Compact flood filter persistence

examples/simple_repeater/MyMesh.cpp

@@ -5001,7 +5001,8 @@ bool MyMesh::loadFloodPacketFilters() {
   bool version_7 = success && memcmp(magic, "FPF7", sizeof(magic)) == 0;
   success = (version_6 || version_7)
       && file.read(&count, sizeof(count)) == sizeof(count)
-      && count <= FLOOD_PACKET_FILTER_SLOTS;
+      && FloodFilterPolicy::forwardPersistenceCountSupported(
+          count, FLOOD_PACKET_FILTER_SLOTS);
 
   for (int i = 0; success && i < count; i++) {
     uint8_t active = 0;
@@ -5762,14 +5763,13 @@ bool MyMesh::saveFloodPacketFilters(bool empty_scope_phase,
   };
 
   const uint8_t magic[4] = {'F', 'P', 'F', '7'};
-  uint8_t count = FLOOD_PACKET_FILTER_SLOTS;
+  const uint8_t count = FloodFilterPolicy::forwardPersistenceCount(
+      flood_packet_filters, FLOOD_PACKET_FILTER_SLOTS,
+      empty_forward_phase);
   bool success = writeExact(magic, sizeof(magic))
       && writeExact(&count, sizeof(count));
-  FloodPacketFilterEntry empty_entry;
-  memset(&empty_entry, 0, sizeof(empty_entry));
-  for (int i = 0; success && i < FLOOD_PACKET_FILTER_SLOTS; i++) {
-    const auto& entry = empty_forward_phase
-        ? empty_entry : flood_packet_filters[i];
+  for (int i = 0; success && i < count; i++) {
+    const auto& entry = flood_packet_filters[i];
     uint8_t active = entry.active ? 1 : 0;
     uint8_t suspend_on_temp_radio = entry.suspend_on_temp_radio ? 1 : 0;
     uint8_t match_blacklisted_path = entry.match_blacklisted_path ? 1 : 0;

src/helpers/FloodFilterPolicy.h

@@ -40,6 +40,25 @@ enum ChannelScopeGate {
   CHANNEL_SCOPE_REQUIRED_REJECTED,
 };
 
+// Persist only through the highest occupied forward-rule slot.  The on-disk
+// formats are dense, so inactive holes before that slot must remain present,
+// while the usually-large inactive tail need not consume LittleFS space.
+// `empty_forward_phase` deliberately wins over the live table for atomic
+// phase-clearing transactions.
+template<typename Entry>
+inline uint8_t forwardPersistenceCount(const Entry entries[],
+                                       uint8_t slot_count,
+                                       bool empty_forward_phase) {
+  if (empty_forward_phase || entries == NULL) return 0;
+  while (slot_count > 0 && !entries[slot_count - 1].active) slot_count--;
+  return slot_count;
+}
+
+inline bool forwardPersistenceCountSupported(uint8_t count,
+                                             uint8_t slot_count) {
+  return count <= slot_count;
+}
+
 inline ChannelScopeGate channelScopeGate(bool table_active,
                                          bool is_group_channel_packet,
                                          bool channel_requires_scope,

test/test_flood_filter_policy/test_flood_filter_policy.cpp

@@ -3,6 +3,41 @@
 #include <helpers/FloodFilterPolicy.h>
 #include <helpers/RegionNameUtils.h>
 
+struct FloodPersistenceRow {
+  bool active;
+};
+
+TEST(FloodFilterPersistence, DefaultRowsTrimTheInactiveTail) {
+  FloodPersistenceRow rows[63] = {};
+  rows[0].active = true;
+  rows[1].active = true;
+
+  EXPECT_EQ(2, FloodFilterPolicy::forwardPersistenceCount(
+                   rows, 63, false));
+}
+
+TEST(FloodFilterPersistence, SparseHighSlotPreservesEveryEarlierPosition) {
+  FloodPersistenceRow rows[63] = {};
+  rows[0].active = true;
+  rows[47].active = true;
+
+  EXPECT_EQ(48, FloodFilterPolicy::forwardPersistenceCount(
+                    rows, 63, false));
+}
+
+TEST(FloodFilterPersistence, EmptyForwardPhaseSerializesNoRows) {
+  FloodPersistenceRow rows[63] = {};
+  rows[62].active = true;
+
+  EXPECT_EQ(0, FloodFilterPolicy::forwardPersistenceCount(
+                   rows, 63, true));
+}
+
+TEST(FloodFilterPersistence, OldFullCountRemainsLoadCompatible) {
+  EXPECT_TRUE(FloodFilterPolicy::forwardPersistenceCountSupported(63, 63));
+  EXPECT_FALSE(FloodFilterPolicy::forwardPersistenceCountSupported(64, 63));
+}
+
 static mesh::Packet makeFloodPacket(uint8_t hash_size,
                                     const uint8_t* path,
                                     uint8_t path_hops) {