Coap Get

In this tutorial, you'll learn about CoAP GET Returns Empty Response. We cover key concepts, practical examples, and best practices to help you understand and apply this topic effectively.

The Problem

CoAP GET request returns a success code but empty payload.

Quick Fix

Wrong

server.on('request', (req, res) => {
  res.code = '2.05'
  res.end()  # No payload
})

Client gets 2.05 Content with empty payload.

Right

const coap = require('coap')

const server = coap.createServer()

server.on('request', (req, res) => {
  if (req.url === '/status') {
    const payload = JSON.stringify({
      uptime: process.uptime(),
      memory: process.memoryUsage(),
      temp: 25.5
    })
    
    res.code = '2.05'
    res.setOption('Content-Format', 'application/json')
    res.end(payload)
  } else {
    res.code = '4.04'
    res.end('Not Found')
  }
})

server.listen(5683)

Client receives 2.05 Content with JSON payload of status data.

Prevention

Always include a payload with 2.05 responses (or 2.03 for no-body). Set Content-Format option: 0 (text/plain), 50 (application/json), 40 (application/link-format). Check res.end() — it must receive a string or Buffer. Use appropriate response codes.

DodaTech engineers apply these same patterns across Doda Browser, DodaZIP, and Durga Antivirus Pro for production IoT reliability.

FAQ