Provided by: python3-flask-socketio_5.3.2-1_all 
NAME
flask-socketio - flask-socketio Documentation
Flask-SocketIO gives Flask applications access to low latency bi-directional
communications between the clients and the server. The client-side application can use any
of the SocketIO client libraries in Javascript, Python, C++, Java and Swift, or any other
compatible client to establish a permanent connection to the server.
INTRODUCTION
Installation
You can install this package in the usual way using pip:
pip install flask-socketio
Requirements
Flask-SocketIO is compatible with Python 3.6+. The asynchronous services that this package
relies on can be selected among three choices:
• eventlet is the best performant option, with support for long-polling and WebSocket
transports.
• gevent is supported in a number of different configurations. The long-polling transport
is fully supported with the gevent package, but unlike eventlet, gevent does not have
native WebSocket support. To add support for WebSocket there are currently two options.
Installing the gevent-websocket package adds WebSocket support to gevent or one can use
the uWSGI web server, which comes with WebSocket functionality. The use of gevent is
also a performant option, but slightly lower than eventlet.
• The Flask development server based on Werkzeug can be used as well, with the caveat that
this web server is intended only for development use, so it should only be used to
simplify the development workflow and not for production.
The extension automatically detects which asynchronous framework to use based on what is
installed. Preference is given to eventlet, followed by gevent. For WebSocket support in
gevent, uWSGI is preferred, followed by gevent-websocket. If neither eventlet nor gevent
are installed, then the Flask development server is used.
If using multiple processes, a message queue service must be configured to allow the
servers to coordinate operations such as broadcasting. The supported queues are Redis,
RabbitMQ, Kafka, and any other message queues supported by the Kombu package.
On the client-side, the official Socket.IO Javascript client library can be used to
establish a connection to the server. There are also official clients written in Swift,
Java and C++. Unofficial clients may also work, as long as they implement the Socket.IO
protocol. The python-socketio package (which provides the Socket.IO server implementation
used by Flask-SocketIO) includes a Python client.
Version compatibility
The Socket.IO protocol has been through a number of revisions, and some of these
introduced backward incompatible changes, which means that the client and the server must
use compatible versions for everything to work.
The version compatibility chart below maps versions of this package to versions of the
JavaScript reference implementation and the versions of the Socket.IO and Engine.IO
protocols.
┌────────────┬───────────┬───────────┬────────────────┬─────────────────┬─────────────────┐
│JavaScript │ Socket.IO │ Engine.IO │ Flask-SocketIO │ python-socketio │ python-engineio │
│Socket.IO │ protocol │ protocol │ version │ version │ version │
│version │ revision │ revision │ │ │ │
└────────────┴───────────┴───────────┴────────────────┴─────────────────┴─────────────────┘
│0.9.x │ 1, 2 │ 1, 2 │ Not supported │ Not supported │ Not supported │
├────────────┼───────────┼───────────┼────────────────┼─────────────────┼─────────────────┤
│1.x and 2.x │ 3, 4 │ 3 │ 4.x │ 4.x │ 3.x │
├────────────┼───────────┼───────────┼────────────────┼─────────────────┼─────────────────┤
│3.x and 4.x │ 5 │ 4 │ 5.x │ 5.x │ 4.x │
└────────────┴───────────┴───────────┴────────────────┴─────────────────┴─────────────────┘
GETTING STARTED
Initialization
The following code example shows how to add Flask-SocketIO to a Flask application:
from flask import Flask, render_template
from flask_socketio import SocketIO
app = Flask(__name__)
app.config['SECRET_KEY'] = 'secret!'
socketio = SocketIO(app)
if __name__ == '__main__':
socketio.run(app)
The init_app() style of initialization is also supported. To start the web server simply
execute your script. Note the way the web server is started. The socketio.run() function
encapsulates the start up of the web server and replaces the app.run() standard Flask
development server start up. When the application is in debug mode the Werkzeug
development server is still used and configured properly inside socketio.run(). In
production mode the eventlet web server is used if available, else the gevent web server
is used. If eventlet and gevent are not installed, the Werkzeug development web server is
used.
The flask run command introduced in Flask 0.11 can be used to start a Flask-SocketIO
development server based on Werkzeug, but this method of starting the Flask-SocketIO
server is not recommended due to lack of WebSocket support. Previous versions of this
package included a customized version of the flask run command that allowed the use of
WebSocket on eventlet and gevent production servers, but this functionality has been
discontinued in favor of the socketio.run(app) startup method shown above which is more
robust.
