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.TH "PYTHON-SOCKETIO" "1" "May 19, 2025" "" "python-socketio"
.SH NAME
python-socketio \- python-socketio Documentation
.sp
This projects implements Socket.IO clients and servers that can run standalone
or integrated with a variety of Python web frameworks.
.SH GETTING STARTED
.SS What is Socket.IO?
.sp
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.
.SS Version compatibility
.sp
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.
.sp
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.
.sp
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.
.TS
box center;
l|l|l|l|l.
T{
JavaScript Socket.IO version
T}	T{
Socket.IO protocol revision
T}	T{
Engine.IO protocol revision
T}	T{
python\-socketio version
T}	T{
python\-engineio version
T}
_
T{
0.9.x
T}	T{
1, 2
T}	T{
1, 2
T}	T{
Not supported
T}	T{
Not supported
T}
_
T{
1.x and 2.x
T}	T{
3, 4
T}	T{
3
T}	T{
4.x
T}	T{
3.x
T}
_
T{
3.x and 4.x
T}	T{
5
T}	T{
4
T}	T{
5.x
T}	T{
4.x
T}
.TE
.SS Client Examples
.sp
The example that follows shows a simple Python client:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
import socketio

sio = socketio.Client()

@sio.event
def connect():
    print(\(aqconnection established\(aq)

@sio.event
def my_message(data):
    print(\(aqmessage received with \(aq, data)
    sio.emit(\(aqmy response\(aq, {\(aqresponse\(aq: \(aqmy response\(aq})

@sio.event
def disconnect():
    print(\(aqdisconnected from server\(aq)

sio.connect(\(aqhttp://localhost:5000\(aq)
sio.wait()
.EE
.UNINDENT
.UNINDENT
.sp
Below is a similar client, coded for \fBasyncio\fP (Python 3.5+ only):
.INDENT 0.0
.INDENT 3.5
.sp
.EX
import asyncio
import socketio

sio = socketio.AsyncClient()

@sio.event
async def connect():
    print(\(aqconnection established\(aq)

@sio.event
async def my_message(data):
    print(\(aqmessage received with \(aq, data)
    await sio.emit(\(aqmy response\(aq, {\(aqresponse\(aq: \(aqmy response\(aq})

@sio.event
async def disconnect():
    print(\(aqdisconnected from server\(aq)

async def main():
    await sio.connect(\(aqhttp://localhost:5000\(aq)
    await sio.wait()

if __name__ == \(aq__main__\(aq:
    asyncio.run(main())
.EE
.UNINDENT
.UNINDENT
.SS Client Features
.INDENT 0.0
.IP \(bu 2
Can connect to other Socket.IO servers that are compatible with the
JavaScript Socket.IO reference server.
.IP \(bu 2
Compatible with Python 3.8+.
.IP \(bu 2
Two versions of the client, one for standard Python and another for
asyncio.
.IP \(bu 2
Uses an event\-based architecture implemented with decorators that
hides the details of the protocol.
.IP \(bu 2
Implements HTTP long\-polling and WebSocket transports.
.IP \(bu 2
Automatically reconnects to the server if the connection is dropped.
.UNINDENT
.SS Server Examples
.sp
The following application is a basic server example that uses the Eventlet
asynchronous server:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
import eventlet
import socketio

sio = socketio.Server()
app = socketio.WSGIApp(sio, static_files={
    \(aq/\(aq: {\(aqcontent_type\(aq: \(aqtext/html\(aq, \(aqfilename\(aq: \(aqindex.html\(aq}
})

@sio.event
def connect(sid, environ):
    print(\(aqconnect \(aq, sid)

@sio.event
def my_message(sid, data):
    print(\(aqmessage \(aq, data)

@sio.event
def disconnect(sid):
    print(\(aqdisconnect \(aq, sid)

if __name__ == \(aq__main__\(aq:
    eventlet.wsgi.server(eventlet.listen((\(aq\(aq, 5000)), app)
.EE
.UNINDENT
.UNINDENT
.sp
Below is a similar application, coded for \fBasyncio\fP (Python 3.5+ only) and the
Uvicorn web server:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
from aiohttp import web
import socketio

sio = socketio.AsyncServer()
app = web.Application()
sio.attach(app)

async def index(request):
    \(dq\(dq\(dqServe the client\-side application.\(dq\(dq\(dq
    with open(\(aqindex.html\(aq) as f:
        return web.Response(text=f.read(), content_type=\(aqtext/html\(aq)

@sio.event
def connect(sid, environ):
    print(\(dqconnect \(dq, sid)

@sio.event
async def chat_message(sid, data):
    print(\(dqmessage \(dq, data)

@sio.event
def disconnect(sid):
    print(\(aqdisconnect \(aq, sid)

app.router.add_static(\(aq/static\(aq, \(aqstatic\(aq)
app.router.add_get(\(aq/\(aq, index)

if __name__ == \(aq__main__\(aq:
    web.run_app(app)
.EE
.UNINDENT
.UNINDENT
.SS Server Features
.INDENT 0.0
.IP \(bu 2
Can connect to servers running other Socket.IO clients that are compatible
with the JavaScript reference client.
.IP \(bu 2
Compatible with Python 3.8+.
.IP \(bu 2
Two versions of the server, one for standard Python and another for
asyncio.
.IP \(bu 2
Supports large number of clients even on modest hardware due to being
asynchronous.
.IP \(bu 2
Can be hosted on any \X'tty: link https://wsgi.readthedocs.io/en/latest/index.html'\fI\%WSGI\fP\X'tty: link' or
\X'tty: link https://asgi.readthedocs.io/en/latest/'\fI\%ASGI\fP\X'tty: link' web server including
\X'tty: link https://gunicorn.org/'\fI\%Gunicorn\fP\X'tty: link', \X'tty: link https://github.com/encode/uvicorn'\fI\%Uvicorn\fP\X'tty: link',
\X'tty: link http://eventlet.net/'\fI\%eventlet\fP\X'tty: link' and \X'tty: link http://www.gevent.org'\fI\%gevent\fP\X'tty: link'\&.
.IP \(bu 2
Can be integrated with WSGI applications written in frameworks such as Flask, Django,
etc.
.IP \(bu 2
Can be integrated with \X'tty: link http://aiohttp.readthedocs.io/'\fI\%aiohttp\fP\X'tty: link',
\X'tty: link https://fastapi.tiangolo.com/'\fI\%FastAPI\fP\X'tty: link', \X'tty: link http://sanic.readthedocs.io/'\fI\%sanic\fP\X'tty: link'
and \X'tty: link http://www.tornadoweb.org/'\fI\%tornado\fP\X'tty: link' \fBasyncio\fP applications.
.IP \(bu 2
Broadcasting of messages to all connected clients, or to subsets of them
assigned to \(dqrooms\(dq.
.IP \(bu 2
Optional support for multiple servers, connected through a messaging queue
such as Redis or RabbitMQ.
.IP \(bu 2
Send messages to clients from external processes, such as Celery workers or
auxiliary scripts.
.IP \(bu 2
Event\-based architecture implemented with decorators that hides the details
of the protocol.
.IP \(bu 2
Support for HTTP long\-polling and WebSocket transports.
.IP \(bu 2
Support for XHR2 and XHR browsers.
.IP \(bu 2
Support for text and binary messages.
.IP \(bu 2
Support for gzip and deflate HTTP compression.
.IP \(bu 2
Configurable CORS responses, to avoid cross\-origin problems with browsers.
.UNINDENT
.SH THE SOCKET.IO CLIENTS
.sp
This package contains two Socket.IO clients:
.INDENT 0.0
.IP \(bu 2
a \(dqsimple\(dq client, which provides a straightforward API that is sufficient
for most applications
.IP \(bu 2
an \(dqevent\-driven\(dq client, which provides access to all the features of the
Socket.IO protocol
.UNINDENT
.sp
Each of these clients comes in two variants: one for the standard Python
library, and another for asynchronous applications built with the \fBasyncio\fP
package.
.SS Installation
.sp
To install the standard Python client along with its dependencies, use the
following command:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
pip install \(dqpython\-socketio[client]\(dq
.EE
.UNINDENT
.UNINDENT
.sp
If instead you plan on using the \fBasyncio\fP client, then use this:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
pip install \(dqpython\-socketio[asyncio_client]\(dq
.EE
.UNINDENT
.UNINDENT
.SS Using the Simple Client
.sp
The advantage of the simple client is that it abstracts away the logic required
to maintain a Socket.IO connection. This client handles disconnections and
reconnections in a completely transparent way, without adding any complexity to
the application.
.SS Creating a Client Instance
.sp
The easiest way to create a Socket.IO client is to use the context manager
interface:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
import socketio

# standard Python
with socketio.SimpleClient() as sio:
    # ... connect to a server and use the client
    # ... no need to manually disconnect!

