CoAP Server Not Responding to Requests

In this tutorial, you'll learn about CoAP Server Not Responding to Requests. We cover key concepts, practical examples, and best practices to help you understand and apply this topic effectively.

The Problem

A CoAP server does not respond to GET requests from a CoAP client.

Quick Fix

Wrong

coap.createServer()  # No resource handler registered

Server starts but returns 4.05 (Method Not Allowed) for all requests.

Right

const coap = require('coap')

const server = coap.createServer()

server.on('request', (req, res) => {
  if (req.method === 'GET') {
    if (req.url === '/temperature') {
      res.code = '2.05'
      res.end(JSON.stringify({ value: 25.5 }))
    } else {
      res.code = '4.04'
      res.end('Not Found')
    }
  } else {
    res.code = '4.05'
    res.end('Method Not Allowed')
  }
})

server.listen(() => {
  console.log('CoAP server listening on port 5683')
})

CoAP client receives "2.05 Content" with temperature JSON.

Prevention

CoAP uses UDP port 5683 (DTLS: 5684). Always register resource handlers. Respond with appropriate CoAP response codes: 2.05 (Content), 2.01 (Created), 4.04 (Not Found), 4.05 (Method Not Allowed). CoAP is REST-like but binary. Use CoAP-specific libraries (not HTTP tools).

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

FAQ