memory leak w/ no Strings involved

Question

I'm trying to read data being transferred via Infrared from my Smartmeter on my ESP8266 using the following sketch:

#include <ESP8266WiFi.h>
#include <ESP8266WebServer.h>
#include <ESP8266HTTPUpdateServer.h>
#include <Ticker.h>
#include <AsyncMqttClient.h>
#ifndef STASSID
#define STASSID "mySSID"
#define STAPSK "myPassword"
#endif
#ifndef MQTT_HOST
#define MQTT_HOST IPAddress(192, 168, 0, 100)
#define MQTT_PORT 1883
#endif
#ifndef IR
#define SerialDebug Serial1
#define IR Serial
#endif
AsyncMqttClient mqttClient;
Ticker mqttReconnectTimer;
WiFiEventHandler wifiConnectHandler;
WiFiEventHandler wifiDisconnectHandler;
Ticker wifiReconnectTimer;
const char* host = "esp8266-webupdate";
const byte firstByte = 0x7E;
const byte lastByte = 0x7E;
uint8_t i;
ESP8266WebServer httpServer(80);
ESP8266HTTPUpdateServer httpUpdater;
void connectToWifi() {
 SerialDebug.println("Connecting to WiFi ...");
 WiFi.begin(STASSID, STAPSK);
}
void connectToMqtt() {
 SerialDebug.println("Connecting to MQTT ...");
 mqttClient.connect();
}
void onWifiConnect(const WiFiEventStationModeGotIP& event) {
 SerialDebug.println("Connected to Wi-Fi.");
 connectToMqtt();
}
void onWifiDisconnect(const WiFiEventStationModeDisconnected& event) {
 SerialDebug.println("Disconnected from Wi-Fi.");
 mqttReconnectTimer.detach();
 wifiReconnectTimer.once(2, connectToWifi);
}
void onMqttConnect(bool sessionPresent) {
 SerialDebug.println("Connected to MQTT.");
 SerialDebug.print("Session present: ");
 SerialDebug.println(sessionPresent);
}
void onMqttDisconnect(AsyncMqttClientDisconnectReason reason) {
 SerialDebug.println("Disconnected from MQTT.");
 if (WiFi.isConnected()) {
 mqttReconnectTimer.once(2, connectToMqtt);
 }
}
void array_to_string(byte array[], unsigned int len, char buffer[]) {
 for (unsigned int i = 0; i < len; i++) {
 byte nib1 = (array[i] >> 4) & 0x0F;
 byte nib2 = (array[i] >> 0) & 0x0F;
 buffer[i*2+0] = nib1 < 0xA ? '0' + nib1 : 'A' + nib1 - 0xA;
 buffer[i*2+1] = nib2 < 0xA ? '0' + nib2 : 'A' + nib2 - 0xA;
 }
 buffer[len*2] = '0円';
}
void setup() {
 SerialDebug.begin(115200);
 IR.begin(9600);
 SerialDebug.println();
 SerialDebug.println("Booting Sketch...");
 
 wifiConnectHandler = WiFi.onStationModeGotIP(onWifiConnect);
 wifiDisconnectHandler = WiFi.onStationModeDisconnected(onWifiDisconnect);
 mqttClient.onConnect(onMqttConnect);
 mqttClient.onDisconnect(onMqttDisconnect);
 mqttClient.setServer(MQTT_HOST, MQTT_PORT);
 connectToWifi();
 httpUpdater.setup(&httpServer);
 httpServer.begin();
 mqttClient.setWill("smartmeter/online", 0, true, "no");
}
void loop() {
 httpServer.handleClient();
 
 uint32_t timeout = 2000;
 
 int readCnt = 0;
 uint32_t start_time = millis();
 byte tempChar = 0;
 byte *readMessage;
 uint32_t messageLen = 0;
 
 while ((tempChar != 0x7E) && (millis() - start_time < timeout)) {
 if (IR.available()) {
 tempChar = IR.read();
 }
 }
 