# asyncio
async with socketio.AsyncSimpleClient() as sio:
    # ... connect to a server and use the client
    # ... no need to manually disconnect!
.EE
.UNINDENT
.UNINDENT
.sp
With this usage the context manager will ensure that the client is properly
disconnected before exiting the \fBwith\fP or \fBasync with\fP block.
.sp
If preferred, a client can be manually instantiated:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
import socketio

# standard Python
sio = socketio.SimpleClient()

# asyncio
sio = socketio.AsyncSimpleClient()
.EE
.UNINDENT
.UNINDENT
.SS Connecting to a Server
.sp
The connection to a server is established by calling the \fBconnect()\fP
method:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
sio.connect(\(aqhttp://localhost:5000\(aq)
.EE
.UNINDENT
.UNINDENT
.sp
In the case of the \fBasyncio\fP client, the method is a coroutine:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
await sio.connect(\(aqhttp://localhost:5000\(aq)
.EE
.UNINDENT
.UNINDENT
.sp
By default the client first connects to the server using the long\-polling
transport, and then attempts to upgrade the connection to use WebSocket. To
connect directly using WebSocket, use the \fBtransports\fP argument:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
sio.connect(\(aqhttp://localhost:5000\(aq, transports=[\(aqwebsocket\(aq])
.EE
.UNINDENT
.UNINDENT
.sp
Upon connection, the server assigns the client a unique session identifier.
The application can find this identifier in the \fBsid\fP attribute:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
print(\(aqmy sid is\(aq, sio.sid)
.EE
.UNINDENT
.UNINDENT
.sp
The Socket.IO transport that is used in the connection can be obtained from the
\fBtransport\fP attribute:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
print(\(aqmy transport is\(aq, sio.transport)
.EE
.UNINDENT
.UNINDENT
.sp
The transport is given as a string, and can be either \fB\(aqwebsocket\(aq\fP or
\fB\(aqpolling\(aq\fP\&.
.SS TLS/SSL Support
.sp
The client supports TLS/SSL connections. To enable it, use a \fBhttps://\fP
connection URL:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
sio.connect(\(aqhttps://example.com\(aq)
.EE
.UNINDENT
.UNINDENT
.sp
Or when using \fBasyncio\fP:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
await sio.connect(\(aqhttps://example.com\(aq)
.EE
.UNINDENT
.UNINDENT
.sp
The client verifies server certificates by default. Consult the documentation
for the event\-driven client for information on how to customize this behavior.
.SS Emitting Events
.sp
The client can emit an event to the server using the \fBemit()\fP method:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
sio.emit(\(aqmy message\(aq, {\(aqfoo\(aq: \(aqbar\(aq})
.EE
.UNINDENT
.UNINDENT
.sp
Or in the case of \fBasyncio\fP, as a coroutine:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
await sio.emit(\(aqmy message\(aq, {\(aqfoo\(aq: \(aqbar\(aq})
.EE
.UNINDENT
.UNINDENT
.sp
The arguments provided to the method are the name of the event to emit and the
optional data that is passed on to the server. The data can be of type \fBstr\fP,
\fBbytes\fP, \fBdict\fP, \fBlist\fP or \fBtuple\fP\&. When sending a \fBlist\fP or a
\fBtuple\fP, the elements in it need to be of any allowed types except \fBtuple\fP\&.
When a tuple is used, the elements of the tuple will be passed as individual
arguments to the server\-side event handler function.
.SS Receiving Events
.sp
The client can wait for the server to emit an event with the \fBreceive()\fP
method:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
event = sio.receive()
print(f\(aqreceived event: \(dq{event[0]}\(dq with arguments {event[1:]}\(aq)
.EE
.UNINDENT
.UNINDENT
.sp
When using \fBasyncio\fP, this method needs to be awaited:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
event = await sio.receive()
print(f\(aqreceived event: \(dq{event[0]}\(dq with arguments {event[1:]}\(aq)
.EE
.UNINDENT
.UNINDENT
.sp
The return value of \fBreceive()\fP is a list. The first element of this list is
the event name, while the remaining elements are the arguments passed by the
server.
.sp
With the usage shown above, the \fBreceive()\fP method will return only when an
event is received from the server. An optional timeout in seconds can be passed
to prevent the client from waiting forever:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
from socketio.exceptions import TimeoutError

try:
    event = sio.receive(timeout=5)
except TimeoutError:
    print(\(aqtimed out waiting for event\(aq)
else:
    print(\(aqreceived event:\(aq, event)
.EE
.UNINDENT
.UNINDENT
.sp
Or with \fBasyncio\fP:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
from socketio.exceptions import TimeoutError

try:
    event = await sio.receive(timeout=5)
except TimeoutError:
    print(\(aqtimed out waiting for event\(aq)
else:
    print(\(aqreceived event:\(aq, event)
.EE
.UNINDENT
.UNINDENT
.SS Disconnecting from the Server
.sp
At any time the client can request to be disconnected from the server by
invoking the \fBdisconnect()\fP method:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
sio.disconnect()
.EE
.UNINDENT
.UNINDENT
.sp
For the \fBasyncio\fP client this is a coroutine:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
await sio.disconnect()
.EE
.UNINDENT
.UNINDENT
.SS Debugging and Troubleshooting
.sp
To help you debug issues, the client can be configured to output logs to the
terminal:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
import socketio

# standard Python
sio = socketio.Client(logger=True, engineio_logger=True)

# asyncio
sio = socketio.AsyncClient(logger=True, engineio_logger=True)
.EE
.UNINDENT
.UNINDENT
.sp
The \fBlogger\fP argument controls logging related to the Socket.IO protocol,
while \fBengineio_logger\fP controls logs that originate in the low\-level
Engine.IO transport. These arguments can be set to \fBTrue\fP to output logs to
\fBstderr\fP, or to an object compatible with Python\(aqs \fBlogging\fP package
where the logs should be emitted to. A value of \fBFalse\fP disables logging.
.sp
Logging can help identify the cause of connection problems, unexpected
disconnections and other issues.
.SS Using the Event\-Driven Client
.SS Creating a Client Instance
.sp
To instantiate an Socket.IO client, simply create an instance of the
appropriate client class:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
import socketio

# standard Python
sio = socketio.Client()

# asyncio
sio = socketio.AsyncClient()
.EE
.UNINDENT
.UNINDENT
.SS Defining Event Handlers
.sp
The Socket.IO protocol is event based. When a server wants to communicate with
a client it \fIemits\fP an event. Each event has a name, and a list of
arguments. The client registers event handler functions with the
\fBsocketio.Client.event()\fP or \fBsocketio.Client.on()\fP decorators:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
@sio.event
def message(data):
    print(\(aqI received a message!\(aq)

@sio.on(\(aqmy message\(aq)
def on_message(data):
    print(\(aqI received a message!\(aq)
.EE
.UNINDENT
.UNINDENT
.sp
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.
.sp
For the \fBasyncio\fP client, event handlers can be regular functions as above,
or can also be coroutines:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
@sio.event
async def message(data):
    print(\(aqI received a message!\(aq)
.EE
.UNINDENT
.UNINDENT
.sp
If the server includes arguments with an event, those are passed to the
handler function as arguments.
.SS Catch\-All Event and Namespace Handlers
.sp
A \(dqcatch\-all\(dq event handler is invoked for any events that do not have an
event handler. You can define a catch\-all handler using \fB\(aq*\(aq\fP as event name:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
@sio.on(\(aq*\(aq)
def any_event(event, sid, data):
     pass
.EE
.UNINDENT
.UNINDENT
.sp
Asyncio servers can also use a coroutine:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
@sio.on(\(aq*\(aq)
async def any_event(event, sid, data):
    pass
.EE
.UNINDENT
.UNINDENT
.sp
A catch\-all event handler receives the event name as a first argument. The
remaining arguments are the same as for a regular event handler.
.sp
The \fBconnect\fP and \fBdisconnect\fP events have to be defined explicitly and are
not invoked on a catch\-all event handler.
.sp
Similarily, a \(dqcatch\-all\(dq namespace handler is invoked for any connected
namespaces that do not have an explicitly defined event handler. As with
catch\-all events, \fB\(aq*\(aq\fP is used in place of a namespace:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
@sio.on(\(aqmy_event\(aq, namespace=\(aq*\(aq)
def my_event_any_namespace(namespace, sid, data):
    pass
.EE
.UNINDENT
.UNINDENT
.sp
For these events, the namespace is passed as first argument, followed by the
regular arguments of the event.
.sp
Lastly, it is also possible to define a \(dqcatch\-all\(dq handler for all events on
all namespaces:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
@sio.on(\(aq*\(aq, namespace=\(aq*\(aq)
def any_event_any_namespace(event, namespace, sid, data):
    pass
.EE
.UNINDENT
.UNINDENT
.sp
Event handlers with catch\-all events and namespaces receive the event name and
the namespace as first and second arguments.
.SS Connect, Connect Error and Disconnect Event Handlers
.sp
The \fBconnect\fP, \fBconnect_error\fP and \fBdisconnect\fP events are special; they
are invoked automatically when a client connects or disconnects from the
server:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
@sio.event
def connect():
    print(\(dqI\(aqm connected!\(dq)

@sio.event
def connect_error(data):
    print(\(dqThe connection failed!\(dq)

