Live Reload in Development

A Laterite application is a compiled binary, so a source change takes effect once the binary is rebuilt and rerun. A small tool loop makes that automatic and keeps the listening port bound across rebuilds, so the browser reconnects on its own instead of hitting a refused connection.

Two tools cover it:

• systemfd binds the listening socket once and passes it to each new build of your server.
• watchexec reruns the server when a source file changes.

cargo install systemfd
brew install watchexec   # or cargo install watchexec-cli

Reuse a passed socket

For systemfd to hand its socket to your server, the server reuses a socket inherited from the environment when one is present, and binds its configured address otherwise. Add listenfd and take the socket in main:

use listenfd::ListenFd;
use tokio::net::TcpListener;

let listener = match ListenFd::from_env().take_tcp_listener(0)? {
    Some(std_listener) => {
        std_listener.set_nonblocking(true)?;
        TcpListener::from_std(std_listener)?
    }
    None => TcpListener::bind("127.0.0.1:8080").await?,
};
axum::serve(listener, app).await?;

The None arm is the normal path: a plain cargo run, and production, bind the address directly. Only the development loop passes a socket.

Run the loop

Wrap the run command with both tools. systemfd stays as the long-lived parent that owns the socket; watchexec restarts the build under it:

systemfd --no-pid -s http::8080 -- \
    watchexec -r -e rs,html,css,toml -- \
    cargo run -p acme-api

The admin templates are compiled into the binary, so watching .html and .css alongside .rs means an edit to a screen’s markup or the stylesheet triggers a rebuild and shows up on the next reconnect. A justfile recipe keeps the command to hand:

dev:
    systemfd --no-pid -s http::8080 -- \
        watchexec -r -e rs,html,css,toml -- \
        cargo run -p acme-api

See compiler errors as you type

The reload loop shows build output in the server’s terminal. For a dedicated, navigable view of compiler and clippy errors while you edit, run bacon in a second terminal:

cargo install bacon   # or brew install bacon
bacon clippy