Request Problem Information (CONNECT 0x17) #1092

Part of the MQTT 5.0 tracking issue #821.

Feature

MQTT 5.0 Request Problem Information — CONNECT property 0x17 (§3.1.2.11.7), default 1.

It gates whether the server may attach a Reason String and/or User Properties to packets other than PUBLISH, CONNACK, and DISCONNECT (i.e. PUBACK/PUBREC/PUBREL/PUBCOMP/SUBACK/UNSUBACK/AUTH). If the client sets it to 0, the server MUST NOT send a Reason String or User Properties on those packets ([MQTT-3.1.2-29]).

Relationship to #823 / #830

This is a gating constraint on:

• Reason string on all ACKs #823 — Reason String on ACKs
• User properties (this should be already handled by mqtt-packet we just have to forward it) #830 — User Properties

It must be honored once either of those is implemented for the affected packet types.

Current status

Benign today: the broker emits neither reasonString nor userProperties on any outbound packet (verified against the mqttv5 branch / PR #1088), so there is currently nothing to suppress and no violation. It becomes a real obligation as soon as #823 / #830 extend Reason String / User Properties to ACKs — at which point those emissions must be gated on this flag. Tracked here so the constraint isn't missed.