nodejs

Node.js Real-Time Clients

Real-time publisher and subscriber clients for Harper using MQTT, WebSocket, and Server-Sent Events (SSE).

Dependencies

• Node.js v14+
• mqtt package (v5.14.1) - for MQTT clients
• ws package (v8.18.0) - for WebSocket clients
• eventsource package (v3.0.2) - for SSE clients

Installation

npm install

Usage

MQTT Clients

Publisher

node mqtt-publish.js

Subscriber

node mqtt-subscribe.js

WebSocket Clients

Publisher

node ws-publish.js

Subscriber

node ws-subscribe.js

SSE (Server-Sent Events) Client

Subscriber

node sse-subscribe.js

Note: SSE is unidirectional (server to client only), so there is no SSE publisher.

Tier Structure

All clients follow the same tier progression:

• Tier 0 (MVP): Single publish, automatic database persistence for WebSocket/SSE
• Tier 1: Database persistence enabled (MQTT: retain: true)
• Tier 2: Continuous publishing every 5 seconds

Protocol Comparison

• MQTT: Full pub/sub broker, topic-based routing, QoS levels
• WebSocket: Bidirectional, direct resource connection, lower overhead
• SSE: Unidirectional (server→client), simple HTTP-based, automatic reconnection