- 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/HelloEspnow/HelloEspnow.ino

@@ -1,8 +1,12 @@
+#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 <EspnowMeshBackend.h>
 #include <TypeConversionFunctions.h>
 #include <assert.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).
@@ -14,8 +18,8 @@
    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.
@@ -41,7 +45,7 @@ void networkFilter(int numberOfNetworks, MeshBackendBase &meshInstance);
 bool broadcastFilter(String &firstTransmission, EspnowMeshBackend &meshInstance);
 
 /* Create the mesh node object */
-EspnowMeshBackend espnowNode = EspnowMeshBackend(manageRequest, manageResponse, networkFilter, broadcastFilter, FPSTR(exampleWiFiPassword), espnowEncryptedConnectionKey, espnowHashKey, FPSTR(exampleMeshName), uint64ToString(ESP.getChipId()), true);
+EspnowMeshBackend espnowNode = EspnowMeshBackend(manageRequest, manageResponse, networkFilter, broadcastFilter, FPSTR(exampleWiFiPassword), espnowEncryptedConnectionKey, espnowHashKey, FPSTR(exampleMeshName), TypeCast::uint64ToString(ESP.getChipId()), true);
 
 /**
    Callback for when other nodes send you a request
@@ -57,10 +61,10 @@ String manageRequest(const String &request, MeshBackendBase &meshInstance) {
   // Of course, it is advised to adjust this approach based on RAM requirements.
 
   // To get the actual class of the polymorphic meshInstance, do as follows (meshBackendCast replaces dynamic_cast since RTTI is disabled)
-  if (EspnowMeshBackend *espnowInstance = meshBackendCast<EspnowMeshBackend *>(&meshInstance)) {
+  if (EspnowMeshBackend *espnowInstance = TypeCast::meshBackendCast<EspnowMeshBackend *>(&meshInstance)) {
     String transmissionEncrypted = espnowInstance->receivedEncryptedTransmission() ? ", Encrypted transmission" : ", Unencrypted transmission";
     Serial.print("ESP-NOW (" + espnowInstance->getSenderMac() + transmissionEncrypted + "): ");
-  } else if (TcpIpMeshBackend *tcpIpInstance = meshBackendCast<TcpIpMeshBackend *>(&meshInstance)) {
+  } else if (TcpIpMeshBackend *tcpIpInstance = TypeCast::meshBackendCast<TcpIpMeshBackend *>(&meshInstance)) {
     (void)tcpIpInstance; // This is useful to remove a "unused parameter" compiler warning. Does nothing else.
     Serial.print("TCP/IP: ");
   } else {
@@ -72,7 +76,12 @@ String manageRequest(const String &request, MeshBackendBase &meshInstance) {
   // If you need to print the whole String it is better to store it and print it in the loop() later.
   // Note that request.substring will not work as expected if the String contains null values as data.
   Serial.print("Request received: ");
-  Serial.println(request.substring(0, 100));
+
+  if (request.charAt(0) == 0) {
+    Serial.println(request);  // substring will not work for multiStrings.
+  } else {
+    Serial.println(request.substring(0, 100));
+  }
 
   /* return a string to send back */
   return ("Hello world response #" + String(responseNumber++) + " from " + meshInstance.getMeshName() + meshInstance.getNodeID() + " with AP MAC " + WiFi.softAPmacAddress() + ".");
@@ -89,10 +98,10 @@ transmission_status_t manageResponse(const String &response, MeshBackendBase &me
   transmission_status_t statusCode = TS_TRANSMISSION_COMPLETE;
 
