Splitting BLE findings and sending out to MQTT line by line using an ESP32 - c++

Question

So I have two ESP32s for this project, one sending BLE scanned device info and the other ESP32 sending the scan results to an MQTT broker. I am currently facing the issue where I cannot break the results up into multiple JSON lines and send them out to the MQTT broker line by line. Please do let me know if you have any solutions. Thank you!!
#include <WiFi.h> //Remove when not MQTT-ing using WiFi
#include <PubSubClient.h>
const char* ssid = "--------";
const char* password = "+++++++++++";
#define RXD2 16
#define TXD2 17
WiFiClient espClient;
PubSubClient client(espClient);
// MQTT Broker
const char* mqtt_broker = "broker.hivemq.com";
const char* topic = "**********";
const int mqtt_port = 1883;
void setup() {
Serial.begin(115200);
Serial2.begin(115200, SERIAL_8N1, RXD2, TXD2);
WiFi.begin(ssid, password);
while (WiFi.status() != WL_CONNECTED) {
delay(500);
Serial.println("Connecting to WiFi..");
}
Serial.println("Connected to the WiFi network");
//connecting to a mqtt broker
client.setServer(mqtt_broker, mqtt_port);
while (!client.connected()) {
String client_id = "esp32-client-";
client_id += String(WiFi.macAddress());
Serial.printf("The client %s connects to the public mqtt broker\n", client_id.c_str());
if (client.connect(client_id.c_str())) {
Serial.println("Public hivemq broker connected");
} else {
Serial.print("failed with state ");
Serial.print(client.state());
delay(2000);
}
}
}
void loop() {
// put your main code here, to run repeatedly:
String msg = "";
msg = Serial2.readString();
//String msg = "test MQTT";
// publish
int index = msg.lastIndexOf('}');
int length = msg.length();
String subMsg = msg.substring(index, length);
client.publish(topic,subMsg.c_str());
Serial.println("Message has been sent is: ");
Serial.println(subMsg.c_str();
delay(5000);
}
This is the output that I have:
{"Device Name":"GXHGA22CF3B9","EDID":"d4:0b:dd:2c:f3:b9","RTID":"FF005802600001F","RSSI":"-77"}
{"Device Name":"","EDID":"d7:9c:0e:1d:e6:a2","RTID":"FF005802600001F","RSSI":"-71"}
{"Device Name":"Buds2","EDID":"d8:4d:72:1f:80:15","RTID":"FF005802600001F","RSSI":"-75"}
{"Device Name":"KBPro_185309","EDID":"dd:34:02:06:33:a8","RTID":"FF005802600001F","RSSI":"-87"}
{"Device Name":"GXHGA2DAEC2A","EDID":"de:1e:da:da:ec:2a","RTID":"FF005802600001F","RSSI":"-86"}
{"Device Name":"","EDID":"e9:c7:1b:79:e1:41","RTID":"FF005802600001F","RSSI":"-76"}
{"Device Name":"","EDID":"e9:f5:80:7f:c8:ea","RTID":"FF005802600001F","RSSI":"-89"}
{"Device Name":"","EDID":"ef:e0:22:b2:c6:d0","RTID":"FF005802600001F","RSSI":"-84"}
{"Device Name":"GXHGA20A5D4A","EDID":"f6:4e:4d:0a:5d:4a","RTID":"FF005802600001F","RSSI":"-84"}
{"Device Name":"","EDID":"ff:65:fa:78:7f:c1","RTID":"FF005802600001F","RSSI":"-93"}
{"Device Name":"","EDID":"00:64:0f:26:92:09","RTID":"FF005802600001F","RSSI":"-90"}

Answer 1

Your current code finds the last } in the message and then takes that as the starting point for a substring to the end of the message. So you will always get a } character. You need to loop through the messages in a single read and find the start and end braces, pulling out each message.
Something like this:
void loop() {
// put your main code here, to run repeatedly:
String msg = "";
msg = Serial2.readString();
int start_idx = 0 ;
while( start_idx >= 0 )
{
start_idx = msg.indexOf('{',start_idx);
if ( start_idx >= 0 )
{
int end_idx = msg.indexOf('}',start_idx+1);
String subMsg = msg.substring(start_idx, end_idx+1);
client.publish(topic,subMsg.c_str());
Serial.println("Message has been sent is: ");
Serial.println(subMsg.c_str();
start_idx = end_idx + 1;
}
}
}
Note - this assumes that the JSON doesn't contain any objects - since the internal braces will also be separated. It also assumes you get complete JSON messages with each Serial read (i.e. they're not truncated). So you may need to handle these cases - but this should give you a start.
I've also removed the delay - I don't know why you'd want to delay for 5 seconds between reads - unless this was just for testing.