Refactor timestamp handling in MQTTMessageBuilder

- Introduced a new method `formatIsoTimestampForMqtt` to centralize ISO-like timestamp formatting for MQTT messages, applying timezone preferences.
- Updated `buildStatusMessage`, `buildPacketJSON`, `buildPacketJSONFromRaw`, and `buildRawJSON` methods to utilize the new timestamp formatting function, improving code clarity and reducing redundancy.
- Adjusted `publishStatusToSlot` and `publishStatus` in MQTTBridge to use the new timestamp formatting method, ensuring consistent timestamp handling across status messages.

src/helpers/MQTTMessageBuilder.cpp

@@ -1,9 +1,21 @@
 #include "MQTTMessageBuilder.h"
 #include <ArduinoJson.h>
+#include <cstring>
 #include <time.h>
 #include <Timezone.h>
 #include "MeshCore.h"
 
+void MQTTMessageBuilder::formatIsoTimestampForMqtt(time_t now, Timezone* timezone, char* buffer, size_t buffer_size) {
+  if (!buffer || buffer_size == 0) return;
+  time_t local_wall = timezone ? timezone->toLocal(now) : now;
+  struct tm* tm_info = localtime(&local_wall);
+  if (tm_info && strftime(buffer, buffer_size, "%Y-%m-%dT%H:%M:%S.000000", tm_info) > 0) {
+    return;
+  }
+  strncpy(buffer, "2024-01-01T12:00:00.000000", buffer_size - 1);
+  buffer[buffer_size - 1] = '\0';
+}
+
 int MQTTMessageBuilder::buildStatusMessage(
   JsonDocument& doc,
   const char* origin,
@@ -182,22 +194,11 @@ int MQTTMessageBuilder::buildPacketJSON(
 ) {
   if (!packet) return 0;
   
-  // Get current device time (should be UTC since system timezone is set to UTC)
   time_t now = time(nullptr);
-  
-  // Convert to local time using timezone library (for timestamp field only)
-  time_t local_time = timezone ? timezone->toLocal(now) : now;
-  struct tm* local_timeinfo = localtime(&local_time);
-  
-  // Format timestamp in ISO 8601 format (LOCAL TIME)
   char timestamp[32];
-  if (local_timeinfo) {
-    strftime(timestamp, sizeof(timestamp), "%Y-%m-%dT%H:%M:%S.000000", local_timeinfo);
-  } else {
-    strcpy(timestamp, "2024-01-01T12:00:00.000000");
-  }
+  formatIsoTimestampForMqtt(now, timezone, timestamp, sizeof(timestamp));
   
-  // Get UTC time (since system timezone is UTC, time() returns UTC)
+  // Packet time/date: UTC (gmtime), same family as meshcoretomqtt serial fields
   struct tm* utc_timeinfo = gmtime(&now);
   
   // Format time and date (ALWAYS UTC)
@@ -266,22 +267,10 @@ int MQTTMessageBuilder::buildPacketJSONFromRaw(
 ) {
   if (!packet || !raw_data || raw_len <= 0) return 0;
   
-  // Get current device time (should be UTC since system timezone is set to UTC)
   time_t now = time(nullptr);
-  
-  // Convert to local time using timezone library (for timestamp field only)
-  time_t local_time = timezone ? timezone->toLocal(now) : now;
-  struct tm* local_timeinfo = localtime(&local_time);
-  
-  // Format timestamp in ISO 8601 format (LOCAL TIME)
   char timestamp[32];
-  if (local_timeinfo) {
-    strftime(timestamp, sizeof(timestamp), "%Y-%m-%dT%H:%M:%S.000000", local_timeinfo);
-  } else {
-    strcpy(timestamp, "2024-01-01T12:00:00.000000");
-  }
+  formatIsoTimestampForMqtt(now, timezone, timestamp, sizeof(timestamp));
   
-  // Get UTC time (since system timezone is UTC, time() returns UTC)
   struct tm* utc_timeinfo = gmtime(&now);
   
   // Format time and date (ALWAYS UTC)
@@ -344,20 +333,9 @@ int MQTTMessageBuilder::buildRawJSON(
 ) {
   if (!packet) return 0;
   
-  // Get current device time
   time_t now = time(nullptr);
-  
-  // Convert to local time using timezone library
-  time_t local_time = timezone ? timezone->toLocal(now) : now;
-  struct tm* timeinfo = localtime(&local_time);
-  
-  // Format timestamp in ISO 8601 format
   char timestamp[32];
-  if (timeinfo) {
-    strftime(timestamp, sizeof(timestamp), "%Y-%m-%dT%H:%M:%S.000000", timeinfo);
-  } else {
-    strcpy(timestamp, "2024-01-01T12:00:00.000000");
-  }
+  formatIsoTimestampForMqtt(now, timezone, timestamp, sizeof(timestamp));
   
