PYTHON-ENGINEIO(1) python-engineio PYTHON-ENGINEIO(1)
NAME
python-engineio - python-engineio Documentation
This project implements Python based Engine.IO client and server that
can run standalone or integrated with a variety of Python web
frameworks and applications.
GETTING STARTED
What is Engine.IO?
Engine.IO is a lightweight 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.
The Engine.IO protocol is extremely simple. Once a connection between a
client and a server is established, either side can send "messages" to
the other side. Event handlers provided by the applications on both
ends are invoked when a message is received, or when a connection is
established or dropped.
Client Examples
The example that follows shows a simple Python client:
import engineio
eio = engineio.Client()
@eio.on('connect')
def on_connect():
print('connection established')
@eio.on('message')
def on_message(data):
print('message received with ', data)
eio.send({'response': 'my response'})
@eio.on('disconnect')
def on_disconnect():
print('disconnected from server')
eio.connect('http://localhost:5000')
eio.wait()
And here is a similar client written using the official Engine.IO
Javascript client:
Client Features
o Can connect to other Engine.IO complaint servers besides the one in
this package.
o Compatible with Python 3.6+.
o Two versions of the client, one for standard Python and another for
asyncio.
o Uses an event-based architecture implemented with decorators that
hides the details of the protocol.
o Implements HTTP long-polling and WebSocket transports.
Server Examples
The following application is a basic example that uses the Eventlet
asynchronous server:
import engineio
import eventlet
eio = engineio.Server()
app = engineio.WSGIApp(eio, static_files={
'/': {'content_type': 'text/html', 'filename': 'index.html'}
})
@eio.on('connect')
def connect(sid, environ):
print("connect ", sid)
@eio.on('message')
def message(sid, data):
print("message ", data)
eio.send(sid, 'reply')
@eio.on('disconnect')
def disconnect(sid):
print('disconnect ', sid)
if __name__ == '__main__':
eventlet.wsgi.server(eventlet.listen(('', 5000)), app)
Below is a similar application, coded for asyncio and the Uvicorn web
server:
import engineio
import uvicorn
eio = engineio.AsyncServer()
app = engineio.ASGIApp(eio, static_files={
'/': {'content_type': 'text/html', 'filename': 'index.html'}
})
@eio.on('connect')
def connect(sid, environ):
print("connect ", sid)
@eio.on('message')
async def message(sid, data):
print("message ", data)
await eio.send(sid, 'reply')
@eio.on('disconnect')
def disconnect(sid):
print('disconnect ', sid)
if __name__ == '__main__':
uvicorn.run('127.0.0.1', 5000)
Server Features
o Can accept clients running other complaint Engine.IO clients besides
the one in this package.
o Compatible with Python 3.6+.
o Two versions of the server, one for standard Python and another for
asyncio.
o Supports large number of clients even on modest hardware due to being
asynchronous.
o Can be hosted on any WSGI and ASGI web servers includind Gunicorn,
Uvicorn, eventlet and gevent.
o Can be integrated with WSGI applications written in frameworks such
as Flask, Django, etc.
o Can be integrated with aiohttp, sanic and tornado asyncio
applications.
o Uses an event-based architecture implemented with decorators that
hides the details of the protocol.
o Implements HTTP long-polling and WebSocket transports.
o Supports XHR2 and XHR browsers as clients.
o Supports text and binary messages.
o Supports gzip and deflate HTTP compression.
o Configurable CORS responses to avoid cross-origin problems with
browsers.
THE ENGINE.IO CLIENT
This package contains two Engine.IO clients:
o The engineio.Client() class creates a client compatible with the
standard Python library.
o The engineio.AsyncClient() class creates a client compatible with the
asyncio package.
The methods in the two clients are the same, with the only difference
that in the asyncio client most methods are implemented as coroutines.
Installation
To install the standard Python client along with its dependencies, use
the following command:
pip install "python-engineio[client]"
If instead you plan on using the asyncio client, then use this:
pip install "python-engineio[asyncio_client]"
Creating a Client Instance
To instantiate an Engine.IO client, simply create an instance of the
appropriate client class:
import engineio
# standard Python
eio = engineio.Client()
# asyncio
eio = engineio.AsyncClient()
Defining Event Handlers
To responds to events triggered by the connection or the server, event
Handler functions must be defined using the on decorator:
@eio.on('connect')
def on_connect():
print('I'm connected!')
@eio.on('message')
def on_message(data):
print('I received a message!')
@eio.on('disconnect')
def on_disconnect():
print('I'm disconnected!')
For the asyncio server, event handlers can be regular functions as
above, or can also be coroutines:
@eio.on('message')
async def on_message(data):
print('I received a message!')
The argument given to the on decorator is the event name. The events
that are supported are connect, message and disconnect. Note that the
disconnect handler is invoked for application initiated disconnects,
server initiated disconnects, or accidental disconnects, for example
due to networking failures.
The data argument passed to the 'message' event handler contains
application-specific data provided by the server with the event.
Connecting to a Server
The connection to a server is established by calling the connect()
method:
eio.connect('http://localhost:5000')
In the case of the asyncio client, the method is a coroutine:
await eio.connect('http://localhost:5000')
Upon connection, the server assigns the client a unique session
identifier. The applicaction can find this identifier in the sid
attribute:
print('my sid is', eio.sid)
Sending Messages
The client can send a message to the server using the send() method:
eio.send({'foo': 'bar'})
Or in the case of asyncio, as a coroutine:
await eio.send({'foo': 'bar'})
The single argument provided to the method is the data that is passed
on to the server. The data can be of type str, bytes, dict or list. The
data included inside dictionaries and lists is also constrained to
these types.
The send() 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.
Disconnecting from the Server
At any time the client can request to be disconnected from the server
by invoking the disconnect() method:
eio.disconnect()
For the asyncio client this is a coroutine:
await eio.disconnect()
Managing Background Tasks
When a client connection to the server is established, a few background
tasks will be spawned to keep the connection alive and handle incoming
events. The application running on the main thread is free to do any
work, as this is not going to prevent the functioning of the Engine.IO
client.