@sio.event
def disconnect(reason):
    print(\(dqI\(aqm disconnected! reason:\(dq, reason)
.EE
.UNINDENT
.UNINDENT
.sp
The \fBconnect_error\fP handler is invoked when a connection attempt fails. If
the server provides arguments, these are passed on to the handler. The server
can use an argument to provide information to the client regarding the
connection failure.
.sp
The \fBdisconnect\fP 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. The handler receives a \fBreason\fP argument which
provides the cause of the disconnection:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
@sio.event
def disconnect(reason):
    if reason == sio.reason.CLIENT_DISCONNECT:
        print(\(aqthe client disconnected\(aq)
    elif reason == sio.reason.SERVER_DISCONNECT:
        print(\(aqthe server disconnected the client\(aq)
    else:
        print(\(aqdisconnect reason:\(aq, reason)
.EE
.UNINDENT
.UNINDENT
.sp
See the The \fBsocketio.Client.reason\fP attribute for a list of possible
disconnection reasons.
.sp
The \fBconnect\fP, \fBconnect_error\fP and \fBdisconnect\fP events have to be
defined explicitly and are not invoked on a catch\-all event handler.
.SS Connecting to a Server
.sp
The connection to a server is established by calling the \fBconnect()\fP
method:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
sio.connect(\(aqhttp://localhost:5000\(aq)
.EE
.UNINDENT
.UNINDENT
.sp
In the case of the \fBasyncio\fP client, the method is a coroutine:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
await sio.connect(\(aqhttp://localhost:5000\(aq)
.EE
.UNINDENT
.UNINDENT
.sp
Upon connection, the server assigns the client a unique session identifier.
The application can find this identifier in the \fBsid\fP attribute:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
print(\(aqmy sid is\(aq, sio.sid)
.EE
.UNINDENT
.UNINDENT
.sp
The Socket.IO transport that is used in the connection can be obtained from the
\fBtransport\fP attribute:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
print(\(aqmy transport is\(aq, sio.transport)
.EE
.UNINDENT
.UNINDENT
.sp
The transport is given as a string, and can be either \fB\(aqwebsocket\(aq\fP or
\fB\(aqpolling\(aq\fP\&.
.SS TLS/SSL Support
.sp
The client supports TLS/SSL connections. To enable it, use a \fBhttps://\fP
connection URL:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
sio.connect(\(aqhttps://example.com\(aq)
.EE
.UNINDENT
.UNINDENT
.sp
Or when using \fBasyncio\fP:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
await sio.connect(\(aqhttps://example.com\(aq)
.EE
.UNINDENT
.UNINDENT
.sp
The client will verify the server certificate by default. To disable
certificate verification, or to use other less common options such as client
certificates, the client must be initialized with a custom HTTP session object
that is configured with the desired TLS/SSL options.
.sp
The following example disables server certificate verification, which can be
useful when connecting to a server that uses a self\-signed certificate:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
http_session = requests.Session()
http_session.verify = False
sio = socketio.Client(http_session=http_session)
sio.connect(\(aqhttps://example.com\(aq)
.EE
.UNINDENT
.UNINDENT
.sp
And when using \fBasyncio\fP:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
connector = aiohttp.TCPConnector(ssl=False)
http_session = aiohttp.ClientSession(connector=connector)
sio = socketio.AsyncClient(http_session=http_session)
await sio.connect(\(aqhttps://example.com\(aq)
.EE
.UNINDENT
.UNINDENT
.sp
Instead of disabling certificate verification, you can provide a custom
certificate authority bundle to verify the certificate against:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
http_session = requests.Session()
http_session.verify = \(aq/path/to/ca.pem\(aq
sio = socketio.Client(http_session=http_session)
sio.connect(\(aqhttps://example.com\(aq)
.EE
.UNINDENT
.UNINDENT
.sp
And for \fBasyncio\fP:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
ssl_context = ssl.create_default_context()
ssl_context.load_verify_locations(\(aq/path/to/ca.pem\(aq)
connector = aiohttp.TCPConnector(ssl=ssl_context)
http_session = aiohttp.ClientSession(connector=connector)
sio = socketio.AsyncClient(http_session=http_session)
await sio.connect(\(aqhttps://example.com\(aq)
.EE
.UNINDENT
.UNINDENT
.sp
Below you can see how to use a client certificate to authenticate against the
server:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
http_session = requests.Session()
http_session.cert = (\(aq/path/to/client/cert.pem\(aq, \(aq/path/to/client/key.pem\(aq)
sio = socketio.Client(http_session=http_session)
sio.connect(\(aqhttps://example.com\(aq)
.EE
.UNINDENT
.UNINDENT
.sp
And for \fBasyncio\fP:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
ssl_context = ssl.create_default_context(ssl.Purpose.CLIENT_AUTH)
ssl_context.load_cert_chain(\(aq/path/to/client/cert.pem\(aq,
                            \(aq/path/to/client/key.pem\(aq)
connector = aiohttp.TCPConnector(ssl=ssl_context)
http_session = aiohttp.ClientSession(connector=connector)
sio = socketio.AsyncClient(http_session=http_session)
await sio.connect(\(aqhttps://example.com\(aq)
.EE
.UNINDENT
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.SS Emitting Events
.sp
The client can emit an event to the server using the \fBemit()\fP method:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
sio.emit(\(aqmy message\(aq, {\(aqfoo\(aq: \(aqbar\(aq})
.EE
.UNINDENT
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.sp
Or in the case of \fBasyncio\fP, as a coroutine:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
await sio.emit(\(aqmy message\(aq, {\(aqfoo\(aq: \(aqbar\(aq})
.EE
.UNINDENT
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.sp
The arguments provided to the method are the name of the event to emit and the
optional data that is passed on to the server. The data can be of type \fBstr\fP,
\fBbytes\fP, \fBdict\fP, \fBlist\fP or \fBtuple\fP\&. When sending a \fBlist\fP or a
\fBtuple\fP, the elements in it need to be of any allowed types except \fBtuple\fP\&.
When a tuple is used, the elements of the tuple will be passed as individual
arguments to the server\-side event handler function.
.sp
The \fBemit()\fP 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.
.SS Event Callbacks
.sp
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:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
@sio.event
def my_event(sid, data):
    # handle the message
    return \(dqOK\(dq, 123
.EE
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.sp
Likewise, the client can request a callback function to be invoked after the
server has processed an event. The \fBsocketio.Server.emit()\fP method has an
optional \fBcallback\fP 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.
.SS Namespaces
.sp
The Socket.IO protocol supports multiple logical connections, all multiplexed
on the same physical connection. Clients can open multiple connections by
specifying a different \fInamespace\fP on each. Namespaces use a path syntax
starting with a forward slash. A list of namespaces can be given by the client
in the \fBconnect()\fP call. For example, this example creates two logical
connections, the default one plus a second connection under the \fB/chat\fP
namespace:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
sio.connect(\(aqhttp://localhost:5000\(aq, namespaces=[\(aq/chat\(aq])
.EE
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.sp
To define event handlers on a namespace, the \fBnamespace\fP argument must be
added to the corresponding decorator:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
@sio.event(namespace=\(aq/chat\(aq)
def my_custom_event(sid, data):
    pass

@sio.on(\(aqconnect\(aq, namespace=\(aq/chat\(aq)
def on_connect():
    print(\(dqI\(aqm connected to the /chat namespace!\(dq)
.EE
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.sp
Likewise, the client can emit an event to the server on a namespace by
providing its in the \fBemit()\fP call:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
sio.emit(\(aqmy message\(aq, {\(aqfoo\(aq: \(aqbar\(aq}, namespace=\(aq/chat\(aq)
.EE
.UNINDENT
.UNINDENT
.sp
If the \fBnamespaces\fP argument of the \fBconnect()\fP call isn\(aqt given, any
namespaces used in event handlers are automatically connected.
.SS Class\-Based Namespaces
.sp
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
\fBsocketio.ClientNamespace\fP:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
class MyCustomNamespace(socketio.ClientNamespace):
    def on_connect(self):
        pass

    def on_disconnect(self, reason):
        pass

    def on_my_event(self, data):
        self.emit(\(aqmy_response\(aq, data)

sio.register_namespace(MyCustomNamespace(\(aq/chat\(aq))
.EE
.UNINDENT
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.sp
For asyncio based servers, namespaces must inherit from
\fBsocketio.AsyncClientNamespace\fP, and can define event handlers as
coroutines if desired:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
class MyCustomNamespace(socketio.AsyncClientNamespace):
    def on_connect(self):
        pass

    def on_disconnect(self, reason):
        pass

    async def on_my_event(self, data):
        await self.emit(\(aqmy_response\(aq, data)

