ESP-32S as Bluetooth classic Server, bi-direction communication with Raspberry Pi/Python

NodeMCU ESP-32S (in Arduino framework) act as a Bluetooth classical (SPP) server:
It echo what received back to sender, and display on SPI ST7735 display.
Also implement callback function to detect esp_spp_cb_event_t.

Python code run on Raspberry Pi, act as GUI Bluetooth classic client, using tkinter/pybluez. Python code refer to: Hello Raspberry Pi - Raspberry Pi/Python as Bluetooth classic client, bi-direction communication with ESP32

Arduino code on ESP32, SPPServer_ESP32.ino.

// ref: Examples > BluetoothSerial > SerialToSerialBT
//with SPI ST735 80x160 IPS Display

#include "BluetoothSerial.h"
#include "esp_bt_device.h"
#include <TFT_eSPI.h> // TFT library
#include <SPI.h>

#if !defined(CONFIG_BT_ENABLED) || !defined(CONFIG_BLUEDROID_ENABLED)
#error Bluetooth is not enabled! Please run `make menuconfig` to and enable it
#endif

BluetoothSerial SerialBT;

TFT_eSPI tft = TFT_eSPI();

const String deviceName = "ESP32_SPP";

String getMAC(){
  const uint8_t* point = esp_bt_dev_get_address();

  String s = "";

  for (int i = 0; i < 6; i++) {
    char str[3];
    sprintf(str, "%02X", (int)point[i]);
    s = s + str;
    if (i < 5){
      s = s+ ":";
    }
  }
  return s;
}

/*
.arduino15/packages/esp32/hardware/esp32/1.0.4/libraries/
BluetoothSerial/src/BluetoothSerial.cpp

 */

void btCallback(esp_spp_cb_event_t event, esp_spp_cb_param_t *param){

  //tft.fillScreen(TFT_BLACK);
  //tft.setCursor(0, 0, 2);
  //tft.setTextSize(1);
  
  switch (event)
    {
    case ESP_SPP_INIT_EVT:
        Serial.println("ESP_SPP_INIT_EVT");
        //tft.println("ESP_SPP_INIT_EVT");
        break;

    case ESP_SPP_SRV_OPEN_EVT://Server connection open
        Serial.println("ESP_SPP_SRV_OPEN_EVT");
        //tft.println("ESP_SPP_SRV_OPEN_EVT");

        tft.fillScreen(TFT_BLACK);
        tft.setCursor(0, 0, 1);
        tft.setTextSize(1);
        break;

    case ESP_SPP_CLOSE_EVT://Client connection closed
        Serial.println("ESP_SPP_CLOSE_EVT");
        //tft.println("ESP_SPP_CLOSE_EVT");

        startUpScr();
        break;

    case ESP_SPP_CONG_EVT://connection congestion status changed
        Serial.println("ESP_SPP_CONG_EVT");
        //tft.println("ESP_SPP_CONG_EVT");
        break;

    case ESP_SPP_WRITE_EVT://write operation completed
        Serial.println("ESP_SPP_WRITE_EVT");
        //tft.println("ESP_SPP_WRITE_EVT");
        break;

    case ESP_SPP_DATA_IND_EVT://connection received data
        Serial.println("ESP_SPP_DATA_IND_EVT");
        //tft.println("ESP_SPP_DATA_IND_EVT");
        break;

    case ESP_SPP_DISCOVERY_COMP_EVT://discovery complete
        Serial.println("ESP_SPP_DISCOVERY_COMP_EVT");
        //tft.println("ESP_SPP_DISCOVERY_COMP_EVT");
        break;

    case ESP_SPP_OPEN_EVT://Client connection open
        Serial.println("ESP_SPP_OPEN_EVT");
        //tft.println("ESP_SPP_OPEN_EVT");
        break;

    case ESP_SPP_START_EVT://server started
        Serial.println("ESP_SPP_START_EVT");
        //tft.println("ESP_SPP_START_EVT");
        break;

    case ESP_SPP_CL_INIT_EVT://client initiated a connection
        Serial.println("ESP_SPP_CL_INIT_EVT");
        //tft.println("ESP_SPP_CL_INIT_EVT");
        break;

    default:
        Serial.println("unknown event!");
        //tft.println("unknown event!");
        break;
    }
}

void startUpScr(){
  tft.fillScreen(TFT_BLACK);
  tft.setCursor(0, 0, 2);
  tft.setTextSize(1);
  tft.println("arduino-er.blogspot.com");
  tft.println(deviceName);
  tft.setTextFont(1);
  tft.setTextSize(2);
  tft.println(getMAC());
}

void setup() {
  Serial.begin(115200);
  Serial.println("\n---Start---");
  SerialBT.begin(deviceName); //Bluetooth device name
  
  Serial.println("The device started, now you can pair it with bluetooth!");
  Serial.println("Device Name: " + deviceName);
  Serial.print("BT MAC: ");
  Serial.print(getMAC());
  Serial.println();
  SerialBT.register_callback(btCallback);

  tft.init();
  tft.setRotation(3);
  startUpScr();

}

void loop() {
  if (Serial.available()) {
    SerialBT.write(Serial.read());
  }
  if (SerialBT.available()) {
    char c = SerialBT.read();
    SerialBT.write(c);
    String s = String(c);
    if(tft.getCursorY() >= 80){
      tft.setCursor(0, 0);
      tft.fillScreen(TFT_BLACK);
    }
    tft.print(s);
  }
  delay(20);
}

To install TFT_eSPI library in Arduino IDE, and prepare custom setup file, refer ESP32 display with 0.96" 80x160 SPI ST7735 IPS Display, using TFT_eSPI lib.

Next:

~ The Client side implemented on ESP32.