If the application does not have anything to do in the main thread and
just wants to wait until the connection ends, it can call the wait()
method:
eio.wait()
Or in the asyncio version:
await eio.wait()
For the convenience of the application, a helper function is provided
to start a custom background task:
def my_background_task(my_argument)
# do some background work here!
pass
eio.start_background_task(my_background_task, 123)
The arguments passed to this method are the background function and any
positional or keyword arguments to invoke the function with.
Here is the asyncio version:
async def my_background_task(my_argument)
# do some background work here!
pass
eio.start_background_task(my_background_task, 123)
Note that this function is not a coroutine, since it does not wait for
the background function to end, but the background function is.
The sleep() method is a second convenience function that is provided
for the benefit of applications working with background tasks of their
own:
eio.sleep(2)
Or for asyncio:
await eio.sleep(2)
The single argument passed to the method is the number of seconds to
sleep for.
Debugging and Troubleshooting
To help you debug issues, the client can be configured to output logs
to the terminal:
import engineio
# standard Python
eio = engineio.Client(logger=True)
# asyncio
eio = engineio.AsyncClient(logger=True)
The logger argument can be set to True to output logs to stderr, or to
an object compatible with Python's logging package where the logs
should be emitted to. A value of False disables logging.
Logging can help identify the cause of connection problems, unexpected
disconnections and other issues.
THE ENGINE.IO SERVER
This package contains two Engine.IO servers:
o The engineio.Server() class creates a server compatible with the
standard Python library.
o The engineio.AsyncServer() class creates a server compatible with the
asyncio package.
The methods in the two servers are the same, with the only difference
that in the asyncio server most methods are implemented as coroutines.
Installation
To install the Python Engine.IO server use the following command:
pip install "python-engineio"
In addition to the server, you will need to select an asynchronous
framework or server to use along with it. The list of supported
packages is covered in the Deployment Strategies section.
Creating a Server Instance
An Engine.IO server is an instance of class engineio.Server. This
instance can be transformed into a standard WSGI application by
wrapping it with the engineio.WSGIApp class:
import engineio
# create a Engine.IO server
eio = engineio.Server()
# wrap with a WSGI application
app = engineio.WSGIApp(eio)
For asyncio based servers, the engineio.AsyncServer class provides the
same functionality, but in a coroutine friendly format. If desired, The
engineio.ASGIApp class can transform the server into a standard ASGI
application:
# create a Engine.IO server
eio = engineio.AsyncServer()
# wrap with ASGI application
app = engineio.ASGIApp(eio)
These two wrappers can also act as middlewares, forwarding any traffic
that is not intended to the Engine.IO server to another application.
This allows Engine.IO servers to integrate easily into existing WSGI or
ASGI applications:
from wsgi import app # a Flask, Django, etc. application
app = engineio.WSGIApp(eio, app)
Serving Static Files
The Engine.IO server can be configured to serve static files to
clients. This is particularly useful to deliver HTML, CSS and
JavaScript files to clients when this package is used without a
companion web framework.
Static files are configured with a Python dictionary in which each
key/value pair is a static file mapping rule. In its simplest form,
this dictionary has one or more static file URLs as keys, and the
corresponding files in the server as values:
static_files = {
'/': 'latency.html',
'/static/engine.io.js': 'static/engine.io.js',
'/static/style.css': 'static/style.css',
}
With this example configuration, when the server receives a request for
/ (the root URL) it will return the contents of the file latency.html
in the current directory, and will assign a content type based on the
file extension, in this case text/html.
Files with the .html, .css, .js, .json, .jpg, .png, .gif and .txt file
extensions are automatically recognized and assigned the correct
content type. For files with other file extensions or with no file
extension, the application/octet-stream content type is used as a
default.
If desired, an explicit content type for a static file can be given as
follows:
static_files = {
'/': {'filename': 'latency.html', 'content_type': 'text/plain'},
}
It is also possible to configure an entire directory in a single rule,
so that all the files in it are served as static files:
static_files = {
'/static': './public',
}
In this example any files with URLs starting with /static will be
served directly from the public folder in the current directory, so for
example, the URL /static/index.html will return local file
./public/index.html and the URL /static/css/styles.css will return
local file ./public/css/styles.css.
If a URL that ends in a / is requested, then a default filename of
index.html is appended to it. In the previous example, a request for
the /static/ URL would return local file ./public/index.html. The
default filename to serve for slash-ending URLs can be set in the
static files dictionary with an empty key:
static_files = {
'/static': './public',
'': 'image.gif',
}
With this configuration, a request for /static/ would return local file
./public/image.gif. A non-standard content type can also be specified
if needed:
static_files = {
'/static': './public',
'': {'filename': 'image.gif', 'content_type': 'text/plain'},
}
The static file configuration dictionary is given as the static_files
argument to the engineio.WSGIApp or engineio.ASGIApp classes:
# for standard WSGI applications
eio = engineio.Server()
app = engineio.WSGIApp(eio, static_files=static_files)
# for asyncio-based ASGI applications
eio = engineio.AsyncServer()
app = engineio.ASGIApp(eio, static_files=static_files)
The routing precedence in these two classes is as follows:
o First, the path is checked against the Engine.IO path.
o Next, the path is checked against the static file configuration, if
present.
o If the path did not match the Engine.IO path or any static file,
control is passed to the secondary application if configured, else a
404 error is returned.
Note: static file serving is intended for development use only, and as
such it lacks important features such as caching. Do not use in a
production environment.
Defining Event Handlers
To responds to events triggered by the connection or the client, event
Handler functions must be defined using the on decorator:
@eio.on('connect')
def on_connect(sid):
print('A client connected!')
@eio.on('message')
def on_message(sid, data):
print('I received a message!')
@eio.on('disconnect')
def on_disconnect(sid):
print('Client disconnected!')
For the asyncio server, event handlers can be regular functions as
above, or can also be coroutines:
@eio.on('message')
async def on_message(sid, data):
print('I received a message!')
The argument given to the on decorator is the event name. The events
that are supported are connect, message and disconnect. Note that the
disconnect handler is invoked for client initiated disconnects, server
initiated disconnects, or accidental disconnects, for example due to
networking failures.
The sid argument passed into all the event handlers is a connection
identifier for the client. All the events from a client will use the
same sid value.