The application must serve a page to the client that loads the Socket.IO library and
establishes a connection:
<script src="https://cdnjs.cloudflare.com/ajax/libs/socket.io/4.0.1/socket.io.js" integrity="sha512-q/dWJ3kcmjBLU4Qc47E4A9kTB4m3wuTY7vkFJDTZKjTs8jhyGQnaUrxa0Ytd0ssMZhbNua9hE+E7Qv1j+DyZwA==" crossorigin="anonymous"></script>
<script type="text/javascript" charset="utf-8">
var socket = io();
socket.on('connect', function() {
socket.emit('my event', {data: 'I\'m connected!'});
});
</script>
Receiving Messages
When using SocketIO, messages are received by both parties as events. On the client side
Javascript callbacks are used. With Flask-SocketIO the server needs to register handlers
for these events, similarly to how routes are handled by view functions.
The following example creates a server-side event handler for an unnamed event:
@socketio.on('message')
def handle_message(data):
print('received message: ' + data)
The above example uses string messages. Another type of unnamed events use JSON data:
@socketio.on('json')
def handle_json(json):
print('received json: ' + str(json))
The most flexible type of event uses custom event names. The message data for these events
can be string, bytes, int, or JSON:
@socketio.on('my event')
def handle_my_custom_event(json):
print('received json: ' + str(json))
Custom named events can also support multiple arguments:
@socketio.on('my_event')
def handle_my_custom_event(arg1, arg2, arg3):
print('received args: ' + arg1 + arg2 + arg3)
When the name of the event is a valid Python identifier that does not collide with other
defined symbols, the @socketio.event decorator provides a more compact syntax that takes
the event name from the decorated function:
@socketio.event
def my_custom_event(arg1, arg2, arg3):
print('received args: ' + arg1 + arg2 + arg3)
Named events are the most flexible, as they eliminate the need to include additional
metadata to describe the message type. The names message, json, connect and disconnect are
reserved and cannot be used for named events.
Flask-SocketIO also supports SocketIO namespaces, which allow the client to multiplex
several independent connections on the same physical socket:
@socketio.on('my event', namespace='/test')
def handle_my_custom_namespace_event(json):
print('received json: ' + str(json))
When a namespace is not specified a default global namespace with the name '/' is used.
For cases when a decorator syntax isn't convenient, the on_event method can be used:
def my_function_handler(data):
pass
socketio.on_event('my event', my_function_handler, namespace='/test')
Clients may request an acknowledgement callback that confirms receipt of a message they
sent. Any values returned from the handler function will be passed to the client as
arguments in the callback function:
@socketio.on('my event')
def handle_my_custom_event(json):
print('received json: ' + str(json))
return 'one', 2
In the above example, the client callback function will be invoked with two arguments,
'one' and 2. If a handler function does not return any values, the client callback
function will be invoked without arguments.
Sending Messages
SocketIO event handlers defined as shown in the previous section can send reply messages
to the connected client using the send() and emit() functions.
The following examples bounce received events back to the client that sent them:
from flask_socketio import send, emit
@socketio.on('message')
def handle_message(message):
send(message)
@socketio.on('json')
def handle_json(json):
send(json, json=True)
@socketio.on('my event')
def handle_my_custom_event(json):
emit('my response', json)
Note how send() and emit() are used for unnamed and named events respectively.
When working with namespaces, send() and emit() use the namespace of the incoming message
by default. A different namespace can be specified with the optional namespace argument:
@socketio.on('message')
def handle_message(message):
send(message, namespace='/chat')
@socketio.on('my event')
def handle_my_custom_event(json):
emit('my response', json, namespace='/chat')
To send an event with multiple arguments, send a tuple:
@socketio.on('my event')
def handle_my_custom_event(json):
emit('my response', ('foo', 'bar', json), namespace='/chat')
SocketIO supports acknowledgment callbacks that confirm that a message was received by the
client:
def ack():
print('message was received!')
@socketio.on('my event')
def handle_my_custom_event(json):
emit('my response', json, callback=ack)
When using callbacks, the Javascript client receives a callback function to invoke upon
receipt of the message. After the client application invokes the callback function the
server invokes the corresponding server-side callback. If the client-side callback is
invoked with arguments, these are provided as arguments to the server-side callback as
well.
