Resonate Basic Ephemeral World Usage — Rust

v0.1.0 caveat. The Resonate Rust SDK is in active development. It is NOT yet published on crates.io; install as a git dependency. APIs may change between releases. Treat every code example as a moving target until the SDK reaches 1.0.

Overview

The ephemeral world is anywhere your Rust program starts: main(), an Axum or Actix handler, a CLI entry point, a background service. You use the Resonate client to register durable functions and invoke them top-level. Once an invocation starts, it crosses into the durable world and Resonate guarantees its completion — retries on failure, resumes after crashes, continues across process restarts.

This skill covers the Client API surface. The Durable World (Context APIs inside #[resonate::function]) lives in resonate-basic-durable-world-usage-rust.

Install

The Rust SDK is a git dependency (v0.1.0; not on crates.io yet):

[dependencies]
resonate = { git = "https://github.com/resonatehq/resonate-sdk-rs", branch = "master" }
tokio = { version = "1", features = ["full"] }
serde = { version = "1", features = ["derive"] }

Most programs also want serde_json for the json!(...) macro used in the promises API.

use resonate::prelude::*;

Initialize

Local mode (zero-dependency; in-memory promise store):

use resonate::prelude::*;

let resonate = Resonate::local();

Remote mode (connects to a Resonate server):

use resonate::prelude::*;

let resonate = Resonate::new(ResonateConfig {
    url: Some("http://localhost:8001".into()),
    ..Default::default()
});

With explicit worker group + auth token:

let resonate = Resonate::new(ResonateConfig {
    url: Some("https://resonate.example.com".into()),
    group: Some("workers".into()),
    token: std::env::var("RESONATE_TOKEN").ok(),
    ..Default::default()
});

The SDK reads environment variables when config fields are not set:

• RESONATE_URL — full base URL
• RESONATE_HOST + RESONATE_PORT — alternate construction
• RESONATE_TOKEN — JWT for authenticated servers
• RESONATE_SCHEME — http by default
• RESONATE_PREFIX — prepended to all promise + task IDs for multi-tenant namespacing

Define a durable function

The #[resonate::function] attribute macro transforms an async function into a durable function. The SDK infers the function kind from the first parameter:

All durable functions MUST return resonate::error::Result<T> (aliased to Result<T> when you use resonate::prelude::*):

use resonate::prelude::*;

#[resonate::function]
async fn process_order(ctx: &Context, order_id: String) -> Result<String> {
    let order = ctx.run(load_order, order_id.clone()).await?;
    Ok(format!("processed {}", order))
}

#[resonate::function]
async fn load_order(order_id: String) -> Result<String> {
    // pure leaf — no context, no Info
    Ok(format!("order-{}", order_id))
}

Override the registered name for RPC cross-process identification:

#[resonate::function(name = "order-processor")]
async fn process_order(ctx: &Context, order_id: String) -> Result<String> {
    // ...
}

Share resources via dependencies

Dependencies (DB pools, HTTP clients, config) are attached to the Resonate instance at construction time with the .with_dependency<T>(value) builder. The SDK uses Rust's type system (not a string key) — you retrieve a dependency by its type inside a durable function via ctx.get_dependency::<T>().

use std::sync::Arc;
use sqlx::PgPool;

struct AppConfig {
    api_key: String,
}

#[tokio::main]
async fn main() -> Result<()> {
    let pool = PgPool::connect(&std::env::var("DATABASE_URL")?).await?;
    let config = AppConfig { api_key: std::env::var("API_KEY")? };

    let resonate = Resonate::new(ResonateConfig::default())
        .with_dependency(pool)
        .with_dependency(config);

    resonate.register(charge_card).unwrap();
    // ...
}

#[resonate::function]
async fn charge_card(ctx: &Context, order_id: String) -> Result<()> {
    let pool = ctx.get_dependency::<PgPool>();       // Arc<PgPool>
    let config = ctx.get_dependency::<AppConfig>();  // Arc<AppConfig>
    // use pool + config in a leaf (see resonate-basic-durable-world-usage-rust)
    Ok(())
}

Type-dispatched DI means you can only have one dependency per type per Resonate instance; for multiple values of the same logical type, wrap them in distinct newtypes (struct PrimaryDb(PgPool) vs struct AnalyticsDb(PgPool)).

Note: with_dependency is a pub fn on Resonate in the v0.1.0 SDK source (resonate-sdk-rs:resonate/src/resonate.rs:271) but not mentioned in docs/develop/rust.mdx as of April 2026. Use with the understanding that docs lag source here.

Register

Registration exposes a function to the Resonate system. Use .unwrap() or handle the Result (registration fails if the name is duplicated):

let resonate = Resonate::local();
resonate.register(process_order).unwrap();
resonate.register(load_order).unwrap();

One .register call per function per process. Register everything your process should handle before invoking anything.

Invoke a durable function

Same process, synchronous (awaits result)

let result: String = resonate
    .run("invocation-id", process_order, "order-123".into())
    .await?;

The builder accepts options before .await:

use std::time::Duration;

let result: String = resonate
    .run("order:123", process_order, "order-123".into())
    .timeout(Duration::from_secs(60))
    .version(2)
    .tags([("tenant".to_string(), "acme".to_string())].into())
    .await?;

resonate.run is the synchronous ephemeral-world entry. For async lifecycles where you want a handle, use .get(id) later.

Remote process, synchronous

let result: String = resonate
    .rpc("invocation-id", "process_order", "order-123".into())
    .target("poll://any@workers")
    .await?;

The target option routes to a worker group; the called function must be registered in a process that polls that target.

