Crate mqtt_typed_client_macros 

MQTT Typed Client Macros

This crate provides procedural macros for generating typed MQTT subscribers and publishers with automatic topic parameter extraction and payload serialization.

Overview

The main macro mqtt_topic allows you to annotate a struct with a topic pattern, automatically generating the necessary trait implementations and helper methods for MQTT subscription and publishing.

Features

• Topic Parameter Extraction: Automatically extracts named parameters from MQTT topics
• Type Safety: Compile-time validation of struct fields against topic patterns
• Flexible Payload Handling: Support for custom payload types with automatic serialization
• Optional Topic Access: Include the full topic match information if needed
• Dual Mode Generation: Generate subscriber, publisher, or both methods
• Generated Helper Methods: Convenient subscription and publishing methods with pattern constants

Quick Start

use mqtt_typed_client_macros::mqtt_topic;
use std::sync::Arc;
use mqtt_typed_client_core::topic::topic_match::TopicMatch;

#[derive(Debug)]
#[mqtt_topic("sensors/{sensor_id}/temperature/{room}")]
struct TemperatureReading {
    sensor_id: u32,           // Extracted from {sensor_id} in topic
    room: String,             // Extracted from {room} in topic
    payload: f64,             // Message payload (temperature value)
    topic: Arc<TopicMatch>,   // Optional: full topic match info
}

// Generated constants:
// TemperatureReading::TOPIC_PATTERN = "sensors/{sensor_id}/temperature/{room}"
// TemperatureReading::MQTT_PATTERN = "sensors/+/temperature/+"

// Generated methods:
// let subscriber = TemperatureReading::subscribe(&client).await?;
// TemperatureReading::publish(&client, sensor_id, room, &data).await?;

Supported Field Types

• Topic Parameters: Any field name matching a {parameter} in the topic pattern
• payload: The message payload, can be any deserializable type
• topic: Must be Arc<TopicMatch>, provides access to full topic information

Topic Pattern Syntax

• {param_name} - Named parameter that becomes a struct field
• + - Anonymous single-level wildcard (not extracted)
• # - Anonymous multi-level wildcard (not extracted, must be last)
• {param_name:#} - Named multi-level wildcard (extracted as string)

⚠️ Publisher Limitations

Multi-level wildcards (# or {param:#}) are not supported for publishers because they represent variable-length topic segments that cannot be constructed from fixed parameters.

use mqtt_typed_client_macros::mqtt_topic;

// ✅ This works for both subscriber and publisher
#[mqtt_topic("sensors/{sensor_id}/data")]
struct SensorData { sensor_id: u32, payload: f64 }

// ✅ This works for subscriber only
#[mqtt_topic("alerts/{category}/#", subscriber)]
struct Alert { category: String, payload: String }

// ❌ This will cause a compile error
// #[mqtt_topic("events/{event_type}/{details:#}")]
// struct Event { /* ... */ }

// 🔧 Solution: Use separate structs
#[mqtt_topic("events/{event_type}/{details:#}", subscriber)]  
struct EventReceived { event_type: String, details: String, payload: Vec<u8> }

#[mqtt_topic("events/{event_type}", publisher)]
struct EventToSend { event_type: String, payload: Vec<u8> }

Attribute Macros

mqtt_topic

Generate a typed MQTT subscriber and/or publisher from a struct and topic pattern