IoT Data Plane

Overview

CloudMock emulates the AWS IoT Data Plane, supporting device shadow operations and MQTT message publishing. Device shadows are JSON documents with state (desired/reported), metadata, and version fields. Versions increment on each update, and delta computation between desired and reported state is supported.

Supported Operations

Operation	Status	Notes
GetThingShadow	Supported	Returns shadow document with state, metadata, version, timestamp
UpdateThingShadow	Supported	Merges state, increments version, computes delta
DeleteThingShadow	Supported	Deletes a shadow document
ListNamedShadowsForThing	Supported	Lists named shadows (excludes classic shadow)
Publish	Supported	Stores message to topic (no actual MQTT delivery)

Shadow Document Structure

{
  "state": {
    "desired": { "temp": 72, "mode": "auto" },
    "reported": { "temp": 70 },
    "delta": { "temp": 72 }
  },
  "metadata": {},
  "version": 3,
  "timestamp": 1234567890
}

Quick Start

Node.js

import { IoTDataPlaneClient, UpdateThingShadowCommand, GetThingShadowCommand } from '@aws-sdk/client-iot-data-plane';

const client = new IoTDataPlaneClient({
  endpoint: 'http://localhost:4566',
  region: 'us-east-1',
  credentials: { accessKeyId: 'test', secretAccessKey: 'test' },
});

// Update shadow (desired and reported)
await client.send(new UpdateThingShadowCommand({
  thingName: 'my-sensor',
  payload: JSON.stringify({
    state: {
      desired: { temp: 72, mode: 'auto' },
      reported: { temp: 70 },
    }
  }),
}));

// Get shadow (includes delta when desired != reported)
const shadow = await client.send(new GetThingShadowCommand({
  thingName: 'my-sensor',
}));
const doc = JSON.parse(new TextDecoder().decode(shadow.payload));
console.log('delta:', doc.state.delta); // { temp: 72 }

Python

import boto3
import json

client = boto3.client('iot-data',
    endpoint_url='http://localhost:4566',
    region_name='us-east-1',
    aws_access_key_id='test',
    aws_secret_access_key='test')

# Update named shadow
client.update_thing_shadow(
    thingName='my-sensor',
    shadowName='config',
    payload=json.dumps({'state': {'desired': {'interval': 30}}}))

# List named shadows
response = client.list_named_shadows_for_thing(thingName='my-sensor')
print(response['results'])  # ['config']

# Publish to topic
client.publish(topic='sensors/temp', payload=b'{"value": 72}', qos=0)

Configuration

cloudmock.yml

services:
  iotdata:
    enabled: true

Known Differences from AWS

• Publish does not deliver messages to MQTT subscribers
• Shadow versioning does not reject stale versions (no version conflict detection)
• Shadow metadata timestamps are set to creation time, not per-field timestamps