   // To get the actual class of the polymorphic meshInstance, do as follows (meshBackendCast replaces dynamic_cast since RTTI is disabled)
-  if (EspnowMeshBackend *espnowInstance = meshBackendCast<EspnowMeshBackend *>(&meshInstance)) {
+  if (EspnowMeshBackend *espnowInstance = TypeCast::meshBackendCast<EspnowMeshBackend *>(&meshInstance)) {
     String transmissionEncrypted = espnowInstance->receivedEncryptedTransmission() ? ", Encrypted transmission" : ", Unencrypted transmission";
     Serial.print("ESP-NOW (" + espnowInstance->getSenderMac() + transmissionEncrypted + "): ");
-  } else if (TcpIpMeshBackend *tcpIpInstance = meshBackendCast<TcpIpMeshBackend *>(&meshInstance)) {
+  } else if (TcpIpMeshBackend *tcpIpInstance = TypeCast::meshBackendCast<TcpIpMeshBackend *>(&meshInstance)) {
     Serial.print("TCP/IP: ");
 
     // Getting the sent message like this will work as long as ONLY(!) TCP/IP is used.
@@ -129,12 +138,12 @@ void networkFilter(int numberOfNetworks, MeshBackendBase &meshInstance) {
 
     /* Connect to any _suitable_ APs which contain meshInstance.getMeshName() */
     if (meshNameIndex >= 0) {
-      uint64_t targetNodeID = stringToUint64(currentSSID.substring(meshNameIndex + meshInstance.getMeshName().length()));
+      uint64_t targetNodeID = TypeCast::stringToUint64(currentSSID.substring(meshNameIndex + meshInstance.getMeshName().length()));
 
-      if (targetNodeID < stringToUint64(meshInstance.getNodeID())) {
-        if (EspnowMeshBackend *espnowInstance = meshBackendCast<EspnowMeshBackend *>(&meshInstance)) {
+      if (targetNodeID < TypeCast::stringToUint64(meshInstance.getNodeID())) {
+        if (EspnowMeshBackend *espnowInstance = TypeCast::meshBackendCast<EspnowMeshBackend *>(&meshInstance)) {
           espnowInstance->connectionQueue().push_back(networkIndex);
-        } else if (TcpIpMeshBackend *tcpIpInstance = meshBackendCast<TcpIpMeshBackend *>(&meshInstance)) {
+        } else if (TcpIpMeshBackend *tcpIpInstance = TypeCast::meshBackendCast<TcpIpMeshBackend *>(&meshInstance)) {
           tcpIpInstance->connectionQueue().push_back(networkIndex);
         } else {
           Serial.println(String(F("Invalid mesh backend!")));
@@ -345,6 +354,15 @@ void loop() {
 
       espnowDelay(100); // Wait for responses (broadcasts can receive an unlimited number of responses, other transmissions can only receive one response).
 
+      // If you have a data array containing null values it is possible to transmit the raw data by making the array into a multiString as shown below.
+      // You can use String::c_str() or String::begin() to retreive the data array later.
+      // Note that certain String methods such as String::substring use null values to determine String length, which means they will not work as normal with multiStrings.
+      uint8_t dataArray[] = {0, '\'', 0, '\'', ' ', '(', 'n', 'u', 'l', 'l', ')', ' ', 'v', 'a', 'l', 'u', 'e'};
+      String espnowMessage = TypeCast::uint8ArrayToMultiString(dataArray, sizeof dataArray) + String(F(" from ")) + espnowNode.getMeshName() + espnowNode.getNodeID() + String(F("."));
+      Serial.println("\nTransmitting: " + espnowMessage);
+      espnowNode.attemptTransmission(espnowMessage, false);
+      espnowDelay(100); // Wait for response.
+
       Serial.println("\nPerforming encrypted ESP-NOW transmissions.");
 
       uint8_t targetBSSID[6] {0};
@@ -352,7 +370,7 @@ void loop() {
       // We can create encrypted connections to individual nodes so that all ESP-NOW communication with the node will be encrypted.
       if (espnowNode.constConnectionQueue()[0].getBSSID(targetBSSID) && espnowNode.requestEncryptedConnection(targetBSSID) == ECS_CONNECTION_ESTABLISHED) {
         // The WiFi scan will detect the AP MAC, but this will automatically be converted to the encrypted STA MAC by the framework.
-        String peerMac = macToString(targetBSSID);
+        String peerMac = TypeCast::macToString(targetBSSID);
 
         Serial.println("Encrypted ESP-NOW connection with " + peerMac + " established!");