- Move all Strings to flash and optimize String usage, saving 4-5 kB of RAM.

- Replace const with constexpr where possible.

- Use default constructor instead of copy constructor for IPAddress variable initialization.

- Add MeshTypeConversionFunctions namespace around TypeConversionFunctions.

- Add MeshUtilityFunctions namespace around UtilityFunctions.

- Add ESP8266WIFIMESH_DISABLE_COMPATIBILITY preprocessor flag to retain compatibility with old code despite new namespaces.

- Add setLogEntryLifetimeMs and setBroadcastResponseTimeoutMs methods to EspnowMeshBackend.

- Move FloodingMesh constant definitions from header to .cpp file to reduce the risk of extra RAM consumption.

- Add deactivateAP method to FloodingMesh.

- Make deactivateAP static and add new non-static deactivateControlledAP method to MeshBackendBase.

- Add example of how to transfer null values using multiStrings to HelloEspnow.ino.

- Improve documentation.

- Improve comments.

libraries/ESP8266WiFiMesh/examples/HelloMesh/HelloMesh.ino

@@ -5,11 +5,15 @@
    That way you will get instant confirmation of the mesh communication without checking the Serial Monitor.
 */
 
+#define ESP8266WIFIMESH_DISABLE_COMPATIBILITY // Excludes redundant compatibility code. Should be used for new code until the compatibility code is removed with release 3.0.0 of the Arduino core.
+
 #include <ESP8266WiFi.h>
 #include <TypeConversionFunctions.h>
 #include <assert.h>
 #include <FloodingMesh.h>
 
+namespace TypeCast = MeshTypeConversionFunctions;
+
 /**
    NOTE: Although we could define the strings below as normal String variables,
    here we are using PROGMEM combined with the FPSTR() macro (and also just the F() macro further down in the file).
@@ -21,8 +25,8 @@
    https://github.com/esp8266/Arduino/issues/1143
    https://arduino-esp8266.readthedocs.io/en/latest/PROGMEM.html
 */
-const char exampleMeshName[] PROGMEM = "MeshNode_"; // The name of the mesh network. Used as prefix for the node SSID and to find other network nodes in the example networkFilter and broadcastFilter functions below.
-const char exampleWiFiPassword[] PROGMEM = "ChangeThisWiFiPassword_TODO"; // The password has to be min 8 and max 64 characters long, otherwise an AP which uses it will not be found during scans.
+constexpr char exampleMeshName[] PROGMEM = "MeshNode_"; // The name of the mesh network. Used as prefix for the node SSID and to find other network nodes in the example networkFilter and broadcastFilter functions below.
+constexpr char exampleWiFiPassword[] PROGMEM = "ChangeThisWiFiPassword_TODO"; // The password has to be min 8 and max 64 characters long, otherwise an AP which uses it will not be found during scans.
 
 // A custom encryption key is required when using encrypted ESP-NOW transmissions. There is always a default Kok set, but it can be replaced if desired.
 // All ESP-NOW keys below must match in an encrypted connection pair for encrypted communication to be possible.
@@ -37,10 +41,10 @@ uint8_t espnowHashKey[16] = {0xEF, 0x44, 0x33, 0x0C, 0x33, 0x44, 0xFE, 0x44, //
 bool meshMessageHandler(String &message, FloodingMesh &meshInstance);
 
 /* Create the mesh node object */
-FloodingMesh floodingMesh = FloodingMesh(meshMessageHandler, FPSTR(exampleWiFiPassword), espnowEncryptedConnectionKey, espnowHashKey, FPSTR(exampleMeshName), uint64ToString(ESP.getChipId()), true);
+FloodingMesh floodingMesh = FloodingMesh(meshMessageHandler, FPSTR(exampleWiFiPassword), espnowEncryptedConnectionKey, espnowHashKey, FPSTR(exampleMeshName), TypeCast::uint64ToString(ESP.getChipId()), true);
 
 bool theOne = true;
-String theOneMac = "";
+String theOneMac;
 
 bool useLED = false; // Change this to true if you wish the onboard LED to mark The One.
 