Broadcasting
Another very useful feature of SocketIO is the broadcasting of messages. Flask-SocketIO
supports this feature with the broadcast=True optional argument to send() and emit():
@socketio.on('my event')
def handle_my_custom_event(data):
emit('my response', data, broadcast=True)
When a message is sent with the broadcast option enabled, all clients connected to the
namespace receive it, including the sender. When namespaces are not used, the clients
connected to the global namespace receive the message. Note that callbacks are not invoked
for broadcast messages.
In all the examples shown until this point the server responds to an event sent by the
client. But for some applications, the server needs to be the originator of a message.
This can be useful to send notifications to clients of events that originated in the
server, for example in a background thread. The socketio.send() and socketio.emit()
methods can be used to broadcast to all connected clients:
def some_function():
socketio.emit('some event', {'data': 42})
Note that socketio.send() and socketio.emit() are not the same functions as the
context-aware send() and emit(). Also note that in the above usage there is no client
context, so broadcast=True is assumed and does not need to be specified.
Rooms
For many applications it is necessary to group users into subsets that can be addressed
together. The best example is a chat application with multiple rooms, where users receive
messages from the room or rooms they are in, but not from other rooms where other users
are. Flask-SocketIO supports this concept of rooms through the join_room() and
leave_room() functions:
from flask_socketio import join_room, leave_room
@socketio.on('join')
def on_join(data):
username = data['username']
room = data['room']
join_room(room)
send(username + ' has entered the room.', to=room)
@socketio.on('leave')
def on_leave(data):
username = data['username']
room = data['room']
leave_room(room)
send(username + ' has left the room.', to=room)
The send() and emit() functions accept an optional to argument that cause the message to
be sent to all the clients that are in the given room.
All clients are assigned a room when they connect, named with the session ID of the
connection, which can be obtained from request.sid. A given client can join any rooms,
which can be given any names. When a client disconnects it is removed from all the rooms
it was in. The context-free socketio.send() and socketio.emit() functions also accept a to
argument to broadcast to all clients in a room.
Since all clients are assigned a personal room, to address a message to a single client,
the session ID of the client can be used as the to argument.
Connection Events
Flask-SocketIO also dispatches connection and disconnection events. The following example
shows how to register handlers for them:
@socketio.on('connect')
def test_connect(auth):
emit('my response', {'data': 'Connected'})
@socketio.on('disconnect')
def test_disconnect():
print('Client disconnected')
The auth argument in the connection handler is optional. The client can use it to pass
authentication data such as tokens in dictionary format. If the client does not provide
authentication details, then this argument is set to None. If the server defines a
connection event handler without this argument, then any authentication data passed by the
client is discarded.
The connection event handler can return False to reject the connection, or it can also
raise ConnectionRefusedError. This is so that the client can be authenticated at this
point. When using the exception, any arguments passed to the exception are returned to the
client in the error packet. Examples:
from flask_socketio import ConnectionRefusedError
@socketio.on('connect')
def connect():
if not self.authenticate(request.args):
raise ConnectionRefusedError('unauthorized!')
Note that connection and disconnection events are sent individually on each namespace
used.
Class-Based Namespaces
As an alternative to the decorator-based event handlers described above, the event
handlers that belong to a namespace can be created as methods of a class. The
flask_socketio.Namespace is provided as a base class to create class-based namespaces:
from flask_socketio import Namespace, emit
class MyCustomNamespace(Namespace):
def on_connect(self):
pass
def on_disconnect(self):
pass
def on_my_event(self, data):
emit('my_response', data)
socketio.on_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 flask_socketio.SocketIO class that
default to the proper namespace when the namespace argument is not given.
If an event has a handler in a class-based namespace, and also a decorator-based function
handler, only the decorated function handler is invoked.
Error Handling
Flask-SocketIO can also deal with exceptions:
@socketio.on_error() # Handles the default namespace
def error_handler(e):
pass
@socketio.on_error('/chat') # handles the '/chat' namespace
def error_handler_chat(e):
pass
@socketio.on_error_default # handles all namespaces without an explicit error handler
def default_error_handler(e):
pass
Error handler functions take the exception object as an argument.
