Esp 8266 parse json async - json

Question

I'm using asyncHTTPrequest for async request to a REST API in ESP8266.
I receive the response in JSON format but can't parse it.
This kind of parsing was working while i used to made sync call to API.
I tried to store the request->responseText() into a String variable because its return a String, but the variable never get any value.
void sendRequest() {
if (request.readyState() == 0 || request.readyState() == 4) {
request.open("GET", "http://192.168.1.103:45456/api/systems/1013/arduino");
request.send();
}
}
void requestCB(void* optParm, asyncHTTPrequest* request, int readyState) {
if (readyState == 4) {
Serial.println(request->responseText());
const size_t capacity = JSON_ARRAY_SIZE(1) + JSON_ARRAY_SIZE(2) + JSON_OBJECT_SIZE(2) + 2*JSON_OBJECT_SIZE(4) + JSON_OBJECT_SIZE(8)+816;
DynamicJsonBuffer jsonBuffer(capacity);
JsonObject& root = jsonBuffer.parseObject(request->responseText());
String a = request->responseText();
Serial.println(a);
JsonObject& schState = root["dataForArduino"][0];
String beginTime = schState["start"]; // "2019-12-02T21:51:00"
}
}
void setup() {
Serial.begin(9600);
wifi.Connect();
request.onReadyStateChange(requestCB);
ticker.attach(5, sendRequest);
}

Answer 1

I have wrote json parsing function (__get_from_json) to get key value from json here
e.g. if you have json response like
{
"timestamp" : "2020-04-01 19:20:49"
}
and in your application you want to parse timestamp value from it then
char response[max_response_size] = "{ \"timestamp\" : \"2020-04-01 19:20:49\" }";
char key[max_key_size] = "timestamp";
char value[max_value_size] = "";
if( __get_from_json( response, key, value, max_value_size ) ){
Serial.println(value);
}

Answer 2

I had the same problem and added .c_str() to get the response to print.
So in your example it would be:
String a = request->responseText();
Serial.println(a.c_str());
For the JSON I also needed to add .c_str()
DynamicJsonDocument jsonDoc(2048);
DeserializeJson(jsonDoc, a.c_str());