A swift client for interacting with NATS servers

What's New


  • The client configuration is now publicly accessible
  • The handling of the connection status has been rewritten and improved
  • The connection setup has been rewritten and improved
  • The connection termination has been rewritten and improved
  • All classes were cleaned up (refactoring)
  • A new license was added (BSD-0)
  • The reconnection code was removed, it is now up to the implementation code - could have been never worked in the original codebase.
  • Provide a reconnect() function to handling reconnect easily. (example given)
  • The subscription queue is an optional property of NatsSubject now


A maintained swift client for interacting with a nats server based on NIO2.

SwiftyNats Logo

Tested with Swift 5.4 on macos and Linux

Swift Version Compatibility:

Platform Compatibility:


Join the #swift channel on nats.io Slack. We'll do our best to help quickly. You can also just drop by and say hello. We're looking forward to developing the community.

Installation via Swift Package Manager

In Package.swift

Add this packages as a dependency in your projects Package.swift file and add the Name to your target like shown in this example:

// swift-tools-version:5.4

import PackageDescription

let package = Package(
    name: "YourApp",
    products: [
        .executable(name: "YourApp", targets: ["YourApp"]),
    dependencies: [
        .package(name: "SwiftyNats", url: "https://github.com/aus-der-technik/swifty-nats.git", from: "2.2.0")
    targets: [
            name: "YourApp",
            dependencies: ["SwiftyNats"]

In an .xcodeproj

Open the project inspector in XCode and select your project. It is importent to select the project and not a target! Klick on the third tab Package Dependencies and add the git url https://github.com/aus-der-technik/swifty-nats.git by selecting the litte +-sign at the end of the package list.

Basic Usage

import SwiftyNats

// register a new client
let client = NatsClient("http://nats.server:4222")

// listen to an event
client.on(.connect) { _ in
    print("Client connected")

// try to connect to the server 
try? client.connect()

// subscribe to a channel with a inline message handler. 
client.subscribe("foo.bar") { message in
    print("payload: \(message.payload)")
    print("size: \(message.byteCount)")
    print("reply subject: \(message.replySubject.subject)")

// publish an event onto the message strem into a subject
client.publish("this event happened", to: "foo.bar")

Setting the loglevel

The default loglevel is .error. You can reset it to see more verbose messages. Possible Values are .debug, .info, .error or .critical

let client = NatsClient("http://nats.server:4222")
client.config.loglevel = .info

Reconnection is up to you

Reconnection is not part of this package, because if a server diconnects your application have to be sure that subscribtions are made up again correctly.

With SwiftyNats this is a very easy step:

// register a new client
let client = NatsClient(url)

// listen to the .disconnected event to try a reconnect 
client.on(.disconnected) { [self] _ in
    try? client.reconnect()

// subscribe to the channels

// private function to subscribe to channels
private func doSubscribe(){
    client.subscribe("foo.bar") { message in
        print("payload: \(message.payload)")

List of events

The public class NatsEvent contains all events you can subscribt to.

event description
connected The client is conected to the server.
disconnected The client disconnects and was connectd before.
response The client gets an response from the server (internal).
error The server sends an error that can't be handled.
dropped The clients droped a message. Mostly because of queue length to short.
reconnecting The client reconencts to the server, (Because of a called reconnect()).
informed The server sends his information data successfully to the client.

Information about the connected server

Since 2.0.2 it is possible to get the informations from the conencted server

let client = NatsClient("http://nats.server:4222")
print("\(client.serverInformation.serverName) has Version: \(client.serverInformation.version))");


Contribution is always welcome. Just send me a pull request.



  • The client configuration is now publicly available
  • The handling of the connection status has been rewritten
  • Rewrite of the connection setup
  • The connection termination was rewritten
  • All classes have been cleaned up (refactoring)
  • A new license was added (BSD-0)
  • The reconnection code was removed
  • Subscription queue is an optional property of NatsSubject


  • rewrite the ChannelHandler: remove a bug that could lead into dropped messages.


  • uses NIO2
  • works with Vapor, now!


  • supports iOS anf tvOS


  • Get information from the connected Server (Version, name, id, ...)


  • Test with GitHub Actions
  • Update Dockerfile to build and test on Swift 5.4 (Linux)
  • Test with a real NATS-Server on macos
  • Cleanup unused definitions
  • Update Informations, do project care


  • Tested with NATS 2.3.4
  • Introduced logging
  • Updated depricated functions


See: Contribution ;)

  • Propper function description is needed


  • Swift Tools 5.0.0
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Last updated: Tue Oct 26 2021 10:41:13 GMT-0500 (GMT-05:00)