The connect handler is the place where the server can perform
authentication. The value returned by this handler is used to determine
if the connection is accepted or rejected. When the handler does not
return any value (which is the same as returning None) or when it
returns True the connection is accepted. If the handler returns False
or any JSON compatible data type (string, integer, list or dictionary)
the connection is rejected. A rejected connection triggers a response
with a 401 status code.
The data argument passed to the 'message' event handler contains
application-specific data provided by the client with the event.
Sending Messages
The server can send a message to any client using the send() method:
eio.send(sid, {'foo': 'bar'})
Or in the case of asyncio, as a coroutine:
await eio.send(sid, {'foo': 'bar'})
The first argument provided to the method is the connection identifier
for the recipient client. The second argument is the data that is
passed on to the server. The data can be of type str, bytes, dict or
list. The data included inside dictionaries and lists is also
constrained to these types.
The send() method can be invoked inside an event handler as a response
to a client event, or in any other part of the application, including
in background tasks.
User Sessions
The server can maintain application-specific information in a user
session dedicated to each connected client. Applications can use the
user session to write any details about the user that need to be
preserved throughout the life of the connection, such as usernames or
user ids.
The save_session() and get_session() methods are used to store and
retrieve information in the user session:
@eio.on('connect')
def on_connect(sid, environ):
username = authenticate_user(environ)
eio.save_session(sid, {'username': username})
@eio.on('message')
def on_message(sid, data):
session = eio.get_session(sid)
print('message from ', session['username'])
For the asyncio server, these methods are coroutines:
@eio.on('connect')
async def on_connect(sid, environ):
username = authenticate_user(environ)
await eio.save_session(sid, {'username': username})
@eio.on('message')
async def on_message(sid, data):
session = await eio.get_session(sid)
print('message from ', session['username'])
The session can also be manipulated with the session() context manager:
@eio.on('connect')
def on_connect(sid, environ):
username = authenticate_user(environ)
with eio.session(sid) as session:
session['username'] = username
@eio.on('message')
def on_message(sid, data):
with eio.session(sid) as session:
print('message from ', session['username'])
For the asyncio server, an asynchronous context manager is used:
@eio.on('connect')
def on_connect(sid, environ):
username = authenticate_user(environ)
async with eio.session(sid) as session:
session['username'] = username
@eio.on('message')
def on_message(sid, data):
async with eio.session(sid) as session:
print('message from ', session['username'])
Note: the contents of the user session are destroyed when the client
disconnects.
Disconnecting a Client
At any time the server can disconnect a client from the server by
invoking the disconnect() method and passing the sid value assigned to
the client:
eio.disconnect(sid)
For the asyncio client this is a coroutine:
await eio.disconnect(sid)
Managing Background Tasks
For the convenience of the application, a helper function is provided
to start a custom background task:
def my_background_task(my_argument)
# do some background work here!
pass
eio.start_background_task(my_background_task, 123)
The arguments passed to this method are the background function and any
positional or keyword arguments to invoke the function with.
Here is the asyncio version:
async def my_background_task(my_argument)
# do some background work here!
pass
eio.start_background_task(my_background_task, 123)
Note that this function is not a coroutine, since it does not wait for
the background function to end, but the background function is.
The sleep() method is a second convenience function that is provided
for the benefit of applications working with background tasks of their
own:
eio.sleep(2)
Or for asyncio:
await eio.sleep(2)
The single argument passed to the method is the number of seconds to
sleep for.
Debugging and Troubleshooting
To help you debug issues, the server can be configured to output logs
to the terminal:
import engineio
# standard Python
eio = engineio.Server(logger=True)
# asyncio
eio = engineio.AsyncServer(logger=True)
The logger argument can be set to True to output logs to stderr, or to
an object compatible with Python's logging package where the logs
should be emitted to. A value of False disables logging.
Logging can help identify the cause of connection problems, 400
responses, bad performance and other issues.
Deployment Strategies
The following sections describe a variety of deployment strategies for
Engine.IO servers.
Uvicorn, Daphne, and other ASGI servers
The engineio.ASGIApp class is an ASGI compatible application that can
forward Engine.IO traffic to an engineio.AsyncServer instance:
eio = engineio.AsyncServer(async_mode='asgi')
app = engineio.ASGIApp(eio)
If desired, the engineio.ASGIApp class can forward any traffic that is
not Engine.IO to another ASGI application, making it possible to deploy
a standard ASGI web application and the Engine.IO server as a bundle:
eio = engineio.AsyncServer(async_mode='asgi')
app = engineio.ASGIApp(eio, other_app)
The ASGIApp instance is a fully complaint ASGI instance that can be
deployed with an ASGI compatible web server.
Aiohttp
aiohttp provides a framework with support for HTTP and WebSocket, based
on asyncio.
Instances of class engineio.AsyncServer will automatically use aiohttp
for asynchronous operations if the library is installed. To request its
use explicitly, the async_mode option can be given in the constructor:
eio = engineio.AsyncServer(async_mode='aiohttp')
A server configured for aiohttp must be attached to an existing
application:
app = web.Application()
eio.attach(app)
The aiohttp application can define regular routes that will coexist
with the Engine.IO server. A typical pattern is to add routes that
serve a client application and any associated static files.
The aiohttp application is then executed in the usual manner:
if __name__ == '__main__':
web.run_app(app)
Tornado
Tornado is a web framework with support for HTTP and WebSocket. Only
Tornado version 5 and newer are supported, thanks to its tight
integration with asyncio.
Instances of class engineio.AsyncServer will automatically use tornado
for asynchronous operations if the library is installed. To request its
use explicitly, the async_mode option can be given in the constructor:
eio = engineio.AsyncServer(async_mode='tornado')
A server configured for tornado must include a request handler for
Engine.IO:
app = tornado.web.Application(
[
(r"/engine.io/", engineio.get_tornado_handler(eio)),
],
# ... other application options
)
The tornado application can define other routes that will coexist with
the Engine.IO server. A typical pattern is to add routes that serve a
client application and any associated static files.
The tornado application is then executed in the usual manner:
app.listen(port)
tornado.ioloop.IOLoop.current().start()
Sanic
Note: Due to some backward incompatible changes introduced in recent
versions of Sanic, it is currently recommended that a Sanic application
is deployed with the ASGI integration instead.
