CoAP Connector

Overview

The CoAP (Constrained Application Protocol) connector enables communication with resource-constrained IoT devices. CoAP is a lightweight protocol designed for low-power devices and lossy networks, commonly used in smart home, industrial IoT, and sensor networks.

Connector Types:

• CoapReader - Read data from CoAP endpoints
• CoapWriter - Write data to CoAP endpoints

Features

• ✅ Multiple transport protocols (UDP, TCP, DTLS)
• ✅ Secure communication with DTLS
• ✅ PSK and certificate-based authentication
• ✅ GET, POST, and PUT methods
• ✅ Polling-based data acquisition

Basic Configuration

CoAP Reader (UDP)

{
  "type": "CoapReader",
  "config": {
    "endpoint": "192.168.1.50:5683",
    "transport": "UDP",
    "pollingRate": 5000,
    "path": "/sensors/temperature"
  }
}

CoAP Reader (TCP)

{
  "type": "CoapReader",
  "config": {
    "endpoint": "192.168.1.50:5683",
    "transport": "TCP",
    "pollingRate": 5000,
    "path": "/sensors/all"
  }
}

CoAP Writer

{
  "type": "CoapWriter",
  "config": {
    "endpoint": "192.168.1.50:5683",
    "transport": "UDP",
    "path": "/actuators/valve",
    "method": "PUT"
  }
}

Configuration Parameters

Reader Config

Parameter	Type	Required	Description
endpoint	string	✅	CoAP server address (host:port)
transport	string	✅	Transport protocol: UDP, TCP, or DTLS
pollingRate	integer	✅	Polling interval in milliseconds
path	string	✅	CoAP resource path (e.g., /sensors/temp)
dtlsConfig	object	❌	DTLS configuration (required for DTLS transport)

Writer Config

Parameter	Type	Required	Description
endpoint	string	✅	CoAP server address (host:port)
transport	string	✅	Transport protocol: UDP, TCP, or DTLS
path	string	✅	CoAP resource path
method	string	✅	HTTP method: POST or PUT
dtlsConfig	object	❌	DTLS configuration (required for DTLS transport)

Transport Protocols

UDP

Standard CoAP over UDP (default port 5683):

{
  "endpoint": "192.168.1.50:5683",
  "transport": "UDP"
}

Best for: Low-latency, resource-constrained devices

TCP

CoAP over TCP for reliable delivery:

{
  "endpoint": "192.168.1.50:5683",
  "transport": "TCP"
}

Best for: Reliable connections, larger payloads

DTLS

Secure CoAP with DTLS encryption (default port 5684):

{
  "endpoint": "192.168.1.50:5684",
  "transport": "DTLS",
  "dtlsConfig": {
    "pskIdentity": "device1",
    "pskKey": "c2VjcmV0a2V5"
  }
}

Best for: Secure communication over untrusted networks

DTLS Security Configuration

Pre-Shared Key (PSK)

{
  "type": "CoapReader",
  "config": {
    "endpoint": "192.168.1.50:5684",
    "transport": "DTLS",
    "pollingRate": 5000,
    "path": "/sensors/secure",
    "dtlsConfig": {
      "pskIdentity": "bXlkZXZpY2U=",
      "pskKey": "c2VjcmV0a2V5MTIz"
    }
  }
}

Note: pskIdentity and pskKey are byte arrays (typically base64-encoded in JSON).

Certificate-Based Authentication

{
  "type": "CoapReader",
  "config": {
    "endpoint": "192.168.1.50:5684",
    "transport": "DTLS",
    "pollingRate": 5000,
    "path": "/sensors/secure",
    "dtlsConfig": {
      "certFile": {
        "mode": "path",
        "data": "/certs/client.crt"
      },
      "keyFile": {
        "mode": "path",
        "data": "/certs/client.key"
      },
      "caCertFile": {
        "mode": "path",
        "data": "/certs/ca.crt"
      }
    }
  }
}

Certificate Files (Base64)

{
  "dtlsConfig": {
    "certFile": {
      "mode": "base64",
      "data": "<base64-encoded-certificate>"
    },
    "keyFile": {
      "mode": "base64",
      "data": "<base64-encoded-private-key>"
    },
    "caCertFile": {
      "mode": "base64",
      "data": "<base64-encoded-ca-certificate>"
    }
  }
}

Data Format

Reader Response

The CoAP reader expects JSON responses from the endpoint:

{
  "temperature": 25.5,
  "humidity": 60,
  "battery": 85
}

Writer Payload

The CoAP writer sends the data payload as JSON:

{
  "valve_position": 75,
  "mode": "auto"
}

Common Use Cases

1. Sensor Network Monitoring

Read from multiple sensor endpoints:

{
  "type": "CoapReader",
  "config": {
    "endpoint": "192.168.1.50:5683",
    "transport": "UDP",
    "pollingRate": 10000,
    "path": "/sensors/environment"
  }
}

2. Secure Device Communication

Connect to devices with DTLS security:

{
  "type": "CoapReader",
  "config": {
    "endpoint": "iot-gateway.local:5684",
    "transport": "DTLS",
    "pollingRate": 5000,
    "path": "/api/v1/data",
    "dtlsConfig": {
      "pskIdentity": "Z2F0ZXdheTE=",
      "pskKey": "c3VwZXJzZWNyZXQ="
    }
  }
}

3. Actuator Control

Send commands to IoT actuators:

{
  "type": "CoapWriter",
  "config": {
    "endpoint": "192.168.1.100:5683",
    "transport": "UDP",
    "path": "/actuators/light",
    "method": "PUT"
  }
}

4. Smart Building Integration

Control building systems via CoAP:

{
  "type": "CoapWriter",
  "config": {
    "endpoint": "building-controller.local:5683",
    "transport": "TCP",
    "path": "/hvac/setpoint",
    "method": "POST"
  }
}

Troubleshooting

Connection Failed

Solutions:

• Verify endpoint address and port
• Check network connectivity
• Ensure CoAP server is running
• Verify transport protocol matches server configuration

DTLS Handshake Failed

Solutions:

• Verify PSK identity and key match server configuration
• Check certificate validity and expiration
• Ensure CA certificate is correct
• Verify cipher suite compatibility

Invalid Response

Solutions:

• Ensure endpoint returns valid JSON
• Check resource path is correct
• Verify content format is application/json
• Check server logs for errors

Request Timeout

Solutions:

• Increase timeout if network is slow
• Check for network congestion
• Verify device is responsive
• Consider using TCP for unreliable networks

Best Practices

1. Use DTLS for Production: Always encrypt sensitive data
2. Appropriate Polling Rate: Balance freshness with device battery life
3. Handle Timeouts: CoAP devices may be intermittently available
4. Use Observe When Available: For real-time updates (future feature)
5. Resource Path Convention: Follow REST-like naming (/sensors/temperature)

Related Connectors

• MQTT - Alternative IoT protocol
• HTTP - REST API for capable devices
• Filter - Filter CoAP data
• InfluxDB - Store sensor data