Every ordinary backoff reconnect and every circuit-breaker probe minted a
fresh JWT and re-applied credentials, with no check of whether the existing
token was still valid. setCredentials() always dirties the esp-mqtt config, so
reconnect() then called esp_mqtt_set_config() as well. On a flapping broker
that is a signing plus a configuration-copy cycle on every retry, and these
observers see ~38 genuine reconnects/day per slot.
The no-bounce renewal change (27bd05a1) only stopped the proactive renewal
from tearing down a live session; it left this retry path untouched, which is
why a soak shows renewals neither firing nor failing for hours while drops
continue — each reconnect silently re-mints and pushes the expiry out.
Reuse the credentials when their validity is provable and refresh them
otherwise. canReuseJwtForReconnect() lives with the other policy predicates so
it is host-testable, and it establishes current_time < token_expires_at before
subtracting: token_expires_at is unsigned, so an already-expired token would
otherwise wrap to ~4e9 seconds and read as valid for decades. The
>= kMinimumValidEpoch term also rejects the 0 that a failed renewal writes.
Minting stays the default for every uncertain case — unsynced clock, missing or
insane expiry, empty token, or an expiry inside kJwtReconnectSafetyMarginSecs
(60 s), which covers the handshake itself.
Two paths still always mint, deliberately:
- The circuit-breaker probe. It is the recovery of last resort for a slot
that has already failed repeatedly, quite possibly on auth, and it runs
once per 30 minutes — so a fresh token there costs nothing worth counting
against keeping that path guaranteed-clean.
- Any slot whose last error was a broker refusal. Before this change, minting
on every retry accidentally recovered from server-side credential
invalidation: key rotation, revocation, broker clock skew, or an audience
change after a reconfigure. Reuse would have retried a rejected credential
until it neared expiry — up to 24 h for every preset that leaves
token_lifetime at the default. onError already detects
MQTT_ERROR_TYPE_CONNECTION_REFUSED and only logged it; it now also sets a
per-slot force-mint flag, cleared on a successful connect and wherever the
credentials it referred to are blanked. The flag is volatile because the
esp-mqtt callback sets it and the bridge loop consumes it.
The reconnect log line reports the decision and its outcome — REUSE, MINT with
a reason, and OK/FAILED for the mint — because a silently failed mint is the
case most likely to end in an auth refusal. It never prints the token.
Host tests cover the reuse boundary: exact margin, already-expired, expiry 0,
sub-epoch expiry, empty token, unsynced clock, and the force-mint override.
agessaman
7d74a73839