NATS Client

nats-client provides runtime-independent NATS protocol primitives for OCaml. It encodes client commands, parses server control lines, represents message headers, and provides subscription id helpers.

Use this package when you need protocol-level building blocks or want to adapt NATS support to a different runtime.

For normal application usage with Jane Street Async, install nats-client-async. That package provides the TCP client, reconnect loop, subscriptions, publishing, and request/reply API built on top of these protocol primitives.

Protocol Encoding

let frame =
  Nats_client.Protocol.encode_pub
    ~subject:"events.created"
    "created"

Use encode_hpub when the message should include NATS headers:

let headers =
  Nats_client.Headers.empty
  |> Nats_client.Headers.add ~name:"content-type" ~value:"application/json"

let frame =
  Nats_client.Protocol.encode_hpub
    ~subject:"events.created"
    ~headers
    {|"created"|}

Server Lines

The protocol parser handles server control lines after the runtime has removed the trailing CRLF:

match Nats_client.Protocol.parse_server_line "PING" with
| Nats_client.Protocol.Ping -> Nats_client.Protocol.encode_pong ()
| _ -> ""

Payload bytes for MSG and HMSG frames are read separately by the runtime client after parsing the metadata line.

Modules

• Nats_client.Protocol contains protocol types, encoders, and parsers.
• Nats_client.Headers represents ordered, repeatable NATS headers.
• Nats_client.Sid creates subscription ids.