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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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49 changes: 40 additions & 9 deletions src/helpers/SimpleMeshTables.h
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Original file line number Diff line number Diff line change
Expand Up @@ -10,34 +10,50 @@

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 _direct_dups, _flood_dups;

public:
SimpleMeshTables() {
SimpleMeshTables() {
memset(_hashes, 0, sizeof(_hashes));
_next_idx = 0;
memset(_last_seen, 0, sizeof(_last_seen));
_direct_dups = _flood_dups = 0;
}

#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 _next_idx, ignore
// 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
}
#endif

bool wasSeen(const mesh::Packet* packet) override {
uint32_t now = millis();
uint8_t hash[MAX_HASH_SIZE];
packet->calculatePacketHash(hash);

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) {
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++;
} else {
Expand All @@ -50,10 +66,24 @@ class SimpleMeshTables : public mesh::MeshTables {
}

void markSeen(const mesh::Packet* packet) override {
uint32_t now = millis();
uint8_t hash[MAX_HASH_SIZE];
packet->calculatePacketHash(hash);
memcpy(&_hashes[_next_idx * MAX_HASH_SIZE], hash, MAX_HASH_SIZE);
_next_idx = (_next_idx + 1) % MAX_PACKET_HASHES;

// Insert into oldest slot (LRU eviction). Empty slots have _last_seen == 0,
// hence maximal age, so they get filled before any real entry is evicted.
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) {
uint32_t age = now - _last_seen[i];
if (age > oldest_age) {
oldest_age = age;
oldest_idx = i;
}
}
memcpy(&_hashes[oldest_idx*MAX_HASH_SIZE], hash, MAX_HASH_SIZE);
_last_seen[oldest_idx] = now;
}

void clear(const mesh::Packet* packet) override {
Expand All @@ -62,8 +92,9 @@ 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