@@ -58,7 +62,7 @@ bool useLED = false; // Change this to true if you wish the onboard LED to mark
 bool meshMessageHandler(String &message, FloodingMesh &meshInstance) {
   int32_t delimiterIndex = message.indexOf(meshInstance.metadataDelimiter());
   if (delimiterIndex == 0) {
-    Serial.print("Message received from STA MAC " + meshInstance.getEspnowMeshBackend().getSenderMac() + ": ");
+    Serial.print(String(F("Message received from STA MAC ")) + meshInstance.getEspnowMeshBackend().getSenderMac() + F(": "));
     Serial.println(message.substring(2, 102));
 
     String potentialMac = message.substring(2, 14);
@@ -95,17 +99,17 @@ bool meshMessageHandler(String &message, FloodingMesh &meshInstance) {
         previousTotalBroadcasts = totalBroadcasts;
 
         if (totalReceivedBroadcasts % 50 == 0) {
-          Serial.println("missed/total: " + String(missedBroadcasts) + '/' + String(totalReceivedBroadcasts));
+          Serial.println(String(F("missed/total: ")) + String(missedBroadcasts) + '/' + String(totalReceivedBroadcasts));
         }
         if (totalReceivedBroadcasts % 500 == 0) {
-          Serial.println("Benchmark message: " + message.substring(0, 100));
+          Serial.println(String(F("Benchmark message: ")) + message.substring(0, 100));
         }
       }
     }
   } else {
     // Only show first 100 characters because printing a large String takes a lot of time, which is a bad thing for a callback function.
     // If you need to print the whole String it is better to store it and print it in the loop() later.
-    Serial.print("Message with origin " + meshInstance.getOriginMac() + " received: ");
+    Serial.print(String(F("Message with origin ")) + meshInstance.getOriginMac() + F(" received: "));
     Serial.println(message.substring(0, 100));
   }
 
@@ -139,7 +143,7 @@ void setup() {
   floodingMesh.activateAP();
 
   uint8_t apMacArray[6] {0};
-  theOneMac = macToString(WiFi.softAPmacAddress(apMacArray));
+  theOneMac = TypeCast::macToString(WiFi.softAPmacAddress(apMacArray));
 
   if (useLED) {
     pinMode(LED_BUILTIN, OUTPUT); // Initialize the LED_BUILTIN pin as an output
@@ -150,7 +154,7 @@ void setup() {
   // The main benefit of AEAD encryption is that it can be used with normal broadcasts (which are substantially faster than encryptedBroadcasts).
   // The main drawbacks are that AEAD only encrypts the message data (not transmission metadata), transfers less data per message and lacks replay attack protection.
   // When using AEAD, potential replay attacks must thus be handled manually.
-  //floodingMesh.getEspnowMeshBackend().setEspnowMessageEncryptionKey("ChangeThisKeySeed_TODO"); // The message encryption key should always be set manually. Otherwise a default key (all zeroes) is used.
+  //floodingMesh.getEspnowMeshBackend().setEspnowMessageEncryptionKey(F("ChangeThisKeySeed_TODO")); // The message encryption key should always be set manually. Otherwise a default key (all zeroes) is used.
   //floodingMesh.getEspnowMeshBackend().setUseEncryptedMessages(true);
 
   floodingMeshDelay(5000); // Give some time for user to start the nodes
@@ -180,8 +184,8 @@ void loop() {
       ledState = ledState ^ bool(benchmarkCount); // Make other nodes' LEDs alternate between on and off once benchmarking begins.
 
       // Note: The maximum length of an unencrypted broadcast message is given by floodingMesh.maxUnencryptedMessageLength(). It is around 670 bytes by default.
-      floodingMesh.broadcast(String(floodingMesh.metadataDelimiter()) + String(ledState) + theOneMac + " is The One.");
-      Serial.println("Proclamation broadcast done in " + String(millis() - startTime) + " ms.");
+      floodingMesh.broadcast(String(floodingMesh.metadataDelimiter()) + String(ledState) + theOneMac + F(" is The One."));
+      Serial.println(String(F("Proclamation broadcast done in ")) + String(millis() - startTime) + F(" ms."));
 
       timeOfLastProclamation = millis();
       floodingMeshDelay(20);
@@ -189,8 +193,8 @@ void loop() {
 
     if (millis() - loopStart > 23000) { // Start benchmarking the mesh once three proclamations have been made
       uint32_t startTime = millis();
-      floodingMesh.broadcast(String(benchmarkCount++) + String(floodingMesh.metadataDelimiter()) + ": Not a spoon in sight.");
-      Serial.println("Benchmark broadcast done in " + String(millis() - startTime) + " ms.");
+      floodingMesh.broadcast(String(benchmarkCount++) + String(floodingMesh.metadataDelimiter()) + F(": Not a spoon in sight."));
+      Serial.println(String(F("Benchmark broadcast done in ")) + String(millis() - startTime) + F(" ms."));
       floodingMeshDelay(20);
     }
   }