 start_time = millis();
 timeout = 1000;
 bool done = false;
 
 if (tempChar == firstByte) { // if first byte == 0x7E
 while ((millis() - start_time) < timeout && !done) {
 if (IR.available()) {
 tempChar = IR.read(); // second byte must be 0xA0
 if(tempChar == 0xA0) {
 while ((millis() - start_time) < timeout && !done) {
 if (IR.available()) {
 tempChar = IR.read(); // 3rd byte tells the legth of the message
 
 readMessage = new byte[tempChar+2];
 memset(readMessage, 0, tempChar+2);
 readMessage[0] = firstByte;
 readMessage[1] = 0xA0;
 readMessage[2] = tempChar;
 messageLen = ((uint32_t)(tempChar))+2;
 readCnt = 3;
 
 while ( readCnt < messageLen && ((millis() - start_time) < timeout)) { // minimum len 120 chars for 0x7E format
 if (IR.available()) {
 readMessage[readCnt] = IR.read(); 
 readCnt++; 
 
 if(readCnt == tempChar+2 && readMessage[readCnt-1] != lastByte) { // correct len but last byte not 0x7E
 done = true;
 SerialDebug.printf("Wrong end byte found - %d\n", readMessage[readCnt-1]);
 } else if(readCnt == tempChar+2) { // correct len and correct last byte
 done = true;
 char str[251] = "";
 array_to_string(readMessage, readCnt, str);
 mqttClient.publish("smartmeter/raw", 0, false, str);
 }
 }
 }
 }
 }
 }
 }
 }
 }
 mqttClient.publish("smartmeter/online", 0, true, "yes");
 char heap[6] = "";
 itoa(ESP.getFreeHeap(), heap, 10);
 mqttClient.publish("smartmeter/freeHeap", 0, false, heap);
}

I'm getting the encoded HEX-data published on my MQTT Topic as desired, the outputs length is 250 characters long (= 125 Bytes) which is correct:

7ea07bcf000200231362b1e6e700db08534d536770075f626120000e32e62addedaede38e64c8c3173035a0a853851a28efc57f7fd76a9df59dbb152f796939328ff0f28df7f257d20b5cb2a458c4eb9188e2c1c251701c891244d859ed9c159714bb4451c090d9b1ed3bbb1fc89785ebafbf59ec4f9d540eb4c90d47e

As I found out, the ESP's heap is decreasing by 100-300 by each iteration of the loop (data is being transmitted every second via Infrared from the power-grid Smartmeter) until the ESP will eventually be rebooted by the watchdog after like 5-8 minutes.

I explicitly did not use String variables in the sketch but I legit cannot find the reason for the memory leak. Tried turning off wifi, webserver and mqtt one after each other which didn't actually made a difference.

The heap-size stays at a constant level though when there is no data being received via the Infrared serial port, so I imagine something is fishy when storing the data in the byte array "readMessage".

Anything obvious that immediately pops into someones eye that I missed?

• Juraj: the 'problem with Strings' is a problem with new hidden in String class. your use of new is not hidden

Answer 1

You do a new inside the loop

 readMessage = new byte[tempChar+2];

which causes the heap to be filled with tempChar+2 bytes, but you never delete this.

Try reusing this memory (making it a local, or make it 'dirty' global).

Probably (not tested) the above line can be rewritten as:

byte readMessage[tempChar+2];

• 1_am_r00t: By now I was already convinced it's something so obvious sigh A simple delete[] readMessage; after the MQTT publish of the "str" variable did the trick! Even if I went a different path so actually solve the problem, you gave the actual hint that guided me there, so I'll mark your answer as accepted. Thank you very much!
• Michel Keijzers: You are welcome ... however, take in mind that a new and delete is not needed in this case, as the data only lives within one function. Typically new / delete is used when the life span of data is higher than one function, or when the amount of data is not known beforehand/varies.
• 1_am_r00t: True that - I will definitely take it into account when I will be implementing parts of this sketch to the final code!