PacketHistory debloat RAM allocations (#7034)

* PacketHistory debloat RAM allocations

* Removed FLOOD_EXPIRE_TIME option. We have static buffer now.

* Remove mx_ prefix from recentPackets

* Remember no less than 100 packet not to make reflood hell

* Cleanup

* PacketHistory max no less than 100

* no less than 100 means max of 100 or a given value of course.

* Care to not do duplicate entries. Cleanups.

---------

Co-authored-by: Ben Meadors <benmmeadors@gmail.com>

src/mesh/PacketHistory.h

@@ -1,49 +1,47 @@
 #pragma once
 
 #include "NodeDB.h"
-#include <unordered_set>
-
-/// We clear our old flood record 10 minutes after we see the last of it
-#ifdef FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION
-#define FLOOD_EXPIRE_TIME (5 * 1000L) // Don't allow too many packets to accumulate when fuzzing.
-#else
-#define FLOOD_EXPIRE_TIME (10 * 60 * 1000L)
-#endif
 
 #define NUM_RELAYERS                                                                                                             \
     3 // Number of relayer we keep track of. Use 3 to be efficient with memory alignment of PacketRecord to 16 bytes
 
-/**
- * A record of a recent message broadcast
- */
-struct PacketRecord {
-    NodeNum sender;
-    PacketId id;
-    uint32_t rxTimeMsec;              // Unix time in msecs - the time we received it
-    uint8_t next_hop;                 // The next hop asked for this packet
-    uint8_t relayed_by[NUM_RELAYERS]; // Array of nodes that relayed this packet
-
-    bool operator==(const PacketRecord &p) const { return sender == p.sender && id == p.id; }
-};
-
-class PacketRecordHashFunction
-{
-  public:
-    size_t operator()(const PacketRecord &p) const { return (std::hash<NodeNum>()(p.sender)) ^ (std::hash<PacketId>()(p.id)); }
-};
-
 /**
  * This is a mixin that adds a record of past packets we have seen
  */
 class PacketHistory
 {
   private:
-    std::unordered_set<PacketRecord, PacketRecordHashFunction> recentPackets;
+    struct PacketRecord { // A record of a recent message broadcast, no need to be visible outside this class.
+        NodeNum sender;
+        PacketId id;
+        uint32_t rxTimeMsec;              // Unix time in msecs - the time we received it,  0 means empty
+        uint8_t next_hop;                 // The next hop asked for this packet
+        uint8_t relayed_by[NUM_RELAYERS]; // Array of nodes that relayed this packet
+    };                                    // 4B + 4B + 4B + 1B + 3B = 16B
 
-    void clearExpiredRecentPackets(); // clear all recentPackets older than FLOOD_EXPIRE_TIME
+    uint32_t recentPacketsCapacity =
+        0; // Can be set in constructor, no need to recompile. Used to allocate memory for mx_recentPackets.
+    PacketRecord *recentPackets = NULL; // Simple and fixed in size. Debloat.
 
+    /** Find a packet record in history.
+     * @param sender NodeNum
+     * @param id PacketId
+     * @return pointer to PacketRecord if found, NULL if not found */
+    PacketRecord *find(NodeNum sender, PacketId id);
+
+    /** Insert/Replace oldest PacketRecord in mx_recentPackets.
+     * @param r PacketRecord to insert or replace */
+    void insert(PacketRecord &r); // Insert or replace a packet record in the history
+
+    /* Check if a certain node was a relayer of a packet in the history given iterator
+     * @return true if node was indeed a relayer, false if not */
+    bool wasRelayer(const uint8_t relayer, PacketRecord &r);
+
+    PacketHistory(const PacketHistory &);            // non construction-copyable
+    PacketHistory &operator=(const PacketHistory &); // non copyable
   public:
-    PacketHistory();
+    explicit PacketHistory(uint32_t size = -1); // Constructor with size parameter, default is PACKETHISTORY_MAX
+    ~PacketHistory();
 
     /**
      * Update recentBroadcasts and return true if we have already seen this packet
@@ -59,10 +57,9 @@ class PacketHistory
      * @return true if node was indeed a relayer, false if not */
     bool wasRelayer(const uint8_t relayer, const uint32_t id, const NodeNum sender);
 
-    /* Check if a certain node was a relayer of a packet in the history given iterator
-     * @return true if node was indeed a relayer, false if not */
-    bool wasRelayer(const uint8_t relayer, std::unordered_set<PacketRecord, PacketRecordHashFunction>::iterator r);
-
     // Remove a relayer from the list of relayers of a packet in the history given an ID and sender
     void removeRelayer(const uint8_t relayer, const uint32_t id, const NodeNum sender);
-};
+
+    // To check if the PacketHistory was initialized correctly by constructor
+    bool initOk(void) { return recentPackets != NULL && recentPacketsCapacity != 0; }
+};