The message and data arguments of the current request can also be inspected with the
request.event variable, which is useful for error logging and debugging outside the event
handler:
from flask import request
@socketio.on("my error event")
def on_my_event(data):
raise RuntimeError()
@socketio.on_error_default
def default_error_handler(e):
print(request.event["message"]) # "my error event"
print(request.event["args"]) # (data,)
Debugging and Troubleshooting
To help you debug issues, the server can be configured to output logs to the terminal:
socketio = SocketIO(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.
IMPLEMENTATION NOTES
Access to Flask's Context Globals
Handlers for SocketIO events are different than handlers for routes and that introduces a
lot of confusion around what can and cannot be done in a SocketIO handler. The main
difference is that all the SocketIO events generated for a client occur in the context of
a single long running request.
In spite of the differences, Flask-SocketIO attempts to make working with SocketIO event
handlers easier by making the environment similar to that of a regular HTTP request. The
following list describes what works and what doesn't:
• An application context is pushed before invoking an event handler making current_app and
g available to the handler.
• A request context is also pushed before invoking a handler, also making request and
session available. But note that WebSocket events do not have individual requests
associated with them, so the request context that started the connection is pushed for
all the events that are dispatched during the life of the connection.
• The request context global is enhanced with a sid member that is set to a unique session
ID for the connection. This value is used as an initial room where the client is added.
• The request context global is enhanced with namespace and event members that contain the
currently handled namespace and event arguments. The event member is a dictionary with
message and args keys.
• The session context global behaves in a different way than in regular requests. A copy
of the user session at the time the SocketIO connection is established is made available
to handlers invoked in the context of that connection. If a SocketIO handler modifies
the session, the modified session will be preserved for future SocketIO handlers, but
regular HTTP route handlers will not see these changes. Effectively, when a SocketIO
handler modifies the session, a "fork" of the session is created exclusively for these
handlers. The technical reason for this limitation is that to save the user session a
cookie needs to be sent to the client, and that requires HTTP request and response,
which do not exist in a SocketIO connection. When using server-side sessions such as
those provided by the Flask-Session or Flask-KVSession extensions, changes made to the
session in HTTP route handlers can be seen by SocketIO handlers, as long as the session
is not modified in the SocketIO handlers.
• The before_request and after_request hooks are not invoked for SocketIO event handlers.
• SocketIO handlers can take custom decorators, but most Flask decorators will not be
appropriate to use for a SocketIO handler, given that there is no concept of a Response
object during a SocketIO connection.
Authentication
A common need of applications is to validate the identity of their users. The traditional
mechanisms based on web forms and HTTP requests cannot be used in a SocketIO connection,
since there is no place to send HTTP requests and responses. If necessary, an application
can implement a customized login form that sends credentials to the server as a SocketIO
message when the submit button is pressed by the user.
However, in most cases it is more convenient to perform the traditional authentication
process before the SocketIO connection is established. The user's identity can then be
recorded in the user session or in a cookie, and later when the SocketIO connection is
established that information will be accessible to SocketIO event handlers.
Recent revisions of the Socket.IO protocol include the ability to pass a dictionary with
authentication information during the connection. This is an ideal place for the client to
include a token or other authentication details. If the client uses this capability, the
server will provide this dictionary as an argument to the connect event handler, as shown
above.
Using Flask-Login with Flask-SocketIO
Flask-SocketIO can access login information maintained by Flask-Login. After a regular
Flask-Login authentication is performed and the login_user() function is called to record
the user in the user session, any SocketIO connections will have access to the
current_user context variable:
@socketio.on('connect')
def connect_handler():
if current_user.is_authenticated:
emit('my response',
{'message': '{0} has joined'.format(current_user.name)},
broadcast=True)
else:
return False # not allowed here
Note that the login_required decorator cannot be used with SocketIO event handlers, but a
custom decorator that disconnects non-authenticated users can be created as follows:
import functools
from flask import request
from flask_login import current_user
from flask_socketio import disconnect, emit
def authenticated_only(f):
@functools.wraps(f)
def wrapped(*args, **kwargs):
if not current_user.is_authenticated:
disconnect()
else:
return f(*args, **kwargs)
return wrapped
@socketio.on('my event')
@authenticated_only
def handle_my_custom_event(data):
emit('my response', {'message': '{0} has joined'.format(current_user.name)},
broadcast=True)
DEPLOYMENT
There are many options to deploy a Flask-SocketIO server, ranging from simple to the
insanely complex. In this section, the most commonly used options are described.
