mqtt_broker - Yuneta Simplified

Full MQTT v3.1.1 + v5.0 broker. The protocol engine (C_PROT_MQTT2) is an adaptation of the Mosquitto logic onto Yuneta GClasses, with sessions, subscriptions, retained messages and per-client queues persisted on TreeDB / TimeRanger2.

Architecture¶

The yuno (main.c) composes two services:

C_AUTHZ (service "authz")        <- authentication / authorization
C_MQTT_BROKER (default service)  <- broker: sessions, subscriptions, queues, retained
    per connection:
      C_CHANNEL > C_PROT_MQTT2   <- one MQTT protocol FSM per client connection

mqtt_broker is a citizen yuno: it does not open its own listening socket. MQTT client connections arrive through the node’s public gateway and are delivered to the broker’s __input_side__ as channels; each channel runs a C_PROT_MQTT2 instance. The same C_PROT_MQTT2 gclass also works as an MQTT client (it carries client-side attrs like mqtt_client_id, mqtt_protocol, will/keepalive).

Protocol support¶

MQTT v5.0 (default), v3.1.1 and v3.1 — negotiated per CONNECT.
QoS 0 / 1 / 2, capped per-listener by max_qos.
Retained messages (retain_available), Last Will & Testament (incl. v5 will-delay / message-expiry properties).
Keepalive / PING, clean vs persistent sessions, session expiry interval (v5; also enforced for v3.x via mqtt_session_expiry_interval).
Normal and shared subscriptions ($share).
Flow control: in-flight and queued-message limits, message_size_limit, max_packet_size.

Persistence¶

When mqtt_persistent_db is true (default), the broker keeps state in a TreeDB (treedb_mqtt_broker, schema treedb_schema_mqtt_broker.c) plus TimeRanger2 queues:

clients / sessions / subscriptions — TreeDB nodes.
retained messages — TreeDB topic retained_msgs.
inflight / queued messages — TimeRanger2 queues (per client).

Persistent sessions survive broker restarts; clean_session clients are transient. Set mqtt_persistent_db=0 for an in-memory-only broker.

Configuration¶

C_MQTT_BROKER (the mqtt_broker service):

Attribute	Default	Purpose
`mqtt_persistent_db`	`true`	Persist clients/sessions/subscriptions/queues/retained
`enable_new_clients`	`false`	Auto-create unknown clients on connect
`deny_subscribes`	—	JSON list of topics for which SUBSCRIBE is refused
`mqtt_service`	(yuno_role)	Service name (multi-service)
`mqtt_tenant`	(yuno_name)	Tenant id (multi-tenant)
`use_internal_schema`	`true`	Use the hardcoded TreeDB schema
`on_critical_error`	`2`	`LOG_OPT_EXIT_ZERO` (exit, no auto-restart) on error

Session limits come from C_AUTHZ (e.g. Authz.max_sessions_per_user, default 4 in main.c).

Per-connection limits live on C_PROT_MQTT2 and apply to each client:

Attribute	Default	Purpose
`max_qos`	`2`	Max QoS allowed for connecting clients
`retain_available`	`true`	Allow retained messages (else RETAIN clients are dropped)
`max_inflight_messages`	`20`	Outgoing QoS 1/2 in flight (1 = strict in-order; 0 = unlimited)
`max_inflight_bytes`	`0`	Byte cap on in-flight messages (0 = no limit)
`max_queued_messages`	`1000`	Per-client queue depth above in-flight (0 = unlimited)
`max_queued_bytes`	`0`	Per-client queue byte cap (0 = no limit)
`message_size_limit`	`0`	Max publish payload accepted (0 = MQTT max)
`max_packet_size`	`0`	Max MQTT packet (v5 advertises it; 0 = no limit)

Commands¶

Command	Description
`list-channels`	Input channels of connected devices
`list-sessions`	Active/persistent sessions
`list-queues`	Per-client message queues
`normal-subs` / `shared-subs`	List normal / shared (`$share`) subscribers
`flatten-subs`	Flattened subscriber view
`list-retains` / `remove-retains`	List / remove retained messages (note: `#` shown as `/`)
`clean-queues`	Drop non-persistent, not-in-use sessions and their queues
`authzs`	Authorization help
`help`	Command help

Debugging¶

GClass	Level	Shows
`C_MQTT_BROKER`	`messages` / `messages2`	Broker-level message flow (verbose / icon form)
`C_PROT_MQTT2`	`traffic`	MQTT packets in/out (no payload)
`C_PROT_MQTT2`	`traffic-payload`	Include payload bytes
`C_PROT_MQTT2`	`show-decode`	Decoded packet structure
`C_PROT_MQTT2`	`messages2`	Simplified per-packet trace (icons)

Enable with ycommand command-yuno id=<id> service=__yuno__ command=set-gclass-trace gclass=<G> set=1 level=<L>.