Hello. I am sending MQTT data from my raspberry PI to the remote nodes ESP8266. In order to be efficient with the data and create as few topics as possible, I am sending a few different objects of information on a single topic as such:
My function node looks like that:
msg.topic = msg.device + '/item_inside'
msg.payload = {}; //create and empy object
msg.payload.item = msg.item
msg.payload.serial = msg.serial
msg.payload.quantity= msg.quantity
return msg
With this topic and payload information, I publish to an MQTT topic and send item, serial and quantity data.
On the ESP8266 side, I am using an example project and the data parsing function looks like that:
void callback(char* topic, byte* payload, unsigned int length) {
Serial.print("Message arrived [");
Serial.print(topic);
Serial.print("] ");
char message[length + 1];
strncpy (message, (char*)payload, length);
message[length] = '\0';
Serial.println(message);
Serial monitor on my ESP8266 when I send data from raspberry PI
Message arrived [device1/item_inside] {"item":"item1","serial":"1A2B","quantity":50}
Also, on my ESP8266 code, I have a structure:
struct item_inside_struct {
char item[30];
char serial[30];
int quantity;
};
item_inside_struct item_inside;
and want to fill that structure from the data that is coming from an MQTT message with topic "item_inside"
The problem is that I am not sure how to properly parse the data.
I can see that in my callback function, the payload data gets converted into a string:
strncpy (message, (char*)payload, length);
So now my "message" contains all the payload information. How do I efficiently parse it so I can assign my structure to the payload values as following?:
item_inside.item = "item1"
item_inside.serial ="1A2B"
item_inside.quantity = 50
You also need to check the length required when declaring or allocating space for a string, as copying past the end of the allocated memory is another frequent error.
