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useNats is your pack’s async transport. It wraps the platform’s NATS bridge so your frontend can talk to your service, react to events from other packs, or broadcast messages across the org.

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Signature

function useNats(): {
  connected: boolean;
  publish: (subject: string, data?: unknown) => void;
  subscribe: (subject: string, callback: (data: unknown, subject: string) => void) => () => void;
  request: (subject: string, data?: unknown, timeoutMs?: number) => Promise<unknown>;
  orgId: string;
  userId: string;
};
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connected
boolean
true when the NATS bridge is online. Re-renders when connection status changes.
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publish
(subject, data?) => void
Fire-and-forget publish. No response, no ack. Payload is JSON-serialized.
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subscribe
(subject, callback) => unsubscribe
Register a handler for a subject (wildcards * and > supported). Returns an unsubscribe function — call it on unmount.
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request
(subject, data?, timeoutMs?) => Promise<unknown>
Send a request and await a reply. Rejects after timeoutMs (default 5000 ms).
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orgId
string
Current org id, synced from useKhalAuth. Use it to scope subjects.
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userId
string
Current user id. Useful for per-user subject segments.

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Basic example — publish and subscribe

import { useNats } from '@khal-os/sdk/app';
import { useEffect } from 'react';

export function ChatFeed() {
  const { connected, subscribe, publish, orgId } = useNats();

  useEffect(() => {
    if (!connected) return;
    const unsub = subscribe(`khal.${orgId}.chat.messages`, (data) => {
      console.log('new message', data);
    });
    return unsub;
  }, [connected, orgId, subscribe]);

  return (
    <button
      type="button"
      onClick={() => publish(`khal.${orgId}.chat.messages`, { text: 'hello' })}
    >
      Say hi
    </button>
  );
}

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Request / reply example

When you need an answer, use request. This pattern is how pack-terminal spawns a PTY session — the frontend requests, the service responds with the new session id. 
const { request, orgId } = useNats();

async function spawnPty(cols: number, rows: number) {
  try {
    const reply = await request(
      `khal.${orgId}.terminal.pty.spawn`,
      { cols, rows },
      10_000,
    );
    return reply as { sessionId: string; pid: number };
  } catch (err) {
    // request timed out or replier rejected
    console.error(err);
    return null;
  }
}
Source: pack-terminal/package/src/views/terminal/useNatsPty.ts.

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Subject naming

Subjects your pack owns should always be scoped by orgId and your pack’s id: 
khal.<orgId>.<packId>.<action>[.<params>]
Examples from pack-terminal:
  • khal.<orgId>.terminal.pty.spawn — request a new PTY session
  • khal.<orgId>.terminal.pty.input.<sessionId> — publish stdin to a session
  • khal.<orgId>.terminal.pty.output.<sessionId> — subscribe to stdout
For dynamic subjects, the SDK ships a small builder: 
import { SubjectBuilder } from '@khal-os/sdk/app';

const ptyInput = new SubjectBuilder('terminal')
  .action('pty')
  .action('input')
  .param()
  .build();

ptyInput(orgId, sessionId); // → 'khal.<orgId>.terminal.pty.input.<sessionId>'

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Error handling

  • publish never throws. If the bridge is offline, the frame is dropped.
  • subscribe never throws. Callbacks that throw are isolated — other subscribers still fire.
  • request rejects with an Error when it times out. Always wrap in try/catch or .catch().
  • Connection drops: read connected and guard side effects on it. Re-subscribing on reconnect is automatic — the bridge replays your active subscriptions.

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Wildcards

Subscribe patterns support NATS wildcards:
  • * matches exactly one token: khal.*.terminal.pty.spawn
  • > matches one or more tokens, and must be last: khal.<orgId>.terminal.pty.>
Never subscribe to khal.internal.* or khal.catalog.*. Those subjects are platform plumbing — they’re not part of the SDK contract, they change without notice, and the bridge will reject subscriptions that aren’t yours. Scope everything under your pack’s id.

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What’s next

useKhalAuth

Current user, org, role — the auth contract your pack receives.

useService

Call into your pack’s own backend service.