add Serial rx callback function

example:

//return false drop char,
bool rxcap(char ch) {
  if (ch == '1') { //if get char '1'
    Serial.println("callback!");
    Serial.setRxCallBack(0); //disable CallBack
    return false; //del char '1' from rx buff
  }
  return true;
}

void setup() {
  Serial.begin(115200);
  Serial.setRxCallBack(rxcap);
}

void loop() {
while(Serial.available())
  Serial.write(Serial.read());
}

~

Author: lshw

cores/arduino/HardwareSerial.h

@@ -106,6 +106,7 @@ class HardwareSerial : public Stream
     volatile rx_buffer_index_t _rx_buffer_tail;
     volatile tx_buffer_index_t _tx_buffer_head;
     volatile tx_buffer_index_t _tx_buffer_tail;
+    bool (*_rxcallback)(char);
 
     // Don't put any members after these buffers, since only the first
     // 32 bytes of this struct can be accessed quickly using the ldd
@@ -137,8 +138,8 @@ class HardwareSerial : public Stream
     // Interrupt handlers - Not intended to be called externally
     inline void _rx_complete_irq(void);
     void _tx_udr_empty_irq(void);
+    void setRxCallBack( bool (*CallBackFun)(char)) { _rxcallback = CallBackFun; }
 };
-
 #if defined(UBRRH) || defined(UBRR0H)
   extern HardwareSerial Serial;
   #define HAVE_HWSERIAL0

cores/arduino/HardwareSerial_private.h

@@ -92,7 +92,8 @@ HardwareSerial::HardwareSerial(
     _ucsra(ucsra), _ucsrb(ucsrb), _ucsrc(ucsrc),
     _udr(udr),
     _rx_buffer_head(0), _rx_buffer_tail(0),
-    _tx_buffer_head(0), _tx_buffer_tail(0)
+    _tx_buffer_head(0), _tx_buffer_tail(0),
+    _rxcallback(0)
 {
 }
 
@@ -104,6 +105,8 @@ void HardwareSerial::_rx_complete_irq(void)
     // No Parity error, read byte and store it in the buffer if there is
     // room
     unsigned char c = *_udr;
+    if(_rxcallback != 0 && !_rxcallback(c))
+       return;
     rx_buffer_index_t i = (unsigned int)(_rx_buffer_head + 1) % SERIAL_RX_BUFFER_SIZE;
 
     // if we should be storing the received character into the location