NanoMQTT

NanoMQTT is the MQTT client included in TrustCore SDK (beginning with the U6 release). It supports MQTT 3.1.1 and MQTT 5, allowing your application to publish and subscribe over plain TCP (port 1883) or TLS (port 8883) by re-using TrustCore SDK NanoSSL transport.

Note

NanoMQTT is a client. You still need an MQTT broker (for example, DigiCert® Device Trust Manager) for testing and production.

Key features

QoS 0, 1, 2 publish/subscribe with retain flag, wildcard topics, and last-will messages.
MQTT 5 properties on CONNECT, PUBLISH, SUBSCRIBE, UNSUBSCRIBE, WILL, and DISCONNECT packets.
Session control using clean start or a session-expiry interval (0 - 4 294 967 295 s).
Transport flexibility by using plain TCP or TLS through NanoSSL.
Proxy support via the --proxy flag (HTTP or HTTPS forward proxies).

Configurable limits

Table 1. Configurable limits notes

Item	Default	Notes
Topic length	65 535 bytes	MQTT spec limit
Publish QoS level (0 / 1 / 2)	0	Select per message via `--mqtt_pub_qos`
Maximum packet size accepted	Unlimited	Limit with MQTT 5 CONNECT property `max_packet_size`
Receive-maximum (parallel QoS 1/2)	Unlimited	Limit with MQTT 5 CONNECT property `receive_maximum`

Protocol compliance

Table 2. Protocol compliance breakdown

Control-packet family	MQTT 3.1.1	MQTT 5 (extensions)
CONNECT / CONNACK	✔	✔ (reason codes, user properties)
PUBLISH flow (ACK, REC, REL, COMP)	✔	✔
SUBSCRIBE / SUBACK	✔	✔ (retain-handling, retain-as-published, no-local)
UNSUBSCRIBE / UNSUBACK	✔	✔
DISCONNECT	✔	✔ (reason codes, session-expiry)
AUTH	—	✔

Using with other TrustCore SDK modules

Table 3. TrustCore SDK module usage

Component	Usage in NanoMQTT
NanoSSL	Provides TLS record protection. Call `MQTT_setTransportSSL()` with an active NanoSSL connection to secure the session.
NanoCrypto	Supplies hashing and cipher routines — no duplicate crypto code.
Common socket layer	NanoMQTT uses the same non-blocking socket helpers as other TrustCore modules, enabling a single event loop.

Quick start

# Build the sample client (adds TLS support)
./scripts/nanomqtt/mqtt_client/build_mqtt_client.sh --ssl

# Terminal 1 — subscribe (plain TCP, port 1883)
./bin/mqtt_client_sample \
--mqtt_servername broker.hivemq.com \
--mqtt_port 1883 \
--mqtt_sub_topic demo/led \
--mqtt_clean_start

# Terminal 2 — publish (TLS, port 8883)
./bin/mqtt_client_sample \
--mqtt_servername broker.hivemq.com \
--mqtt_port 8883 \
--mqtt_transport SSL \
--ssl_ca_file /etc/ssl/certs/ca-bundle.crt \
--mqtt_pub_topic demo/led \
--mqtt_pub_message "ON" \
--mqtt_clean_start

The subscriber prints:

demo/led  ON

Tip

During early tests you can add --ssl_allow_untrusted to skip certificate validation. Do not use this flag in production.

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