ESP8266 Community Forum

- Thu Aug 23, 2018 8:16 am #77884 Hello everyone! I'm trying to receive JSON messages (AWS thing shadow) from the AWS IoT core with my ESP8266 SoC using the pubSubClient library but it looks like the callback function isn't called when the thing shadow is updated, isn't it possible to receive JSON messages using this library? I have no idea what's going on. I also read solutions based on the library "AmazonIOTClient.h" like: https://www.youtube.com/watch?v=WJuXv5usXcY but it doesn't work for me. I only want to receive the shadow status when it has been updated!

I attach the code I've been using:

#include <ESP8266WiFi.h>
#include <PubSubClient.h>

//incomplete array
unsigned char private_der[] = {
0x30, 0x82, 0x04, 0xa3, 0x02, 0x01, 0x00, 0x02, 0x82, 0x01, 0x01, 0x00,
0xae, 0x59, 0x05, 0xf3, 0x01, 0x27, 0x6f, 0xab, 0x3d, 0x6c, 0xdf, 0x1a,
0x2b, 0x42, 0x06, 0x5e};
unsigned int private_der_len = 1191;

//incomplete array
unsigned char cert_der[] = {
0x30, 0x82, 0x03, 0x5a, 0x30, 0x82, 0x02, 0x42, 0xa0, 0x03, 0x02, 0x01,
0x02, 0x02, 0x15, 0x00, 0xba, 0x70, 0x77, 0x25, 0xdd, 0x0f, 0x56, 0xcb,
0x6c, 0xb7, 0x17, 0x0f};
unsigned int cert_der_len = 862;

const char* ssid = "my_ssid";
const char* password = "my_password";
const char* mqtt_server = "xxxxxxxxx.iot.eu-west-2.amazonaws.com";

WiFiClientSecure wifiClient;
PubSubClient mqttClient(wifiClient);

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]);

Serial.println();
}

void reconnect() {
// Loop until we're reconnected
while (!mqttClient.connected()) {
Serial.print("Attempting MQTT connection...");
// Create a random client ID
String clientId = "ESP8266Client-";
clientId += String(random(0xffff), HEX);
// Attempt to connect
if (mqttClient.connect(clientId.c_str())) {
Serial.println("connected");
mqttClient.subscribe("$aws/things/ESP8266/shadow/get/accepted");
} else {
Serial.print("failed, rc=");
Serial.print(mqttClient.state());
Serial.println(" try again in 5 seconds");
// Wait 5 seconds before retrying
delay(5000);
}
}
}

void setup_wifi() {
delay(10);
// We start by connecting to a WiFi network
Serial.println();
Serial.print("Connecting to ");
Serial.println(ssid);

WiFi.begin(ssid, password);

while (WiFi.status() != WL_CONNECTED) {
delay(500);
Serial.print(".");
}

randomSeed(micros());

Serial.println("");
Serial.println("WiFi connected");
Serial.println("IP address: ");
Serial.println(WiFi.localIP());
}

void setup_wifiClient() {
wifiClient.setCertificate(cert_der, cert_der_len);
wifiClient.setPrivateKey(private_der, private_der_len);
}

void setup_mqttClient() {
mqttClient.setServer(mqtt_server, 8883);
mqttClient.setCallback(callback);
}

void setup() {
Serial.begin (115200);

setup_wifi();

setup_wifiClient();

setup_mqttClient();
}

void loop() {

if (!mqttClient.connected()) {
reconnect();
}
mqttClient.loop();
mqttClient.publish("$aws/things/ESP8266/shadow/get","");
delay(10000);
}


The thing shadow has a JSON format like this:

{
"desired": {
"welcome": "aws-iot"
},
"reported": {
"welcome": "aws-iot"
}
}