Asynchronous Server Gateway Interface
Calling convention for web servers
The Asynchronous Server Gateway Interface (ASGI) is a calling convention for web servers to forward requests to asynchronous-capable Python frameworks, and applications. It is built as a successor to the Web Server Gateway Interface (WSGI).
Where WSGI provided a standard for synchronous Python applications, ASGI provides one for both asynchronous and synchronous applications, with a WSGI backwards-compatibility implementation and multiple servers and application frameworks.
01Example
An ASGI-compatible "Hello, World!" application written in Python:
async def application(scope, receive, send): event = await receive() ... await send({"type": "websocket.send", ...})Where:
- Line 1 defines an asynchronous function named application, which takes three parameters (unlike in WSGI which takes only two), scope, receive and send.
- scope is a dict containing details about current connection, like the protocol, headers, etc.
- receive and send are asynchronous callables which let the application receive and send messages from/to the client.
- Line 2 receives an incoming event, for example, HTTP request or WebSocket message. The await keyword is used because the operation is asynchronous.
- Line 4 asynchronously sends a response back to the client. In this case, it is a WebSocket communication.
02Web Server Gateway Interface (WSGI) compatibility
ASGI is also designed to be a superset of WSGI, and there's a defined way of translating between the two, allowing WSGI applications to be run inside ASGI servers through a translation wrapper (provided in the asgiref library). A threadpool can be used to run the synchronous WSGI applications away from the async event loop.
Sources and credits
This article is adapted from the Wikipedia article “Asynchronous Server Gateway Interface”, written by its contributors and licensed under CC BY-SA 4.0. Fathomly has changed the layout, removed citation markers, navigation and maintenance notices, and adjusted punctuation. This adapted version is shared under the same license. For references, see the original article.
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