Embedded MQTT v3.11 / v5.0 broker

[dgarske]

Adds embedded MQTT broker (src/mqtt_broker) supporting v3.1.1/v5.0 clients with optional TLS.

Features

Protocol

• QoS 0/1/2 (full PUBREC/PUBREL/PUBCOMP flow)
• Retained messages
• LWT with v5 Will Delay Interval & Message Expiry
• Wildcard subscriptions (+, #)
• Client ID enforcement & takeover
• Keep-alive monitoring

Security

• TLS 1.2/1.3 via wolfSSL
• Mutual TLS (RSA/ECC)
• Username/password auth

MQTT v5

• CONNACK properties (Retain Available, Max QoS, etc.)
• PUBLISH property forwarding
• Reason codes in UNSUBACK/DISCONNECT
• Multi-topic UNSUBACK compliance

Resource Management

• Static memory mode (WOLFMQTT_STATIC_MEMORY) - zero malloc
• Dynamic mode (linked lists)
• Configurable limits (clients: 8, subs: 32, retained: 16)
• 4KB RX/TX buffers

Logging

• 3 levels (ERROR/INFO/DEBUG), runtime control (-v)
• Compile-time disable (--disable-broker-log)

Build

Autotools:

./configure --enable-broker [--disable-broker-{retained,will,wildcards,auth,log}]
make

[Copilot]

Pull request overview

This pull request implements a simple MQTT v5.0 broker for the wolfMQTT library. The implementation provides a lightweight, embeddable broker that supports both static and dynamic memory allocation, making it suitable for both resource-constrained embedded systems and server environments. The broker includes essential MQTT features such as pub/sub messaging, retained messages, Last Will and Testament (LWT), QoS 0-1 support, client authentication, and optional TLS encryption.

Changes:

• Added complete broker implementation with support for MQTT v3.1.1 and v5.0 protocols
• Exposed packet encoding/decoding functions as public API for broker use via WOLFMQTT_BROKER build option
• Fixed existing bug in MQTT_CONNECT_FLAG_GET_QOS macro (missing & operator)
• Added comprehensive test suite with 14 test cases covering core functionality and TLS support
• Integrated broker into build systems (autotools and CMake) and CI/CD pipeline

Reviewed changes

Copilot reviewed 12 out of 13 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
wolfmqtt/mqtt_types.h	Added XSTRCMP macro for string comparison abstraction
wolfmqtt/mqtt_packet.h	Changed WOLFMQTT_LOCAL to WOLFMQTT_API for broker-needed functions; fixed QoS extraction macro bug; added broker-specific decode/encode API declarations
wolfmqtt/mqtt_broker.h	New header defining broker types (MqttBroker, BrokerClient, BrokerSub, etc.) and public API
src/mqtt_packet.c	Implemented broker-side packet decode/encode functions (Connect, ConnectAck, Subscribe, Unsubscribe, UnsubscribeAck, Disconnect)
src/mqtt_broker.c	Main broker implementation (2371 lines) with client management, subscription handling, retained messages, topic matching, and LWT support
wolfmqtt/include.am	Added mqtt_broker.h to installed headers
src/include.am	Added mqtt_broker binary to build
scripts/include.am	Added broker.test script to distribution
scripts/broker.test	Comprehensive test script with 14 test cases using mosquitto_pub/sub clients
scripts/broker_test/*.pem	Test certificates for TLS testing
configure.ac	Added --enable-broker option; fixed trailing whitespace
CMakeLists.txt	Added WOLFMQTT_BROKER option and broker executable target
.gitignore	Added configure~ and src/mqtt_broker to ignore list
.github/workflows/broker-check.yml	New CI workflow testing broker with 4 configurations (dynamic/static memory, with/without TLS)

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[Copilot]

Pull request overview

Copilot reviewed 16 out of 17 changed files in this pull request and generated 5 comments.

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[embhorn]

Excellent. Couple small build issues I saw.

[embhorn]

This is a great start. I think it's good to publish.