Embedded Server
The simplest deployment strategy is to start the web server by calling socketio.run(app)
as shown in examples above. This will look through the packages that are installed for the
best available web server start the application on it. The current web server choices that
are evaluated are eventlet, gevent and the Flask development server.
If eventlet or gevent are available, socketio.run(app) starts a production-ready server
using one of these frameworks. If neither of these are installed, then the Flask
development web server is used, and in this case the server is not intended to be used in
a production deployment.
Unfortunately this option is not available when using gevent with uWSGI. See the uWSGI
section below for information on this option.
Gunicorn Web Server
An alternative to socketio.run(app) is to use gunicorn as web server, using the eventlet
or gevent workers. For this option, eventlet or gevent need to be installed, in addition
to gunicorn. The command line that starts the eventlet server via gunicorn is:
gunicorn --worker-class eventlet -w 1 module:app
If you prefer to use gevent, the command to start the server is:
gunicorn -k gevent -w 1 module:app
When using gunicorn with the gevent worker and the WebSocket support provided by
gevent-websocket, the command that starts the server must be changed to select a custom
gevent web server that supports the WebSocket protocol. The modified command is:
gunicorn -k geventwebsocket.gunicorn.workers.GeventWebSocketWorker -w 1 module:app
A third option with Gunicorn is to use the threaded worker, along with the
simple-websocket package for WebSocket support. This is a particularly good solution for
applications that are CPU heavy or are otherwise incompatible with eventlet and gevent use
of green threads. The command to start a threaded web server is:
gunicorn -w 1 --threads 100 module:app
In all these commands, module is the Python module or package that defines the application
instance, and app is the application instance itself.
Due to the limited load balancing algorithm used by gunicorn, it is not possible to use
more than one worker process when using this web server. For that reason, all the examples
above include the -w 1 option.
The workaround to use multiple worker processes with gunicorn is to launch several
single-worker instances and put them behind a more capable load balancer such as nginx.
uWSGI Web Server
When using the uWSGI server in combination with gevent, the Socket.IO server can take
advantage of uWSGI’s native WebSocket support.
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 example application app.py on port 5000:
$ uwsgi --http :5000 --gevent 1000 --http-websockets --master --wsgi-file app.py --callable app
Using nginx as a WebSocket Reverse Proxy
It is possible to use nginx as a front-end reverse proxy that passes requests to the
application. However, only releases of nginx 1.4 and newer support proxying of the
WebSocket protocol. Below is a basic nginx configuration that proxies HTTP and WebSocket
requests:
server {
listen 80;
server_name _;
location / {
include proxy_params;
proxy_pass http://127.0.0.1:5000;
}
location /static {
alias <path-to-your-application>/static;
expires 30d;
}
location /socket.io {
include proxy_params;
proxy_http_version 1.1;
proxy_buffering off;
proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection "Upgrade";
proxy_pass http://127.0.0.1:5000/socket.io;
}
}
The next example adds the support for load balancing multiple Socket.IO servers:
upstream socketio_nodes {
ip_hash;
server 127.0.0.1:5000;
server 127.0.0.1:5001;
server 127.0.0.1:5002;
# to scale the app, just add more nodes here!
}
server {
listen 80;
server_name _;
location / {
include proxy_params;
proxy_pass http://127.0.0.1:5000;
}
location /static {
alias <path-to-your-application>/static;
expires 30d;
}
location /socket.io {
include proxy_params;
proxy_http_version 1.1;
proxy_buffering off;
proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection "Upgrade";
proxy_pass http://socketio_nodes/socket.io;
}
}
While the above examples can work as an initial configuration, be aware that a production
install of nginx will need a more complete configuration covering other deployment aspects
such as SSL support.
Using Multiple Workers
Flask-SocketIO supports multiple workers behind a load balancer starting with release 2.0.
Deploying multiple workers gives applications that use Flask-SocketIO the ability to
spread the client connections among multiple processes and hosts, and in this way scale to
support very large numbers of concurrent clients.
There are two requirements to use multiple Flask-SocketIO workers:
• The load balancer must be configured to forward all HTTP requests from a given client
always to the same worker. This is sometimes referenced as "sticky sessions". For nginx,
use the ip_hash directive to achieve this. Gunicorn cannot be used with multiple
workers because its load balancer algorithm does not support sticky sessions.
