Demo application for asyncio, for teaching purposes.
The goal is to show how to build a non-trivial application, since a common (and justified) criticism of many asyncio tutorials is that they're too simple to be useful for building real-world applications.
Requires Python >= 3.7
- Open a new terminal, run
$ python srv.py
- Open a new terminal, run
$ python client.py
- Open a second new terminal, run
$ python client.py
There should be two GUI windows open, and if you type a message into the bottom edit box and hit ENTER
, you should see the message appear in the other GUI.
This is a chat client/server application, perhaps like IRC or Slack. These are the specific features that are demonstrated in the demo code:
- server application with many concurrent connections
- using
asyncio.start_server()
- using
- separate client application that connects to the server. Multiple client instances can be started.
- using
asyncio.open_connection()
- handle server outage with a reconnection loop
- using
- new asyncio APIs like
asyncio.run()
andasyncio.create_task
- Using the asyncio Streams API
- decoupling tasks for sending and receiving
- SSL connections
- client application has a Tkinter GUI.
- show how to run the asyncio loop in a separate thread
- Tkinter UI loop runs in the main thread
- This is a similar problem you will encounter with many game frameworks
- Signal handling to control shutdown
- Linux:
SIGINT
andSIGTERM
- Windows:
SIGINT
(actuallyCTRL-C
) andSIGBREAK
- Linux:
- Keeping track of current connections/clients, using
weakref
containers to make it easier to stay up-to-date. - Using queues in the client UI application to pass data between the main thread (UI) and the asyncio thread (IO)
- Creating a message protocol, by using a size prefix, and converting from the stream bytes to an integer using
int.frombytes()
- Passing JSON between client and server
- A Tkinter GUI app that can be sized and maximised
See Doug Hellman's block for how to set up the SSL connection. In particular, for generating the cert and key:
$ openssl req -newkey rsa:2048 -nodes -keyout chat.key \
-x509 -days 365 -out chat.crt
This creates chat.key
and chat.crt
in the current dir.