Sanic is a very efficient asynchronous web server for Python.
Instances of class engineio.AsyncServer will automatically use Sanic
for asynchronous operations if the framework is installed. To request
its use explicitly, the async_mode option can be given in the
constructor:
eio = engineio.AsyncServer(async_mode='sanic')
A server configured for Sanic must be attached to an existing
application:
app = Sanic()
eio.attach(app)
The Sanic application can define regular routes that will coexist with
the Engine.IO server. A typical pattern is to add routes that serve a
client application and any associated static files to this application.
The Sanic application is then executed in the usual manner:
if __name__ == '__main__':
app.run()
It has been reported that the CORS support provided by the Sanic
extension sanic-cors is incompatible with this package's own support
for this protocol. To disable CORS support in this package and let
Sanic take full control, initialize the server as follows:
eio = engineio.AsyncServer(async_mode='sanic', cors_allowed_origins=[])
On the Sanic side you will need to enable the CORS_SUPPORTS_CREDENTIALS
setting in addition to any other configuration that you use:
app.config['CORS_SUPPORTS_CREDENTIALS'] = True
Eventlet
Eventlet is a high performance concurrent networking library for Python
2 and 3 that uses coroutines, enabling code to be written in the same
style used with the blocking standard library functions. An Engine.IO
server deployed with eventlet has access to the long-polling and
WebSocket transports.
Instances of class engineio.Server will automatically use eventlet for
asynchronous operations if the library is installed. To request its use
explicitly, the async_mode option can be given in the constructor:
eio = engineio.Server(async_mode='eventlet')
A server configured for eventlet is deployed as a regular WSGI
application using the provided engineio.WSGIApp:
app = engineio.WSGIApp(eio)
import eventlet
eventlet.wsgi.server(eventlet.listen(('', 8000)), app)
Eventlet with Gunicorn
An alternative to running the eventlet WSGI server as above is to use
gunicorn, a fully featured pure Python web server. The command to
launch the application under gunicorn is shown below:
$ gunicorn -k eventlet -w 1 module:app
Due to limitations in its load balancing algorithm, gunicorn can only
be used with one worker process, so the -w 1 option is required. Note
that a single eventlet worker can handle a large number of concurrent
clients.
Another limitation when using gunicorn is that the WebSocket transport
is not available, because this transport it requires extensions to the
WSGI standard.
Note: Eventlet provides a monkey_patch() function that replaces all the
blocking functions in the standard library with equivalent asynchronous
versions. While python-engineio does not require monkey patching, other
libraries such as database drivers are likely to require it.
Gevent
Gevent is another asynchronous framework based on coroutines, very
similar to eventlet. An Engine.IO server deployed with gevent has
access to the long-polling and websocket transports.
Instances of class engineio.Server will automatically use gevent for
asynchronous operations if the library is installed and eventlet is not
installed. To request gevent to be selected explicitly, the async_mode
option can be given in the constructor:
eio = engineio.Server(async_mode='gevent')
A server configured for gevent is deployed as a regular WSGI
application using the provided engineio.WSGIApp:
from gevent import pywsgi
app = engineio.WSGIApp(eio)
pywsgi.WSGIServer(('', 8000), app).serve_forever()
Gevent with Gunicorn
An alternative to running the gevent WSGI server as above is to use
gunicorn, a fully featured pure Python web server. The command to
launch the application under gunicorn is shown below:
$ gunicorn -k gevent -w 1 module:app
Same as with eventlet, due to limitations in its load balancing
algorithm, gunicorn can only be used with one worker process, so the -w
1 option is required. Note that a single gevent worker can handle a
large number of concurrent clients.
Note: Gevent provides a monkey_patch() function that replaces all the
blocking functions in the standard library with equivalent asynchronous
versions. While python-engineio does not require monkey patching, other
libraries such as database drivers are likely to require it.
uWSGI
When using the uWSGI server in combination with gevent, the Engine.IO
server can take advantage of uWSGI's native WebSocket support.
Instances of class engineio.Server will automatically use this option
for asynchronous operations if both gevent and uWSGI are installed and
eventlet is not installed. To request this asynchoronous mode
explicitly, the async_mode option can be given in the constructor:
# gevent with uWSGI
eio = engineio.Server(async_mode='gevent_uwsgi')
A complete explanation of the configuration and usage of the uWSGI
server is beyond the scope of this documentation. The uWSGI server is a
fairly complex package that provides a large and comprehensive set of
options. It must be compiled with WebSocket and SSL support for the
WebSocket transport to be available. As way of an introduction, the
following command starts a uWSGI server for the latency.py example on
port 5000:
$ uwsgi --http :5000 --gevent 1000 --http-websockets --master --wsgi-file latency.py --callable app
Standard Threads
While not comparable to eventlet and gevent in terms of performance,
the Engine.IO server can also be configured to work with multi-threaded
web servers that use standard Python threads. This is an ideal setup to
use with development servers such as Werkzeug.
Instances of class engineio.Server will automatically use the threading
mode if neither eventlet nor gevent are not installed. To request the
threading mode explicitly, the async_mode option can be given in the
constructor:
eio = engineio.Server(async_mode='threading')
A server configured for threading is deployed as a regular web
application, using any WSGI complaint multi-threaded server. The
example below deploys an Engine.IO application combined with a Flask
web application, using Flask's development web server based on
Werkzeug:
eio = engineio.Server(async_mode='threading')
app = Flask(__name__)
app.wsgi_app = engineio.WSGIApp(eio, app.wsgi_app)
# ... Engine.IO and Flask handler functions ...
if __name__ == '__main__':
app.run()
The example that follows shows how to start an Engine.IO application
using Gunicorn's threaded worker class:
$ gunicorn -w 1 --threads 100 module:app
With the above configuration the server will be able to handle up to
100 concurrent clients.
When using standard threads, WebSocket is supported through the
simple-websocket package, which must be installed separately. This
package provides a multi-threaded WebSocket server that is compatible
with Werkzeug and Gunicorn's threaded worker. Other multi-threaded web
servers are not supported and will not enable the WebSocket transport.
