Rust-NATS is a Rust client library for the NATS message queue.

The crate is called nats and can be added as a dependency using Cargo:

[dependencies]
nats = "*"

It was written for Rust-nightly, but support for Rust beta will be added later.

The library was designed to be robust. It doesn't use any usafe code, it never calls panic!() and failed commands are automatically retried on different cluster nodes.

It provides a simple low-level interface that makes it easy to send/receive messages over Rust channels if needed.

Single-node client connection:

extern crate nats;
use nats::*;

let client = Client::new("nats://user:[email protected]").unwrap();

The username and password are optional.

Connecting to a cluster:

let cluster = vec!("nats://user:[email protected]", "nats://127.0.0.2");
let mut client = nats::Client::new(cluster).unwrap();

By default, commands are sent in fire-and-forget mode. In order to wait for an acknowledgment after each command, the synchronous ("verbose") mode can be turned on:

client.set_synchronous(true);

The client name can also be customized:

client.set_name("app");

client.publish("subject.test", "test".as_bytes()).unwrap();

In order to use NATS for RPC, the Client.make_request() function creates an ephemeral subject ("inbox"), subscribes to it, schedules the removal of the subscription after the first received message, publishes the initial request, and returns the inbox subject name:

let inbox = client.make_request("subject.rpc", "test".as_bytes()).unwrap();

Client.subscribe() adds a subscription to a subject, with an optional group:

let s1 = client.subscribe("subject", None).unwrap();
let s2 = client.subscribe("subject.*", Some("app")).unwrap();

With group membership, a given message will be only delivered to one client in the group.

Client.unsubscribe() removes a subscription:

client.unsubscribe(s1).unwrap();

Or to remove it after n messages have been received:

client.unsubscribe_after(s1, n).unwrap();

Client.wait() waits for a new event, and transparently responds to server PING requests.

let event = client.wait();

This returns an Event structure:

pub struct Event {
    pub subject: String,
    pub channel: Channel,
    pub msg: Vec<u8>,
    pub inbox: Option<String>
}

Alternatively, events can be received using an iterator:

for event in client.events() {
    ...
}