Add exponential flood advert reduction based on hop count

Implements #1223

Adds cli config flood.advert.base
0 = forwarding flood adverts off
1 = forwarding flood adverts on (unrestricted)
0.308 (default) = prob. forwarding according to #1223

Author: mattzzw

examples/simple_repeater/MyMesh.cpp

@@ -433,6 +433,15 @@ bool MyMesh::allowPacketForward(const mesh::Packet *packet) {
     MESH_DEBUG_PRINTLN("allowPacketForward: unknown transport code, or wildcard not allowed for FLOOD packet");
     return false;
   }
+  // Limit flood advert paket forwarding using a probabilistic reduction defined by P(h) = 0.308^(hops-1)
+  // https://github.com/meshcore-dev/MeshCore/issues/1223
+   if (packet->getPayloadType() == PAYLOAD_TYPE_ADVERT && packet->isRouteFlood()) {
+    double roll_dice = (double)rand() / RAND_MAX;
+    double forw_prob = pow(_prefs.flood_advert_base, packet->path_len - 1);
+    if (roll_dice > forw_prob)
+      return false;
+  }
+
   if (packet->isRouteFlood() && _prefs.loop_detect != LOOP_DETECT_OFF) {
     const uint8_t* maximums;
     if (_prefs.loop_detect == LOOP_DETECT_MINIMAL) {
@@ -885,6 +894,7 @@ MyMesh::MyMesh(mesh::MainBoard &board, mesh::Radio &radio, mesh::MillisecondCloc
   _prefs.tx_power_dbm = LORA_TX_POWER;
   _prefs.advert_interval = 1;        // default to 2 minutes for NEW installs
   _prefs.flood_advert_interval = 12; // 12 hours
+  _prefs.flood_advert_base = 0.308f;
   _prefs.flood_max = 64;
   _prefs.interference_threshold = 0; // disabled
 

src/helpers/CommonCLI.cpp

@@ -89,6 +89,8 @@ void CommonCLI::loadPrefsInt(FILESYSTEM* fs, const char* filename) {
     file.read((uint8_t *)&_prefs->adc_multiplier, sizeof(_prefs->adc_multiplier));                 // 166
     file.read((uint8_t *)_prefs->owner_info, sizeof(_prefs->owner_info));                          // 170
     file.read((uint8_t *)&_prefs->rx_boosted_gain, sizeof(_prefs->rx_boosted_gain));              // 290
+    file.read((uint8_t *)&_prefs->flood_advert_base, sizeof(_prefs->flood_advert_base));                 // 290
+
     // next: 291
 
     // sanitise bad pref values
@@ -119,6 +121,7 @@ void CommonCLI::loadPrefsInt(FILESYSTEM* fs, const char* filename) {
 
     // sanitise settings
     _prefs->rx_boosted_gain = constrain(_prefs->rx_boosted_gain, 0, 1); // boolean
+    _prefs->flood_advert_base = constrain(_prefs->flood_advert_base, 0, 1);
 
     file.close();
   }
@@ -181,6 +184,7 @@ void CommonCLI::savePrefs(FILESYSTEM* fs) {
     file.write((uint8_t *)_prefs->owner_info, sizeof(_prefs->owner_info));                          // 170
     file.write((uint8_t *)&_prefs->rx_boosted_gain, sizeof(_prefs->rx_boosted_gain));              // 290
     // next: 291
+    file.write((uint8_t *)&_prefs->flood_advert_base, sizeof(_prefs->flood_advert_base));            
 
     file.close();
   }
@@ -508,6 +512,15 @@ void CommonCLI::handleSetCmd(uint32_t sender_timestamp, char* command, char* rep
       savePrefs();
       strcpy(reply, "OK");
     }
+  } else if (memcmp(config, "flood.advert.base ", 18) == 0) {
+    float f = atof(&config[18]);
+    if (f >= 0.0f && f <= 1.0f) {
+      _prefs->flood_advert_base = f;
+      savePrefs();
+      strcpy(reply, "OK");
+    } else {
+      strcpy(reply, "Error: base must be between 0 and 1");
+  }            
   } else if (memcmp(config, "advert.interval ", 16) == 0) {
     int mins = _atoi(&config[16]);
     if ((mins > 0 && mins < MIN_LOCAL_ADVERT_INTERVAL) || (mins > 240)) {
@@ -752,6 +765,8 @@ void CommonCLI::handleGetCmd(uint32_t sender_timestamp, char* command, char* rep
     sprintf(reply, "> %s", _prefs->allow_read_only ? "on" : "off");
   } else if (memcmp(config, "flood.advert.interval", 21) == 0) {
     sprintf(reply, "> %d", ((uint32_t) _prefs->flood_advert_interval));
+  } else if (memcmp(config, "flood.advert.base", 17) == 0) {
+    sprintf(reply, "> %s", StrHelper::ftoa(_prefs->flood_advert_base));  
   } else if (memcmp(config, "advert.interval", 15) == 0) {
     sprintf(reply, "> %d", ((uint32_t) _prefs->advert_interval) * 2);
   } else if (memcmp(config, "guest.password", 14) == 0) {

src/helpers/CommonCLI.h

@@ -61,6 +61,7 @@ struct NodePrefs { // persisted to file
   uint8_t rx_boosted_gain; // power settings
   uint8_t path_hash_mode;   // which path mode to use when sending
   uint8_t loop_detect;
+  float flood_advert_base;
 };
 
 class CommonCLICallbacks {