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rmqtt-auto-subscription

Auto-subscription plugin for RMQTT. Automatically subscribes clients to predefined topic filters when they connect.

Overview

When a client connects, the plugin subscribes them to configured topic filters without requiring the client to send SUBSCRIBE packets. This is useful for:

• Forcing clients to receive specific system or telemetry topics
• Ensuring all clients have a baseline set of subscriptions
• Reducing client-side logic by pre-configuring subscriptions on the broker

Each subscription entry supports configurable QoS, No Local, Retain as Published, and Retain Handling options (MQTTv5 properties).

Variable Interpolation

Topic filter expressions can use ${clientid} to represent the client ID and ${username} to represent the client username, allowing dynamic per-client subscription topics.

Usage

Add the dependency to Cargo.toml:

rmqtt-auto-subscription = "0.22"

Register the plugin in your broker startup code:

rmqtt_auto_subscription::register(&scx, true, false).await?;

Configuration

File: rmqtt-auto-subscription.toml

Subscription Entry Fields

Each entry in the subscribes array supports:

Default Subscriptions

subscribes = [
    { topic_filter = "x/+/#", qos = 1, no_local = false, retain_as_published = false, retain_handling = 0 },
    { topic_filter = "foo/${clientid}/#", qos = 1, no_local = false, retain_as_published = false, retain_handling = 0 },
    { topic_filter = "iot/${username}/#", qos = 1 }
]

Placeholder Variables

Example: Device-Specific Subscriptions

subscribes = [
    # All clients subscribe to a common telemetry topic
    { topic_filter = "telemetry/#", qos = 1 },

    # Each client subscribes to its own device-specific control topic
    { topic_filter = "control/${clientid}/#", qos = 2 },

    # Subscribe to user-specific configuration topics
    { topic_filter = "config/${username}/#", qos = 1 }
]

Dependencies

• rmqtt (feature plugin)

License

MIT OR Apache-2.0