Feather Huzzah MQTT - arduino

Question

I'm attempting to connect my Feather Huzzah to a local MQTT server but the program keeps blowing up and throwing a stack trace. When I attempt to decode the stack trace it's just empty, more frequently I only get part of the stack trace. Here's the code that I'm running, most of it is pretty similar to the pub/sub client example code for Arduino. I've tried erasing the flash on the device, that didn't seem to help.
Even stranger is that it worked once, but as soon as I tried it again adding the callback the code stopped working and blows up. If I try removing the callback nothing changes. I've tried stripping out a lot of the code just to see if I can get a consistent connection to MQTT, but that doesn't seem to be working either. The MQTT server is the latest Mosquitto from Ubuntu 18.04.
#include <ESP8266WiFi.h>
#include <ArduinoJson.h>
#include <NTPClient.h>
#include <WiFiUdp.h>
#include <PubSubClient.h>
const char* ssid = "xxxxxxxx";
const char* password = "xxxxxxxxx";
const int hallPin = 14;
const int ledPin = 0;
const char* mqtt_server = "mosquitto.localdomain";
long lastMsg = 0;
char msg[100];
int value = 0;
int hallState = 0;
WiFiClient espClient;
PubSubClient client(espClient);
WiFiUDP ntpUDP;
// By default 'time.nist.gov' is used with 60 seconds update interval and
// no offset
NTPClient timeClient(ntpUDP);
// Setup and connect to the wifi
void setup_wifi() {
delay(100);
Serial.print("Connecting to: ");
Serial.println(ssid);
WiFi.begin(ssid, password);
while (WiFi.status() != WL_CONNECTED) {
delay(500);
Serial.print(".");
}
Serial.println("");
Serial.println("Wifi connected");
Serial.println("IP address: ");
Serial.println(WiFi.localIP());
Serial.println("Gateway: ");
Serial.println(WiFi.gatewayIP());
}
//Reconnect to the MQTT broker
void reconnect() {
// Loop until we're reconnected
while (!client.connected()) {
Serial.print("Attempting MQTT connection...");
// Create a random client ID
String clientId = "ESP8266Client-";
clientId += String(random(0xffff), HEX);
// Attempt to connect
if (client.connect(clientId.c_str())) {
Serial.println("connected");
// Once connected, publish an announcement...
client.publish("/homeassistant/devices/doorbell", "hello world");
// ... and resubscribe
client.subscribe("/homeassistant/doorbell/receiver");
} else {
Serial.print("failed, rc=");
Serial.print(client.state());
Serial.println(" try again in 5 seconds");
// Wait 5 seconds before retrying
delay(5000);
}
}
}
//Process messages incoming from the broker
void callback(char* topic, byte* payload, unsigned int length) {
Serial.print("Message arrived [");
Serial.print(topic);
Serial.print("] ");
for (int i = 0; i < length; i++) {
Serial.print((char)payload[i]);
}
}
void setup() {
pinMode(ledPin, OUTPUT);
pinMode(hallPin, INPUT);
Serial.begin(115200);
setup_wifi();
timeClient.begin();
client.setServer(mqtt_server, 1883);
client.setCallback(callback);
}
void loop() {
if (WiFi.status() != WL_CONNECTED) {
setup_wifi();
}
if (!client.connected()) {
reconnect();
}
hallState = digitalRead(hallPin);
if (hallState == LOW) {
digitalWrite(ledPin, HIGH);
generateAndSendMessage();
delay(1000); //Add in a delay so it doesn't send messages extremely rapidly
} else {
digitalWrite(ledPin, LOW);
}
}
void generateAndSendMessage() {
timeClient.update();
StaticJsonBuffer<100> jsonBuffer;
JsonObject& root = jsonBuffer.createObject();
root["sensor"] = "doorbell";
root["time"] = timeClient.getEpochTime();
root["value"] = 1;
root.printTo(msg);
Serial.println(msg);
client.publish("/homeassistant/devices/doorbell", msg);
}

Answer 1

Looking at the generateAndSendMessage function, I believe you are having an issue due to the size of the MQTT buffer.
The MQTT buffer is by default set to 128 bytes. This includes the length of the channel name along with the message.
The length of you channel is 32 bytes, and the json buffer you used to make the message is 100 bytes long. So you might just be exceeding the 128 byte mark.
Just declare this before including the PubSubClient.h
#define MQTT_MAX_PACKET_SIZE 200
This macro defines the buffer size of the PubSubClient to 200. You can change it to whatever you believe is required.
I hope this helps.