sio.register_namespace(MyCustomNamespace(\(aq/chat\(aq))
.EE
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.sp
A catch\-all class\-based namespace handler can be defined by passing \fB\(aq*\(aq\fP as
the namespace during registration:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
sio.register_namespace(MyCustomNamespace(\(aq*\(aq))
.EE
.UNINDENT
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.sp
When class\-based namespaces are used, any events received by the client are
dispatched to a method named as the event name with the \fBon_\fP prefix. For
example, event \fBmy_event\fP will be handled by a method named \fBon_my_event\fP\&.
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.
.sp
As a convenience to methods defined in a class\-based namespace, the namespace
instance includes versions of several of the methods in the
\fBsocketio.Client\fP and \fBsocketio.AsyncClient\fP classes that
default to the proper namespace when the \fBnamespace\fP argument is not given.
.sp
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.
.SS Disconnecting from the Server
.sp
At any time the client can request to be disconnected from the server by
invoking the \fBdisconnect()\fP method:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
sio.disconnect()
.EE
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For the \fBasyncio\fP client this is a coroutine:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
await sio.disconnect()
.EE
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.SS Managing Background Tasks
.sp
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.
.sp
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 \fBwait()\fP method:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
sio.wait()
.EE
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.UNINDENT
.sp
Or in the \fBasyncio\fP version:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
await sio.wait()
.EE
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.sp
For the convenience of the application, a helper function is provided to
start a custom background task:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
def my_background_task(my_argument):
    # do some background work here!
    pass

task = sio.start_background_task(my_background_task, 123)
.EE
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.sp
The arguments passed to this method are the background function and any
positional or keyword arguments to invoke the function with.
.sp
Here is the \fBasyncio\fP version:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
async def my_background_task(my_argument):
    # do some background work here!
    pass

task = sio.start_background_task(my_background_task, 123)
.EE
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.sp
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.
.sp
The \fBsleep()\fP method is a second convenience function that is provided for
the benefit of applications working with background tasks of their own:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
sio.sleep(2)
.EE
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.sp
Or for \fBasyncio\fP:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
await sio.sleep(2)
.EE
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.sp
The single argument passed to the method is the number of seconds to sleep
for.
.SS Debugging and Troubleshooting
.sp
To help you debug issues, the client can be configured to output logs to the
terminal:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
import socketio

# standard Python
sio = socketio.Client(logger=True, engineio_logger=True)

# asyncio
sio = socketio.AsyncClient(logger=True, engineio_logger=True)
.EE
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.sp
The \fBlogger\fP argument controls logging related to the Socket.IO protocol,
while \fBengineio_logger\fP controls logs that originate in the low\-level
Engine.IO transport. These arguments can be set to \fBTrue\fP to output logs to
\fBstderr\fP, or to an object compatible with Python\(aqs \fBlogging\fP package
where the logs should be emitted to. A value of \fBFalse\fP disables logging.
.sp
Logging can help identify the cause of connection problems, unexpected
disconnections and other issues.
.SH THE SOCKET.IO SERVER
.sp
This package contains two Socket.IO servers:
.INDENT 0.0
.IP \(bu 2
The \fBsocketio.Server()\fP class creates a server compatible with the
Python standard library.
.IP \(bu 2
The \fBsocketio.AsyncServer()\fP class creates a server compatible with
the \fBasyncio\fP package.
.UNINDENT
.sp
The methods in the two servers are the same, with the only difference that in
the \fBasyncio\fP server most methods are implemented as coroutines.
.SS Installation
.sp
To install the Socket.IO server along with its dependencies, use the following
command:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
pip install python\-socketio
.EE
.UNINDENT
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.SS Creating a Server Instance
.sp
A Socket.IO server is an instance of class \fBsocketio.Server\fP:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
import socketio

# create a Socket.IO server
sio = socketio.Server()
.EE
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.sp
For asyncio based servers, the \fBsocketio.AsyncServer\fP class provides
the same functionality, but in a coroutine friendly format:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
import socketio

# create a Socket.IO server
sio = socketio.AsyncServer()
.EE
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.SS Running the Server
.sp
To run the Socket.IO application it is necessary to configure a web server to
receive incoming requests from clients and forward them to the Socket.IO
server instance. To simplify this task, several integrations are available,
including support for the \X'tty: link https://wsgi.readthedocs.io/en/latest/what.html'\fI\%WSGI\fP\X'tty: link'
and \X'tty: link https://asgi.readthedocs.io/en/latest/'\fI\%ASGI\fP\X'tty: link' standards.
.SS Running as a WSGI Application
.sp
To configure the Socket.IO server as a WSGI application wrap the server
instance with the \fBsocketio.WSGIApp\fP class:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
# wrap with a WSGI application
app = socketio.WSGIApp(sio)
.EE
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.sp
The resulting WSGI application can be executed with supported WSGI servers
such as \X'tty: link https://werkzeug.palletsprojects.com'\fI\%Werkzeug\fP\X'tty: link' for development and
\X'tty: link https://gunicorn.org/'\fI\%Gunicorn\fP\X'tty: link' for production.
.sp
When combining Socket.IO with a web application written with a WSGI framework
such as Flask or Django, the \fBWSGIApp\fP class can wrap both applications
together and route traffic to them:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
from mywebapp import app  # a Flask, Django, etc. application
app = socketio.WSGIApp(sio, app)
.EE
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.SS Running as an ASGI Application
.sp
To configure the Socket.IO server as an ASGI application wrap the server
instance with the \fBsocketio.ASGIApp\fP class:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
# wrap with ASGI application
app = socketio.ASGIApp(sio)
.EE
.UNINDENT
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.sp
The resulting ASGI application can be executed with an ASGI compliant web
server, for example \X'tty: link https://www.uvicorn.org/'\fI\%Uvicorn\fP\X'tty: link'\&.
.sp
Socket.IO can also be combined with a web application written with an ASGI
web framework such as FastAPI. In that case, the \fBASGIApp\fP class can wrap
both applications together and route traffic to them:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
from mywebapp import app  # a FastAPI or other ASGI application
app = socketio.ASGIApp(sio, app)
.EE
.UNINDENT
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.SS Serving Static Files
.sp
The Socket.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.
.sp
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:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
static_files = {
    \(aq/\(aq: \(aqlatency.html\(aq,
    \(aq/static/socket.io.js\(aq: \(aqstatic/socket.io.js\(aq,
    \(aq/static/style.css\(aq: \(aqstatic/style.css\(aq,
}
.EE
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.sp
With this example configuration, when the server receives a request for \fB/\fP
(the root URL) it will return the contents of the file \fBlatency.html\fP in the
current directory, and will assign a content type based on the file extension,
in this case \fBtext/html\fP\&.
.sp
Files with the \fB\&.html\fP, \fB\&.css\fP, \fB\&.js\fP, \fB\&.json\fP, \fB\&.jpg\fP, \fB\&.png\fP,
\fB\&.gif\fP and \fB\&.txt\fP file extensions are automatically recognized and
assigned the correct content type. For files with other file extensions or
with no file extension, the \fBapplication/octet\-stream\fP content type is used
as a default.
.sp
If desired, an explicit content type for a static file can be given as follows:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
static_files = {
    \(aq/\(aq: {\(aqfilename\(aq: \(aqlatency.html\(aq, \(aqcontent_type\(aq: \(aqtext/plain\(aq},
}
.EE
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.sp
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:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
static_files = {
    \(aq/static\(aq: \(aq./public\(aq,
}
.EE
.UNINDENT
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.sp
In this example any files with URLs starting with \fB/static\fP will be served
directly from the \fBpublic\fP folder in the current directory, so for example,
the URL \fB/static/index.html\fP will return local file \fB\&./public/index.html\fP
and the URL \fB/static/css/styles.css\fP will return local file
\fB\&./public/css/styles.css\fP\&.
.sp
If a URL that ends in a \fB/\fP is requested, then a default filename of
\fBindex.html\fP is appended to it. In the previous example, a request for the
\fB/static/\fP URL would return local file \fB\&./public/index.html\fP\&. The default
filename to serve for slash\-ending URLs can be set in the static files
dictionary with an empty key:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
static_files = {
    \(aq/static\(aq: \(aq./public\(aq,
    \(aq\(aq: \(aqimage.gif\(aq,
}
.EE
.UNINDENT
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.sp
With this configuration, a request for \fB/static/\fP would return
local file \fB\&./public/image.gif\fP\&. A non\-standard content type can also be
specified if needed:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
static_files = {
    \(aq/static\(aq: \(aq./public\(aq,
    \(aq\(aq: {\(aqfilename\(aq: \(aqimage.gif\(aq, \(aqcontent_type\(aq: \(aqtext/plain\(aq},
}
.EE
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.sp
The static file configuration dictionary is given as the \fBstatic_files\fP
argument to the \fBsocketio.WSGIApp\fP or \fBsocketio.ASGIApp\fP classes:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
# 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)
.EE
.UNINDENT
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.sp
The routing precedence in these two classes is as follows:
.INDENT 0.0
.IP \(bu 2
First, the path is checked against the Socket.IO endpoint.
.IP \(bu 2
Next, the path is checked against the static file configuration, if present.
.IP \(bu 2
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.
.UNINDENT
.sp
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.
.SS Events
.sp
The Socket.IO protocol is event based. When a client wants to communicate with
the server, or the server wants to communicate with one or more clients, they
\fIemit\fP an event to the other party. Each event has a name, and an optional list
of arguments.
.SS Listening to Events
.sp
To receive events from clients, the server application must register event
handler functions. These functions are invoked when the corresponding events
are emitted by clients. To register a handler for an event, the
\fBsocketio.Server.event()\fP or \fBsocketio.Server.on()\fP decorators are used:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
@sio.event
def my_event(sid, data):
    pass

