Added lambda feature for onMessage callback. Fixes #147

src/MQTTClient.cpp

@@ -101,8 +101,8 @@ static void MQTTClientHandler(lwmqtt_client_t * /*client*/, void *ref, lwmqtt_st
     return;
   }
 
-  // return if simple callback is not set
-  if (cb->simple == nullptr) {
+  // return if simple and lambda callbacks are not set
+  if (cb->simple == nullptr && cb->lambda == nullptr) {
     return;
   }
 
@@ -115,6 +115,14 @@ static void MQTTClientHandler(lwmqtt_client_t * /*client*/, void *ref, lwmqtt_st
     str_payload = String((const char *)message.payload);
   }
 
+#if has_functional
+  // call the lambda callback and return if available
+  if (cb->lambda != nullptr) {
+    cb->lambda(str_topic, str_payload);
+    return;
+  }
+#endif
+
   // call simple callback
   cb->simple(str_topic, str_payload);
 }
@@ -163,17 +171,29 @@ void MQTTClient::begin(const char _hostname[], int _port, Client &_client) {
   lwmqtt_set_callback(&this->client, (void *)&this->callback, MQTTClientHandler);
 }
 
+#if has_functional
+void MQTTClient::onMessage(MQTTClientCallbackSimpleLambda cb) {
+  // set callback
+  this->callback.client = this;
+  this->callback.simple = nullptr;
+  this->callback.lambda = cb;
+  this->callback.advanced = nullptr;
+}
+#endif
+
 void MQTTClient::onMessage(MQTTClientCallbackSimple cb) {
   // set callback
   this->callback.client = this;
   this->callback.simple = cb;
+  this->callback.lambda = nullptr;
   this->callback.advanced = nullptr;
 }
 
 void MQTTClient::onMessageAdvanced(MQTTClientCallbackAdvanced cb) {
   // set callback
   this->callback.client = this;
   this->callback.simple = nullptr;
+  this->callback.lambda = nullptr;
   this->callback.advanced = cb;
 }
 

src/MQTTClient.h

@@ -4,6 +4,12 @@
 #include <Arduino.h>
 #include <Client.h>
 #include <Stream.h>
+#if __has_include(<functional>)
+  #include <functional>
+  #define has_functional 1
+#else
+  #define has_functional 0
+#endif
 
 extern "C" {
 #include "lwmqtt/lwmqtt.h"
@@ -25,10 +31,17 @@ class MQTTClient;
 typedef void (*MQTTClientCallbackSimple)(String &topic, String &payload);
 typedef void (*MQTTClientCallbackAdvanced)(MQTTClient *client, char topic[], char bytes[], int length);
 
+#if has_functional
+typedef std::function<void(String&, String&)> MQTTClientCallbackSimpleLambda;
+#endif
+
 typedef struct {
   MQTTClient *client = nullptr;
   MQTTClientCallbackSimple simple = nullptr;
   MQTTClientCallbackAdvanced advanced = nullptr;
+#if has_functional
+  MQTTClientCallbackSimpleLambda lambda = nullptr;
+#endif
 } MQTTClientCallback;
 
 class MQTTClient {
@@ -69,6 +82,10 @@ class MQTTClient {
   void onMessage(MQTTClientCallbackSimple cb);
   void onMessageAdvanced(MQTTClientCallbackAdvanced cb);
 
+#if has_functional
+  void onMessage(MQTTClientCallbackSimpleLambda cb);
+#endif
+
   void setClockSource(MQTTClientClockSource cb);
 
   void setHost(const char _hostname[]) { this->setHost(_hostname, 1883); }