Scalability Notes
Engine.IO is a stateful protocol, which makes horizontal scaling more
difficult. To deploy a cluster of Engine.IO processes hosted on one or
multiple servers the following conditions must be met:
o Each Engine.IO server process must be able to handle multiple
requests concurrently. This is required because long-polling clients
send two requests in parallel. Worker processes that can only handle
one request at a time are not supported.
o The load balancer must be configured to always forward requests from
a client to the same process. Load balancers call this sticky
sessions, or session affinity.
Cross-Origin Controls
For security reasons, this server enforces a same-origin policy by
default. In practical terms, this means the following:
o 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.
o No restrictions are imposed on incoming requests that do not include
the Origin header.
If necessary, the cors_allowed_origins option can be used to allow
other origins. This argument can be set to a string to set a single
allowed origin, or to a list to allow multiple origins. A special value
of '*' can be used to instruct the server to allow all origins, but
this should be done with care, as this could make the server vulnerable
to Cross-Site Request Forgery (CSRF) attacks.
API REFERENCE
class engineio.Client(logger=False, json=None, request_timeout=5,
http_session=None, ssl_verify=True, handle_sigint=True,
websocket_extra_options=None)
An Engine.IO client.
This class implements a fully compliant Engine.IO web client
with support for websocket and long-polling transports.
Parameters
o logger -- To enable logging set to True or pass a
logger object to use. To disable logging set to False.
The default is False. Note that fatal errors are logged
even when logger is False.
o json -- An alternative json module to use for encoding
and decoding packets. Custom json modules must have
dumps and loads functions that are compatible with the
standard library versions.
o request_timeout -- A timeout in seconds for requests.
The default is 5 seconds.
o http_session -- an initialized requests.Session object
to be used when sending requests to the server. Use it
if you need to add special client options such as proxy
servers, SSL certificates, custom CA bundle, etc.
o ssl_verify -- True to verify SSL certificates, or False
to skip SSL certificate verification, allowing
connections to servers with self signed certificates.
The default is True.
o handle_sigint -- Set to True to automatically handle
disconnection when the process is interrupted, or to
False to leave interrupt handling to the calling
application. Interrupt handling can only be enabled
when the client instance is created in the main thread.
o websocket_extra_options -- Dictionary containing
additional keyword arguments passed to
websocket.create_connection().
connect(url, headers=None, transports=None,
engineio_path='engine.io')
Connect to an Engine.IO server.
Parameters
o url -- The URL of the Engine.IO server. It can
include custom query string parameters if
required by the server.
o headers -- A dictionary with custom headers to
send with the connection request.
o transports -- The list of allowed transports.
Valid transports are 'polling' and 'websocket'.
If not given, the polling transport is connected
first, then an upgrade to websocket is
attempted.
o engineio_path -- The endpoint where the
Engine.IO server is installed. The default value
is appropriate for most cases.
Example usage:
eio = engineio.Client()
eio.connect('http://localhost:5000')
wait() Wait until the connection with the server ends.
Client applications can use this function to block the
main thread during the life of the connection.
send(data)
Send a message to the server.
Parameters
data -- The data to send to the server. Data can
be of type str, bytes, list or dict. If a list or
dict, the data will be serialized as JSON.
disconnect(abort=False)
Disconnect from the server.
Parameters
abort -- If set to True, do not wait for
background tasks associated with the connection to
end.
start_background_task(target, *args, **kwargs)
Start a background task.
This is a utility function that applications can use to
start a background task.
Parameters
o target -- the target function to execute.
o args -- arguments to pass to the function.
o kwargs -- keyword arguments to pass to the
function.
This function returns an object that represents the
background task, on which the join() method can be
invoked to wait for the task to complete.
sleep(seconds=0)
Sleep for the requested amount of time.
create_queue(*args, **kwargs)
Create a queue object.
create_event(*args, **kwargs)
Create an event object.
on(event, handler=None)
Register an event handler.
Parameters
o event -- The event name. Can be 'connect',
'message' or 'disconnect'.
o handler -- The function that should be invoked
to handle the event. When this parameter is not
given, the method acts as a decorator for the
handler function.
Example usage:
# as a decorator:
@eio.on('connect')
def connect_handler():
print('Connection request')
# as a method:
def message_handler(msg):
print('Received message: ', msg)
eio.send('response')
eio.on('message', message_handler)
transport()
Return the name of the transport currently in use.
The possible values returned by this function are
'polling' and 'websocket'.
class engineio.AsyncClient(logger=False, json=None, request_timeout=5,
http_session=None, ssl_verify=True, handle_sigint=True,
websocket_extra_options=None)
An Engine.IO client for asyncio.
This class implements a fully compliant Engine.IO web client
with support for websocket and long-polling transports,
compatible with the asyncio framework on Python 3.5 or newer.
Parameters
o logger -- To enable logging set to True or pass a
logger object to use. To disable logging set to False.
The default is False. Note that fatal errors are logged
even when logger is False.
o json -- An alternative json module to use for encoding
and decoding packets. Custom json modules must have
dumps and loads functions that are compatible with the
standard library versions.
o request_timeout -- A timeout in seconds for requests.
The default is 5 seconds.
o http_session -- an initialized aiohttp.ClientSession
object to be used when sending requests to the server.
Use it if you need to add special client options such
as proxy servers, SSL certificates, etc.
o ssl_verify -- True to verify SSL certificates, or False
to skip SSL certificate verification, allowing
connections to servers with self signed certificates.
The default is True.
o handle_sigint -- Set to True to automatically handle
disconnection when the process is interrupted, or to
False to leave interrupt handling to the calling
application. Interrupt handling can only be enabled
when the client instance is created in the main thread.
o websocket_extra_options -- Dictionary containing
additional keyword arguments passed to
aiohttp.ws_connect().
async connect(url, headers=None, transports=None,
engineio_path='engine.io')
Connect to an Engine.IO server.
Parameters
o url -- The URL of the Engine.IO server. It can
include custom query string parameters if
required by the server.
o headers -- A dictionary with custom headers to
send with the connection request.
o transports -- The list of allowed transports.
Valid transports are 'polling' and 'websocket'.
If not given, the polling transport is connected
first, then an upgrade to websocket is
attempted.
o engineio_path -- The endpoint where the
Engine.IO server is installed. The default value
is appropriate for most cases.