Scheduled (cron) invocation

The Rust SDK has first-class cron scheduling:

let schedule = resonate
    .schedule("daily-reconciliation", "0 2 * * *", "reconcile", "2026-04-16".into())
    .await?;

// ...later, to delete:
schedule.delete().await?;

(Python SDK does not expose a top-level .schedule(...) at v0.6.7; Rust does at v0.1.0. Cross-SDK parity is not yet achieved — see Related notes below.)

Subscribe to an existing invocation

let mut handle = resonate.get::<String>("invocation-id").await?;
let result = handle.result().await?;

The type parameter on .get::<T> deserializes the result; you need to know or agree on T with the invocation site.

External promises

External promises let code outside the durable function resolve or reject it — the primitive for human-in-the-loop workflows and webhook-driven resumption:

use serde_json::json;

// create a promise with a timeout (ms since Unix epoch), initial param, and tags
let timeout_at_ms: i64 = (std::time::SystemTime::now()
    .duration_since(std::time::UNIX_EPOCH)?
    .as_millis() as i64) + 30 * 60 * 1000; // 30 minutes from now

resonate.promises.create("approval:order-123", timeout_at_ms, json!({}), json!({})).await?;

// elsewhere (webhook, CLI, UI):
resonate.promises.resolve("approval:order-123", json!({"approved": true})).await?;

// or reject:
resonate.promises.reject("approval:order-123", json!({"reason": "over-budget"})).await?;

// or cancel (settles as rejected_canceled):
resonate.promises.cancel("approval:order-123", json!(null)).await?;

// query state:
let promise = resonate.promises.get("approval:order-123").await?;

The data arguments are serde_json::Value; use the json! macro for ergonomic literals.

Graceful shutdown

resonate.stop().await?;

Stops background tasks (heartbeat, subscription loops). Good citizen for long-running daemons or CLI tools.

Complete example: a worker binary

use resonate::prelude::*;
use tokio::signal;

#[tokio::main]
async fn main() -> Result<()> {
    let resonate = Resonate::new(ResonateConfig {
        url: std::env::var("RESONATE_URL").ok(),
        group: Some("order-workers".into()),
        ..Default::default()
    });

    resonate.register(process_order).unwrap();
    resonate.register(load_order).unwrap();

    // wait for Ctrl+C; the SDK polls in the background
    signal::ctrl_c().await?;

    resonate.stop().await?;
    Ok(())
}

#[resonate::function]
async fn process_order(ctx: &Context, order_id: String) -> Result<String> {
    let order = ctx.run(load_order, order_id).await?;
    Ok(order)
}

#[resonate::function]
async fn load_order(order_id: String) -> Result<String> {
    Ok(format!("order-{}", order_id))
}

Distinct Rust idioms

• `Result<T>` everywhere — both Client API methods and durable functions return Result. Use ? for concise propagation.
• `ResonateConfig { ... , ..Default::default() }` — Rust's struct-update syntax; always include ..Default::default() when partially constructing.
• `Some(...)` / `.ok()` / `std::env::var(...).ok()` for optional config — the SDK accepts Option<String> throughout.
• `tokio::main` — durable functions are async; your main must be async. #[tokio::main] sets up the runtime.
• `serde_json::json!` macro for promise data — explicit serialization; matches Rust's strong-typing discipline.
• `Duration::from_secs(N)` / `from_millis(N)` for timeouts — not raw numbers. Use std::time::Duration.
• Turbofish syntax on `.rpc::<T>(...)` and `.get::<T>(...)` — Rust's type inference needs help when the result type isn't constrained by the call site.

Rust SDK API coverage status

Honest reading of v0.1.0 as of April 2026, verified against resonate-sdk-rs source (not just docs):

In the SDK source + documented in rust.mdx

• Resonate::new/local, .register/run/rpc/schedule/get/stop/promises.*
• #[resonate::function] macro + 3 function kinds (Workflow / Leaf with Info / Pure leaf)
• ctx.run/rpc/sleep + .spawn() double-await pattern
• Context accessors ctx.id/parent_id/origin_id/func_name/timeout_at
• Builder options .timeout(Duration), .target(&str) (context), .version/.tags (ephemeral)

In the SDK source BUT not in rust.mdx (use with eyes open)

• resonate.with_dependency<T>(value) — ephemeral-side DI (covered above)
• ctx.get_dependency::<T>() — durable-side DI (see resonate-basic-durable-world-usage-rust)
• ctx.promise::<T>() — Context-side HITL primitive (see resonate-basic-durable-world-usage-rust + resonate-human-in-the-loop-pattern-rust)
• ctx.info() — returns an Info struct with extra accessors branch_id and tags

These are pub fn with docstring-level examples in the source; they appear intended for users, just not yet covered by the docs. Until rust.mdx catches up, cite the source path (e.g., resonate/src/context.rs:115) when reviewers question whether the API exists.

NOT in the SDK source at v0.1.0

• ctx.detached — fire-and-forget; parallelism is via .spawn() instead
• ctx.random.random() / ctx.time.time() — no deterministic time/random helpers
• ctx.panic() / ctx.assert() — use Rust's own panic!/assert! + Result propagation

Treat the last three as "may land in future versions; verify when v0.2.0+ ships."

Related skills

• resonate-basic-durable-world-usage-rust — Context APIs, #[resonate::function] mechanics, .spawn() for parallelism, builder options
• resonate-basic-debugging-rust — Rust-specific failure modes: v0.1.0 caveat, git-dep install issues, serde errors, Result<T> handling
• durable-execution + resonate-philosophy — foundational concepts; read these first if new to Resonate
• resonate-basic-ephemeral-world-usage-typescript + -python — sibling SDKs' ephemeral-world surfaces for comparison