ASGI (Asynchronous Server Gateway Interface)¶
This chapter contains information about using ASGI with Pyramid. Read about the ASGI specification.
The example app below uses the WSGI to ASGI wrapper from the asgiref library to transform normal WSGI requests into ASGI responses. This allows the application to be run with an ASGI server, such as uvicorn or daphne.
WSGI -> ASGI application¶
This example uses the wrapper provided by asgiref to convert a WSGI application to ASGI, allowing it to be run by an ASGI server.
Please note that not all extended features of WSGI may be supported, such as file handles for incoming POST bodies.
# app.py
from asgiref.wsgi import WsgiToAsgi
from pyramid.config import Configurator
from pyramid.response import Response
def hello_world(request):
return Response("Hello")
# Configure a normal WSGI app then wrap it with WSGI -> ASGI class
with Configurator() as config:
config.add_route("hello", "/")
config.add_view(hello_world, route_name="hello")
wsgi_app = config.make_wsgi_app()
app = WsgiToAsgi(wsgi_app)
Extended WSGI -> ASGI WebSocket application¶
This example extends the asgiref wrapper to enable routing ASGI consumers alongside the converted WSGI application.
This is just one potential solution for routing ASGI consumers.
# app.py
from asgiref.wsgi import WsgiToAsgi
from pyramid.config import Configurator
from pyramid.response import Response
class ExtendedWsgiToAsgi(WsgiToAsgi):
"""Extends the WsgiToAsgi wrapper to include an ASGI consumer protocol router"""
def __init__(self, *args, **kwargs):
super().__init__(*args, **kwargs)
self.protocol_router = {"http": {}, "websocket": {}}
async def __call__(self, scope, *args, **kwargs):
protocol = scope["type"]
path = scope["path"]
try:
consumer = self.protocol_router[protocol][path]
except KeyError:
consumer = None
if consumer is not None:
await consumer(scope, *args, **kwargs)
await super().__call__(scope, *args, **kwargs)
if consumer is not None:
await consumer(scope, *args, **kwargs)
try:
await super().__call__(scope, *args, **kwargs)
except ValueError as e:
# The developer may wish to improve handling of this exception.
# See https://github.com/Pylons/pyramid_cookbook/issues/225 and
# https://asgi.readthedocs.io/en/latest/specs/www.html#websocket
pass
except Exception as e:
raise e
def route(self, rule, *args, **kwargs):
try:
protocol = kwargs["protocol"]
except KeyError:
raise Exception("You must define a protocol type for an ASGI handler")
def _route(func):
self.protocol_router[protocol][rule] = func
return _route
HTML_BODY = """<!DOCTYPE html>
<html>
<head>
<title>ASGI WebSocket</title>
</head>
<body>
<h1>ASGI WebSocket Demo</h1>
<form action="" onsubmit="sendMessage(event)">
<input type="text" id="messageText" autocomplete="off"/>
<button>Send</button>
</form>
<ul id='messages'>
</ul>
<script>
var ws = new WebSocket("ws://127.0.0.1:8000/ws");
ws.onmessage = function(event) {
var messages = document.getElementById('messages')
var message = document.createElement('li')
var content = document.createTextNode(event.data)
message.appendChild(content)
messages.appendChild(message)
};
function sendMessage(event) {
var input = document.getElementById("messageText")
ws.send(input.value)
input.value = ''
event.preventDefault()
}
</script>
</body>
</html>
"""
# Define normal WSGI views
def hello_world(request):
return Response(HTML_BODY)
# Configure a normal WSGI app then wrap it with WSGI -> ASGI class
with Configurator() as config:
config.add_route("hello", "/")
config.add_view(hello_world, route_name="hello")
wsgi_app = config.make_wsgi_app()
app = ExtendedWsgiToAsgi(wsgi_app)
# Define ASGI consumers
@app.route("/ws", protocol="websocket")
async def hello_websocket(scope, receive, send):
while True:
message = await receive()
if message["type"] == "websocket.connect":
await send({"type": "websocket.accept"})
elif message["type"] == "websocket.receive":
text = message.get("text")
if text:
await send({"type": "websocket.send", "text": text})
else:
await send({"type": "websocket.send", "bytes": message.get("bytes")})
elif message["type"] == "websocket.disconnect":
break
Running & Deploying¶
The application can be run using an ASGI server:
$ uvicorn app:app
or
$ daphne app:app
There are several potential deployment options, one example would be to use nginx and supervisor.
Below are example configuration files that run the application using uvicorn, however daphne may be used as well.
Example nginx configuration¶
upstream app {
server unix:/tmp/uvicorn.sock;
}
server {
listen 80;
server_name <server-name>;
location / {
proxy_pass http://app;
proxy_set_header Host $host;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header X-Forwarded-Proto $scheme;
proxy_buffering off;
proxy_http_version 1.1;
proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection "Upgrade";
proxy_redirect off;
}
location /static {
root </path-to-static>;
}
}
Example Supervisor configuration¶
[program:asgiapp]
directory=/path/to/app/
command=</path-to-virtualenv>/bin/uvicorn app:app --uds /tmp/uvicorn.sock --workers 2 --access-log --log-level error
user=<app-user>
autostart=true
autorestart=true
redirect_stderr=True
[supervisord]