boolean Sensor::readMessage() {
uint8_t len = RF24::getDynamicPayloadSize();
RF24::read(&msg, len);

if (!(msg.header.messageType==M_INTERNAL && msg.header.type == I_PING_ACK)) {
	delay(ACK_SEND_DELAY); // Small delay here to let other side switch to reading mode
	RF24::stopListening();
	RF24::openWritingPipe(TO_ADDR(msg.header.last));
	RF24::write(&radioId, sizeof(uint8_t));
	RF24::closeReadingPipe(WRITE_PIPE); // Stop listening to write-pipe after transmit
	RF24::startListening();
	debug(PSTR("Sent ack msg to %d\n"), msg.header.last);
}
uint8_t valid = validate(len-sizeof(header_s));
boolean ok = valid == VALIDATE_OK;

// Make sure string gets terminated ok for full sized messages.
msg.data[len - sizeof(header_s) ] = '\0';
debug(PSTR("Rx: fr=%d,to=%d,la=%d,ci=%d,mt=%d,t=%d,cr=%d(%s): %s\n"),
		msg.header.from,msg.header.to, msg.header.last, msg.header.childId, msg.header.messageType, msg.header.type, msg.header.crc, valid==0?"ok":valid==1?"ec":"ev", msg.data);
return ok;

}

Is this correct? Isn't better to first validante message and then send confirmation if it is ok. Like this:

boolean Sensor::readMessage() {
uint8_t len = RF24::getDynamicPayloadSize();
RF24::read(&msg, len);

uint8_t valid = validate(len-sizeof(header_s));
boolean ok = valid == VALIDATE_OK;**
**
if (ok && !(msg.header.messageType==M_INTERNAL && msg.header.type == I_PING_ACK)) {
delay(ACK_SEND_DELAY); // Small delay here to let other side switch to reading mode
RF24::stopListening();
RF24::openWritingPipe(TO_ADDR(msg.header.last));
RF24::write(&radioId, sizeof(uint8_t));
RF24::closeReadingPipe(WRITE_PIPE); // Stop listening to write-pipe after transmit
RF24::startListening();
debug(PSTR("Sent ack msg to %d\n"), msg.header.last);
}

// Make sure string gets terminated ok for full sized messages.
msg.data[len - sizeof(header_s) ] = '\0';
debug(PSTR("Rx: fr=%d,to=%d,la=%d,ci=%d,mt=%d,t=%d,cr=%d(%s): %s\n"),
		msg.header.from,msg.header.to, msg.header.last, msg.header.childId, msg.header.messageType, msg.header.type, msg.header.crc, valid==0?"ok":valid==1?"ec":"ev", msg.data);
return ok;

}