How do i store data from HTTPREAD into a variable? - http

Question

I need a way to store HTTPREAD data into a variable because I will be comparing its value to another variable. Is there any way?
{
myGsm.print("AT+HTTPPARA=\"URL\",\"http://7ae0eae2.ngrok.io/get-ignition/ccb37bd2-a59e-4e56-a7e1-68fd0d7cf845"); // Send PARA command
myGsm.print("\"\r\n");
delay(1000);
printSerialData();
myGsm.println();
myGsm.println("AT+HTTPACTION=0");//submit the GET request
delay(8000);//the delay is important if the return datas are very large, the time required longer.
printSerialData();
myGsm.println("AT+HTTPREAD=0,17");// read the data from the website you access
delay(3000);
printSerialData();
delay(1000);
}
void printSerialData()
{
while(myGsm.available()!=0)
Serial.write(myGsm.read());
}

Answer 1

I am assuming that the Serial.write(myGsm.read()) is where you want to get the data from. In other words, you are receiving the data through the serial connection, and you want to parse the data returned from the AT+HTTPREAD command.
Since you did not provide any clue about what that command is returning in the serial, I gonna use as an example a different command that I know the output, the below one:
TX=> AT+CCLK?
RX=> AT+CCLK?\n\r
\t+CCLK: "2020/03/03, 22:00:14"\n\r
So, the string you are going to get from the above AT+CCLK? command is this (I am assigning to a char pointer for the sake of understanding):
char *answer = "AT+CCLK?\n\r\t+CCLK: "2020/03/03, 22:00:14"\n\r";
What you need is to parse the answer (the char *answer in this example) to get the "numbers" into variables.
How to do that?
You need to walk over that string, moving to specific places. For example, to be able to convert the 2020 into a variable, you need to be at position answer[19], and then you can use, let's say, the strtoul() to convert to an integer and store it into a variable.
uint32_t year = strtoul(&answer[19], NULL, 10);
Then, to get the month, you need to walk a bit more to reach the position at the month on the string:
uint32_t month = strtoul(&answer[24], NULL, 10);
And so on, but you are using magic numbers for that, in other words, the numbers 19, 24 are positions specific for this string.
Then, how to make this "walking" smarter?
You can use tokens in conjunction with the strstr() to go to the specific points you want in the string. In this case, we want to move the pointer to the first 2, so we can pass that pointer to the strtoul() to convert it into an integer.
#include <stdlib.h>
#include <stdio.h>
#include <stdint.h>
int main() {
char *answer = "AT+CCLK?\n\r\t+CCLK: "2020/03/03, 22:00:14"\n\r";
char *token = "CCLK: \"";
char *ptr;
uint32_t year;
ptr = strstr(answer, token);
if (ptr == NULL) {
printf("Token not found\n");
return -1;
}
year = strtoul(++ptr, NULL, 10);
printf("Year = %d\n", year);
Then, to make this code into a function to be more generic, here it is:
bool parse_answer_to_uint32(char *buff, char *tokens[], uint32_t *val)
{
char *ptr;
int i;
if (val == NULL)
return false;
for (i = 0; buff != NULL && tokens[i] != NULL; i++) {
ptr = strstr(buff, tokens[i]);
if (ptr == NULL)
return false;
buff = (ptr + strlen(tokens[i]));
}
// Here, you reached the point you want, based on the tokens you seek
if (buff == NULL)
return false;
*val = strtoul(buff, NULL, 10);
}
So, you can be able to call this function like this:
char *tokens[] = { "CCLK: \"" };
uint32_t year;
if (parse_answer_to_uint32(myGsm.read().c_str(), tokens, &year) == false)
return -1;
printf("year is = %d\n", year);
The printf will print 2020 based on the example above.
This function is pretty flexible and generic enough. All you need is to pass different tokens to reach different points of the string and reach the value you want.

Answer 2

Take character buffer, Concat data comming from serial into this buffer, and process that buffer for comparison.