From f0cc4d123c101759e68fe2f2f733240bd773db3d Mon Sep 17 00:00:00 2001
From: "Jokob @NetAlertX" <96159884+jokob-sk@users.noreply.github.com>
Date: Thu, 28 May 2026 05:31:09 +0000
Subject: [PATCH] Enhance carbon-copy behavior to prevent overwriting
 devPresentLastScan in sync operations #1651

---
 front/plugins/sync/sync.py         | 16 +++++++++++++---
 test/db_test_helpers.py            |  3 ++-
 test/plugins/test_sync_protocol.py | 30 ++++++++++++++++++++++++++++++
 3 files changed, 45 insertions(+), 4 deletions(-)

diff --git a/front/plugins/sync/sync.py b/front/plugins/sync/sync.py
index dc464d52..e98de315 100755
--- a/front/plugins/sync/sync.py
+++ b/front/plugins/sync/sync.py
@@ -326,12 +326,22 @@ def main():
                     placeholders = ', '.join('?' for _ in insert_cols)
 
                     if sync_behavior == 'carbon-copy':
-                        # UPSERT: on MAC conflict update all columns except devMac.
+                        # UPSERT: on MAC conflict update all columns except devMac and
+                        # devPresentLastScan.
                         # devMac is the PRIMARY KEY so it is excluded from the SET clause.
-                        # NOTE: this raw SQL bypasses can_overwrite_field() — ALL fields
+                        # devPresentLastScan is excluded to prevent a node's offline report
+                        # from clobbering the hub's own scan result: if a device is online
+                        # on the hub network but offline on a node, the raw UPSERT would
+                        # flip devPresentLastScan = 0 every sync cycle, triggering
+                        # Connected/Disconnected events on each scan and causing the device
+                        # to be flagged as Flapping.  Presence is owned by
+                        # update_presence_from_CurrentScan(); the carbon-copy path respects
+                        # that contract by leaving devPresentLastScan to the normal pipeline.
+                        # NOTE: this raw SQL bypasses can_overwrite_field() — ALL other fields
                         # including USER/LOCKED-sourced ones are overwritten. Node is fully
                         # authoritative in this mode.
-                        update_cols   = [col for col in insert_cols if col != 'devMac']
+                        _CARBON_COPY_SKIP = {'devMac', 'devPresentLastScan'}
+                        update_cols   = [col for col in insert_cols if col not in _CARBON_COPY_SKIP]
                         update_clause = ', '.join(f'{col}=excluded.{col}' for col in update_cols)
                         sql = (
                             f'INSERT INTO Devices ({columns}) VALUES ({placeholders}) '
diff --git a/test/db_test_helpers.py b/test/db_test_helpers.py
index 7af01c4a..c61d2ec9 100644
--- a/test/db_test_helpers.py
+++ b/test/db_test_helpers.py
@@ -351,7 +351,8 @@ def sync_insert_devices(
     placeholders = ", ".join("?" for _ in insert_cols)
 
     if behavior == "carbon-copy":
-        update_cols   = [col for col in insert_cols if col != "devMac"]
+        _CARBON_COPY_SKIP = {"devMac", "devPresentLastScan"}
+        update_cols   = [col for col in insert_cols if col not in _CARBON_COPY_SKIP]
         update_clause = ", ".join(f"{col}=excluded.{col}" for col in update_cols)
         sql = (
             f"INSERT INTO Devices ({columns}) VALUES ({placeholders}) "
diff --git a/test/plugins/test_sync_protocol.py b/test/plugins/test_sync_protocol.py
index 4b5e443e..387cd211 100644
--- a/test/plugins/test_sync_protocol.py
+++ b/test/plugins/test_sync_protocol.py
@@ -668,6 +668,36 @@ class TestSyncBehavior:
         cur.execute("SELECT COUNT(*) AS cnt FROM Devices WHERE devMac = ?", ("aa:bb:cc:dd:ee:01",))
         assert cur.fetchone()["cnt"] == 1
 
+    def test_carbon_copy_does_not_overwrite_devPresentLastScan(self, conn):
+        """Regression: carbon-copy must NOT clobber devPresentLastScan.
+
+        Scenario: device is online on the hub (devPresentLastScan=1) but the
+        node reports it as offline (devPresentLastScan=0).  Without the fix the
+        UPSERT would flip presence to 0, triggering a Device Down event on the
+        next scan cycle and a Connected event on the scan after that, causing
+        the device to accumulate enough churn events to be flagged as Flapping.
+        """
+        cur = conn.cursor()
+        # Hub already knows this device and currently sees it as online.
+        cur.execute(
+            "INSERT INTO Devices (devMac, devName, devPresentLastScan) VALUES (?, ?, ?)",
+            ("aa:bb:cc:dd:ee:01", "HubDevice", 1),
+        )
+        conn.commit()
+
+        # Node reports same MAC as offline.
+        device = make_device_dict(mac="aa:bb:cc:dd:ee:01", devPresentLastScan=0)
+        sync_insert_devices(conn, [device], behavior="carbon-copy")
+
+        cur.execute(
+            "SELECT devPresentLastScan FROM Devices WHERE devMac = ?",
+            ("aa:bb:cc:dd:ee:01",),
+        )
+        row = cur.fetchone()
+        assert row["devPresentLastScan"] == 1, (
+            "carbon-copy must not overwrite devPresentLastScan with a node's offline value"
+        )
+
     # ------------------------------------------------------------------
     # hub-defaults — no direct write, hub pipeline handles it
     # ------------------------------------------------------------------