@sio.on(\(aqmy custom event\(aq)
def another_event(sid, data):
    pass
.EE
.UNINDENT
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.sp
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.
.sp
For asyncio servers, event handlers can optionally be given as coroutines:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
@sio.event
async def my_event(sid, data):
    pass
.EE
.UNINDENT
.UNINDENT
.sp
The \fBsid\fP argument that is passed to all handlers is the Socket.IO session
id, a unique identifier that Socket.IO assigns to each client connection. All
the events sent by a given client will have the same \fBsid\fP value.
.SS Connect and Disconnect Events
.sp
The \fBconnect\fP and \fBdisconnect\fP events are special; they are invoked
automatically when a client connects or disconnects from the server:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
@sio.event
def connect(sid, environ, auth):
    print(\(aqconnect \(aq, sid)

@sio.event
def disconnect(sid, reason):
    print(\(aqdisconnect \(aq, sid, reason)
.EE
.UNINDENT
.UNINDENT
.sp
The \fBconnect\fP event is an ideal place to perform user authentication, and
any necessary mapping between user entities in the application and the \fBsid\fP
that was assigned to the client.
.sp
In addition to the \fBsid\fP, the connect handler receives \fBenviron\fP as an
argument, with the request information in standard WSGI format, including HTTP
headers. The connect handler also receives the \fBauth\fP argument with any
authentication details passed by the client, or \fBNone\fP if the client did not
pass any authentication.
.sp
After inspecting the arguments, the connect event handler can return \fBFalse\fP
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 \fBFalse\fP
a \fBsocketio.exceptions.ConnectionRefusedError\fP exception can be raised,
and all of its arguments will be sent to the client with the rejection
message:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
@sio.event
def connect(sid, environ, auth):
    raise ConnectionRefusedError(\(aqauthentication failed\(aq)
.EE
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.UNINDENT
.sp
The disconnect handler receives the \fBsid\fP assigned to the client and a
\fBreason\fP, which provides the cause of the disconnection:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
@sio.event
def disconnect(sid, reason):
    if reason == sio.reason.CLIENT_DISCONNECT:
        print(\(aqthe client disconnected\(aq)
    elif reason == sio.reason.SERVER_DISCONNECT:
        print(\(aqthe server disconnected the client\(aq)
    else:
        print(\(aqdisconnect reason:\(aq, reason)
.EE
.UNINDENT
.UNINDENT
.sp
See the The \fBsocketio.Server.reason\fP attribute for a list of possible
disconnection reasons.
.SS Catch\-All Event Handlers
.sp
A \(dqcatch\-all\(dq event handler is invoked for any events that do not have an
event handler. You can define a catch\-all handler using \fB\(aq*\(aq\fP as event name:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
@sio.on(\(aq*\(aq)
def any_event(event, sid, data):
     pass
.EE
.UNINDENT
.UNINDENT
.sp
Asyncio servers can also use a coroutine:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
@sio.on(\(aq*\(aq)
async def any_event(event, sid, data):
    pass
.EE
.UNINDENT
.UNINDENT
.sp
A catch\-all event handler receives the event name as a first argument. The
remaining arguments are the same as for a regular event handler.
.sp
Note that the \fBconnect\fP and \fBdisconnect\fP events have to be defined
explicitly and are not invoked on a catch\-all event handler.
.SS Emitting Events to Clients
.sp
Socket.IO is a bidirectional protocol, so at any time the server can send an
event to its connected clients. The \fBsocketio.Server.emit()\fP method is
used for this task:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
sio.emit(\(aqmy event\(aq, {\(aqdata\(aq: \(aqfoobar\(aq})
.EE
.UNINDENT
.UNINDENT
.sp
The first argument is the event name, followed by an optional data payload of
type \fBstr\fP, \fBbytes\fP, \fBlist\fP, \fBdict\fP or \fBtuple\fP\&. When sending a
\fBlist\fP, \fBdict\fP or \fBtuple\fP, the elements are also constrained to the same
data types. When a \fBtuple\fP is sent, the elements of the tuple will be passed
as multiple arguments to the client\-side event handler function.
.sp
The above example will send the event to all the clients are connected.
Sometimes the server may want to send an event just to one particular client.
This can be achieved by adding a \fBto\fP argument to the emit call, with the
\fBsid\fP of the client:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
sio.emit(\(aqmy event\(aq, {\(aqdata\(aq: \(aqfoobar\(aq}, to=user_sid)
.EE
.UNINDENT
.UNINDENT
.sp
The \fBto\fP argument is used to identify the client that should receive the
event, and is set to the \fBsid\fP value assigned to that client\(aqs connection
with the server. When \fBto\fP is omitted, the event is broadcasted to all
connected clients.
.SS Acknowledging Events
.sp
When a client sends an event to the server, it can optionally request to
receive acknowledgment from the server. The sending of acknowledgements is
automatically managed by the Socket.IO server, but the event handler function
can provide a list of values that are to be passed on to the client with the
acknowledgement simply by returning them:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
@sio.event
def my_event(sid, data):
    # handle the message
    return \(dqOK\(dq, 123  # <\-\- client will have these as acknowledgement
.EE
.UNINDENT
.UNINDENT
.SS Requesting Client Acknowledgements
.sp
Similar to how clients can request acknowledgements from the server, when the
server is emitting to a single client it can also ask the client to acknowledge
the event, and optionally return one or more values as a response.
.sp
The Socket.IO server supports two ways of working with client acknowledgements.
The most convenient method is to replace \fBsocketio.Server.emit()\fP with
\fBsocketio.Server.call()\fP\&. The \fBcall()\fP method will emit the event, and
then wait until the client sends an acknowledgement, returning any values
provided by the client:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
response = sio.call(\(aqmy event\(aq, {\(aqdata\(aq: \(aqfoobar\(aq}, to=user_sid)
.EE
.UNINDENT
.UNINDENT
.sp
A much more primitive acknowledgement solution uses callback functions. The
\fBsocketio.Server.emit()\fP method has an optional \fBcallback\fP 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:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
def my_callback():
    print(\(dqcallback invoked!\(dq)

sio.emit(\(aqmy event\(aq, {\(aqdata\(aq: \(aqfoobar\(aq}, to=user_sid, callback=my_callback)
.EE
.UNINDENT
.UNINDENT
.SS Rooms
.sp
To make it easy for the server to emit events to groups of related clients,
the application can put its clients into \(dqrooms\(dq, and then address messages to
these rooms.
.sp
In previous examples, the \fBto\fP argument of the \fBsocketio.SocketIO.emit()\fP
method was used to designate a specific client as the recipient of the event.
The \fBto\fP argument can also be given the name of a room, and then all the
clients that are in that room will receive the event.
.sp
The application can create as many rooms as needed and manage which clients are
in them using the \fBsocketio.Server.enter_room()\fP and
\fBsocketio.Server.leave_room()\fP methods. Clients can be in as many
rooms as needed and can be moved between rooms when necessary.
.INDENT 0.0
.INDENT 3.5
.sp
.EX
@sio.event
def begin_chat(sid):
    sio.enter_room(sid, \(aqchat_users\(aq)

@sio.event
def exit_chat(sid):
    sio.leave_room(sid, \(aqchat_users\(aq)
.EE
.UNINDENT
.UNINDENT
.sp
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 \fBsocketio.Server.emit()\fP method provides an
optional \fBskip_sid\fP argument to indicate a client that should be skipped
during the broadcast.
.INDENT 0.0
.INDENT 3.5
.sp
.EX
@sio.event
def my_message(sid, data):
    sio.emit(\(aqmy reply\(aq, data, room=\(aqchat_users\(aq, skip_sid=sid)
.EE
.UNINDENT
.UNINDENT
.SS Namespaces
.sp
The Socket.IO protocol supports multiple logical connections, all multiplexed
on the same physical connection. Clients can open multiple connections by
specifying a different \fInamespace\fP on each. A namespace is given by the client
as a pathname following the hostname and port. For example, connecting to
\fIhttp://example.com:8000/chat\fP would open a connection to the namespace
\fI/chat\fP\&.
.sp
Each namespace works independently from the others, with separate session
IDs (\fBsid\fPs), event handlers and rooms. Namespaces can be defined directly
in the event handler functions, or they can also be created as classes.
.SS Decorator\-Based Namespaces
.sp
Decorator\-based namespaces are regular event handlers that include the
\fBnamespace\fP argument in their decorator:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
@sio.event(namespace=\(aq/chat\(aq)
def my_custom_event(sid, data):
    pass

