example of how to build a custom backend, since the kombu backend is perfectly
adequate to support a Redis message queue.
To use a Redis backend, initialize the Server instance as follows:
server = socketio.Server(client_manager=socketio.AsyncRedisManager(
'redis://hostname:port/0'))
Parameters
• url -- The connection URL for the Redis server. For a default Redis store running on the
same host, use redis://. To use an SSL connection, use rediss://.
• channel -- The channel name on which the server sends and receives notifications. Must be
the same in all the servers.
• write_only -- If set ot True, only initialize to emit events. The default of False
initializes the class for emitting and receiving.
AsyncAioPikaManager class
class socketio.AsyncAioPikaManager(url='amqp://guest:guest@localhost:5672//', channel='socketio',
write_only=False, logger=None)
Client manager that uses aio_pika for inter-process messaging under asyncio.
This class implements a client manager backend for event sharing across multiple processes, using
RabbitMQ
To use a aio_pika backend, initialize the Server instance as follows:
url = 'amqp://user:password@hostname:port//'
server = socketio.Server(client_manager=socketio.AsyncAioPikaManager(
url))
Parameters
• url -- The connection URL for the backend messaging queue. Example connection URLs are
'amqp://guest:guest@localhost:5672//' for RabbitMQ.
• channel -- The channel name on which the server sends and receives notifications. Must be
the same in all the servers. With this manager, the channel name is the exchange name in
rabbitmq
• write_only -- If set ot True, only initialize to emit events. The default of False
initializes the class for emitting and receiving.
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AUTHOR
Miguel Grinberg
COPYRIGHT
2018, Miguel Grinberg
Dec 24, 2020 PYTHON-SOCKETIO(1)