ASGI

What is ASGI?

An ASGI server sits at the front of a web application receiving and sending HTTP and WebSocket messages. The client code simply sends and receives dictionaries which describe the HTTP messages.

At it's heart ASGI is a specification. You can find the ASGI specification here.

Why?

Back in the days of Python 2 where there was no async/await functionality, a lot of effort was required to make a responsive web server in python. Essentially it was necessary to have a separate service which would create a new process to service the request.

Out of this emerged the WSGI specification, and Python applications which conformed to the specification could choose from a selection of servers which supported the spec.

The ASGI specification is an asynchronous version of WSGI, which supports the async/await functionlity of Python 3. This allows us to write a responsive web service without the necessity of creating multiple processes, although this may still be desirable for more performance.

Servers

A number of servers have been written that support the specification. I have been using:

• hypercorn
• uvicorn