MQTT disconnects from AWS when publishing a message

Question

Please look at this sketch for ESP32. It does nothing but:

1. connects to WiFi
2. connects to AWS MQTT
3. subscribes to the /get/accepted topic
4. every 5 s publish an empty message to the /get topic to retrieve the shadow file

#include <SPIFFS.h>
#include <WiFi.h>
#include <WiFiClientSecure.h>
#define ETH_CLK_MODE ETH_CLOCK_GPIO17_OUT
#define ETH_PHY_POWER 12
#include <ETH.h>
#include <SSLClient.h>
#include <PubSubClient.h>
#define MQTT_PACKET_SIZE      4096
#define ID "myid"
WiFiClientSecure networkClient;
PubSubClient pubsub;
char rootCA;
char privateKey;
char *certificate;
unsigned long old_millis = 0;
bool readFile(const char path, char *buffer)
{
  File file = SPIFFS.open(path);
size_t size = file.size();
  buffer = (char ) malloc(size + 1);
char p = buffer;
  while(file.available()) p++ = file.read();
  p = '\0';
  return true;
}
void callback(char topic, byte payload, unsigned int length)
{
  Serial.print("Received ");
  Serial.print(length);
  Serial.print(" bytes @ ");
  Serial.println(topic);
  Serial.println((char *) payload);
}
void setup() 
{
  Serial.begin(115200);
  SPIFFS.begin();
  WiFi.mode(WIFI_STA);
  WiFi.begin("myssid", "mypassword");
  while (WiFi.status() != WL_CONNECTED)
  {
    Serial.println(".");
    delay(1000);
  }
Serial.println(WiFi.localIP());
char filename[64];
  readFile("/AmazonRootCA1.pem", &rootCA);
  networkClient.setCACert(rootCA);
sprintf(filename, "/%s-cert.pem.crt", ID);
  readFile(filename, &certificate);
  networkClient.setCertificate(certificate);
sprintf(filename, "/%s-private.pem.key", ID);
  readFile(filename, &privateKey);
  networkClient.setPrivateKey(privateKey);
pubsub.setServer("myendpoint-ats.iot.us-east-2.amazonaws.com", 8883);
  pubsub.setBufferSize(MQTT_PACKET_SIZE);
  pubsub.setClient(networkClient);
  pubsub.setCallback(callback);
old_millis = millis();
}
void loop() 
{
  char topic[64];
if (pubsub.connected())
  {
    pubsub.loop();
if (millis() - old_millis &gt; 5000)
{
  sprintf(topic, &quot;$aws/things/%s/shadow/name/module-1/get&quot;, ID);
  pubsub.publish(topic, &quot;&quot;);
  Serial.print(&quot;Publish to &quot;);
  Serial.println(topic);
  old_millis = millis();
}

}
  else
  {
    Serial.print("State ");
    Serial.println(pubsub.state());
    if (pubsub.connect(ID))
    {
      Serial.println("MQTT connected");
      sprintf(topic, "$aws/things/%s/shadow/name/module-1/get/accepted", ID);
      if (pubsub.subscribe(topic)) Serial.print("Subscribed to: ");
      else Serial.print("Error while subscribing to: ");
      Serial.println(topic);
    }
    else
    {
      Serial.print("failed, rc=");
      Serial.println(pubsub.state());
      delay(1000);
    }

  }
}

Here the output:

.
.
.
09:52:35.752 -> .
09:52:36.745 -> .
09:52:37.738 -> 192.168.1.41
09:52:37.837 -> State -1
09:52:40.716 -> MQTT connected
09:52:40.716 -> Subscribed to: $aws/things/myid/shadow/name/module-1/get/accepted
09:52:42.834 -> Publish to $aws/things/myid/shadow/name/module-1/get
09:52:42.967 -> State -3
09:52:45.945 -> MQTT connected
09:52:45.945 -> Subscribed to: $aws/things/myid/shadow/name/module-1/get/accepted
09:52:47.831 -> Publish to $aws/things/myid/shadow/name/module-1/get
09:52:47.997 -> State -3
09:52:50.975 -> MQTT connected
09:52:50.975 -> Subscribed to: $aws/things/myid/shadow/name/module-1/get/accepted
09:52:52.828 -> Publish to $aws/things/myid/shadow/name/module-1/get
09:52:52.993 -> State -3

Every time it publish the message the MQTT connection is lost. Why? What is my mistake?

Answer 1

Some quick possibilities:

1. You don't actually have a thing with the name of "myid".
2. You haven't given this client the rights to the topics you're subscribing to or publishing on.
3. There's not a named shadow with that name (though that should have got you an empty shadow I'd assume.). Try doing a put (after giving it rights to do so).

Also, does the default shadow work?