Note: this method is a coroutine.
Example usage:
eio = engineio.Client()
await eio.connect('http://localhost:5000')
async wait()
Wait until the connection with the server ends.
Client applications can use this function to block the
main thread during the life of the connection.
Note: this method is a coroutine.
async send(data)
Send a message to the server.
Parameters
data -- The data to send to the server. Data can
be of type str, bytes, list or dict. If a list or
dict, the data will be serialized as JSON.
Note: this method is a coroutine.
async disconnect(abort=False)
Disconnect from the server.
Parameters
abort -- If set to True, do not wait for
background tasks associated with the connection to
end.
Note: this method is a coroutine.
start_background_task(target, *args, **kwargs)
Start a background task.
This is a utility function that applications can use to
start a background task.
Parameters
o target -- the target function to execute.
o args -- arguments to pass to the function.
o kwargs -- keyword arguments to pass to the
function.
The return value is a asyncio.Task object.
async sleep(seconds=0)
Sleep for the requested amount of time.
Note: this method is a coroutine.
create_queue()
Create a queue object.
create_event()
Create an event object.
on(event, handler=None)
Register an event handler.
Parameters
o event -- The event name. Can be 'connect',
'message' or 'disconnect'.
o handler -- The function that should be invoked
to handle the event. When this parameter is not
given, the method acts as a decorator for the
handler function.
Example usage:
# as a decorator:
@eio.on('connect')
def connect_handler():
print('Connection request')
# as a method:
def message_handler(msg):
print('Received message: ', msg)
eio.send('response')
eio.on('message', message_handler)
transport()
Return the name of the transport currently in use.
The possible values returned by this function are
'polling' and 'websocket'.
class engineio.Server(async_mode=None, ping_interval=25,
ping_timeout=20, max_http_buffer_size=1000000, allow_upgrades=True,
http_compression=True, compression_threshold=1024, cookie=None,
cors_allowed_origins=None, cors_credentials=True, logger=False,
json=None, async_handlers=True, monitor_clients=None, transports=None,
**kwargs)
An Engine.IO server.
This class implements a fully compliant Engine.IO web server
with support for websocket and long-polling transports.
Parameters
o async_mode -- The asynchronous model to use. See the
Deployment section in the documentation for a
description of the available options. Valid async modes
are "threading", "eventlet", "gevent" and
"gevent_uwsgi". If this argument is not given,
"eventlet" is tried first, then "gevent_uwsgi", then
"gevent", and finally "threading". The first async
mode that has all its dependencies installed is the one
that is chosen.
o ping_interval -- The interval in seconds at which the
server pings the client. The default is 25 seconds. For
advanced control, a two element tuple can be given,
where the first number is the ping interval and the
second is a grace period added by the server.
o ping_timeout -- The time in seconds that the client
waits for the server to respond before disconnecting.
The default is 20 seconds.
o max_http_buffer_size -- The maximum size that is
accepted for incoming messages. The default is
1,000,000 bytes. In spite of its name, the value set in
this argument is enforced for HTTP long-polling and
WebSocket connections.
o allow_upgrades -- Whether to allow transport upgrades
or not. The default is True.
o http_compression -- Whether to compress packages when
using the polling transport. The default is True.
o compression_threshold -- Only compress messages when
their byte size is greater than this value. The default
is 1024 bytes.
o cookie -- If set to a string, it is the name of the
HTTP cookie the server sends back tot he client
containing the client session id. If set to a
dictionary, the 'name' key contains the cookie name and
other keys define cookie attributes, where the value of
each attribute can be a string, a callable with no
arguments, or a boolean. If set to None (the default),
a cookie is not sent to the client.
o cors_allowed_origins -- Origin or list of origins that
are allowed to connect to this server. Only the same
origin is allowed by default. Set this argument to '*'
to allow all origins, or to [] to disable CORS
handling.
o cors_credentials -- Whether credentials (cookies,
authentication) are allowed in requests to this server.
The default is True.
o logger -- To enable logging set to True or pass a
logger object to use. To disable logging set to False.
The default is False. Note that fatal errors are logged
even when logger is False.
o json -- An alternative json module to use for encoding
and decoding packets. Custom json modules must have
dumps and loads functions that are compatible with the
standard library versions.
o async_handlers -- If set to True, run message event
handlers in non-blocking threads. To run handlers
synchronously, set to False. The default is True.
o monitor_clients -- If set to True, a background task
will ensure inactive clients are closed. Set to False
to disable the monitoring task (not recommended). The
default is True.
o transports -- The list of allowed transports. Valid
transports are 'polling' and 'websocket'. Defaults to
['polling', 'websocket'].
o kwargs -- Reserved for future extensions, any
additional parameters given as keyword arguments will
be silently ignored.
send(sid, data)
Send a message to a client.
Parameters
o sid -- The session id of the recipient client.
o data -- The data to send to the client. Data can
be of type str, bytes, list or dict. If a list
or dict, the data will be serialized as JSON.
send_packet(sid, pkt)
Send a raw packet to a client.
Parameters
o sid -- The session id of the recipient client.
o pkt -- The packet to send to the client.
get_session(sid)
Return the user session for a client.
Parameters
sid -- The session id of the client.
The return value is a dictionary. Modifications made to
this dictionary are not guaranteed to be preserved unless
save_session() is called, or when the session context
manager is used.
save_session(sid, session)
Store the user session for a client.
Parameters
o sid -- The session id of the client.
o session -- The session dictionary.
session(sid)
Return the user session for a client with context manager
syntax.
Parameters
sid -- The session id of the client.
This is a context manager that returns the user session
dictionary for the client. Any changes that are made to
this dictionary inside the context manager block are
saved back to the session. Example usage:
@eio.on('connect')
def on_connect(sid, environ):
username = authenticate_user(environ)
if not username:
return False
with eio.session(sid) as session:
session['username'] = username
@eio.on('message')
def on_message(sid, msg):
with eio.session(sid) as session:
print('received message from ', session['username'])
disconnect(sid=None)
Disconnect a client.
Parameters
sid -- The session id of the client to close. If
this parameter is not given, then all clients are
closed.
handle_request(environ, start_response)
Handle an HTTP request from the client.
