Core concepts: Handlers, Conn, and Adapters

The most important concepts in Trillium are the Handler trait and the Conn type. Every Trillium application — from a one-liner to a full middleware stack — is a Handler that receives a Conn and returns a Conn.

Here's a minimal application:

trillium_smol::run(|conn: trillium::Conn| async move {
    conn.ok("hello from trillium!")
});

In this example:

• trillium_smol::run is the runtime adapter — it listens for TCP connections and drives the async executor.
• The closure is a Handler — it receives each incoming Conn and returns it with a 200 response and a body.

Add this to your Cargo.toml with:

cargo add trillium trillium-smol

Run it with cargo run, then visit http://localhost:8080. You won't see any output in the terminal because Trillium is silent by default — add a logger if you want request output.

The pages that follow go deeper into each of these concepts:

• Handlers — the trait, tuple composition, and built-in implementations
• Conn — request/response data, state, and the conn extension pattern
• Runtime Adapters, TLS, and HTTP/3 — choosing a runtime, configuration, TLS, and QUIC