initial bloom filter to optimize mesh

src/mesh/CoverageFilter.cpp

@@ -0,0 +1,95 @@
+#include "CoverageFilter.h"
+
+#include <functional> // std::hash
+
+CoverageFilter::CoverageFilter()
+{
+    bits_.fill(0);
+}
+
+void CoverageFilter::add(NodeNum item)
+{
+    // For k=2, we just do two separate hash functions.
+    size_t idx1 = hash1(item);
+    size_t idx2 = hash2(item);
+
+    setBit(idx1);
+    setBit(idx2);
+}
+
+bool CoverageFilter::check(NodeNum item) const
+{
+    // Check both hash positions. If either bit is 0, item is definitely not in.
+    size_t idx1 = hash1(item);
+    if (!testBit(idx1))
+        return false;
+
+    size_t idx2 = hash2(item);
+    if (!testBit(idx2))
+        return false;
+
+    // Otherwise, it might be in (false positive possible).
+    return true;
+}
+
+void CoverageFilter::merge(const CoverageFilter &other)
+{
+    // Bitwise OR the bits.
+    for (size_t i = 0; i < BLOOM_FILTER_SIZE_BYTES; i++) {
+        bits_[i] |= other.bits_[i];
+    }
+}
+
+void CoverageFilter::clear()
+{
+    bits_.fill(0);
+}
+
+// ------------------------
+// Private / Helper Methods
+// ------------------------
+
+void CoverageFilter::setBit(size_t index)
+{
+    if (index >= BLOOM_FILTER_SIZE_BITS)
+        return; // out-of-range check
+    size_t byteIndex = index / 8;
+    uint8_t bitMask = 1 << (index % 8);
+    bits_[byteIndex] |= bitMask;
+}
+
+bool CoverageFilter::testBit(size_t index) const
+{
+    if (index >= BLOOM_FILTER_SIZE_BITS)
+        return false;
+    size_t byteIndex = index / 8;
+    uint8_t bitMask = 1 << (index % 8);
+    return (bits_[byteIndex] & bitMask) != 0;
+}
+
+/**
+ * Very simplistic hash: combine item with a seed and use std::hash
+ */
+size_t CoverageFilter::hash1(NodeNum value)
+{
+    static const uint64_t seed1 = 0xDEADBEEF;
+    uint64_t combined = value ^ (seed1 + (value << 6) + (value >> 2));
+
+    // Use standard library hash on that combined value
+    std::hash<uint64_t> hasher;
+    uint64_t hashOut = hasher(combined);
+
+    // Map to [0..127]
+    return static_cast<size_t>(hashOut % BLOOM_FILTER_SIZE_BITS);
+}
+
+size_t CoverageFilter::hash2(NodeNum value)
+{
+    static const uint64_t seed2 = 0xBADC0FFE;
+    uint64_t combined = value ^ (seed2 + (value << 5) + (value >> 3));
+
+    std::hash<uint64_t> hasher;
+    uint64_t hashOut = hasher(combined);
+
+    return static_cast<size_t>(hashOut % BLOOM_FILTER_SIZE_BITS);
+}

