Fusee DocsRust quickstart
Ten minutes. You will start a workflow, kill the process in the middle of it, and watch it carry on from where it was.
Before you begin, follow the Rust installation instructions. If you already started the sample there, continue at Run it.
1. A project
mkdir hello && cd hello
fusee init --lang rustfusee init writes Cargo.toml and src/main.rs, and AGENTS.md (which a
CLAUDE.md imports) with the rules a coding assistant needs. The workflow is a
reference (WorkflowRef) and a function:
pub const GREET: WorkflowRef<String, String> = WorkflowRef::new("greet");
pub const APPROVE: Signal<bool> = Signal::new("approve");
engine.register(GREET, |ctx: Ctx, name: String| async move {
let greeting: String = ctx
.step("compose", || async { Ok::<_, Error>(format!("hello {name}")) })
.await?;
ctx.sleep("pause", Duration::from_secs(5)).await?;
let ok = ctx.wait_for(APPROVE).timeout(Duration::from_secs(3600)).await?;
Ok(if ok == Some(true) { greeting } else { format!("{greeting} (not approved)") })
});A step's result is recorded once it runs. When the code runs again after a
crash, compose returns its recorded result instead of running again; the
sleep and the wait pick up where they were.
2. Run it
fusee dev -- cargo runUnder fusee dev the engine runs with the dev profile (FUSEE_PROFILE=dev):
it keeps every run's history, replays each run against the code when it
waits or ends, and serves the UI:
fusee: dev profile (/path/to/hello/.fusee/dev): every run's history is kept, each run is replayed against the code when it waits or ends. Not for production.
fusee: UI and HTTP API at http://127.0.0.1:7601
started greet-1; approve it: fusee runs signal greet-1 approve trueOpen http://127.0.0.1:7601 to see the run.
3. Kill it
Within the five seconds of the pause, in another terminal:
pkill -9 fusee-appfusee dev starts the app again; the run continues from its journal, and
compose does not run twice.
4. Approve it
fusee runs signal greet-1 approve trueThe app prints hello world.
5. Test it
Move the workflow's closure into a function,
async fn greet(ctx: Ctx, name: String) -> fusee::Result<String>, so a test
can register it too, and add the test kit to Cargo.toml:
[dev-dependencies]
fusee = { path = "../fusee/crates/fusee", features = ["testing"] }#[tokio::test]
async fn greets_after_approval() -> fusee::Result<()> {
let t = fusee::testing::TestEngine::open().await?;
t.register(GREET, greet);
let run = t.engine().start(GREET, "g-1", &"test".to_string()).await?;
run.signal(APPROVE, &true).await?;
// The five-second pause is skipped: virtual time.
assert_eq!(t.result::<String>("g-1").await?, "hello test");
t.check().await // strict replay
}