Allow to add custom callback in BT Serial (#2081)

This allow to catch the events when connected /disconnected,, etc...
This also allow to get parameters of events like the remote address of connected devices, etc...
Small change but lot of flexibility

libraries/BluetoothSerial/src/BluetoothSerial.cpp

@@ -51,6 +51,7 @@ static SemaphoreHandle_t _spp_tx_done = NULL;
 static TaskHandle_t _spp_task_handle = NULL;
 static EventGroupHandle_t _spp_event_group = NULL;
 static boolean secondConnectionAttempt;
+static esp_spp_cb_t * custom_spp_callback = NULL;
 
 #define SPP_RUNNING     0x01
 #define SPP_CONNECTED   0x02
@@ -231,6 +232,7 @@ static void esp_spp_cb(esp_spp_cb_event_t event, esp_spp_cb_param_t *param)
     default:
         break;
     }
+    if(custom_spp_callback)(*custom_spp_callback)(event, param);
 }
 
 static bool _init_bt(const char *deviceName)
@@ -437,4 +439,10 @@ void BluetoothSerial::end()
     _stop_bt();
 }
 
+esp_err_t BluetoothSerial::register_callback(esp_spp_cb_t * callback)
+{
+    custom_spp_callback = callback;
+    return ESP_OK;
+}
+
 #endif

libraries/BluetoothSerial/src/BluetoothSerial.h

@@ -21,6 +21,7 @@
 
 #include "Arduino.h"
 #include "Stream.h"
+#include <esp_spp_api.h>
 
 class BluetoothSerial: public Stream
 {
@@ -38,6 +39,7 @@ class BluetoothSerial: public Stream
         size_t write(const uint8_t *buffer, size_t size);
         void flush();
         void end(void);
+        esp_err_t register_callback(esp_spp_cb_t * callback);
 
     private:
         String local_name;