I used SQLite when I wrote the initial code. Install sqlx-cli and follow the docs via this documentation to get started.
My sqlite3 DB resides in the ./data directory, but it can live anywhere, as long as the DATABSE_URL in your .env points to the DB file on your local file system.
Create an .env file in the root directory and copy the contents of .env.example into it, replacing the placeholder values with real ones.
Once you have your sqlite DB set up and your .env file's DATABASE_URL is set correctly, you should be able to run the migrations with
sqlx migrate runcargo updatecargo run
Should be good to go after that.
This app is by no means finished. A half-assed session + cookie layer has been implemented, but still needs proper session expiration checks. There are a couple of TERA templates that render the /chat, /login, and /sign-up pages. Visiting the index page (/) should check your session cookie and redirect you to /login or/chat, depending on its presence/validity. The websocket layer establishes a connection, but actual back n' forth chat functionality is yet to be implemented.