src/mesh/CoverageFilter.h

@@ -0,0 +1,71 @@
+#include "MeshTypes.h"
+#include <array>
+#include <cstddef>
+#include <cstdint>
+
+/**
+ * CoverageFilter:
+ * A simplified Bloom filter container designed to store coverage information,
+ * such as which node IDs are "probably covered" by a packet or route.
+ *
+ * Here is the worst case False Postiive Rate based on the constraints defined.
+ * False Positive Rate = (1-e^(-kn/m))^k
+ * False Positive Rate:  k=2 (2 hash functions, 2 bits flipped), n=60 (20 nodes per hop), m=128 bits
+ * False Positive Rate = 37%
+ */
+class CoverageFilter
+{
+  public:
+    /**
+     * Default constructor: Initialize the bit array to all zeros.
+     */
+    CoverageFilter();
+
+    /**
+     * Insert an item (e.g., nodeID) into the bloom filter.
+     * This sets multiple bits (in this example, 2).
+     * @param item: A node identifier to add to the filter.
+     */
+    void add(NodeNum item);
+
+    /**
+     * Check if the item might be in the bloom filter.
+     * Returns true if likely present; false if definitely not present.
+     * (False positives possible, false negatives are not.)
+     */
+    bool check(NodeNum item) const;
+
+    /**
+     * Merge (bitwise OR) another CoverageFilter into this one.
+     * i.e., this->bits = this->bits OR other.bits
+     */
+    void merge(const CoverageFilter &other);
+
+    /**
+     * Clear all bits (optional utility).
+     * This makes the filter empty again (no items).
+     */
+    void clear();
+
+    /**
+     * Access the underlying bits array for reading/writing,
+     * e.g., if you want to store it in a packet header or Protobuf.
+     */
+    const std::array<uint8_t, BLOOM_FILTER_SIZE_BYTES> &getBits() const { return bits_; }
+    void setBits(const std::array<uint8_t, BLOOM_FILTER_SIZE_BYTES> &newBits) { bits_ = newBits; }
+
+  private:
+    // The underlying bit array: 128 bits => 16 bytes
+    std::array<uint8_t, BLOOM_FILTER_SIZE_BYTES> bits_;
+
+    // Helper to set a bit at a given index [0..127].
+    void setBit(size_t index);
+
+    // Helper to check if a bit is set.
+    bool testBit(size_t index) const;
+
+    // Two example hash functions for demonstration.
+    // TODO: consider MurmurHash, xxHash, etc.
+    static size_t hash1(NodeNum value);
+    static size_t hash2(NodeNum value);
+};

src/mesh/FloodingRouter.cpp

@@ -58,23 +58,39 @@ bool FloodingRouter::perhapsRebroadcast(const meshtastic_MeshPacket *p)
     if (!isToUs(p) && (p->hop_limit > 0) && !isFromUs(p)) {
         if (p->id != 0) {
             if (isRebroadcaster()) {
-                meshtastic_MeshPacket *tosend = packetPool.allocCopy(*p); // keep a copy because we will be sending it
+                CoverageFilter incomingCoverage;
+                loadCoverageFilterFromPacket(p, incomingCoverage);
 
-                tosend->hop_limit--; // bump down the hop count
+                float forwardProb = calculateForwardProbability(incomingCoverage);
+
+                float rnd = static_cast<float>(rand()) / static_cast<float>(RAND_MAX);
+                if (rnd <= forwardProb) {
+
+                    meshtastic_MeshPacket *tosend = packetPool.allocCopy(*p); // keep a copy because we will be sending it
+
+                    tosend->hop_limit--; // bump down the hop count
 #if USERPREFS_EVENT_MODE
-                if (tosend->hop_limit > 2) {
-                    // if we are "correcting" the hop_limit, "correct" the hop_start by the same amount to preserve hops away.
-                    tosend->hop_start -= (tosend->hop_limit - 2);
-                    tosend->hop_limit = 2;
-                }
+                    if (tosend->hop_limit > 2) {
+                        // if we are "correcting" the hop_limit, "correct" the hop_start by the same amount to preserve hops away.
+                        tosend->hop_start -= (tosend->hop_limit - 2);
+                        tosend->hop_limit = 2;
+                    }
 #endif
 
-                LOG_INFO("Rebroadcast received floodmsg");
-                // Note: we are careful to resend using the original senders node id
-                // We are careful not to call our hooked version of send() - because we don't want to check this again
-                Router::send(tosend);
+                    LOG_INFO("Rebroadcasting packet ID=0x%x with ForwardProb=%.2f", p->id, forwardProb);
 