• Since each of the servers owns only a subset of the client connections, a message queue
such as Redis or RabbitMQ is used by the servers to coordinate complex operations such
as broadcasting and rooms.
When working with a message queue, there are additional dependencies that need to be
installed:
• For Redis, the package redis must be installed (pip install redis).
• For RabbitMQ, the package kombu must be installed (pip install kombu).
• For Kafka, the package kafka-python must be installed (pip install kafka-python).
• For other message queues supported by Kombu, see the Kombu documentation to find out
what dependencies are needed.
• If eventlet or gevent are used, then monkey patching the Python standard library is
normally required to force the message queue package to use coroutine friendly functions
and classes.
For eventlet, monkey patching is done with:
import eventlet
eventlet.monkey_patch()
For gevent, you can monkey patch the standard library with:
from gevent import monkey
monkey.patch_all()
In both cases it is recommended that you apply the monkey patching at the top of your main
script, even above your imports.
To start multiple Flask-SocketIO servers, you must first ensure you have the message queue
service running. To start a Socket.IO server and have it connect to the message queue, add
the message_queue argument to the SocketIO constructor:
socketio = SocketIO(app, message_queue='redis://')
The value of the message_queue argument is the connection URL of the queue service that is
used. For a redis queue running on the same host as the server, the 'redis://' URL can be
used. Likewise, for a default RabbitMQ queue the 'amqp://' URL can be used. For Kafka, use
a kafka:// URL. The Kombu package has a documentation section that describes the format
of the URLs for all the supported queues.
Emitting from an External Process
For many types of applications, it is necessary to emit events from a process that is not
the SocketIO server, for an example a Celery worker. If the SocketIO server or servers are
configured to listen on a message queue as shown in the previous section, then any other
process can create its own SocketIO instance and use it to emit events in the same way the
server does.
For example, for an application that runs on an eventlet web server and uses a Redis
message queue, the following Python script broadcasts an event to all clients:
socketio = SocketIO(message_queue='redis://')
socketio.emit('my event', {'data': 'foo'}, namespace='/test')
When using the SocketIO instance in this way, the Flask application instance is not passed
to the constructor.
The channel argument to SocketIO can be used to select a specific channel of communication
through the message queue. Using a custom channel name is necessary when there are
multiple independent SocketIO services sharing the same queue.
Flask-SocketIO does not apply monkey patching when eventlet or gevent are used. But when
working with a message queue, it is very likely that the Python package that talks to the
message queue service will hang if the Python standard library is not monkey patched.
It is important to note that an external process that wants to connect to a SocketIO
server does not need to use eventlet or gevent like the main server. Having a server use a
coroutine framework, while an external process is not a problem. For example, Celery
workers do not need to be configured to use eventlet or gevent just because the main
server does. But if your external process does use a coroutine framework for whatever
reason, then monkey patching is likely required, so that the message queue accesses
coroutine friendly functions and classes.
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.
UPGRADING TO FLASK-SOCKETIO 5.X FROM THE 4.X RELEASES
The Socket.IO protocol recently introduced a series of backwards incompatible changes. The
5.x releases of Flask-SocketIO adopted these changes, and for that reason it can only be
used with clients that have also been updated to the current version of the protocol. In
particular, this means that the JavaScript client must be upgraded to a 3.x release, and
if your client hasn't been upgraded to the latest version of the Socket.IO protocol, then
you must use a Flask-SocketIO 4.x release.
The following protocol changes are of importance, as they may affect existing
applications:
• The default namespace '/' is not automatically connected anymore, and is now treated in
the same way as other namespaces.
• Each namespace connection has its own sid value, different from the others and different
from the Engine.IO sid.
• Flask-SocketIO now uses the same ping interval and timeout values as the JavaScript
reference implementation, which are 25 and 5 seconds respectively.
• The ping/pong mechanism has been reversed. In the current version of the protocol, the
server issues a ping and the client responds with a pong.
• The default allowed payload size for long--polling packets has been lowered from 100MB
to 1MB.
• The io cookie is not sent to the client anymore by default.
API REFERENCE
• Index
• Module Index
• Search Page
AUTHOR
Miguel Grinberg
COPYRIGHT
2018, Miguel Grinberg
Jan 16, 2023 FLASK-SOCKETIO(1)