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/me/ Topic Pattern - SENTIENT SCADA Implementation

Overview

This document describes the handling of /me/ topic patterns in the SENTIENT SCADA MQTT implementation.

IMPORTANT: As of the latest update, rumqttd does NOT perform topic substitution. Topics are passed through unchanged to the backend, which handles /me/ resolution using session-aware processing.

Background

Original Approach (Deprecated)

Initially, this implementation substituted /me/ with {client_id} at the broker layer. This approach had several issues:

  • Required client_id to be the device UUID
  • Device ID could be spoofed via client_id
  • Did not match ThingsBoard's actual implementation
  • Did not work with standard MQTT tools (mosquitto_pub)

ThingsBoard's Actual Approach

After analyzing the ThingsBoard codebase, we discovered that ThingsBoard does NOT substitute /me/ in topics. Instead:

  1. Authentication Phase (MQTT CONNECT):

    • Device provides access token as MQTT username
    • Backend validates token and retrieves device ID
    • Device ID is stored in session context

  2. Message Processing Phase (MQTT PUBLISH):

    • Topic "v1/devices/me/telemetry" is received unchanged
    • Topic is matched literally (string comparison)
    • Backend uses device ID from the authenticated session (not from topic)

  3. Key Insight:

    • The "me" is not a placeholder - it's a literal topic string
    • Device identity comes from session authentication, not topic parsing
    • MQTT client_id is completely ignored

Current Implementation

rumqttd (Broker Layer)

File: rumqttd/src/router/routing.rs

Topics are NOT modified. All PUBLISH, SUBSCRIBE, and UNSUBSCRIBE packets pass through unchanged:

// Topics pass through unchanged - backend handles /me/ resolution via session context

Backend (Application Layer)

File: transport/src/mqtt/broker.rs

The backend implements session-aware /me/ topic resolution:

  1. When a device connects, authentication creates a session mapping: client_id → device_id
  2. When a message arrives on a /me/ topic:
    • Backend looks up the session by client_id
    • Retrieves the authenticated device_id from session
    • Processes message using the authenticated device_id

This matches ThingsBoard's approach and provides:

  • ✅ Security: Device ID cannot be spoofed
  • ✅ Compatibility: Works with any MQTT client
  • ✅ Standards compliance: No client_id requirements
  • ✅ Tool support: Works with mosquitto_pub

Usage

Device Connection

# Only access token is required
mosquitto_pub \
  -h 127.0.0.1 -p 1883 \
  -t "v1/devices/me/telemetry" \
  -u "ACCESS_TOKEN" \
  -m '{"temperature":25}'

# Note: -i (client_id) is optional

Topic Patterns Supported

  • v1/devices/me/telemetry - Device telemetry
  • v1/devices/me/attributes - Device attributes
  • v1/devices/me/rpc/request/{id} - RPC requests
  • v1/devices/me/rpc/response/{id} - RPC responses

Implementation Details

See /home/mz/Work/Development/INVENIA_IIoT/SENTIENT_SCADA/THINGSBOARD_ME_TOPIC_IMPLEMENTATION.md for:

  • Complete ThingsBoard code flow analysis
  • Security comparison
  • Detailed implementation plan
  • Testing strategies