-                return true;
+                    CoverageFilter updatedCoverage = incomingCoverage;
+                    mergeMyCoverage(updatedCoverage);
+                    storeCoverageFilterInPacket(updatedCoverage, tosend);
+
+                    // Note: we are careful to resend using the original senders node id
+                    // We are careful not to call our hooked version of send() - because we don't want to check this again
+                    Router::send(tosend);
+
+                    return true;
+                } else {
+                    LOG_DEBUG("No rebroadcast: Random number %f > Forward Probability %f", rnd, forwardProb);
+                }
             } else {
                 LOG_DEBUG("No rebroadcast: Role = CLIENT_MUTE or Rebroadcast Mode = NONE");
             }
@@ -99,4 +115,62 @@ void FloodingRouter::sniffReceived(const meshtastic_MeshPacket *p, const meshtas
 
     // handle the packet as normal
     Router::sniffReceived(p, c);
+}
+
+void FloodingRouter::loadCoverageFilterFromPacket(const meshtastic_MeshPacket *p, CoverageFilter &filter)
+{
+    // If packet has coverage bytes (16 bytes), copy them into filter
+    // e.g. p->coverage_filter is a 16-byte array in your packet struct
+    std::array<uint8_t, BLOOM_FILTER_SIZE_BYTES> bits;
+    memcpy(bits.data(), p->coverage_filter.bytes, BLOOM_FILTER_SIZE_BYTES);
+    filter.setBits(bits);
+}
+
+void FloodingRouter::storeCoverageFilterInPacket(const CoverageFilter &filter, meshtastic_MeshPacket *p)
+{
+    auto bits = filter.getBits();
+    memcpy(p->coverage_filter.bytes, bits.data(), BLOOM_FILTER_SIZE_BYTES);
+}
+
+void FloodingRouter::mergeMyCoverage(CoverageFilter &coverage)
+{
+    // Retrieve recent direct neighbors within the time window
+    std::vector<NodeNum> recentNeighbors = nodeDB->getDistinctRecentDirectNeighborIds(RECENCY_THRESHOLD_MINUTES * 60);
+    for (auto &nodeId : recentNeighbors) {
+        coverage.add(nodeId);
+    }
+}
+
+float FloodingRouter::calculateForwardProbability(const CoverageFilter &incoming)
+{
+    // Retrieve recent direct neighbors within the time window
+    std::vector<NodeNum> recentNeighbors = nodeDB->getDistinctRecentDirectNeighborIds(RECENCY_THRESHOLD_MINUTES * 60);
+
+    if (recentNeighbors.empty()) {
+        // No neighbors to add coverage for
+        LOG_DEBUG("No recent direct neighbors to add coverage for.");
+        return 0.0f;
+    }
+
+    // Count how many neighbors are NOT yet in the coverage
+    int uncovered = 0;
+    for (auto nodeId : recentNeighbors) {
+        if (!incoming.check(nodeId)) {
+            uncovered++;
+        }
+    }
+
+    // Calculate coverage ratio
+    float coverageRatio = static_cast<float>(uncovered) / static_cast<float>(recentNeighbors.size());
+
+    // Calculate forwarding probability
+    float forwardProb = BASE_FORWARD_PROB + (coverageRatio * COVERAGE_SCALE_FACTOR);
+
+    // Clamp probability between 0 and 1
+    forwardProb = std::min(std::max(forwardProb, 0.0f), 1.0f);
+
+    LOG_DEBUG("CoverageRatio=%.2f, ForwardProb=%.2f (Uncovered=%d, Total=%zu)", coverageRatio, forwardProb, uncovered,
+              recentNeighbors.size());
+
+    return forwardProb;
 }

src/mesh/FloodingRouter.h

@@ -1,5 +1,6 @@
 #pragma once
 
+#include "CoverageFilter.h"
 #include "PacketHistory.h"
 #include "Router.h"
 
@@ -35,6 +36,14 @@ class FloodingRouter : public Router, protected PacketHistory
      * @return true if rebroadcasted */
     bool perhapsRebroadcast(const meshtastic_MeshPacket *p);
 
+    void loadCoverageFilterFromPacket(const meshtastic_MeshPacket *p, CoverageFilter &filter);
+
+    void storeCoverageFilterInPacket(const CoverageFilter &filter, meshtastic_MeshPacket *p);
+
+    void mergeMyCoverage(CoverageFilter &coverage);
+
+    float calculateForwardProbability(const CoverageFilter &incoming);
+
   public:
     /**
      * Constructor

src/mesh/MeshTypes.h

@@ -40,6 +40,27 @@ enum RxSource {
 /// We normally just use max 3 hops for sending reliable messages
 #define HOP_RELIABLE 3
 
