Module services 

Service Calls and Promise API

client.call(&request) returns a Promise immediately — no blocking. The reply can be polled with try_recv() or .awaited.

Sync polling (no async runtime)

Drive I/O with spin_once() while polling the promise:

use nros::prelude::*;
use example_interfaces::srv::{AddTwoInts, AddTwoIntsRequest};

let config = ExecutorConfig::from_env().node_name("client");
let mut executor: Executor = Executor::open(&config)?;
let mut node = executor.create_node("client")?;
let mut client = node.create_client::<AddTwoInts>("/add_two_ints")?;

let mut promise = client.call(&AddTwoIntsRequest { a: 1, b: 2 })?;

let reply = loop {
    executor.spin_once(core::time::Duration::from_millis(10));
    if let Ok(Some(reply)) = promise.try_recv() {
        break reply;
    }
};
println!("sum = {}", reply.sum);

Async (background spin task)

Spawn spin_async() as a background task, then .await promises:

use nros::prelude::*;
use example_interfaces::srv::{AddTwoInts, AddTwoIntsRequest};

#[tokio::main(flavor = "current_thread")]
async fn main() {
    let config = ExecutorConfig::from_env().node_name("client");
    let mut executor: Executor = Executor::open(&config).unwrap();
    let mut client = {
        let mut node = executor.create_node("client").unwrap();
        node.create_client::<AddTwoInts>("/add_two_ints").unwrap()
    };

    let local = tokio::task::LocalSet::new();
    local.run_until(async move {
        tokio::task::spawn_local(async move {
            executor.spin_async().await;
        });
        let reply = client.call(&AddTwoIntsRequest { a: 1, b: 2 })
            .unwrap().await.unwrap();
        println!("sum = {}", reply.sum);
    }).await;
}

The Promise and spin_async() APIs use only core::future — no external runtime dependency. They work on no_std/no_alloc targets. For async combinators (select, join), add embassy-futures.

See examples/native/rust/service-client-async/ (tokio) for a complete working example. The Zephyr Embassy variant was dropped 2026-06-02 per Phase 212.M-F.5 — pending an async-Node trait decision.