Asynchronous Server Gateway Interface
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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).
| Version | 3.0 |
|---|---|
| Developer | ASGI Team |
| Release date | 2019-03-04[1] |
| Website | asgi |
| License | public domain[2] |
| Status | Draft |
Where WSGI provided a standard for synchronous Python application, ASGI provides one for both asynchronous and synchronous applications, with a WSGI backwards-compatibility implementation and multiple servers and application frameworks.
Example
An ASGI-compatible "Hello, World!" application written in Python:<syntaxhighlight lang="python3" line="1"> async def application(scope, receive, send):
event = await receive()
...
await send({"type": "websocket.send", ...})
</syntaxhighlight>Where:
- Line 1 defines an asynchronous function named <syntaxhighlight lang="Python" inline="1">application</syntaxhighlight>, which takes three parameters (unlike in WSGI which takes only two), <syntaxhighlight lang="Python" inline="1">scope</syntaxhighlight>, <syntaxhighlight lang="Python" inline="1">receive</syntaxhighlight> and <syntaxhighlight lang="Python" inline="1">send</syntaxhighlight>.
- <syntaxhighlight lang="Python" inline="1">scope</syntaxhighlight> is a <syntaxhighlight lang="Python" inline="1">dict</syntaxhighlight> containing details about current connection, like the protocol, headers, etc.
- <syntaxhighlight lang="Python" inline="1">receive</syntaxhighlight> and <syntaxhighlight lang="Python" inline="1">send</syntaxhighlight> 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 <syntaxhighlight lang="Python" inline="1">await</syntaxhighlight> 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.
Web 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.
See also
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References
- ^ "Version History".
- ^ "Copyright". GitHub. Retrieved 2022-09-14.