+// Maximum number of neighbors a node adds to the Bloom filter per hop
+#define MAX_NEIGHBORS_PER_HOP 20
+
+// Size of the Bloom filter in bytes (128 bits)
+#define BLOOM_FILTER_SIZE_BYTES 16
+
+// Size of the Bloom filter in bits (128 bits)
+#define BLOOM_FILTER_SIZE_BITS (BLOOM_FILTER_SIZE_BYTES * 8)
+
+// Number of hash functions to use in the Bloom filter
+#define NUM_HASH_FUNCTIONS 2
+
+// Base forwarding probability - never drop below this value
+#define BASE_FORWARD_PROB 0.1f
+
+// Coverage scaling factor
+#define COVERAGE_SCALE_FACTOR 0.9f
+
+// Recency threshold in minutes
+#define RECENCY_THRESHOLD_MINUTES 5
+
 typedef int ErrorCode;
 
 /// Alloc and free packets to our global, ISR safe pool

src/mesh/NodeDB.cpp

@@ -807,6 +807,82 @@ void NodeDB::clearLocalPosition()
     setLocalPosition(meshtastic_Position_init_default);
 }
 
+/**
+ * @brief Retrieves a list of distinct recent direct neighbor NodeNums.
+ *
+ * Filters out:
+ * - The local node itself.
+ * - Ignored nodes.
+ * - Nodes not within the direct neighbor (hops_away == 0).
+ * - Nodes heard via MQTT.
+ * - Nodes not heard within the specified time window.
+ *
+ * @param timeWindowSecs The time window in seconds to consider a node as "recently heard."
+ * @return std::vector<NodeNum> A vector containing the NodeNums of recent direct neighbors.
+ */
+std::vector<NodeNum> NodeDB::getDistinctRecentDirectNeighborIds(uint32_t timeWindowSecs)
+{
+    uint32_t now = getTime();
+    NodeNum localNode = getNodeNum();
+
+    // Temporary vector to hold neighbors with their SNR for sorting
+    std::vector<std::pair<NodeNum, float>> neighborsWithSnr;
+    neighborsWithSnr.reserve(MAX_NEIGHBORS_PER_HOP); // Reserve space to avoid multiple reallocations
+
+    for (size_t i = 0; i < numMeshNodes; ++i) {
+        const meshtastic_NodeInfoLite &node = meshNodes->at(i);
+
+        // Skip our own node entry
+        if (node.num == localNode) {
+            continue;
+        }
+
+        // Skip ignored nodes
+        if (node.is_ignored) {
+            continue;
+        }
+
+        // Check if this node is a direct neighbor (hops_away == 0)
+        if (!node.has_hops_away || node.hops_away != 0) {
+            continue;
+        }
+
+        // Skip nodes heard via MQTT
+        if (node.via_mqtt) {
+            continue;
+        }
+
+        // Check if the node was heard recently within the time window
+        if (node.last_heard > 0 && (now - node.last_heard <= timeWindowSecs)) {
+            neighborsWithSnr.emplace_back(node.num, node.snr);
+        }
+    }
+
+    LOG_DEBUG("Found %zu candidates before limiting.", neighborsWithSnr.size());
+
+    // If the number of candidates exceeds MAX_NEIGHBORS_PER_HOP, select the top N based on SNR
+    if (neighborsWithSnr.size() > MAX_NEIGHBORS_PER_HOP) {
+        // Use nth_element to partially sort the vector, bringing the top N SNRs to the front
+        std::nth_element(neighborsWithSnr.begin(), neighborsWithSnr.begin() + MAX_NEIGHBORS_PER_HOP, neighborsWithSnr.end(),
+                         [](const std::pair<NodeNum, float> &a, const std::pair<NodeNum, float> &b) {
+                             return a.second > b.second; // Sort in descending order of SNR
+                         });
+
+        // Resize to keep only the top N neighbors
+        neighborsWithSnr.resize(MAX_NEIGHBORS_PER_HOP);
+    }
+
+    // Extract NodeNums from the sorted and limited list
+    std::vector<NodeNum> recentNeighbors;
+    recentNeighbors.reserve(neighborsWithSnr.size());
+    for (const auto &pair : neighborsWithSnr) {
+        recentNeighbors.push_back(pair.first);
+    }
+
+    LOG_DEBUG("Returning %zu recent direct neighbors within %u seconds.", recentNeighbors.size(), timeWindowSecs);
+    return recentNeighbors;
+}
+
 void NodeDB::cleanupMeshDB()
 {
     int newPos = 0, removed = 0;
@@ -1500,4 +1576,4 @@ void recordCriticalError(meshtastic_CriticalErrorCode code, uint32_t address, co
     LOG_ERROR("A critical failure occurred, portduino is exiting");
     exit(2);
 #endif
-}
+}