   // Convert packet to hex
   // MAX_TRANS_UNIT is 255, so max hex size is 510 chars + null = 511 bytes

src/helpers/MQTTMessageBuilder.h

@@ -11,12 +11,24 @@
  * This class handles the formatting of mesh packets and device status
  * into JSON messages for MQTT publishing according to the MeshCore
  * packet capture specification.
+ *
+ * Timestamps in JSON use the configured Timezone (prefs) for status, packet, and
+ * raw topics. Packet payloads also include separate `time` and `date` strings in
+ * UTC (gmtime) so they stay aligned with meshcoretomqtt serial regex fields.
  */
 class MQTTMessageBuilder {
 private:
   static const int JSON_BUFFER_SIZE = 1024;
   
 public:
+  /**
+   * Format the MQTT JSON `timestamp` field (same rule for status, packet, raw).
+   * Applies Timezone prefs via `timezone->toLocal(now)`; if timezone is nullptr,
+   * uses `now` unchanged. Output is naive local wall time, ISO-like
+   * "%Y-%m-%dT%H:%M:%S.000000".
+   */
+  static void formatIsoTimestampForMqtt(time_t now, Timezone* timezone, char* buffer, size_t buffer_size);
+
   /**
    * Build status message JSON
    *
@@ -27,7 +39,7 @@ public:
    * @param radio Radio information
    * @param client_version Client version
    * @param status Connection status ("online" or "offline")
-   * @param timestamp ISO 8601 timestamp
+   * @param timestamp ISO-like timestamp (see formatIsoTimestampForMqtt)
    * @param buffer Output buffer for JSON string
    * @param buffer_size Size of output buffer
    * @param battery_mv Battery voltage in millivolts (optional, -1 to omit)
@@ -71,10 +83,10 @@ public:
    *
    * @param origin Device name
    * @param origin_id Device public key (hex string)
-   * @param timestamp ISO 8601 timestamp
+   * @param timestamp ISO-like timestamp (see formatIsoTimestampForMqtt)
    * @param direction Packet direction ("rx" or "tx")
-   * @param time Time in HH:MM:SS format
-   * @param date Date in DD/MM/YYYY format
+   * @param time Time in HH:MM:SS (UTC, gmtime; meshcoretomqtt serial parity)
+   * @param date Date in DD/MM/YYYY (UTC, gmtime)
    * @param len Total packet length
    * @param packet_type Packet type code
    * @param route Routing type
@@ -114,7 +126,7 @@ public:
    *
    * @param origin Device name
    * @param origin_id Device public key (hex string)
-   * @param timestamp ISO 8601 timestamp
+   * @param timestamp ISO-like timestamp (see formatIsoTimestampForMqtt)
    * @param raw Raw packet data (hex string)
    * @param buffer Output buffer for JSON string
    * @param buffer_size Size of output buffer

src/helpers/bridges/MQTTBridge.cpp

@@ -4,6 +4,7 @@
 #include <NTPClient.h>
 #include <WiFiUdp.h>
 #include <Timezone.h>
+#include <time.h>
 
 #ifdef WITH_SNMP
 #include "../SNMPAgent.h"
@@ -1676,13 +1677,9 @@ void MQTTBridge::publishStatusToSlot(int index) {
   char timestamp[32];
   char radio_info[64];
 
-  // Get current timestamp in ISO 8601 format
-  struct tm timeinfo;
-  if (getLocalTime(&timeinfo)) {
-    strftime(timestamp, sizeof(timestamp), "%Y-%m-%dT%H:%M:%S.000000", &timeinfo);
-  } else {
-    strcpy(timestamp, "2024-01-01T12:00:00.000000");
-  }
+  // Status timestamp: same prefs-based wall clock as packet/raw JSON `timestamp`
+  // (not libc getLocalTime — SNTP uses UTC offset 0; prefs Timezone is separate).
+  MQTTMessageBuilder::formatIsoTimestampForMqtt(time(nullptr), _timezone, timestamp, sizeof(timestamp));
 
   snprintf(radio_info, sizeof(radio_info), "%.6f,%.1f,%d,%d",
            _prefs->freq, _prefs->bw, _prefs->sf, _prefs->cr);
@@ -2370,13 +2367,9 @@ bool MQTTBridge::publishStatus() {
   char timestamp[32];
   char radio_info[64];
 
-  // Get current timestamp in ISO 8601 format
-  struct tm timeinfo;
-  if (getLocalTime(&timeinfo)) {
-    strftime(timestamp, sizeof(timestamp), "%Y-%m-%dT%H:%M:%S.000000", &timeinfo);
-  } else {
-    strcpy(timestamp, "2024-01-01T12:00:00.000000");
-  }
+  // Status timestamp: same prefs-based wall clock as packet/raw JSON `timestamp`
+  // (not libc getLocalTime — SNTP uses UTC offset 0; prefs Timezone is separate).
+  MQTTMessageBuilder::formatIsoTimestampForMqtt(time(nullptr), _timezone, timestamp, sizeof(timestamp));
 
   snprintf(radio_info, sizeof(radio_info), "%.6f,%.1f,%d,%d",
            _prefs->freq, _prefs->bw, _prefs->sf, _prefs->cr);