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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.
Host unit tests
Fast, hardware-free unit tests for the fork's pure logic, run on the host with
GoogleTest via PlatformIO's native environment. They cover the extractable
observer/WebConfig logic (validation, preset table, topic templates, key
parsing) — the parts that don't depend on the ESP32, radio, or network stack.
Integration behavior (AsyncTCP transport, WiFi/MQTT, SoftAP) is exercised
separately; see "Local testing without hardware" in MQTT_IMPLEMENTATION.md.
Running
pio test -e native # all suites
pio test -e native -f test_webconfig_keys # a single suite
A green [PASSED] per suite means GoogleTest returned 0 (all assertions
passed). PlatformIO's "0 test cases" line is just its Unity-style counter and
does not reflect the GoogleTest count — run the built binary directly
(.pio/build/native/program) to see the per-assertion breakdown.
Suites
| Suite | Source under test | Covers |
|---|---|---|
test_mqtt_presets |
src/helpers/MQTTPresets.h |
preset lookup; table integrity (unique names, non-empty URLs, JWT-audience invariant, names fit the slot buffer); mqttPresetNeedsSlotCredentials; slot-count constants |
test_observer_validation |
src/helpers/MQTTObserverValidation.h |
IATA (exactly 3 alphanumerics), owner key (64 hex), NTP hostname, and the buffer-fit check behind the #17 length validation — including boundaries and nulls |
test_webconfig_keys |
src/helpers/WebConfigKeys.h |
POST-key allowlist, secret detection, admin-password classification/validation, slot-index bounds, and the short-key out-of-bounds guard (attacker-supplied keys) |
test_topic_template |
src/helpers/MQTTTopicTemplate.h |
{iata}/{device}/{token}/{type} expansion, overflow/NUL-termination, and a buffer-size fuzz |
test_mqtt_topic_router |
src/helpers/MQTTTopicRouter.h |
complete preset/custom topic-routing contract; MeshRank all types except raw; required identifiers; invalid inputs/slots; exact buffer boundaries |
test_mqtt_connection_policy |
src/helpers/MQTTConnectionPolicy.h |
reconnect guard/backoff/stagger and breaker transitions; stable reset; JWT lifetime/renewal policy; exact timing boundaries and 32-bit millis() rollover |
test_mqtt_packet_queue_policy |
src/helpers/MQTTPacketQueuePolicy.h |
queue-full eviction; stale-disconnect flush; adaptive drain limits; bounded QoS0 retries; exact timing boundaries and 32-bit millis() rollover |
test_mqtt_packet_filter |
src/helpers/MQTTPacketFilter.h |
per-slot 0-15 allowlist parsing/formatting, numeric and named spellings; exact bounds; membership; candidate/eligible split and retry-completion policy; pre-queue union gate; default-mask detection |
test_mqtt_runtime_buffer_lifecycle |
src/helpers/MQTTRuntimeBufferLifecycle.h |
idempotent allocation/release; partial-allocation degradation; retry of only missing buffers |
test_mqtt_prefs_codec |
src/helpers/MQTTPrefsStorage.h, src/helpers/MQTTPrefsCodec.h |
binary pre-slot/3-slot/6-slot migration fixtures; v1 header integrity; downgrade preservation; shortest-payload write policy (default filters stay downgrade-readable) |
test_mqtt_prefs_atomic_store |
src/helpers/MQTTPrefsAtomicStore.h |
transactional MQTT writes and legacy /node_prefs handoff; exact short-write detection; begin/finish/rename failure cleanup; original-file preservation |
test_mqtt_payload_builder |
src/helpers/MQTTPayloadBuilder.cpp |
status/packet/raw JSON contracts; optional fields; escaping; RX metrics and path; score handling; exact buffer bounds; maximum representative payloads |
test_utils |
src/Utils.cpp |
Utils::toHex (upstream) |
Conventions (and how to add a suite)
- Each
test/test_<name>/directory builds into its own GoogleTest program and must define its ownmain()(::testing::InitGoogleTest+RUN_ALL_TESTS). - Tests are host-only: include only pure headers. Arduino/crypto stubs live
in
test/mocks/(on the include path via-I test/mocks). - Firmware headers are included from
src(via-I src, e.g.#include "helpers/MQTTPresets.h"). Some are guarded or ESP-flavored, so a suite may need shims before the include — e.g.test_mqtt_presetsdoes#define WITH_MQTT_BRIDGE 1(the preset table is behind that flag) and#define PROGMEM(the embedded CA-cert strings are PROGMEM-qualified). - To add a suite: create
test/test_<name>/test_<name>.cppwith amain(), and add any host-only source it links to thenativeenv'sbuild_src_filterinplatformio.ini(header-only code needs no source entry). No other wiring. - Keep logic testable by extracting pure functions into headers (as
MQTTObserverValidation.h/WebConfigKeys.h/MQTTTopicTemplate.hdo) and having the firmware call the same functions.