@sio.on(\(aqmy custom event\(aq, namespace=\(aq/chat\(aq)
def my_custom_event(sid, data):
    pass
.EE
.UNINDENT
.UNINDENT
.sp
When emitting an event, the \fBnamespace\fP optional argument is used to specify
which namespace to send it on. When the \fBnamespace\fP argument is omitted, the
default Socket.IO namespace, which is named \fB/\fP, is used.
.sp
It is important that applications that use multiple namespaces specify the
correct namespace when setting up their event handlers and rooms using the
optional \fBnamespace\fP argument. This argument must also be specified when
emitting events under a namespace. Most methods in the \fBsocketio.Server\fP
class have the optional \fBnamespace\fP argument.
.SS Class\-Based Namespaces
.sp
As an alternative to the decorator\-based namespaces, the event handlers that
belong to a namespace can be created as methods in a subclass of
\fBsocketio.Namespace\fP:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
class MyCustomNamespace(socketio.Namespace):
    def on_connect(self, sid, environ):
        pass

    def on_disconnect(self, sid, reason):
        pass

    def on_my_event(self, sid, data):
        self.emit(\(aqmy_response\(aq, data)

sio.register_namespace(MyCustomNamespace(\(aq/test\(aq))
.EE
.UNINDENT
.UNINDENT
.sp
For asyncio based servers, namespaces must inherit from
\fBsocketio.AsyncNamespace\fP, and can define event handlers as coroutines
if desired:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
class MyCustomNamespace(socketio.AsyncNamespace):
    def on_connect(self, sid, environ):
        pass

    def on_disconnect(self, sid, reason):
        pass

    async def on_my_event(self, sid, data):
        await self.emit(\(aqmy_response\(aq, data)

sio.register_namespace(MyCustomNamespace(\(aq/test\(aq))
.EE
.UNINDENT
.UNINDENT
.sp
When class\-based namespaces are used, any events received by the server are
dispatched to a method named as the event name with the \fBon_\fP prefix. For
example, event \fBmy_event\fP will be handled by a method named \fBon_my_event\fP\&.
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.
.sp
As a convenience to methods defined in a class\-based namespace, the namespace
instance includes versions of several of the methods in the
\fBsocketio.Server\fP and \fBsocketio.AsyncServer\fP classes that default
to the proper namespace when the \fBnamespace\fP argument is not given.
.sp
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.
.sp
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.
.SS Catch\-All Namespaces
.sp
Similarily to catch\-all event handlers, a \(dqcatch\-all\(dq namespace can be used
when defining event handlers for any connected namespaces that do not have an
explicitly defined event handler. As with catch\-all events, \fB\(aq*\(aq\fP is used in
place of a namespace:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
@sio.on(\(aqmy_event\(aq, namespace=\(aq*\(aq)
def my_event_any_namespace(namespace, sid, data):
    pass
.EE
.UNINDENT
.UNINDENT
.sp
For these events, the namespace is passed as first argument, followed by the
regular arguments of the event.
.sp
A catch\-all class\-based namespace handler can be defined by passing \fB\(aq*\(aq\fP as
the namespace during registration:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
sio.register_namespace(MyCustomNamespace(\(aq*\(aq))
.EE
.UNINDENT
.UNINDENT
.sp
A \(dqcatch\-all\(dq handler for all events on all namespaces can be defined as
follows:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
@sio.on(\(aq*\(aq, namespace=\(aq*\(aq)
def any_event_any_namespace(event, namespace, sid, data):
    pass
.EE
.UNINDENT
.UNINDENT
.sp
Event handlers with catch\-all events and namespaces receive the event name and
the namespace as first and second arguments.
.SS User Sessions
.sp
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.
.sp
The \fBsave_session()\fP and \fBget_session()\fP methods are used to store and
retrieve information in the user session:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
@sio.event
def connect(sid, environ):
    username = authenticate_user(environ)
    sio.save_session(sid, {\(aqusername\(aq: username})

@sio.event
def message(sid, data):
    session = sio.get_session(sid)
    print(\(aqmessage from \(aq, session[\(aqusername\(aq])
.EE
.UNINDENT
.UNINDENT
.sp
For the \fBasyncio\fP server, these methods are coroutines:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
@sio.event
async def connect(sid, environ):
    username = authenticate_user(environ)
    await sio.save_session(sid, {\(aqusername\(aq: username})

@sio.event
async def message(sid, data):
    session = await sio.get_session(sid)
    print(\(aqmessage from \(aq, session[\(aqusername\(aq])
.EE
.UNINDENT
.UNINDENT
.sp
The session can also be manipulated with the \fIsession()\fP context manager:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
@sio.event
def connect(sid, environ):
    username = authenticate_user(environ)
    with sio.session(sid) as session:
        session[\(aqusername\(aq] = username

@sio.event
def message(sid, data):
    with sio.session(sid) as session:
        print(\(aqmessage from \(aq, session[\(aqusername\(aq])
.EE
.UNINDENT
.UNINDENT
.sp
For the \fBasyncio\fP server, an asynchronous context manager is used:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
@sio.event
async def connect(sid, environ):
    username = authenticate_user(environ)
    async with sio.session(sid) as session:
        session[\(aqusername\(aq] = username

@sio.event
async def message(sid, data):
    async with sio.session(sid) as session:
        print(\(aqmessage from \(aq, session[\(aqusername\(aq])
.EE
.UNINDENT
.UNINDENT
.sp
The \fBget_session()\fP, \fBsave_session()\fP and \fBsession()\fP methods take an
optional \fBnamespace\fP argument. If this argument isn\(aqt provided, the session
is attached to the default namespace.
.sp
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.
.SS Cross\-Origin Controls
.sp
For security reasons, this server enforces a same\-origin policy by default. In
practical terms, this means the following:
.INDENT 0.0
.IP \(bu 2
If an incoming HTTP or WebSocket request includes the \fBOrigin\fP 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.
.IP \(bu 2
No restrictions are imposed on incoming requests that do not include the
\fBOrigin\fP header.
.UNINDENT
.sp
If necessary, the \fBcors_allowed_origins\fP 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 \fB\(aq*\(aq\fP 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.
.SS Monitoring and Administration
.sp
The Socket.IO server can be configured to accept connections from the official
\X'tty: link https://socket.io/docs/v4/admin-ui/'\fI\%Socket.IO Admin UI\fP\X'tty: link'\&. This tool provides
real\-time information about currently connected clients, rooms in use and
events being emitted. It also allows an administrator to manually emit events,
change room assignments and disconnect clients. The hosted version of this tool
is available at \X'tty: link https://admin.socket.io'\fI\%https://admin.socket.io\fP\X'tty: link'\&.
.sp
Given that enabling this feature can affect the performance of the server, it
is disabled by default. To enable it, call the
\fBinstrument()\fP method. For example:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
import os
import socketio

sio = socketio.Server(cors_allowed_origins=[
    \(aqhttp://localhost:5000\(aq,
    \(aqhttps://admin.socket.io\(aq,
])
sio.instrument(auth={
    \(aqusername\(aq: \(aqadmin\(aq,
    \(aqpassword\(aq: os.environ[\(aqADMIN_PASSWORD\(aq],
})
.EE
.UNINDENT
.UNINDENT
.sp
This configures the server to accept connections from the hosted Admin UI
client. Administrators can then open \X'tty: link https://admin.socket.io'\fI\%https://admin.socket.io\fP\X'tty: link' in their web
browsers and log in with username \fBadmin\fP and the password given by the
\fBADMIN_PASSWORD\fP environment variable. To ensure the Admin UI front end is
allowed to connect, CORS is also configured.
.sp
Consult the reference documentation to learn about additional configuration
options that are available.
.SS Debugging and Troubleshooting
.sp
To help you debug issues, the server can be configured to output logs to the
terminal:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
import socketio