src/mesh/NodeDB.h

@@ -167,6 +167,14 @@ class NodeDB
 
     bool hasValidPosition(const meshtastic_NodeInfoLite *n);
 
+    /**
+     * @brief Retrieves a list of distinct recent direct neighbor NodeNums.
+     *
+     * @param timeWindowSecs The time window in seconds to consider a node as "recently heard."
+     * @return std::vector<NodeNum> A vector containing the NodeNums of recent direct neighbors.
+     */
+    std::vector<NodeNum> getDistinctRecentDirectNeighborIds(uint32_t timeWindowSecs);
+
   private:
     uint32_t lastNodeDbSave = 0; // when we last saved our db to flash
     /// Find a node in our DB, create an empty NodeInfoLite if missing

src/mesh/RadioInterface.h

@@ -10,7 +10,7 @@
 #define MAX_TX_QUEUE 16 // max number of packets which can be waiting for transmission
 
 #define MAX_LORA_PAYLOAD_LEN 255 // max length of 255 per Semtech's datasheets on SX12xx
-#define MESHTASTIC_HEADER_LENGTH 16
+#define MESHTASTIC_HEADER_LENGTH 32
 #define MESHTASTIC_PKC_OVERHEAD 12
 
 #define PACKET_FLAGS_HOP_LIMIT_MASK 0x07
@@ -43,6 +43,9 @@ typedef struct {
 
     // ***For future use*** Last byte of the NodeNum of the node that will relay/relayed this packet
     uint8_t relay_node;
+
+    // A 16-byte Bloom filter that tracks coverage of the current node.
+    std::array<uint8_t, BLOOM_FILTER_SIZE_BYTES> coverage_filter;
 } PacketHeader;
 
 /**

src/mesh/generated/meshtastic/mesh.pb.h

@@ -690,6 +690,7 @@ typedef struct _meshtastic_MqttClientProxyMessage {
 
 typedef PB_BYTES_ARRAY_T(256) meshtastic_MeshPacket_encrypted_t;
 typedef PB_BYTES_ARRAY_T(32) meshtastic_MeshPacket_public_key_t;
+typedef PB_BYTES_ARRAY_T(16) meshtastic_MeshPacket_coverage_filter_t;
 /* A packet envelope sent/received over the mesh
  only payload_variant is sent in the payload portion of the LORA packet.
  The other fields are either not sent at all, or sent in the special 16 byte LORA header. */
@@ -770,6 +771,8 @@ typedef struct _meshtastic_MeshPacket {
     /* Last byte of the node number of the node that will relay/relayed this packet.
  Set by the firmware internally, clients are not supposed to set this. */
     uint8_t relay_node;
+
+    meshtastic_MeshPacket_coverage_filter_t coverage_filter;
 } meshtastic_MeshPacket;
 
 /* The bluetooth to device link:
@@ -1766,4 +1769,4 @@ extern const pb_msgdesc_t meshtastic_ChunkedPayloadResponse_msg;
 } /* extern "C" */
 #endif
 
-#endif
+#endif