picobroker 0.1.1

Pure no_std core library for PicoBroker MQTT 3.1.1 broker
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PicoBroker

crates.io License: MIT GitHub

A minimal MQTT 3.1.1 broker for embedded systems (no_std) and standard environments.

Features

  • ✅ no_std - Fully embedded, no standard library (core library)
  • ✅ MQTT 3.1.1 compliant - Protocol specification compliant
  • ✅ QoS 0 - Fire and forget messaging
  • ✅ QoS 1 (best-effort) - Accepts QoS 1 and sends PUBACK, but no retry/store-and-forward
  • ✅ Topic wildcards - Supports + (single-level) and # (multi-level) wildcards
  • ✅ Heapless (Embassy) - Zero heap usage on embedded with Embassy
  • ✅ Platform-agnostic - Works with Tokio (std) or Embassy (embedded)
  • ✅ Configurable - Compile-time configuration via const generics

Limitations

For maximum minimalism:

  • QoS 0 only - Full QoS 1/2 with retry/store-and-forward not implemented
  • No retained messages - Retain flag not handled
  • No authentication/authorization - No username/password or ACL support
  • No TLS/SSL - Plain TCP only

Default Limits (configurable via const generics)

Parameter Default Description
MAX_TOPICS 32 Maximum unique topics system-wide
MAX_SESSIONS 4 Maximum concurrent client sessions
MAX_SUBSCRIBERS_PER_TOPIC 8 Maximum clients subscribed to one topic
MAX_TOPIC_NAME_LENGTH 64 Maximum bytes in topic name
MAX_PAYLOAD_SIZE 256 Maximum bytes in message payload

Protocol Support

Packet Type Supported Notes
CONNECT ✅ MQTT 3.1.1 protocol
CONNACK ✅ Always accepts connections
PUBLISH ✅ QoS 0 fully, QoS 1 best-effort (PUBACK)
SUBSCRIBE ✅ Supports wildcards (+, #)
SUBACK ✅ Grants requested QoS level
PUBACK ✅ Sent for QoS 1+ publishes
PINGREQ ✅ Keep-alive ping
PINGRESP ✅ Ping response
DISCONNECT ✅ Graceful disconnect
Others ❌ QoS 2 handshake, retained messages, etc.

Examples

See the examples/ directory for complete examples:

  • tokio_mqtt_server - Full Tokio-based MQTT broker server
  • rp2040_mqtt_server - Complete MQTT broker for Raspberry Pi Pico W with WiFi

Running the Tokio Example

cd examples/tokio_mqtt_server

cargo run

Running the RP2040 Example

cd examples/rp2040_mqtt_server

# Set your WiFi credentials as environment variables

export WIFI_SSID="YourNetwork"

export WIFI_PASSWORD="YourPassword"

cargo build --release

# Flash to your RP2040 device with probe-rs or elf2uf2-rs

License

MIT