@rep-protocol/sdk

Client SDK for the Runtime Environment Protocol.

Zero-dependency, framework-agnostic, ~1.5KB gzipped. Reads environment variables injected by the REP gateway at runtime — no build tool plugins, no framework coupling.

Install

npm install @rep-protocol/sdk

Usage

import { rep } from '@rep-protocol/sdk';

// PUBLIC tier — synchronous, immediate, no network call.
const apiUrl = rep.get('API_URL');
const flags = rep.get('FEATURE_FLAGS', '').split(',');

// SENSITIVE tier — async, fetches session key, decrypts.
const analyticsKey = await rep.getSecure('ANALYTICS_KEY');

// All public vars as a frozen object.
const all = rep.getAll();

// Verify payload integrity.
if (!rep.verify()) {
  console.error('Config may have been tampered with!');
}

// Hot reload (if gateway has --hot-reload enabled).
const unsub = rep.onChange('FEATURE_FLAGS', (newVal, oldVal) => {
  console.log(`Flags changed: ${oldVal} → ${newVal}`);
});

// Cleanup.
unsub();

API

| Method | Returns | Description | |---|---|---| | rep.get(key, default?) | string \| undefined | Synchronous. PUBLIC tier variable. | | rep.getSecure(key) | Promise<string> | Async. SENSITIVE tier variable (decrypts via session key). | | rep.getAll() | Record<string, string> | All PUBLIC vars as a frozen object. | | rep.verify() | boolean | Check payload integrity. | | rep.meta() | REPMeta \| null | Payload metadata (version, counts, status). | | rep.onChange(key, cb) | () => void | Subscribe to hot reload changes. Returns unsubscribe fn. | | rep.onAnyChange(cb) | () => void | Subscribe to all changes. Returns unsubscribe fn. |

Development Mode

Without the REP gateway, rep.get() returns undefined. Use defaults:

const apiUrl = rep.get('API_URL', 'http://localhost:3000');

Or mock the payload in your index.html during development:

<script id="__rep__" type="application/json">
{"public":{"API_URL":"http://localhost:3000"},"_meta":{"version":"0.1.0","injected_at":"2026-01-01T00:00:00Z","integrity":"hmac-sha256:dev","ttl":0}}
</script>

Specification

Implements REP-RFC-0001 §5 — Client SDK Specification.

License

Apache 2.0