# standard Python
sio = socketio.Server(logger=True, engineio_logger=True)

# asyncio
sio = socketio.AsyncServer(logger=True, engineio_logger=True)
.EE
.UNINDENT
.UNINDENT
.sp
The \fBlogger\fP argument controls logging related to the Socket.IO protocol,
while \fBengineio_logger\fP controls logs that originate in the low\-level
Engine.IO transport. These arguments can be set to \fBTrue\fP to output logs to
\fBstderr\fP, or to an object compatible with Python\(aqs \fBlogging\fP package
where the logs should be emitted to. A value of \fBFalse\fP disables logging.
.sp
Logging can help identify the cause of connection problems, 400 responses,
bad performance and other issues.
.SS Concurrency and Web Server Integration
.sp
The Socket.IO server can be configured with different concurrency models
depending on the needs of the application and the web server that is used. The
concurrency model is given by the \fBasync_mode\fP argument in the server. For
example:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
sio = socketio.Server(async_mode=\(aqthreading\(aq)
.EE
.UNINDENT
.UNINDENT
.sp
The following sub\-sections describe the available concurrency options for
synchronous and asynchronous servers.
.SS Standard Modes
.INDENT 0.0
.IP \(bu 2
\fBthreading\fP: the server will use Python threads for concurrency and will
run on any multi\-threaded WSGI server. This is the default mode when no other
concurrency libraries are installed.
.IP \(bu 2
\fBgevent\fP: the server will use greenlets through the
\X'tty: link http://www.gevent.org/'\fI\%gevent\fP\X'tty: link' library for concurrency. A web server that
is compatible with \fBgevent\fP is required.
.IP \(bu 2
\fBgevent_uwsgi\fP: a variation of the \fBgevent\fP mode that is designed to work
with the \X'tty: link https://uwsgi-docs.readthedocs.io/en/latest/'\fI\%uWSGI\fP\X'tty: link' web server.
.IP \(bu 2
\fBeventlet\fP: the server will use greenlets through the
\X'tty: link http://eventlet.net/'\fI\%eventlet\fP\X'tty: link' library for concurrency. A web server that
is compatible with \fBeventlet\fP is required. Use of \fBeventlet\fP is not
recommended due to this project being in maintenance mode.
.UNINDENT
.SS Asyncio Modes
.sp
The asynchronous options are all based on the
\X'tty: link https://docs.python.org/3/library/asyncio.html'\fI\%asyncio\fP\X'tty: link' package of the
Python standard library, with minor variations depending on the web server
platform that is used.
.INDENT 0.0
.IP \(bu 2
\fBasgi\fP: use of any
\X'tty: link https://asgi.readthedocs.io/en/latest/'\fI\%ASGI\fP\X'tty: link' web server is required.
.IP \(bu 2
\fBaiohttp\fP: use of the \X'tty: link http://aiohttp.readthedocs.io/'\fI\%aiohttp\fP\X'tty: link' web
framework and server is required.
.IP \(bu 2
\fBtornado\fP: use of the \X'tty: link http://www.tornadoweb.org/'\fI\%Tornado\fP\X'tty: link' web framework
and server is required.
.IP \(bu 2
\fBsanic\fP: use of the \X'tty: link http://sanic.readthedocs.io/'\fI\%Sanic\fP\X'tty: link' web framework
and server is required. When using Sanic, it is recommended to use the
\fBasgi\fP mode instead.
.UNINDENT
.SS Deployment Strategies
.sp
The following sections describe a variety of deployment strategies for
Socket.IO servers.
.SS Gunicorn
.sp
The simplest deployment strategy for the Socket.IO server is to use the popular
\X'tty: link http://gunicorn.org'\fI\%Gunicorn\fP\X'tty: link' web server in multi\-threaded mode. The
Socket.IO server must be wrapped by the \fBsocketio.WSGIApp\fP class, so
that it is compatible with the WSGI protocol:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
sio = socketio.Server(async_mode=\(aqthreading\(aq)
app = socketio.WSGIApp(sio)
.EE
.UNINDENT
.UNINDENT
.sp
If desired, the \fBsocketio.WSGIApp\fP class can forward any traffic that is not
Socket.IO to another WSGI application, making it possible to deploy a standard
WSGI web application built with frameworks such as Flask or Django and the
Socket.IO server as a bundle:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
sio = socketio.Server(async_mode=\(aqthreading\(aq)
app = socketio.WSGIApp(sio, other_wsgi_app)
.EE
.UNINDENT
.UNINDENT
.sp
The example that follows shows how to start a Socket.IO application using
Gunicorn\(aqs threaded worker class:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
$ gunicorn \-\-workers 1 \-\-threads 100 \-\-bind 127.0.0.1:5000 module:app
.EE
.UNINDENT
.UNINDENT
.sp
With the above configuration the server will be able to handle close to 100
concurrent clients.
.sp
It is also possible to use more than one worker process, but this has two
additional requirements:
.INDENT 0.0
.IP \(bu 2
The clients must connect directly over WebSocket. The long\-polling transport
is incompatible with the way Gunicorn load balances requests among workers.
To disable long\-polling in the server, add \fBtransports=[\(aqwebsocket\(aq]\fP in
the server constructor. Clients will have a similar option to initiate the
connection with WebSocket.
.IP \(bu 2
The \fBsocketio.Server()\fP instances in each worker must be configured with
a message queue to allow the workers to communicate with each other. See the
\fI\%Using a Message Queue\fP section for more information.
.UNINDENT
.sp
When using multiple workers, the approximate number of connections the server
will be able to accept can be calculated as the number of workers multiplied by
the number of threads per worker.
.sp
Note that Gunicorn can also be used alongside \fBuvicorn\fP, \fBgevent\fP and
\fBeventlet\fP\&. These options are discussed under the appropriate sections below.
.SS Uvicorn (and other ASGI web servers)
.sp
When working with an asynchronous Socket.IO server, the easiest deployment
strategy is to use an ASGI web server such as
\X'tty: link https://www.uvicorn.org/'\fI\%Uvicorn\fP\X'tty: link'\&.
.sp
The \fBsocketio.ASGIApp\fP class is an ASGI compatible application that can
forward Socket.IO traffic to a \fBsocketio.AsyncServer\fP instance:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
sio = socketio.AsyncServer(async_mode=\(aqasgi\(aq)
app = socketio.ASGIApp(sio)
.EE
.UNINDENT
.UNINDENT
.sp
If desired, the \fBsocketio.ASGIApp\fP class can forward any traffic that is not
Socket.IO to another ASGI application, making it possible to deploy a standard
ASGI web application built with a framework such as FastAPI and the Socket.IO
server as a bundle:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
sio = socketio.AsyncServer(async_mode=\(aqasgi\(aq)
app = socketio.ASGIApp(sio, other_asgi_app)
.EE
.UNINDENT
.UNINDENT
.sp
The following example starts the application with Uvicorn:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
uvicorn \-\-port 5000 module:app
.EE
.UNINDENT
.UNINDENT
.sp
Uvicorn can also be used through its Gunicorn worker:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
gunicorn \-\-workers 1 \-\-worker\-class uvicorn.workers.UvicornWorker \-\-bind 127.0.0.1:5000
.EE
.UNINDENT
.UNINDENT
.sp
See the Gunicorn section above for information on how to use Gunicorn with
multiple workers.
.SS Hypercorn, Daphne, and other ASGI servers
.sp
To use an ASGI web server other than Uvicorn, configure the application for
ASGI as shown above for Uvicorn, then follow the documentation of your chosen
web server to start the application.
.SS Aiohttp
.sp
Another option for deploying an asynchronous Socket.IO server is to use the
\X'tty: link http://aiohttp.readthedocs.io/'\fI\%Aiohttp\fP\X'tty: link' web framework and server. Instances
of class \fBsocketio.AsyncServer\fP will automatically use Aiohttp
if the library is installed. To request its use explicitly, the \fBasync_mode\fP
option can be given in the constructor:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
sio = socketio.AsyncServer(async_mode=\(aqaiohttp\(aq)
.EE
.UNINDENT
.UNINDENT
.sp
A server configured for Aiohttp must be attached to an existing application:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
app = web.Application()
sio.attach(app)
.EE
.UNINDENT
.UNINDENT
.sp
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.
.sp
The Aiohttp application is then executed in the usual manner:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
if __name__ == \(aq__main__\(aq:
    web.run_app(app)
.EE
.UNINDENT
.UNINDENT
.SS Gevent
.sp
When a multi\-threaded web server is unable to satisfy the concurrency and
scalability requirements of the application, an option to try is
\X'tty: link http://www.gevent.org'\fI\%Gevent\fP\X'tty: link'\&. Gevent is a coroutine\-based concurrency library
based on greenlets, which are significantly lighter than threads.
.sp
Instances of class \fBsocketio.Server\fP will automatically use Gevent if the
library is installed. To request gevent to be selected explicitly, the
\fBasync_mode\fP option can be given in the constructor:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
sio = socketio.Server(async_mode=\(aqgevent\(aq)
.EE
.UNINDENT
.UNINDENT
.sp
The Socket.IO server must be wrapped by the \fBsocketio.WSGIApp\fP class, so
that it is compatible with the WSGI protocol:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
app = socketio.WSGIApp(sio)
.EE
.UNINDENT
.UNINDENT
.sp
If desired, the \fBsocketio.WSGIApp\fP class can forward any traffic that is not
Socket.IO to another WSGI application, making it possible to deploy a standard
WSGI web application built with frameworks such as Flask or Django and the
Socket.IO server as a bundle:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
sio = socketio.Server(async_mode=\(aqgevent\(aq)
app = socketio.WSGIApp(sio, other_wsgi_app)
.EE
.UNINDENT
.UNINDENT
.sp
A server configured for Gevent is deployed as a regular WSGI application
using the provided \fBsocketio.WSGIApp\fP:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
from gevent import pywsgi

