C ++ templates work great, the main thing is not to use class->virtual and RTTI. I write C ++ fluently, it's easier for me.
Thanks for your reply and sorry for my "bad" english.

Yes, I found
It may be useful for those who might come across this issue later:

Git MYCONTROLLER repo

Code for sending RSSI from loop function.
It is not necessary to announce (present) the RSSI sensor.

                    MY_CRITICAL_SECTION {
                        char *buff = new char[18]{};
                        (void) snprintf(buff, 17, "rssi:%d", rssi);
                        reportMsg(getId(), V_VAR5, buff);
                        delete [] buff;
                    }

Yes, I found
It may be useful for those who might come across this issue later:

Git MYCONTROLLER repo

Code for sending RSSI from loop function.
It is not necessary to announce (present) the RSSI sensor.

                    MY_CRITICAL_SECTION {
                        char *buff = new char[18]{};
                        (void) snprintf(buff, 17, "rssi:%d", rssi);
                        reportMsg(getId(), V_VAR5, buff);
                        delete [] buff;
                    }

Many thanks to all who answered, regarding MyController I think I will have to look at the source code, in which topic and with what identifier it expects a message about the RSSI evel.

@Clone-Tv said in Where to send messages about battery charge and signal strength?:

message.sender

Thanks for the clarification about message.sender, but then it is not entirely clear why this is used to receive messages? In essence, this should create a regeneration loop of messages ...

Unfortunately, it was not possible to deliver the RSSI level as applied to the MyController interface. The data itself is of course sent and received, but there is no display in the corresponding column. I used the S_SOUND and V_LEVEL identifiers.

Here's a screenshot of where it should be, but it's not there

Do I understand correctly that if (message.sender == 1) is a broadcast message? and it is sent to all nodes at once?

https://github.com/mfalkvidd/Arduino-MySensors-ESP8266-RFM69-Gateway/blob/030be620d45f2fd6cf02bc3633879e8bf35f7ef0/Arduino-MySensors-ESP8266-RFM69-Gateway.ino#L122

C ++ templates work great, the main thing is not to use class->virtual and RTTI. I write C ++ fluently, it's easier for me.
Thanks for your reply and sorry for my "bad" english.

If I send a message with a sensor ID of NODE_SENSOR_ID, I get the following duplicate message errors:

reportMsg(NODE_SENSOR_ID, I_SIGNAL_REPORT_RESPONSE, static_cast<uint16_t>(rssi));

errors:

951492 !MCO:PRO:RC=1
951525 !MCO:PRO:RC=1
951558 !MCO:PRO:RC=1
.. more ..

Everyone a good day.

Where to send messages about battery charge and signal strength? they are not visible in the corresponding fields of MyController.
Explain the topology of sending RSSI system messages and battery level.

Who initiates the request for battery charge and signal strength? Or does the sensor send itself at its own discretion? It seemed to me that there are the following tags: In and Out, so this is all the same dialogue on demand?

I am sending data something like this:

reportMsg(getId(), I_SIGNAL_REPORT_RESPONSE, static_cast<uint16_t>(rssi));

....

template<typename T>
void reportMsg(const uint8_t & id, const mysensors_internal_t & tag, const T & val) {
    _sendRoute(build(_msgTmp, GATEWAY_ADDRESS, id, C_SET, tag, false).set(val));
}

but I don't see the data .. something goes wrong. The same story with battery power, I send data from loop, without external request. Is it correct?

If you press the InclusionMode button and hold it for 10 seconds, the device will restart. In general, typical behavior for many Internet devices.
The patch is attached link.

Strange, but the forum does not allow you to upload anything other than pictures ..

It would be nice to see this in the main code of the repository. So that when updating the version, do not apply the patch separately

Sorry, that was the test the text is irrelevant to the topic.
But, since we are talking about 64-bit numbers on Arduino-like platforms, I'm ready to translate the code that solves this situation.

Int64String.h

#if !defined(INT64STRING_H)
# define INT64STRING_H 1

# if (defined(ARDUINO) && (ARDUINO >= 100))
#  include "Arduino.h"
# else
#  include "WString.h"
# endif

String Int64ToString(uint64_t, uint8_t = DEC, bool = false, bool = false);
String Int64ToString(int64_t, uint8_t = DEC, bool = false);
uint64_t StringToInt64(String);
uint64_t StringToInt64(const char*, uint16_t);

#endif

Int64String.cpp

#include "Int64String.h"
#define base16char(A) ("0123456789ABCDEF"[A])

String Int64ToString(uint64_t value, uint8_t base, bool prefix, bool sign) {
  if (base < 2)
    base = 2;
  else if (base > 16)
    base = 16;

  uint8_t i = 64;
  char buffer[66] = {0};

  if (value == 0)
    buffer[i--] = '0';
  else {
    uint8_t base_multiplied = 3;
    uint16_t multiplier = base * base * base;

    if (base < 16) {
      multiplier *= base;
      base_multiplied++;
    }
    if (base < 8) {
      multiplier *= base;
      base_multiplied++;
    }
    while (value > multiplier) {
      uint64_t q = value / multiplier;
      uint16_t r = value - q * multiplier;

      for (uint8_t j = 0; j < base_multiplied; j++) {
        uint16_t rq = r / base;
        buffer[i--] = base16char(r - rq * base);
        r = rq;
      }
      value = q;
    }

    uint16_t remaining = value;
    while (remaining > 0) {
      uint16_t q = remaining / base;
      buffer[i--] = base16char(remaining - q * base);
      remaining = q;
    }
  }

  if (base == DEC && sign)
    buffer[i--] = '-';
  else if (prefix) {
    if (base == HEX) {
      buffer[i--] = 'x';
      buffer[i--] = '0';
    }
    else if (base == OCT)
      buffer[i--] = '0';
    else if (base == BIN)
      buffer[i--] = 'B';
  }
  return String(&buffer[i + 1]);
}

String Int64ToString(int64_t value, uint8_t base, bool prefix) {
  bool sign = base == DEC && value < 0;
  uint64_t uvalue = sign ? -value : value;
  return Int64ToString(uvalue, base, prefix, sign);
}

uint64_t StringToInt64(String str) {
  return StringToInt64(str.c_str(), str.length());
}

uint64_t StringToInt64(const char *s, uint16_t sz = 0U) {
  uint64_t val = 0ULL;
  if (s == nullptr)
    return val;

  if (sz <= 0)
    sz = strlen(s);

  if (sz <= 2)
    return val;
  
  uint16_t i = (((s[0] == '0') && ((s[1] == 'x') || (s[1] == 'X'))) ? 2U : 0U);
  for (; i < sz; i++) {
    const char c = s[i];
    if (!isxdigit(c))
      return -1ULL;
    
    val *= 16;
    val += (c >= '0' && c <= '9') ? c - '0' : c - 'A' + 10;
  }
  return val;
}

I gave the sources as an apology for the created topic