email_newsletter_api/docs/actix_web.md

Actix-web Notes

• Actix-web runtime model: Spins up a worker process per CPU core. Each worker runs its own copy of of the application provided in the closure that HttpServer takes as an argument. Therefore, everything in the closure (including app_data below) has to implement the Clone trait.

app_data

When we set up our web app, we can attach a resource to the app with app_data. And then our route handlers can access this application data with HttpRequest::app_data(). It is similar to FastAPI's dependency injection.

In our app, we want to inject a db_conn to the route handlers, so that these routes can handle PostgreSQL read/write.

Since the database connection is a TCP connection that is NOT Clone-able. We use Rust's Arc (Atomic Reference Counter) as a wrapper around this connection. Each instance of our web app, instead of getting a raw TCP connection to the PostgreSQL database, will be given the pointer to the memory region of db_conn.