pywsgi.WSGIServer((\(aq\(aq, 8000), app).serve_forever()
.EE
.UNINDENT
.UNINDENT
.SS Gevent with Gunicorn
.sp
An alternative to running the gevent WSGI server as above is to use
\fI\%Gunicorn\fP with its Gevent worker. The command to launch the
application under Gunicorn and Gevent is shown below:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
$ gunicorn \-k gevent \-w 1 \-b 127.0.0.1:5000 module:app
.EE
.UNINDENT
.UNINDENT
.sp
See the Gunicorn section above for information on how to use Gunicorn with
multiple workers.
.sp
Gevent provides a \fBmonkey_patch()\fP function that replaces all the blocking
functions in the standard library with equivalent asynchronous versions. While
the Socket.IO server does not require monkey patching, other libraries such as
database or message queue drivers are likely to require it.
.SS Gevent with uWSGI
.sp
When using the uWSGI server in combination with gevent, the Socket.IO server
can take advantage of uWSGI\(aqs native WebSocket support.
.sp
Instances of class \fBsocketio.Server\fP 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
\fBasync_mode\fP option can be given in the constructor:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
# gevent with uWSGI
sio = socketio.Server(async_mode=\(aqgevent_uwsgi\(aq)
.EE
.UNINDENT
.UNINDENT
.sp
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 \fBlatency.py\fP example on port 5000:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
$ uwsgi \-\-http :5000 \-\-gevent 1000 \-\-http\-websockets \-\-master \-\-wsgi\-file latency.py \-\-callable app
.EE
.UNINDENT
.UNINDENT
.SS Tornado
.sp
Instances of class \fBsocketio.AsyncServer\fP will automatically use
\X'tty: link http://www.tornadoweb.org//'\fI\%Tornado\fP\X'tty: link' if the library is installed. To
request its use explicitly, the \fBasync_mode\fP option can be given in the
constructor:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
sio = socketio.AsyncServer(async_mode=\(aqtornado\(aq)
.EE
.UNINDENT
.UNINDENT
.sp
A server configured for Tornado must include a request handler for
Socket.IO:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
app = tornado.web.Application(
    [
        (r\(dq/socket.io/\(dq, socketio.get_tornado_handler(sio)),
    ],
    # ... other application options
)
.EE
.UNINDENT
.UNINDENT
.sp
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.
.sp
The Tornado application is then executed in the usual manner:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
app.listen(port)
tornado.ioloop.IOLoop.current().start()
.EE
.UNINDENT
.UNINDENT
.SS Eventlet
.sp
\fBNOTE:\fP
.INDENT 0.0
.INDENT 3.5
Eventlet is not in active development anymore, and for that reason the
current recommendation is to not use it for new projects.
.UNINDENT
.UNINDENT
.sp
\X'tty: link http://eventlet.net/'\fI\%Eventlet\fP\X'tty: link' is a high performance concurrent networking
library for Python 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.
.sp
Instances of class \fBsocketio.Server\fP will automatically use eventlet for
asynchronous operations if the library is installed. To request its use
explicitly, the \fBasync_mode\fP option can be given in the constructor:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
sio = socketio.Server(async_mode=\(aqeventlet\(aq)
.EE
.UNINDENT
.UNINDENT
.sp
A server configured for eventlet is deployed as a regular WSGI application
using the provided \fBsocketio.WSGIApp\fP:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
import eventlet

app = socketio.WSGIApp(sio)
eventlet.wsgi.server(eventlet.listen((\(aq\(aq, 8000)), app)
.EE
.UNINDENT
.UNINDENT
.SS Eventlet with Gunicorn
.sp
An alternative to running the eventlet WSGI server as above is to use
\fI\%gunicorn\fP, a fully featured pure Python web server. The
command to launch the application under gunicorn is shown below:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
$ gunicorn \-k eventlet \-w 1 module:app
.EE
.UNINDENT
.UNINDENT
.sp
See the Gunicorn section above for information on how to use Gunicorn with
multiple workers.
.sp
Eventlet provides a \fBmonkey_patch()\fP 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.
.SS Sanic
.sp
\fBNOTE:\fP
.INDENT 0.0
.INDENT 3.5
The Sanic integration has not been updated in a long time. It is currently
recommended that a Sanic application is deployed with the ASGI integration.
.UNINDENT
.UNINDENT
.SS Using a Message Queue
.sp
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:
.INDENT 0.0
.IP \(bu 2
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.
.IP \(bu 2
Applications that use work queues such as
\X'tty: link http://www.celeryproject.org/'\fI\%Celery\fP\X'tty: link' 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.
.UNINDENT
.sp
As a solution to the above problems, the Socket.IO server can be configured
to connect to a message queue such as \X'tty: link http://redis.io/'\fI\%Redis\fP\X'tty: link' or
\X'tty: link https://www.rabbitmq.com/'\fI\%RabbitMQ\fP\X'tty: link', to communicate with other related
Socket.IO servers or auxiliary workers.
.SS Redis
.sp
To use a Redis message queue, a Python Redis client must be installed:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
# socketio.Server class
pip install redis
.EE
.UNINDENT
.UNINDENT
.sp
The Redis queue is configured through the \fBsocketio.RedisManager\fP and
\fBsocketio.AsyncRedisManager\fP classes. These classes connect directly to
the Redis store and use the queue\(aqs pub/sub functionality:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
# socketio.Server class
mgr = socketio.RedisManager(\(aqredis://\(aq)
sio = socketio.Server(client_manager=mgr)

# socketio.AsyncServer class
mgr = socketio.AsyncRedisManager(\(aqredis://\(aq)
sio = socketio.AsyncServer(client_manager=mgr)
.EE
.UNINDENT
.UNINDENT
.sp
The \fBclient_manager\fP argument instructs the server to connect to the given
message queue, and to coordinate with other processes connected to the queue.
.SS Kombu
.sp
\X'tty: link http://kombu.readthedocs.org/en/latest/'\fI\%Kombu\fP\X'tty: link' is a Python package that
provides access to RabbitMQ and many other message queues. It can be installed
with pip:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
pip install kombu
.EE
.UNINDENT
.UNINDENT
.sp
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:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
pip install redis
.EE
.UNINDENT
.UNINDENT
.sp
The queue is configured through the \fBsocketio.KombuManager\fP:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
mgr = socketio.KombuManager(\(aqamqp://\(aq)
sio = socketio.Server(client_manager=mgr)
.EE
.UNINDENT
.UNINDENT
.sp
The connection URL passed to the \fBKombuManager\fP constructor is passed
directly to Kombu\(aqs \X'tty: link http://kombu.readthedocs.org/en/latest/userguide/connections.html'\fI\%Connection object\fP\X'tty: link', so
the Kombu documentation should be consulted for information on how to build
the correct URL for a given message queue.
.sp
Note that Kombu currently does not support asyncio, so it cannot be used with
the \fBsocketio.AsyncServer\fP class.
.SS Kafka
.sp
\X'tty: link https://kafka.apache.org/'\fI\%Apache Kafka\fP\X'tty: link' is supported through the
\X'tty: link https://kafka-python.readthedocs.io/en/master/index.html'\fI\%kafka\-python\fP\X'tty: link'
package:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
pip install kafka\-python
.EE
.UNINDENT
.UNINDENT
.sp
Access to Kafka is configured through the \fBsocketio.KafkaManager\fP
class:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
mgr = socketio.KafkaManager(\(aqkafka://\(aq)
sio = socketio.Server(client_manager=mgr)
.EE
.UNINDENT
.UNINDENT
.sp
Note that Kafka currently does not support asyncio, so it cannot be used with
the \fBsocketio.AsyncServer\fP class.
.SS AioPika
.sp
A RabbitMQ message queue is supported in asyncio applications through the
\X'tty: link https://aio-pika.readthedocs.io/en/latest/'\fI\%AioPika\fP\X'tty: link' package::
You need to install aio_pika with pip:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
pip install aio_pika
.EE
.UNINDENT
.UNINDENT
.sp
The RabbitMQ queue is configured through the
\fBsocketio.AsyncAioPikaManager\fP class:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
mgr = socketio.AsyncAioPikaManager(\(aqamqp://\(aq)
sio = socketio.AsyncServer(client_manager=mgr)
.EE
.UNINDENT
.UNINDENT
.SS Horizontal Scaling
.sp
Socket.IO is a stateful protocol, which makes horizontal scaling more
difficult. When deploying a cluster of Socket.IO processes, all processes must
connect to the message queue by passing the \fBclient_manager\fP argument to the
server instance. This enables the workers to communicate and coordinate complex
operations such as broadcasts.
.sp
If the long\-polling transport is used, then there are two additional
requirements that must be met:
.INDENT 0.0
.IP \(bu 2
Each Socket.IO process must be able to handle multiple requests
concurrently. This is needed because long\-polling clients send two
requests in parallel. Worker processes that can only handle one request at a
time are not supported.
.IP \(bu 2
The load balancer must be configured to always forward requests from a
client to the same worker process, so that all requests coming from a client
are handled by the same node. Load balancers call this \fIsticky sessions\fP, or
\fIsession affinity\fP\&.
.UNINDENT
.SS Emitting from external processes
.sp
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 \fBwrite_only\fP argument should be set to \fBTrue\fP to disable the
creation of a listening thread, which only makes sense in a server. For
example:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
# connect to the redis queue as an external process
external_sio = socketio.RedisManager(\(aqredis://\(aq, write_only=True)

# emit an event
external_sio.emit(\(aqmy event\(aq, data={\(aqfoo\(aq: \(aqbar\(aq}, room=\(aqmy room\(aq)
.EE
.UNINDENT
.UNINDENT
.sp
A limitation of the write\-only client manager object is that it cannot receive
callbacks when emitting. When the external process needs to receive callbacks,
using a client to connect to the server with read and write support is a better
option than a write\-only client manager.
.SH API REFERENCE
.INDENT 0.0
.IP \(bu 2
\fI\%Index\fP
.IP \(bu 2
\fI\%Module Index\fP
.IP \(bu 2
\fI\%Search Page\fP
.UNINDENT
.SH AUTHOR
Miguel Grinberg
.SH COPYRIGHT
2018, Miguel Grinberg
.\" Generated by docutils manpage writer.
.