NATS - OCaml Client

OCaml client for the NATS messaging system.

Warning

In active development! You can view the progress here.

Basics

• CONNECT
• INFO
• PUB
• HPUB
• HMSG
• SUB/UNSUB
• MSG
• PING/PONG
• OK/ERR

Features

• Drain mechanism
• Request mechanism

Packages

The project provides several packages with different implementations for any contexts.

Package	Description	Require OCaml
nats-client	implementation independent protocol abstracts	>= 4.14 (LTS)
nats-client-lwt	lwt.unix-based client implementation

Quick start

Installation

Currently only a development version is available. You can pin it using the OPAM package manager.

$ opam pin nats-client-lwt.dev https://github.com/romanchechyotkin/nats.ocaml.git

Publish-Subscribe example

This example shows how to publish to a subject and handle its messages.

open Lwt.Infix

let main =
  (* Create a switch for automatic dispose resources. *)
  Lwt_switch.with_switch @@ fun switch ->
  
  (* Connect to a NATS server by address 127.0.0.1:4222 with ECHO flag. *)
  let%lwt client =
    Nats_client_lwt.connect ~switch ~settings:[ `Echo ]
      (Uri.of_string "nats://127.0.0.1:4222")
  in

  (* Publish 'hello' message to greet.joe subject. *)
  Nats_client_lwt.pub client ~subject:"greet.joe" "hello";%lwt

  (* Subscribe to greet.* subject. *)
  let%lwt subscription =
    Nats_client_lwt.sub ~switch client ~subject:"greet.*" ()
  in

  (* Publishes 'hello' message to three subjects. *)
  Lwt_list.iter_s
    (fun subject -> Nats_client_lwt.pub client ~subject "hello")
    [ "greet.sue"; "greet.bob"; "greet.pam" ];%lwt

  (* Handle first three incoming messages to the greet.* subject. *)
  Lwt_stream.nget 3 subscription.messages
  >>= Lwt_list.iter_s (fun (message : Nats_client.Protocol.msg) ->
          Lwt_io.printlf "'%s' received on %s" message.payload.contents
            message.subject)

let () = Lwt_main.run main

Take it from examples/natsbyexample/publish_subscribe.ml.

$ docker start -a nats-server
$ dune exec ./examples/natsbyexample/publish_subscribe.exe

'hello' received on greet.sue       
'hello' received on greet.bob
'hello' received on greet.pam

By Examples

See more examples at examples/ directory.

Messaging

• Core Publish-Subscribe
• Request-Reply
• JSON for Message Payloads
• Protobuf for Message Payloads
• Concurrent Message Processing
• Iterating Over Multiple Subscriptions

References

• NATS documentation
• NATS Client protocol documentation

Contributing

The is an open source project under the Apache 2.0 license. Contributions are very welcome! Let's build a great ecosystem together! Please be sure to read the CONTRIBUTING.md before your first commit.