This is the entry point of the Engine.IO application,
using the same interface as a WSGI application. For the
typical usage, this function is invoked by the Middleware
instance, but it can be invoked directly when the
middleware is not used.
Parameters
o environ -- The WSGI environment.
o start_response -- The WSGI start_response
function.
This function returns the HTTP response body to deliver
to the client as a byte sequence.
shutdown()
Stop Socket.IO background tasks.
This method stops background activity initiated by the
Socket.IO server. It must be called before shutting down
the web server.
start_background_task(target, *args, **kwargs)
Start a background task using the appropriate async
model.
This is a utility function that applications can use to
start a background task using the method that is
compatible with the selected async mode.
Parameters
o target -- the target function to execute.
o args -- arguments to pass to the function.
o kwargs -- keyword arguments to pass to the
function.
This function returns an object that represents the
background task, on which the join() methond can be
invoked to wait for the task to complete.
sleep(seconds=0)
Sleep for the requested amount of time using the
appropriate async model.
This is a utility function that applications can use to
put a task to sleep without having to worry about using
the correct call for the selected async mode.
create_event(*args, **kwargs)
Create an event object using the appropriate async model.
This is a utility function that applications can use to
create an event without having to worry about using the
correct call for the selected async mode.
create_queue(*args, **kwargs)
Create a queue object using the appropriate async model.
This is a utility function that applications can use to
create a queue without having to worry about using the
correct call for the selected async mode.
generate_id()
Generate a unique session id.
get_queue_empty_exception()
Return the queue empty exception for the appropriate
async model.
This is a utility function that applications can use to
work with a queue without having to worry about using the
correct call for the selected async mode.
on(event, handler=None)
Register an event handler.
Parameters
o event -- The event name. Can be 'connect',
'message' or 'disconnect'.
o handler -- The function that should be invoked
to handle the event. When this parameter is not
given, the method acts as a decorator for the
handler function.
Example usage:
# as a decorator:
@eio.on('connect')
def connect_handler(sid, environ):
print('Connection request')
if environ['REMOTE_ADDR'] in blacklisted:
return False # reject
# as a method:
def message_handler(sid, msg):
print('Received message: ', msg)
eio.send(sid, 'response')
eio.on('message', message_handler)
The handler function receives the sid (session ID) for
the client as first argument. The 'connect' event handler
receives the WSGI environment as a second argument, and
can return False to reject the connection. The 'message'
handler receives the message payload as a second
argument. The 'disconnect' handler does not take a second
argument.
transport(sid)
Return the name of the transport used by the client.
The two possible values returned by this function are
'polling' and 'websocket'.
Parameters
sid -- The session of the client.
class engineio.AsyncServer(async_mode=None, ping_interval=25,
ping_timeout=20, max_http_buffer_size=1000000, allow_upgrades=True,
http_compression=True, compression_threshold=1024, cookie=None,
cors_allowed_origins=None, cors_credentials=True, logger=False,
json=None, async_handlers=True, monitor_clients=None, transports=None,
**kwargs)
An Engine.IO server for asyncio.
This class implements a fully compliant Engine.IO web server
with support for websocket and long-polling transports,
compatible with the asyncio framework on Python 3.5 or newer.
Parameters
o async_mode -- The asynchronous model to use. See the
Deployment section in the documentation for a
description of the available options. Valid async modes
are "aiohttp", "sanic", "tornado" and "asgi". If this
argument is not given, "aiohttp" is tried first,
followed by "sanic", "tornado", and finally "asgi". The
first async mode that has all its dependencies
installed is the one that is chosen.
o ping_interval -- The interval in seconds at which the
server pings the client. The default is 25 seconds. For
advanced control, a two element tuple can be given,
where the first number is the ping interval and the
second is a grace period added by the server.
o ping_timeout -- The time in seconds that the client
waits for the server to respond before disconnecting.
The default is 20 seconds.
o max_http_buffer_size -- The maximum size that is
accepted for incoming messages. The default is
1,000,000 bytes. In spite of its name, the value set in
this argument is enforced for HTTP long-polling and
WebSocket connections.
o allow_upgrades -- Whether to allow transport upgrades
or not.
o http_compression -- Whether to compress packages when
using the polling transport.
o compression_threshold -- Only compress messages when
their byte size is greater than this value.
o cookie -- If set to a string, it is the name of the
HTTP cookie the server sends back tot he client
containing the client session id. If set to a
dictionary, the 'name' key contains the cookie name and
other keys define cookie attributes, where the value of
each attribute can be a string, a callable with no
arguments, or a boolean. If set to None (the default),
a cookie is not sent to the client.
o cors_allowed_origins -- Origin or list of origins that
are allowed to connect to this server. Only the same
origin is allowed by default. Set this argument to '*'
to allow all origins, or to [] to disable CORS
handling.
o cors_credentials -- Whether credentials (cookies,
authentication) are allowed in requests to this server.
o logger -- To enable logging set to True or pass a
logger object to use. To disable logging set to False.
Note that fatal errors are logged even when logger is
False.
o json -- An alternative json module to use for encoding
and decoding packets. Custom json modules must have
dumps and loads functions that are compatible with the
standard library versions.
o async_handlers -- If set to True, run message event
handlers in non-blocking threads. To run handlers
synchronously, set to False. The default is True.
o transports -- The list of allowed transports. Valid
transports are 'polling' and 'websocket'. Defaults to
['polling', 'websocket'].
o kwargs -- Reserved for future extensions, any
additional parameters given as keyword arguments will
be silently ignored.
attach(app, engineio_path='engine.io')
Attach the Engine.IO server to an application.
async send(sid, data)
Send a message to a client.
Parameters
o sid -- The session id of the recipient client.
o data -- The data to send to the client. Data can
be of type str, bytes, list or dict. If a list
or dict, the data will be serialized as JSON.
Note: this method is a coroutine.
async send_packet(sid, pkt)
Send a raw packet to a client.
Parameters
o sid -- The session id of the recipient client.
o pkt -- The packet to send to the client.
Note: this method is a coroutine.
async get_session(sid)
Return the user session for a client.
Parameters
sid -- The session id of the client.
