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Implement LRU cache for storing hashes to filter out for flood repeating #1380

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Implement LRU cache for storing hashes to filter out for flood repeating #1380

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5be0979
Implement LRU cache for storing hashes to filter
weebl2000 Jan 12, 2026
91e5322
Stick to actual timestamps and no timeout eviction
weebl2000 Jan 13, 2026
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56 changes: 43 additions & 13 deletions src/helpers/SimpleMeshTables.h
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Original file line number Diff line number Diff line change
Expand Up @@ -11,15 +11,15 @@

class SimpleMeshTables : public mesh::MeshTables {
uint8_t _hashes[MAX_PACKET_HASHES*MAX_HASH_SIZE];
int _next_idx;
uint32_t _last_seen[MAX_PACKET_HASHES]; // timestamp for LRU eviction
uint32_t _acks[MAX_PACKET_ACKS];
int _next_ack_idx;
uint32_t _direct_dups, _flood_dups;

public:
SimpleMeshTables() {
SimpleMeshTables() {
memset(_hashes, 0, sizeof(_hashes));
_next_idx = 0;
memset(_last_seen, 0, sizeof(_last_seen));
memset(_acks, 0, sizeof(_acks));
_next_ack_idx = 0;
_direct_dups = _flood_dups = 0;
Expand All @@ -28,13 +28,26 @@ class SimpleMeshTables : public mesh::MeshTables {
#ifdef ESP32
void restoreFrom(File f) {
f.read(_hashes, sizeof(_hashes));
f.read((uint8_t *) &_next_idx, sizeof(_next_idx));
int dummy_idx;
f.read((uint8_t *) &dummy_idx, sizeof(dummy_idx)); // legacy, ignore
f.read((uint8_t *) &_acks[0], sizeof(_acks));
f.read((uint8_t *) &_next_ack_idx, sizeof(_next_ack_idx));
// Treat restored hashes as just seen - give them fresh timestamps
uint32_t now = millis();
const uint8_t* sp = _hashes;
for (int i = 0; i < MAX_PACKET_HASHES; i++, sp += MAX_HASH_SIZE) {
// Check if slot has data (not all zeros)
bool empty = true;
for (int j = 0; j < MAX_HASH_SIZE && empty; j++) {
if (sp[j] != 0) empty = false;
}
_last_seen[i] = empty ? 0 : now;
}
}
void saveTo(File f) {
f.write(_hashes, sizeof(_hashes));
f.write((const uint8_t *) &_next_idx, sizeof(_next_idx));
int dummy_idx = 0;
f.write((const uint8_t *) &dummy_idx, sizeof(dummy_idx)); // legacy format
f.write((const uint8_t *) &_acks[0], sizeof(_acks));
f.write((const uint8_t *) &_next_ack_idx, sizeof(_next_ack_idx));
}
Expand All @@ -45,7 +58,7 @@ class SimpleMeshTables : public mesh::MeshTables {
uint32_t ack;
memcpy(&ack, packet->payload, 4);
for (int i = 0; i < MAX_PACKET_ACKS; i++) {
if (ack == _acks[i]) {
if (ack == _acks[i]) {
if (packet->isRouteDirect()) {
_direct_dups++; // keep some stats
} else {
Expand All @@ -54,29 +67,45 @@ class SimpleMeshTables : public mesh::MeshTables {
return true;
}
}

_acks[_next_ack_idx] = ack;
_next_ack_idx = (_next_ack_idx + 1) % MAX_PACKET_ACKS; // cyclic table
_next_ack_idx = (_next_ack_idx + 1) % MAX_PACKET_ACKS; // cyclic table
return false;
}

uint32_t now = millis();
uint8_t hash[MAX_HASH_SIZE];
packet->calculatePacketHash(hash);

int oldest_idx = 0;
uint32_t oldest_age = 0;

const uint8_t* sp = _hashes;
for (int i = 0; i < MAX_PACKET_HASHES; i++, sp += MAX_HASH_SIZE) {
if (memcmp(hash, sp, MAX_HASH_SIZE) == 0) {
uint32_t age = now - _last_seen[i];

if (memcmp(hash, sp, MAX_HASH_SIZE) == 0 && _last_seen[i] != 0) {
// Match found - refresh timestamp (LRU touch) and return true
_last_seen[i] = now;
if (packet->isRouteDirect()) {
_direct_dups++; // keep some stats
} else {
_flood_dups++;
}
return true;
}

// Track oldest entry for LRU eviction
if (age > oldest_age) {
oldest_age = age;
oldest_idx = i;
}
}

memcpy(&_hashes[_next_idx*MAX_HASH_SIZE], hash, MAX_HASH_SIZE);
_next_idx = (_next_idx + 1) % MAX_PACKET_HASHES; // cyclic table
// Not found - evict oldest (LRU)
int insert_idx = oldest_idx;
memcpy(&_hashes[insert_idx*MAX_HASH_SIZE], hash, MAX_HASH_SIZE);
_last_seen[insert_idx] = now;
return false;
}

Expand All @@ -85,7 +114,7 @@ class SimpleMeshTables : public mesh::MeshTables {
uint32_t ack;
memcpy(&ack, packet->payload, 4);
for (int i = 0; i < MAX_PACKET_ACKS; i++) {
if (ack == _acks[i]) {
if (ack == _acks[i]) {
_acks[i] = 0;
break;
}
Expand All @@ -96,8 +125,9 @@ class SimpleMeshTables : public mesh::MeshTables {

uint8_t* sp = _hashes;
for (int i = 0; i < MAX_PACKET_HASHES; i++, sp += MAX_HASH_SIZE) {
if (memcmp(hash, sp, MAX_HASH_SIZE) == 0) {
if (memcmp(hash, sp, MAX_HASH_SIZE) == 0) {
memset(sp, 0, MAX_HASH_SIZE);
_last_seen[i] = 0;
break;
}
}
Expand Down