HL7 v2 over MLLP, with the hard parts handled.

import { createStarterClient, createStarterServer } from "@cosyte/mllp";

const committed: Buffer[] = [];

// Port 0: the OS picks a free port. The host defaults to loopback, 127.0.0.1.
const server = await createStarterServer({
  port: 0,
  onMessage: async (payload) => {
    committed.push(payload); // your durable commit: a throw here answers AE, never AA
  },
});

const client = await createStarterClient({ host: "127.0.0.1", port: server.getStats().port ?? 0 });

const ack = await client.send(
  Buffer.from(
    "MSH|^~\\&|SENDING_APP|SENDING_FAC|RECEIVING_APP|RECEIVING_FAC|20260101120000||ADT^A01|CTRL0001|P|2.5.1\r",
  ),
);

// Log the shape of the acknowledgement, never its field values.
const msa = ack
  .toString("utf8")
  .split("\r")
  .find((segment) => segment.startsWith("MSA|"))
  ?.split("|");
console.log("acknowledgement code:", msa?.[1]);
console.log("MSA-2 echoes the control id sent:", msa?.[2] === "CTRL0001");
console.log("messages committed:", committed.length);

await client.close();
await server.close();