How to send measurements to a server and receive data from sensor at the same time?

Question

I'm trying to process data from my sensors, and simultaneously, upload data to the server(Thingspeak).

The problem is, whenever server connection(using wifi) ends(and i couldn't find a way to extend my session to prevent timeout), reconnecting takes time and during that time, i can't process the data from the sensors, resulting occasional holes in my data.

I heard there's some way of resolving this problem by using callback functions, somehow making the core to wait for the response from the server each time I try to connect to server, and at the same time, process the data i'm getting from the sensor.

My code right now is like this

loop
{
    while(now==prev)
    {
        processdata;
    }
    prev=now;
    count++;
    if(count==15)
    {
        count=0;
        senddata();
    }
}
senddata()
{
    if(!serverconnected)
    {
        if(!send connect request()) error message; //after this function calls,
        if(!receive connection confirmed()) error message; //takes too long time until this function finishes executing.
    }
    send data.
}

actual function names for the commented parts are

client.connect(host, port)
client,verify(fingerprint, host)

functions from WiFiClientSecure.h

is there any way to use callback methods to fix this issue? While searching for the solution, I found the following header file

espconn.h

which seems to have callback functions that I can use... but I'm not sure if this is using different methods of establishing wifi connections to the server, nor how to use the functions itself.

Answer 1

As long as you use rest api you will not be able to comfortably keep the session alive. So you better have websocket or MQTT like protocol where session is handled by them an you will be only responsible to push the data to server instantly on any time.

This link describes how an mqtt client connection to be done on Thingspeak and pushing the data to it.

Some code cuts from the link :

#include <PubSubClient.h>

WiFiClient client;
PubSubClient mqttClient(client);
const char* server = "mqtt.thingspeak.com";

mqttClient.setServer(server, 1883);