The return value is a dictionary. Modifications made to
this dictionary are not guaranteed to be preserved. If
you want to modify the user session, use the session
context manager instead.
async save_session(sid, session)
Store the user session for a client.
Parameters
o sid -- The session id of the client.
o session -- The session dictionary.
session(sid)
Return the user session for a client with context manager
syntax.
Parameters
sid -- The session id of the client.
This is a context manager that returns the user session
dictionary for the client. Any changes that are made to
this dictionary inside the context manager block are
saved back to the session. Example usage:
@eio.on('connect')
def on_connect(sid, environ):
username = authenticate_user(environ)
if not username:
return False
with eio.session(sid) as session:
session['username'] = username
@eio.on('message')
def on_message(sid, msg):
async with eio.session(sid) as session:
print('received message from ', session['username'])
async disconnect(sid=None)
Disconnect a client.
Parameters
sid -- The session id of the client to close. If
this parameter is not given, then all clients are
closed.
Note: this method is a coroutine.
async handle_request(*args, **kwargs)
Handle an HTTP request from the client.
This is the entry point of the Engine.IO application.
This function returns the HTTP response to deliver to the
client.
Note: this method is a coroutine.
async shutdown()
Stop Socket.IO background tasks.
This method stops background activity initiated by the
Socket.IO server. It must be called before shutting down
the web server.
start_background_task(target, *args, **kwargs)
Start a background task using the appropriate async
model.
This is a utility function that applications can use to
start a background task using the method that is
compatible with the selected async mode.
Parameters
o target -- the target function to execute.
o args -- arguments to pass to the function.
o kwargs -- keyword arguments to pass to the
function.
The return value is a asyncio.Task object.
async sleep(seconds=0)
Sleep for the requested amount of time using the
appropriate async model.
This is a utility function that applications can use to
put a task to sleep without having to worry about using
the correct call for the selected async mode.
Note: this method is a coroutine.
create_queue(*args, **kwargs)
Create a queue object using the appropriate async model.
This is a utility function that applications can use to
create a queue without having to worry about using the
correct call for the selected async mode. For asyncio
based async modes, this returns an instance of
asyncio.Queue.
get_queue_empty_exception()
Return the queue empty exception for the appropriate
async model.
This is a utility function that applications can use to
work with a queue without having to worry about using the
correct call for the selected async mode. For asyncio
based async modes, this returns an instance of
asyncio.QueueEmpty.
create_event(*args, **kwargs)
Create an event object using the appropriate async model.
This is a utility function that applications can use to
create an event without having to worry about using the
correct call for the selected async mode. For asyncio
based async modes, this returns an instance of
asyncio.Event.
generate_id()
Generate a unique session id.
on(event, handler=None)
Register an event handler.
Parameters
o event -- The event name. Can be 'connect',
'message' or 'disconnect'.
o handler -- The function that should be invoked
to handle the event. When this parameter is not
given, the method acts as a decorator for the
handler function.
Example usage:
# as a decorator:
@eio.on('connect')
def connect_handler(sid, environ):
print('Connection request')
if environ['REMOTE_ADDR'] in blacklisted:
return False # reject
# as a method:
def message_handler(sid, msg):
print('Received message: ', msg)
eio.send(sid, 'response')
eio.on('message', message_handler)
The handler function receives the sid (session ID) for
the client as first argument. The 'connect' event handler
receives the WSGI environment as a second argument, and
can return False to reject the connection. The 'message'
handler receives the message payload as a second
argument. The 'disconnect' handler does not take a second
argument.
transport(sid)
Return the name of the transport used by the client.
The two possible values returned by this function are
'polling' and 'websocket'.
Parameters
sid -- The session of the client.
class engineio.WSGIApp(engineio_app, wsgi_app=None, static_files=None,
engineio_path='engine.io')
WSGI application middleware for Engine.IO.
This middleware dispatches traffic to an Engine.IO application.
It can also serve a list of static files to the client, or
forward unrelated HTTP traffic to another WSGI application.
Parameters
o engineio_app -- The Engine.IO server. Must be an
instance of the engineio.Server class.
o wsgi_app -- The WSGI app that receives all other
traffic.
o static_files -- A dictionary with static file mapping
rules. See the documentation for details on this
argument.
o engineio_path -- The endpoint where the Engine.IO
application should be installed. The default value is
appropriate for most cases.
Example usage:
import engineio
import eventlet
eio = engineio.Server()
app = engineio.WSGIApp(eio, static_files={
'/': {'content_type': 'text/html', 'filename': 'index.html'},
'/index.html': {'content_type': 'text/html',
'filename': 'index.html'},
})
eventlet.wsgi.server(eventlet.listen(('', 8000)), app)
class engineio.ASGIApp(engineio_server, other_asgi_app=None,
static_files=None, engineio_path='engine.io', on_startup=None,
on_shutdown=None)
ASGI application middleware for Engine.IO.
This middleware dispatches traffic to an Engine.IO application.
It can also serve a list of static files to the client, or
forward unrelated HTTP traffic to another ASGI application.
Parameters
o engineio_server -- The Engine.IO server. Must be an
instance of the engineio.AsyncServer class.
o static_files -- A dictionary with static file mapping
rules. See the documentation for details on this
argument.
o other_asgi_app -- A separate ASGI app that receives all
other traffic.
o engineio_path -- The endpoint where the Engine.IO
application should be installed. The default value is
appropriate for most cases.
o on_startup -- function to be called on application
startup; can be coroutine
o on_shutdown -- function to be called on application
shutdown; can be coroutine
Example usage:
import engineio
import uvicorn
eio = engineio.AsyncServer()
app = engineio.ASGIApp(eio, static_files={
'/': {'content_type': 'text/html', 'filename': 'index.html'},
'/index.html': {'content_type': 'text/html',
'filename': 'index.html'},
})
uvicorn.run(app, '127.0.0.1', 5000)
async not_found(receive, send)
Return a 404 Not Found error to the client.
class engineio.Middleware(engineio_app, wsgi_app=None,
engineio_path='engine.io')
This class has been renamed to WSGIApp and is now deprecated.
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AUTHOR
Miguel Grinberg
COPYRIGHT
2024, Miguel Grinberg
May 4, 2024 PYTHON-ENGINEIO(1)